Implementation of AD in E&W

Implementation of AD in England & Wales: Balancing optimal outputs with minimal environmental impacts - Impact of using purpose grown crops

Report to Defra Restricted Commercial

AEAT/ENV/R/3220

November 2011

Final Report Restricted – Commercial AEA/ENV/R/3220

ii AEA / ADAS

(Photograph on the front cover: courtesy of Bywater (2011)) Title Implementation of AD in England and Wales: Balancing

optimal outputs with minimal environmental impacts - Impact of using purpose grown crops

Customer DEFRA

Customer reference FFG 1001 / Contract Reference AC0409

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This report is the Copyright of the Department for Environment Food and Rural Affairs (DEFRA) and has been prepared by AEA Technology plc (in association with ADAS) under contract to Defra (Contract Reference AC0409). The contents of the report may not be reproduced in whole or in part, nor passed to any other organisation or person without the specific prior written permission of Defra. AEA Technology plc accepts no liability whatsoever to any third party for any loss or damage arising from any interpretation or use of the information contained in this report, or reliance on any views expressed therein.

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(AEA), J Webb (AEA), Lucy Wilson (ADAS), Phil Metcalfe (ADAS), Susan Twining (ADAS), Baltazar Solano-Rodriguez (AEA)

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Date 2nd

November 2011

Restricted – Commercial Final report AEA/ENV/R/3162

AEA / ADAS iii

Executive summary

This report examines the potential scope for co-digesting purpose grown crops in anaerobic digestion (AD) of agricultural residues and food wastes. The use of purpose grown crops is under consideration in the UK because they benefit the AD system both by extending the season for farm-based AD systems when the animals are not housed; and by improving the operational efficiency of the process (primarily through increased yields of biogas).

The examination uses the Multi Criteria Decision Support (MCDS) tool developed by AEA and ADAS under Defra project AC0409. This MCDS tool provides analysis of the interaction between economic factors, GHG mitigation and other environmental outcomes from AD. The tool was designed to study outputs for economically attractive AD plants (with IRR>15%) and viable AD plants (with IRR>0%) on a regional basis. The most economically attractive AD plants (IRR >15%) are usually food waste-based systems, due to the gate fee attracted by the food waste. However, given that farmers traditionally have tended to settle for lower than 15% returns on their investment, we also examined the impact of purpose grown crops on all economically viable plants (i.e. IRR>0%). Thus economically viable plants tend to be smaller scale.

The recent changes in the FiT were first examined using the MCDS tool. These changes lead to a rise in overall viable AD plants and economically attractive plants. Viable AD plants increase from 855 to 903 (i.e. by 48 AD plants); whereas those economically attractive (IRR > 15%) increase from 333 to 372 (i.e. by 39). There is also a 10% increase in agricultural feedstock utilisation but only 1% increase in food waste. The analysis also shows that there is likely to be a marginal increase in energy generation but a marginal reduction in GHG saving.

In order to investigate the impact of the use of purpose grown crops in AD system the tool had to be modified, as described in Section 1. The three crops most likely to be purpose grown for AD in the UK are: grass, forage maize and forage wheat. The choice will depend on soil type and climate, production economics and market prices, and agronomic issues.

The analysis conducted using the MCDS tool shows that purpose grown crops influence the economic viability of the more economically attractive plants. When only agricultural waste feedstocks are considered (i.e. no food waste), increasing the percentage of purpose grown crops in the feedstock makes the number of economically attractive plants decrease from 81 with no silage to none with 50% maize silage (grown on temporary grassland). This is due to increasing operational cost, linked to the price and quantity of purpose grown crops.

Conversely the use of purpose grown crops improves the economic viability of smaller scale plants. Our results show an increase in economically viable AD plants from 309 to 451 when a system using maize silage grown on temporary grassland was used for up to 50% of the AD plant feedstock. Other key results for this system are:

Agricultural waste utilisation within the economically attractive AD plants falls from ~1.1 Mt/y of

agricultural waste to nothing; whereas it is quite variable with the viable AD plants, but rises to

around 4.6 Mt/y with 50% purpose grown crop in the feedstock.

For economically viable plants, the area of crop displacement rises to around 2,000ha at 10%

crop feed but then declines to nothing at 50% crop feed, as no plants remain economically

attractive. However, when viable AD plants are considered the crop displacement area rises

gradually to 116,000ha with 50% purpose grown crops.

Net methane (or biogas) production within economically attractive AD plants decreases from

~1TWh to zero; whereas that for all viable AD plants increases from 2.3TWh to 7.3TWh.

GHG saving decreases for economically attractive AD plants; but when all viable AD plants

are considered they increase from ~0.6 MtCO2/y saving to ~1.5 MtCO2/y.

When all wastes are considered, increasing the percentage of purpose grown crops in the feedstock makes the number of economically attractive plants decrease from 429 with no silage to 220 with 50% maize silage (grown on temporary grassland). For economically viable AD plants the number rises from 1020 to 1095 when 50% purpose grown crop is used. Other key results for this system are:


iv AEA / ADAS

Resource utilisation decreases within the economically attractive AD plants; whereas it is fairly

constant with the economically viable AD plants.

The area of crop displacement rises to around 25,000ha for economically attractive AD plants

and up to around 270,000ha for viable AD plants.


~7TWh to 6TWh; whereas that for all viable AD plants increases from 11TWh to 22TWh.

GHG saving decreases for economically attractive AD plants (due to fall in their number); but

when all viable AD plants are considered they increase from ~5 MtCO2/y saving to ~7

MtCO2/y.

Similar results can be observed for other scenarios in which different crop displacement and purpose grown crop systems were examined.

It should be noted that in the UK crop land use varies on an annual basis due to weather and crop economics. The wheat area has ranged by over 200,000ha (2.0%) in recent years, for example, and other crops have had larger variations in area. It is therefore possible that up to 50% purpose grown crops in AD feed could be accommodated without major impacts on other uses. Overall, this is unlikely to have any great impact on food security.

The analysis also examined the impact of changing gate fees linked to food waste. These gate fees improve the economic attractiveness of AD plants, leading to much higher utilisation of „all‟ feedstocks, agricultural waste as well as food waste. When the food waste gate fee is zero, not only is there a decrease in the use of food waste, but there is a significant decline in agricultural waste utilisation. This reflects the importance of the gate fee linked with food waste.

There may be other impacts, such as soil erosion from increased maize production; and biodiversity may be affected if large areas are dedicated to monoculture crops, such as maize. The subject of the wider impacts is fraught with scientific and technical uncertainties, particularly regarding the GHG emissions due to the cultivation of purpose grown crops. This includes a lack of understanding of indirect land use change and how to account for it. In addition, there is a degree of uncertainty around technology, economics and environmental issues related to AD plants. More research is required into the production and use of agricultural crops and their environmental impacts.


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Table of contents

1 Introduction ...................................................................................................... 6

1.1 Background ........................................................................................................................ 6

1.2 Growing Crops for AD ........................................................................................................ 6

1.3 Aims and Objectives .......................................................................................................... 7

1.4 MCDS Tool: Conditions of Use .......................................................................................... 8

2 Agricultural and Environmental Issues ........................................................ 10

2.1 Choice of purpose grown crop ......................................................................................... 10

2.2 Factors affecting uptake .................................................................................................. 11

2.3 Food security issues ........................................................................................................ 13

2.4 GHG Emissions from Purpose Grown Crops .................................................................. 14

2.5 Modeling Purpose Grown Crop Use in AD ...................................................................... 18

3 Modeling the use of purpose grown crops .................................................. 24

3.1 Technical and Economic Assessment ............................................................................. 24

3.2 AD Tool Modifications ...................................................................................................... 25

3.3 Impact of the Changes in Feed in Tariff .......................................................................... 26

3.4 Using the MCDS Tool for Purpose Grown Crops ............................................................ 28

4 Results for Selected Scenarios and Discussion ......................................... 33

4.1 Agricultural Wastes with Purpose Grown Crops .............................................................. 33

4.2 All wastes with Purpose Grown Crops ............................................................................ 39

4.3 Constraints on AD Implementation .................................................................................. 45

4.4 Using Greater Proportion of Purpose Grown Crops ........................................................ 46

4.5 Other Comments.............................................................................................................. 49

5 Conclusions .................................................................................................... 51

Appendix 1: Outputs for Scenarios 1-5: Agricultural Wastes only .............................................. 56

Appendix 2: Outputs for Scenarios 1-5: all wastes ..................................................................... 66

Appendix 3: Stoke Bardolph AD plant based on purpose grown crops ...................................... 76


6 AEA / ADAS

1 Introduction

1.1 Background

In April 2011 AEA, in association with ADAS, developed a tool for Defra that facilitates policy and strategy based examination of anaerobic digestion (AD) plants across England and Wales (E&W). The tool can be used to examine economic and environmental priorities that may influence the types and locations of AD plants in E&W, based on criteria around feedstock mix, energy and digestate outputs as well as markets and economic incentives. It also allows the potential for AD to be examined under a range of environmental and social scenarios (such as greenhouse gas (GHG) abatement, job creation, water and air quality, biodiversity and land uptake). The real benefit of this multi-criteria decision support (MCDS) tool is that it provides fundamental analysis that can inform Defra‟s work to encourage wide-scale implementation of AD in England and Wales, particularly by providing analysis of the interaction between economic factors, GHG mitigation and other environmental outcomes from AD. A limited number of runs carried out for the purpose of illustrating the model output, show that an ambition of having around 900 AD plants in E&W alone is realistic. The inclusion of food waste enhances the economic and environmental credits that can be gained from AD plants. This is reflected in the significant increase in the feedstock utilisation. In fact, the impact on GHG saving alone would be huge, with over 3 million tonnes of CO2 saved with all wastes compared to only around 63,000 tonnes with agricultural feedstocks only. This stems from greater economies of scale of AD plants and increased utilisation of food wastes and agricultural feedstocks (i.e. 28 Mt/y giving 14 TWh biogas compared to 16 Mt/y with agricultural feedstocks driven solution giving 5 TWh biogas) and also due to greater diversion of wastes from routes that currently emit GHGs.

1.2 Growing Crops for AD

In addition to use of feedstocks such as slurry and food waste for AD there is growing interest in the potential for use of energy crops for AD in the UK. Energy crops are those crops grown as a feedstock for energy generation; the term refers to a wide range of crops that can be grown for biofuels, heat and power or AD. To differentiate between these uses we use the term „purpose grown crops‟ to refer to crops that are appropriate for AD in this report. The most common examples of purpose grown crops for AD in the UK are maize and grass, although wheat, sugar beet and oil meals are also possible and the International Energy Agency‟s Bioenergy Task lists many more (IEA 2010). Commonly these crops are ensiled for the purposes of storage, so that they can be used all year round, rather than just at harvest time. There have been a number of proposals to use purpose grown crops as feedstock for AD in the UK and interest is increasing, stimulated by the success of such plants in Europe. Purpose grown crops can be used on their own or in co-digestion with other feedstocks such as food waste or slurry. The relatively high yields obtained from digestion of purpose grown crops are among the main drivers for this interest. Yields of methane from crops such as maize have been reported to be between 300 and 650 m

3/t of volatile solids (IEA 2010). However, this benefit has to be weighed against the cost of

producing the crops, ensilage and storage; and the low cost of alternative feedstocks. Currently most UK plant developers are considering the use of purpose grown crops as supplementary feedstocks for AD plants during the summer months, when animal manures/slurries are not available. It is possible that purpose grown crop production could be integrated into existing production systems as an alternative break crop, although maize is not easy to integrate into an arable rotation because its late harvest characteristics are logistically difficult. Furthermore, grass silage which has become redundant in some areas where livestock numbers are decreasing and its alternative use for AD may help to maintain landscapes and biodiversity. The greatest use of purpose grown crops is in Germany, where there are now over 4000 AD plants. This situation has been driven by the favourable feed in tariffs in Germany, which has encouraged the development of AD using maize silage. Currently there are 500,000-650,000ha dedicated to purpose grown crops (mainly maize) for AD in Germany (Encrop 2009, IEA 2011). This has lead to concerns in


AEA / ADAS 7

some areas regarding the loss of biodiversity and increasing water nitrate levels as a consequence (Murphy-Bokern 2011). In fact, there are general concerns about the sustainability of purpose grown crops for AD, particularly with respect to land use and biodiversity. It is not clear that UK incentives would encourage such an expansion into AD of purpose grown crops. UK developers will need to consider the advantages of digestion of purpose grown crops against alternative uses for the land on which the crops are grown and the potential costs of disposal of slurry or food waste. Sustainability will also be an important consideration: the UK incentives require quarterly reporting on the sustainability of feedstocks for installations starting from 1 MWth capacity, based on the requirements of the Renewable Energy Directive.

1 Participants are required to provide

information on their biomass feedstock, including the country of origin, the source material and details of any applicable environmental quality assurance schemes. Currently it is intended that the Renewable Heat Incentive (RHI) will consult on mandatory sustainability criteria in 2013. In addition there will be a consultation for the Renewables Obligation (RO) to examine the potential for introducing mandatory greenhouse gas emission savings and compliance with restrictions on using materials from land deemed important on carbon or biodiversity grounds. The RHI states that the Government recognises “at farm scale, some energy crops may be required in combination with slurries and that such crops can be grown as part of the normal agricultural rotation. Furthermore, there is land available which is not suitable for the production of food crops but which could, therefore, be used to supply energy-crop only AD plants. It is not our policy, however, to encourage energy crops–based AD, particularly where these are grown to the exclusion of food producing crops. If evidence shows that there is a large scale use of crops in AD and a resulting conversion or change in land used for crops to support AD, then measures will be considered to address this.”

1.3 Aims and Objectives The aim of this stage of the project was to further develop the multi-criteria decision support (MCDS) tool to allow analysis of greater use of purpose grown crops in AD plants to be undertaken. As indicated above, Defra recognise the role AD can play to reduce on farm energy use emissions, but have concerns around potential large scale diversion of food and forage crops to AD. This work is therefore focused on examination of the economic, environmental and production implications of increasing levels of purpose grown crop into the feedstock mix over a range of threshold ceilings. This is designed to further inform Defra of the relative risk to food production implied by uptake of on farm AD under current economic conditions. The subject of the wider impacts is fraught with scientific and technical uncertainties, particularly regarding the GHG emissions due to the cultivation of purpose grown crops. This includes a lack of understanding of indirect land use change and how to account for it. In addition, there is a degree of uncertainty around technology, economics and environmental issues related to AD plants. As such a number of simplifying assumptions have been made to enable the quantitative analysis to be undertaken. This is complemented by qualitative discussion to explore implications of greater use of purpose grown crops in AD plants in E&W. The specific objectives were:

1. Develop the basis and assumptions in estimating GHG emissions and savings due to energy crop use in AD plants that incorporate waste digestion with purpose grown crops.

2. Model the use of purpose grown crops in AD plants in E&W (extending the scope of the model).

3. Provide commentary on the sustainability of using purpose grown crops for AD in England & Wales.

We provide, as final deliverables:

1 Smaller participants will be exempt from this reporting requirement.

The Renewable Heat Incentive is available from: http://www.decc.gov.uk/assets/decc/What%20we%20do/UK%20energy%20supply/Energy%20mix/Renewable%20energy/policy/renewableheat/1387-renewable-heat-incentive.pdf

http://www.decc.gov.uk/assets/decc/What%20we%20do/UK%20energy%20supply/Energy%20mix/Renewable%20energy/policy/renewableheat/1387-renewable-heat-incentive.pdf

http://www.decc.gov.uk/assets/decc/What%20we%20do/UK%20energy%20supply/Energy%20mix/Renewable%20energy/policy/renewableheat/1387-renewable-heat-incentive.pdf


8 AEA / ADAS

A revised version of the MCDS tool, that allows examination of the effect of varying levels of energy crop input into AD plants (provided separately); and

This report containing key findings based on the potential use of purpose grown crops for AD in the UK, including an appreciation of the type of land use that might be expected, the amount of land required and the GHG impacts of the use of purpose grown crops for on farm AD.

Overall, this extended work is intended to provide an appreciation of the reasons why and how purpose grown crops might proceed or be allowed for use in AD, while simultaneously estimating their GHG impact and highlighting other environmental issues of concern.

1.4 MCDS Tool: Conditions of Use “The Tool” comprising Excel spreadsheet model and the associated database is supplied for use by Defra and other government department stakeholders to whom Defra release the Tool (“Other Government Users”) solely for the purposes of the project undertaken under Defra contract (Contract Reference AC0409). AEA Technology plc and ADAS accept no liability whatsoever for any:

use of the Tool, or information resulting from use of the Tool, for purposes other than those for

which the Tool is intended and described in Contract Reference AC0409;

adjustments and/or further developments made to the Tool made by Defra, Other Government

Users or any third party without the prior knowledge and approval of AEA;

incorrect use of the Tool by Defra, Other Government Users or any third party;

incorrect outcomes arising from the use of inaccurate or incomplete data entered by Defra,

Other Government Users or any third party.

This model and output should be used to discern trends and broad analysis and should not be used to „read specific outputs‟ on a plant by plant or area by area basis. This is because the GIS datasets, used within 10km grid cells to consider individual plants, are a crude approximation of the likely situation. The tool delivered herewith also differs from that delivered in April 2011 as given in Table 1 below.

Table 1: Differences between the original tool delivered in April 2011 and this extension tool

Tool delivered in April 2011 This tool and as illustrated herein

The basis of the tool and its use was illustrated in the report delivered in April 2011.

The key changes and selective use of this tool are illustrated in this report.

Use of purpose grown crops (maize silage, grass silage or wheat silage) was linked to the seasonal variations of dairy and beef cattle slurry.

Use of purpose grown crop (maize silage, grass silage or wheat silage) can be selected by the user, up to 50% in the feed, measured on the agricultural feedstock basis.

2

Was devised to examine multi-criteria issues surrounding AD plants based on waste arisings and supplementary use of purpose grown crops (as given above) to smooth out seasonal fluctuations in cattle slurries.

We advise using this tool for discerning economic and GHG emission trends only.

The option to select other priorities (such as water quality, job creation) has been left in the tool, but it is not central to the analysis that this tool is designed to assist.

The tool showed a „static‟ view of the situation – the most recent land use and livestock data were used to calculate economics of potential AD plants.

The new tool creates potential scenarios with different land use patterns occurring due to the introduction of purpose grown crops.

2 Measured as a percentage of overall agricultural feedstock (livestock and crop wastes); i.e. on food waste free

basis.


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Nitrate leaching values represented the modelled land use (obtained using NEAP-N model)

As nitrate leaching values were external to the model, the effects of energy crop induced land use change on nitrate leaching are not included in this tool.


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2 Agricultural and Environmental Issues

2.1 Choice of purpose grown crop

In the UK there are three most likely options for purpose grown crop feedstocks for AD units, usually to be used in combination with other feedstocks. These are grass, forage maize and forage wheat. The choice of crop will depend on energy value as a feedstock and how that relates to the monetary value of the crop relative to the costs of production, but along side this there are agronomic considerations. Grass will be a popular option where land is not suitable for arable crops, and may have attractions for conversion of marginal arable land to grassland in some situations. Where arable land is to be used, forage wheat is an option, particularly in the more northern regions where forage maize is later to establish (unless grown under biodegradable polythene, which is increasingly used). However wheat does have higher management and input requirements than forage maize and must be grown in a rotation in order to maximise yields. More simply, grass feedstock may be an option where changes in livestock production leaves excess grass, or demand could result in an increase in intensity of some grassland. Forage maize is an attractive option as it is a spring sown crop which helps to spread the workload; and it has relatively simple management and relatively low inputs, including lower requirements for nitrogen fertiliser, compared to other arable crops. In addition, where farmers have heavy black-grass infestations, which are a problem in other arable crops with resistance to some herbicides, the growing of a spring sown crops such as maize can help reduce the problem. There may be soil limitations for forage maize with it being less suitable on heavy soils, on which it can be more difficult to achieve a good seedbed in the spring, and there are latitudinal differences due to the need for minimum soil temperatures before sowing and the maturation date, making it more suited to the southern half of the UK. There are, however, new varieties and growing techniques which are enabling its growth further north. An added attraction of forage maize is the ability to grow it continuously without any serious drop in yields, although there can be an increase in more difficult to control weeds after a number of years, and an increase in intensity in a particular area may make it more susceptible to pests and disease. Forage maize could be grown within an arable rotation. However, there are drawbacks in that many current varieties are later harvesting than most other arable crops, which could be an issue if the aim is to follow with winter cereals, so it is, perhaps, most suited to those with spring crops in the rotation, such as sugar beet or potatoes. There is also an increased risk of fusarium in wheat when following maize, although these risks can be mitigated to some extent by appropriate cultivations. If maize was to be grown in an arable rotation it is most likely that it would be grown continuously for 2-3 years, rather than replacing a particular crop in the rotation. Forage maize will be most attractive to those already growing the crop in rotation with grassland on dairy farms, if land is available. The use of forage wheat as a feedstock is also a realistic option in some situations where local demand could create a switch in market. This is most likely on more marginal arable land, but could also be an option for farmers who have problem weeds such as black-grass as the early harvest and longer gap between harvest and redrilling could reduce its incidence and severity. The use of wheat may also be encouraged with further work on suitability of varieties. Work has already been undertaken for use of wheat grain in ethanol production, where varieties and crop management have been investigated, although similar work has not yet been undertaken for use as an AD feedstock.


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2.2 Factors affecting uptake

2.2.1 Land availability

There are annual variations in the arable crop land use depending on crop economics/market conditions and weather, and changes in Government policy. Most changes are gradual with few large swings in cropping, although there have been large variations due to changes in Government support e.g. change in support to single payment rather than for each ha of crop in 2005 and the removal of the requirement for set-aside in 2008, which temporarily increased the wheat area, and weather such as the poor autumn conditions for the 2001 and 2009 harvest, which changed the cropping balance between winter and spring. In recent years the crop areas have also become more volatile as farmers have responded to market prices (e.g. low spring barley prices in 2010 resulted in a drop in area of almost 150,000ha in England compared to the previous year, which had been very high due to the poor winter planting conditions for the 2009 crop). Similarly the wheat area in England is 1.82Mha for 2011, 30,000ha higher than 2010 encouraged by high market prices. The winter oilseed rape area has increased from 493,000ha in 2009 (low due to wet conditions), to 600,000ha in 2010 and 650,000ha in 2011, due to good market prices and crop economics relative to other break crops and good planting conditions.

Figure 1 Changes in UK crop area 2001 to 1009

There is therefore already significant volatility in the crop areas and the accommodation of 100,000ha of purpose grown crops may not have a large impact on production depending on the crops it will replace. UK wheat production is normally around 15Mt, of which 3Mt is for bread making and 9Mt for livestock feed, with the remainder exported, although there is an increasing demand for biofuel which could account for the remainder in the future. Should UK production drop to below 12Mt, the domestic food and feed markets will require increased imports to meet the demand, but this would require a reduction in wheat area of around 375,000ha. Depending on the development of the biofuels sector, there is therefore sufficient land to provide 100,000ha of land for AD feedstocks without impacting on UK food and feed wheat demands. The impact that will have on rotations will depend on the crop grown and the location.

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

20012002

20032004

20052006

20072008

2009

Crops for stockfeeding

Other crops not for stockfeeding

Horticulture

Temporary grass (< 5 years)

Other cereals

Pulses

Potatoes

Sugar beet

Oilseeds

Set-aside

Spring barley

Winter barley

Wheat


12 AEA / ADAS

2.2.2 Crop economics

Table 2. Average gross margins for the main rotational crops

Ave: average

Crop Gross margin, £/ha Source

Forage maize 398-780 Based on variable costs in Nix (2011)

OSR – low 285 Nix (2011)

OSR – med 545 Nix (2011)

OSR – high 805 Nix (2011)

Feed barley - low 325 Nix (2011)

Feed barley - ave 486 Nix (2011)

Feed barley - high 601 Nix (2011)

Feed wheat - low 423 Nix (2011)

Feed wheat - ave 615 Nix (2011)

Feed wheat - high 783 Nix (2011)

Maincrop potatoes 2533-4384 Nix (2011)

Sugar beet 693-1227 Nix (2011)

Linseed 164-612 Nix (2011)

Field beans 310-634 Nix (2011)

Field peas 254-633 Nix (2011)

Individual crop gross margins vary depending on the soil type, local weather and crop management. Farmers select crops for a rotation in order to maximise rotational gross margin income, but also consider practicalities such as land suitability, workload at peak times, management expertise, storage and markets. In order to attract farmers to grow suitable AD feedstocks the gross margin must be competitive with existing rotations or offer practical advantages in agronomy. Forage maize and wheat for AD feedstock is potentially competitive with many arable crops, other than the highest yielding wheat crops. Feedstock maize production is unlikely to be competitive with winter sown cereals and oilseed rape, however it may be more competitive with the spring cereals and break crops, and some farms with black-grass weed problems may find it an attractive spring option to help reduce the incidence of the weed. It may also be an option on farms where the stocking levels are being reduced, releasing some land for production of maize.

2.2.3 Agronomy

There are rotational constraints on most crops, which ideally should not be grown in the rotation more than once in every 3-4 years and with a longer interval for potatoes. Cereals, however, can be grown continuously, although there is a yield penalty which means most farmers operate a rotation with non-cereal crops, with a maximum of 2 consecutive wheats. Growing wheat as a feedstock has the advantage that there will be no changes in current rotations and, although management of the crop can be more complex than forage maize, it is generally well understood by farmers. The earlier harvest date can be an advantage in helping to control difficult weeds, such as resistant black-grass, allowing an opportunity for a stale seedbed before the next crop. In the future management may be developed specifically for forage wheat crops that might reduce inputs of pesticides. Growing maize as a feedstock will be an option depending on soil type (it is better suited to medium soils, due to the need for spring cultivation and minimum soil temperatures before sowing); and geography (further north it is more difficult to get high yields due to the colder springs unless grown under biodegradable polythene initially, but this adds to the costs). It is a relatively simple agronomy with currently few problem weeds (although they can build up if crops are grown continuously) pests or disease problems. The nitrogen requirements are generally lower than other cereal crops and, as it is a spring planted crop, there is the opportunity to use manures/digestate to keep costs low. A key issue


AEA / ADAS 13

is drilling into warm soils and a potentially late harvest date, although recent varieties developments have focussed on early maturation. It may also be an option on arable farms where there is a resistant black-grass weed problem, as switching to spring cropping can help reduce incidence to manageable levels, reducing pesticide inputs. There are potentially environmental issues with continuous forage maize, which is associated with increased soil erosion risks over winter; however a shift to spring cropping can have biodiversity benefits. Spring cropping in general has advantages for biodiversity due the availability of stubble over winter which can help provide food and habitat for insects and birds. Forage maize, with a late spring planting date, can provide improved biodiversity opportunities, but it is dependent on the previous crop and its management. For example a weedier crop tends to provide greater food sources than a crop with few weeds. The biodiversity benefit of spring cropping may be lower where there is continuous cropping of maize with good weed control. Similarly the biodiversity benefits may be reduced if the naturally regenerated cover is destroyed over the winter by early cultivations or applications of manures.

Its place in the rotation will depend on its value relative to other crops. Where it can be grown continuously it may be an option to replace all the crops in a rotation, so its value relative to the average rotational gross margin will be important, rather than using it as a replacement break crop. It is unlikely to be an option where sugar beet and potatoes are grown, as they produce higher margins. Sugar beet is largely confined to the East Midland and Eastern regions, with smaller areas in Yorkshire and the West Midlands, following the rationalisation of the British Sugar processing plants. Similarly, there has been rationalisation within the potato industry to concentrate production with fewer growers with a larger area. Where sugar beet and potatoes are no longer grown, farmers have tended to move to growing oilseed rape as the preferred break crops, and although replacement of oilseed rape with maize is feasible, it is unlikely, given the late harvesting of maize and the increased risk of fusarium in following cereal crops, along with the current high market price for oilseed rape.

It is most likely that growing maize will result in changes to a farm rotation, rather than just slotting it in instead of a particular crop, with perhaps 2 or 3 years of maize before growing other cereals or break crops.

If maize is used as a break crop in a wheat rotation, the later harvesting date typically in October in southern UK and later further north, can affect the establishment and management of the following wheat crop. This is changing with the development of earlier maturing varieties and the use of growing techniques such as biodegradable polythene which allows earlier drilling and establishment and results in earlier maturation and harvesting.

The optimum window for sowing winter wheat is 20 September to 20 October, and later drilling than this requires higher seed rates, slows germination and establishment, making it more vulnerable to pest attacks, and less competitive with weeds. There is a reduced yield potential from later sowing of wheat crops (HGCA Wheat growth guide), and little time to correct any soil structure issued from the later harvesting of maize, with the worst case scenario resulting in the farmers having to switch to spring sown wheat or other spring crop. Growing wheat following maize also increases the risks of mycotoxin infections, which now have maximum limits for marketing of milling wheat so it will restrict the farmer to feed wheat.

Maize does offer advantages compared to other break crops in terms of weed control, with a range of effective products available, and the opportunity to use stale seedbed techniques and cultivations/non-selective herbicides to reduce the weed burden before drilling the maize. This can be particularly useful for farmers who have problems with resistant black-grass, although these growers tend to be on the heavier soil types, where spring cropping can be less reliable due to difficulties in cultivating the soils.

2.3 Food security issues

We can make a reasonable first estimate of the likely impact of land take for purpose grown crops on food security in the UK in the next five years, taking account of expected increases in yields and projected population growth. The calculations are explained in the box below.


14 AEA / ADAS

Crop area 20103

The area of arable land in England and Wales is approximately 4.9 M ha; the area of permanent grassland is approximately 4.3 M ha and the area of rough grazing is approximately 1.3 M ha. Total crop production adjusted for area potentially taken up by purpose grown crops Estimates suggest that for AD plants taking purpose grown crops as feedstock, 100ha per AD plant is required to grow these crops. The potential for 1000 AD plants in England and Wales would result in a land take of 100,000 ha if all of these used purpose grown crops as a feedstock. This is equivalent to 2.0% of arable land, 1.1% of agricultural land excluding rough grazing and 1.0% of total agricultural land. Population growth According to the World Bank, the UK population in 2005 was 60,226,000. This was expected to grow to 63.5 million by 2025 and to just over 65 million by 2050

4. This projection is equivalent to 0.27% per

annum (2005-2025), therefore over 5 years, the population should grow by 1.35%. This is likely to be an underestimate however, since the UK population in 2010 was 62,262,000 – equivalent to an increase of 0.7% per year over the period 2005-2010; a total increase of 3.4% over 5 years. Increase in crop yield An annual increase of 1% in crop yields and livestock production is forecast to occur over the next 5 years. This equates to a 5% increase in total. Accounting for the assumption that the area used for food production is reduced by between 1% and 2% due to the planting of purpose grown crops, the total food production over 5 years will increase by between 4.90% and 4.95%. The UK population may increase by between 1.4% and 3.4% depending on which forecast we use. These figures perhaps provide us with an upper and lower estimate; however both are exceeded by the potential increase in food production as a result of increases in yield, despite potential loss of agricultural land due to the planting of purpose grown crops for energy.

The crude analysis presented suggests that this level of land take will not have any great impact on food security. It is, however, recommended that a more detailed study is undertaken to properly assess where land may be taken out of food production, which crops or livestock might be displaced, and specific forecasts made of productivity improvements for each of these crops or livestock. It is true that over the past 40 years yields of arable and horticulture crops have increased due to advances in technology such as plant breeding, pesticides, fertiliser, irrigation and mechanisation. Wheat yields have on average increased by 1% per year and it would seem likely that they would continue to do so. However, there is some evidence in the UK and other countries that the continued yield increase is stalling. There are other technological advances that may help boost yields including further advances in breeding (including genetic modifications and other novel breeding techniques) and new pesticides may also help boost yields. It is somewhat simplistic to equate increases in production with feeding the UK population as we have a much more dynamic food system of imports and exports that this analysis suggests. Changes in dietary habits (such as eating less meat) could have a greater impact on land use than AD plants supplementing seasonal agricultural feedstock with purpose grown crops.

2.4 GHG Emissions from Purpose Grown Crops

2.4.1 Background

Until about five years ago, biofuels were considered a robust option for reducing CO2 emissions. This was based on the understanding that biofuels displace fossil fuels in the transport sector. The case for biomethane or biogas can be seen in a similar way, as it can be used as an energy source for electricity, heat or transport fuel, displacing fossil fuels in each application.

3 Source – June Census of Agriculture and Horticulture, 2010 (Defra)

4 World Bank, 2003


AEA / ADAS 15

However, net carbon emissions do occur, because the cultivation of primary crops requires inputs of fertiliser, the use of diesel for agricultural machinery, energy in processing the feedstock to fuels, etc. The use and/or production of these inputs generate greenhouse gas emissions, too. This is reflected in the sustainability criteria incorporated in the Renewable Energy Directive (RED) that was published in 2009. The RED requires that the whole production chain from cultivation of the feedstock up to use of the biofuels is considered, including direct conversion of land to grow biofuels feedstock. Recently much evidence has emerged that this thinking is only part of the story and that it does not capture the full climate impact of biofuels. In particular, the RED does not take into account the potential indirect effects of biofuels production. When biofuels are grown on existing arable land, indirect land use change (ILUC) may ensue, since demand for food and animal feed will push these production activities into new areas such as forests or grasslands. The extent to which this may occur will depend upon the scale of demand for feedstocks. The amounts of crops derived from a hectare of land have increased steadily over the last 50 years and productivity is forecast to continue to increase at circa 1% per year over the next 10-20 years. Hence, if the aggregate demand for feedstocks is only a few percent of current production this demand may be met by increased productivity without the need for ILUC. However, should the demand for feedstocks exceed the growth in productivity, ILUC will take place. Conversion of forest or grassland to agricultural land can lead to very significant releases of carbon to the atmosphere. ILUC is difficult to measure and the EC is currently funding research to develop an agreed approach to this issue. There is also scope for leakage if the displaced food products are produced less efficiently elsewhere, i.e. there might not be a „like for like‟ swap.

2.4.2 Method for estimation of GHG emissions

Defra project IS0205 (Williams et al., 2006) quantified the resource use and environmental burdens arising from the production of ten key commodities using Life Cycle Assessment (LCA). All inputs to on-farm production were traced back to primary resources, and all activities supporting farm production were included. Individual GHG emissions, such as CO2 and N2O, were quantified and aggregated into a value for global warming potential (GWP) for each component and commodity. Global warming potential is a relative measure of how much heat a GHG traps in the atmosphere. It uses factors to project over a specific time interval, usually 20, 100 or 500 years and is expressed as a factor of carbon dioxide (whose GWP is 1). An excel-based model was produced, and is available to download on the Cranfield University website. Development of the model continues under Defra project IS0222. The model includes a table of the inventory calculations, from which values for conventional production (as opposed to organic) for each of the three feed crops were used to estimate GHG emissions and savings due to energy crop use in AD plants. Modelled animal feed crops included feed wheat, which was modelled as bread wheat but using higher yielding, lower protein varieties; maize silage, with data on crop composition and fertilisation needs taken from Wilkinson et al. (1999); and grass silage, with grass yield modelled using the grass site class system (Brockman & Gwynn, 1988). Denitrification to nitrous oxide was calculated for each of these feed crops using the IPCC method (IPCC, 1997) as reported in the UK GHG emission inventory (Baggot et al., 2004). It was assumed that all direct inputs of N into soil are associated with an emission of N2O and each is associated with an emission factor. The following direct inputs were included;

1. Synthetic fertiliser 2. Biologically fixed nitrogen by legumes 3. Ploughed-in crop residues 4. Land spreading of organic fertilisers (animal manures, compost or sewage sludge) 5. Direct deposition of manures by grazing animals

And two indirect emission sources were estimated;


16 AEA / ADAS

1. Emission of N2O from atmospheric deposition of N 2. Emission of N2O from leaching of agricultural nitrate

In the LCA model (Williams et al., 2006) estimates were made on the quantity of manure nitrogen becoming available to the various crops as fertiliser, based on the proportion of each major crop receiving manure reported by Chalmers (2001). For winter cereals and OSR this value was 12%, and for forage maize the value was 100%. This means that the „normal‟ fertiliser level in the analysis is the sum of the average synthetic fertiliser use from the British Survey of Fertiliser Practice and the value for plant available N from manure. For grassland, the analysis included the fertiliser N applied, defined as the amount that makes the N available without atmospheric N, equal to the economic optimum; and the N in grazed animal excrement that is not lost. Carbon dioxide emissions associated with crop production include primary energy usage, taking into account cultivation, spraying, fertiliser application, harvesting, crop storage & drying or cooling, pesticide manufacture and fertiliser manufacture. The latter dominates in arable field operations (52%), followed by field work (35%). Primary energy is only a minor contributor to the global warming potential of crop production. The main contributor is N2O-N emissions at ~80%, since they are 400 times more potent than CO2.

2.4.3 Yield and Emission Estimates

Five-year average annual yields, GHG emissions, nitrate leaching to water and average N fertiliser applications for the purpose grown crops under consideration, as well as those crops that they are expected to replace, are given in Table 3. Regional yields for cereal crops and OSR are provided in fw: fresh weight Table 4. These values were used in the MCDS tool to predict changes in GHG emissions and nitrate leaching under scenarios incorporating purpose grown crops as an AD feedstock (see Section 3).


AEA / ADAS 17

Table 3. Yield and dry matter content of purpose grown crops and crops that they are likely to replace, along with the estimated greenhouse gas emissions and nitrate losses to water calculated using LCA. All estimates from Cranfield LCA (Williams et al., 2006) unless otherwise stated.

Maize silage

Grass silage

Wholecrop Wheat

5

Feed Wheat

Winter Barley

Winter OSR

Lowland Grazing

Average Yield (t/ha/yr) 40 6 45 6 28 6 7.7

7 6.27 3.47 28-33

Dry Matter content (%) 33 6 30 6 55 6 85 85 91 25

GWP 100, kg CO2eq per tonne (fw) 100 91 126 458 415 1050 82

N2O-N to air, kg per tonne (fw) 0.13 0.13 0.17 0.62 0.52 1.4 0.15

CO2 (total) to air, kg per tonne (fw) 36 25 39 141 149 no data 9

CH4 to air, kg per tonne (fw) 0.03 0.03 0.06 0.2 0.2 no data 0

NO3-N to water, kg per tonne (fw) 0.9 1.2 1.2 4.3 3.2 no data 0.9

N fertiliser use (kg/ha) 8 64 127 196 196 144 201 100

fw: fresh weight

Table 4. Average regional cereal and OSR yields from the Defra cereals and OSR production estimates for 2006-2010

Regional cereal and OSR yields

GOR Winter Wheat Yield (t/ha/yr)

Winter Barley Yield (t/ha/yr)

Winter OSR Yield (t/ha/yr)

North East 8.09 6.51 3.23

North West 5.86 5.61 3.52

Yorkshire & Humber 8.20 6.68 3.49

East Midlands 8.26 6.39 3.24

West Midlands 7.57 6.11 3.48

Eastern 8.26 6.29 3.42

South East & London 8.14 6.40 3.19

South West 7.48 6.13 3.41

5 GHG emissions and nitrate losses assumed to be the same as for feed wheat on an area basis.

6 Estimate from Hopwood, L. (2011) Farm-Scale Anaerobic Digestion Plant Efficiency. Final Project Report to DECC.

7 Defra 5-year average (2006-2010)

8 2010 average field rates for England and Wales from the British Survey of Fertiliser Practice.


18 AEA / ADAS

Assumptions Although the long term trend in wheat yields is a 1% increase per year, there is evidence that cereal and rape yields have been static in recent years in the UK. It was therefore assumed that an average of yields in recent years would provide a more robust estimate than the 2010 figures available at the time of carrying out this work. The yields were averaged over five years (2006-2010) rather three years, as is standard practice for agricultural LCA studies, since unusual weather conditions in recent years may have led to some atypical yields. No regional yield data are available for maize silage, grass silage or whole crop wheat; however there are few constraints on growing of these three crops in England and Wales, particularly as it is becoming more common to start maize under plastic. Milling wheat typically yields less grain than feed wheat; the yield of feed wheat is cited as being typically 8.5% greater than milling wheat (Nix, 2009). Since purpose grown wheat crops will be feed wheat rather than milling wheat varieties, the wheat yield estimates used in this study were based on the yields and fertiliser-nitrogen (N) application rates applicable to feed wheat only. For the same reason we based barley and OSR yields on those of winter varieties, since the greater yielding winter varieties are a more likely choice for feedstock than the spring sown crops. Information on fertiliser use by crop was obtained from the British Survey of Fertiliser Practice.

9

Average annual applications of N fertilisers (kg/N/ha) were used. As there is relatively little year-to-year fluctuation in fertiliser use and the long term trend is for gradual reductions in fertiliser application, we considered it acceptable to use application rates for the most recent year available (2010) rather than three- or five-year averages. The quoted N fertiliser input to grass silage is the maximum recommended by the British Grassland Society. Actual N-inputs will vary depending on the Soil Nitrogen Supply (SNS) status, which are detailed in the RB209 (Anon 2010) guidelines. Little information is available on fertiliser applications to wholecrop wheat, so the same rates were assumed as for feed wheat. Estimates of leaching of nitrate N to water (kg/tonne) were obtained per crop from the Cranfield LCA data. These leaching estimates and typical N applications per crop were used to provide an estimate of the relative increase or decrease in N leaching as a result of changes in cropping for the purpose of producing feedstock for AD under the four scenarios presented here. These estimates are not spatially explicit, but provide an overall indication of the impact of the changes on nitrate leaching under each scenario.

2.5 Modeling Purpose Grown Crop Use in AD

As discussed in the preceding sections, a number of considerations should be made when selecting scenarios for modelling purpose grown crop use in AD. Scenarios were chosen to represent the best and worst economic cases, and the best and worst environmental cases, whilst still being feasible.

1. Best economic case – Maize silage grown on grass land (i.e. displacement of temporary grass for maize). Farmers could expand maize growing into grass and temporary pasture and even onto permanent pasture where land capability permits, although this would be associated with significant soil carbon loss. The loss of temporary grassland will impact on the availability of silage for livestock feed, so may be accompanied by a change in farm system, such as reduced livestock numbers. Based on a yield of 45t/ha for grass silage and 40t/ha for maize, the associated decrease in emissions (GWP 100) from the displacement of temporary grassland (used for silage) by maize would be approximately 95 kg CO2eq/ ha.

2. Worst economic case – Maize silage grown on wheat land (i.e. displacement of wheat for maize). It may be unrealistic to displace wheat for maize silage when the price of wheat is high, as at present. In fact the substitution of wheat for maize may only be feasible on poorer land or when prices are low. Displacement of feed wheat was thought to be more likely than displacement of milling wheat. Discussions with NNFCC indicated that a price of £200/tonne for wheat would be required to make it more profitable than growing an energy crop, which

9 The British Survey of Fertiliser Practice. Fertiliser use on farm crops for crop year 2010. Defra, 2011


AEA / ADAS 19

currently sells for around £150/tonne. However, what matters to the farmer is the Gross Margin, and forage maize will be less expensive to grow than wheat. Unlike other major crops, there is no specific figure available in the Farm Management Pocket book (Nix, 2011) for the Gross Margin on forage maize. Variable costs are given, based on a yield of 40t/ha, of £387/ha. This equates to a Gross Margin of £398-780/ha, which begins to make the crop look attractive, albeit at the lower average prices of £120 for feed wheat and £135 for Milling wheat. Based on a yield of 7.7t/ha for feed wheat and 40t/ha for maize, the associated increase in emissions (GWP 100) from the displacement of wheat by maize would be approximately 473 kg CO2eq/ ha.

3. Worst environmental case – Maize silage grown on permanent pastures

Forage maize is an annual crop requiring cultivation to incorporate unharvested residues and prepare a seedbed. The ploughing out of permanent grass to grow forage maize will lead to mineralization of some of the organic matter accumulated under grass and emissions of CO2. Increased emissions of CO2 are likely to continue for several years. Moreover permanent pasture may often, although by no means invariably, be found on sloping soils with moderate erosion risk. Hence conversion to forage maize will increase the risk of erosion. Yields of maize will be depressed due to marginality so the cost of production will increase. Maize is a crop at the edge of its environmental limit. Based on a yield of 30t/ha for grazing pasture and 40t/ha for maize, the associated increase in emissions (GWP 100) from the displacement of lowland grazing by maize would be approximately 1.54 tonnes CO2eq/ ha.

4. Best environmental case – Grass silage grown on permanent pasture land. This scenario is the most environmentally advantageous since grass silage has the lowest GHG emissions per tonne of the purpose grown crops (Table 3) and growing of a silage crop on permanent pasture would result in less soil erosion and loss of soil structure when compared to a maize crop. Limitations include a potentially lower grass yield on land used for permanent pasture (there will be environmental reasons for this land being permanent pasture in the first place) and loss of livestock grazing land. Based on a yield of 30t/ha for grazing pasture and 45t/ha for grass silage, the associated increase in emissions (GWP 100) from the displacement of lowland grazing by grass silage would be approximately 1.64 tonnes CO2eq/ ha.

5. Final scenario – Wheat silage from premium wheat land. This is the simplest of switch as rotations and management will remain similar to previous rotations. It will be attractive to farmers if the AD feedstock price is competitive. There may also be advantages of an early harvest allowing the timely drilling of the following oilseed rape crop, or to allow additional time to help control weeds prior to drilling following crop. This scenario is also likely to occur where an AD plant is built in a predominantly wheat growing area. The economic viability of growing a wheat crop for AD would therefore become greater, given the proximity to the plant. Farmers tend to stick to what they know, therefore if they are used to growing feed wheat and a competitive price is offered for wholecrop, they may continue to grow wheat but for a different purpose.

A listing of the considered scenarios and those chosen for purpose grown crop replacement of food production system crops is shown in Table 5.

Table 5 Likely scenarios and those chosen for illustrative purposes in this report

Scenarios presented herein

Purpose grown crop Displaced area/crops

1 Maize silage Temporary grass (best economic case)

2 Maize silage Premium wheat land (worst economic case)

Maize silage Barley

Maize silage OSR

3 Maize silage Permanent pastures (worst environmental case)

Grass silage Premium wheat land

Grass silage Barley

Grass silage OSR


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4 Grass silage Permanent pastures (best environmental case)

5 Wheat silage Premium wheat land (final scenario)

Wheat silage Barley

Wheat silage OSR

Wheat silage Temporary grass (only if pulling out of dairy and grass silage not needed).

2.5.1 Additional GHG emissions arising from the ploughing up of permanent grass

The approach described in section 2.4 calculates annual emissions arising from agrochemical inputs, mainly manufactured fertilizers. The land is deemed to be tillage land remaining as tillage land. As there is no change of land use the soil carbon (C) stock remains unchanged according to IPCC methodology. However, the ploughing out of permanent grass will lead to mineralization of soil organic matter (SOM) and significant emissions of CO2. Hence for scenario 3 these emissions of CO2 arising from SOM breakdown need to be taken into account. They have also been considered for scenario 4 where grass silage is grown on land in permanent grass as a new sward of more productive grasses better suited to silage production may need to be sown. Additional CO2 emissions generated by ploughing out permanent pasture for purpose grown crops - this approach is for any crop following permanent grass These estimates were made using the guidance provided in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories:

Chapter 2 Generic Methodologies Applicable to Multiple Landuse Categories.

Chapter 5, Cropland.

Chapter 6 Grassland.

Land converted to cropland

In order to estimate the additional GHG emissions arising from the conversion of permanent pasture to the production of any crop purpose grown for AD we need to estimate the annual change in C stocks from all C pools and sources, which are:

Biomass (above-ground and below-ground biomass).

Dead organic matter (dead wood and litter).

Soils (soil organic matter). Estimates of annual change in C stocks from all C pools and sources: Biomass (above-ground and below-ground biomass); As a result of conversion to Cropland, it is assumed (in Tier 1) that the dominant vegetation is removed entirely leading to emissions, resulting in near zero amounts of C remaining in biomass. The Tier 1 method estimates the amount of biomass that is cleared for cropland by multiplying the area converted in one year by the average C stock in biomass in the grassland prior to conversion. This is the destruction of the grass sward by herbicide, cultivation or a combination of both. Default biomass C stocks in grassland are supposedly provided in Table 5.8 of IPCC chapter 5. However, in fact Table 5.8 refers to Chapter 6 for C stocks in a range of grassland types by climate regions. In chapter 6 the only appropriate data for estimating biomass C in grassland is found in Table 6.4 (Default biomass stocks present on grassland, after conversion from other land use). This indicates that for the cold temperate - wet IPCC agroclimatic zone (the zone that covers the UK) the total (above-ground and below-ground) non-woody biomass is 13.6 (tonnes d.m. ha

-1). The default

value for conversion of biomass to C is given as 0.50 tonne of C per tonne of biomass (dry weight) (paragraph 6.1.2.4). Hence the amount of biomass C killed and released as CO2 from the permanent grass field is:


AEA / ADAS 21

6.8 tonnes d.m. ha

-1.

An estimate of the total biomass in the forage maize crop is provided by Table 5.9 (default biomass C stocks present on land converted to cropland in the year following conversion) as 5.0 (tonnes C ha

-1)

for a temperate climate under all moisture regimes. The difference between these two values is the net loss of C from conversion to forage maize cultivation. When considering winter wheat, the same default value, 5.0 t C ha

-1 is used. For grassland it can be

assumed that the biomass will be equal to the biomass of the previous grass.

Dead organic matter (dead wood and litter); No value is given for litter in chapter 6 as it is assumed to be stable under grassland. Nor is any default given in Chapter 5 (Cropland). Since all crops will produce some litter, dead leaves etc., and since all purpose-grown crops are removed whole, it is reasonable to assume the amounts of litter are approximately equal for both crops and there is no net change from conversion from permanent grass to forage maize. Soils (soil organic matter). The greatest C emissions are likely to arise from the loss of soil organic C (SOC) as a result of annual cultivations to plant forage maize and the lack of crop cover over winter. No default values are given by IPCC, other than broad reference categories for soil types under different climate regimes (Table 2.3, chapter 2). These are not subdivided by land use or crop type. Instead 'stock change factors' are quoted in Table 5.5 (of chapter 5). This is a ratio enabling calculation of changes arising from land use change over 20 years. Of the limited range of options, 'long-term cultivated for temperate/boreal climates under moist precipitation' was the most appropriate. This is however based on the land already being under cultivation. Nevertheless, it can be used to represent the decrease in SOC by using as the starting point current estimates of SOC under permanent grassland in the UK to obtain an estimate of the likely decrease over 20 years. An estimate of the typical SOC concentration under permanent grass in the UK is available in Table 2.3.10.1. of the Environment Agency report 'The Development and Use of Soil Quality Indicators for Assessing the Role of Soil in Environmental Interactions', Science Report SC030265 (March 2006), which gives a mean SOC of 3.2% for sandy loam and 5.4% for clay soils. For the purposes of this study we have used the value for sandy loam soils as being more representative of the types of soils which might be used for purpose-grown crops of forage maize. Since the Environment Agency report cites SOC as a % it needs to be converted to t ha

-1. Sandy loam

soils under grassland in England and Wales were reported to have an average bulk density of 1.12 t m

-3 in the Environment Agency report. One ha (10,000 m

2) of soil, to a depth of 25 cm, regarded as

the average cultivation depth and the depth to which surface bulk density applies, has a volume of: 10,000 * 0.25 = 2500 m

3.

At a bulk density of 1.12 t m

-3 this gives a soil weight of:

2500 * 1.12 = 2800 t. Hence if SOC is 3.2% by weight, then the weight of soil C per ha is: 2800 * 3.2/100 = 89.6 t Hence the estimated annual change over 20 years, using the Stock Change Factor =: (SOCpg * 0.69)/20 Where:


22 AEA / ADAS

SOCpg = Average UK SOC (tonnes C ha

-1) for permanent grass

0.69 = The Relative Stock Change Factor over a 20 year period for predominantly arable crops. Values used to estimate CO2 emissions arising from the conversion of permanent grassland to purpose grown forage maize and winter wheat

P grass

forage maize

Difference

Biomass (tonnes C ha-1

) 6.8 5.0 1.8 Dead OM NA NA 0 Soil OC Stock change 0.69 Average UK estimate for soil C (tonnes C ha

-1) (EA, 2006) 89.6

Imputed difference over 20 years (tonnes C ha-1

) 27.8 Average annual change in soil C (tonnes C ha

-1) 1.4 1.4

Annual totals C emission in year 1, litter plus annual change in SOC (tonnes C ha

-1)

3.2

Average annual change after year 1 (tonnes C ha-1

) 1.4 1.4 Average yield of forage maize, fresh weight, t ha

-1 40

Annual totals for calculation per t forage maize C emission in year 1, litter plus annual change in SOC (kg C ha

-1)

80

Average annual change after year 1 (kg C ha-1

) 35

Thus the release of carbon from ploughing up of permanent grass to grow forage maize, expressed as kg CO2 per t fresh weight of maize, will be: In year 1, 80 kg C = 293 kg CO2 per t fresh weight of purpose-grown crop. In subsequent years, 35 kg C, = 128 kg CO2 per t fresh weight of purpose-grown crop. The easiest way to express these additional emissions is to average the year 1 emission over 20 years. Hence the value to be added each year will be 136 kg CO2 per t fresh weight. The table below indicates the period over which the additional emissions will occur. Forage maize and winter wheat

Year(s) Additional CO2 emissions per t fresh weight

1 293 2-20 128 20+ 0 Average for years 1-20 136

Permanent grass ploughed out for silage grass There will be a loss of C in year 1, from soil C that breaks down after the permanent grass, which may have lost productivity due to a gradual replacement of high-yielding ryegrasses with lower yielding grasses, is ploughed out. But after the grass has been improved by re-sowing with ryegrass there will be an accumulation of soil C as there will be no further soil disturbance for several years. However, the IPCC guidelines do not explicitly cover this. In table 6.2 of IPCC chapter 6, which deals with grassland, the relative stock change factor for improved grassland is given as 1.0. This factor applies to improved grassland where no additional management inputs have been used and this is the most appropriate scenario for this project. There is also the loss of litter which arises from the ploughing up of grass. However, no estimates are given of the litter in first year grass, so it seems reasonable to conclude that there will be no additional emissions of GHGs arising from the reseeding of permanent pasture to create a sward more suitable for silage production.


AEA / ADAS 23

Other assumptions used in the model It should be noted that the model assumes the use of fossil fuel based nitrogen fertiliser for conventional agricultural crops, but that once an anaerobic digester is built the digestate is used as fertiliser for purpose grown crops. The model also assumes fugitive emissions from the AD process equivalent to 1% of the methane arising.


24 AEA / ADAS

3 Modeling the use of purpose grown crops

In the MCDS tool delivered in April 2011, we modelled the use of purpose grown crops (wheat, maize or grass silage which the user could choose) to examine the scope for AD plants (size, their economics etc). The modelling was done around the operator‟s need to smooth out seasonal variation in dairy/beef farm slurries, to be able to provide a more continuous (guaranteed) energy output; i.e. it was used as a „supplementary feedstock‟. Since then the FiT rates have been changed by the Government and their impact is examined in Section 3.3. In order to study the effect of increasing the use of purpose grown crops in AD, the tool has been added with new modules and has been changed to facilitate greater proportion of purpose grown crops to be considered in the feedstock; rather than as supplementary feedstock. In this exercise we have presented the economics of AD plants by comparing „economically attractive‟ and „economically viable‟ plants. For commercial AD plants, an IRR of greater than 15% is used as the benchmark. Defra has published some analysis looking at returns on capital in agriculture, which has found that the majority of farms operate on very low returns; sometimes even negative (Defra Farming and Food Brief, September 2011). The fact that AD also provides other benefits, including those which are specific to on-farm use such as manure management and controlling diffuse water pollution, are other reasons why farmers would accept much lower returns. Consequently we have designed the model to help evaluate all those with positive returns on investment (i.e. with IRR>0%). The user will, however, be able to undertake a greater scrutiny of the output by viewing IRR in different bands.

3.1 Technical and Economic Assessment

In our previous tool, we used a set of technical and economic data, derived from known and published sets of AD plant costs. Correlations were developed for capital and operating costs for use in the model. These are used for the analysis herein as most of the AD plants that use purpose grown energy crops, do so by forming a mix that can be digested in the widely applied continuous stirred tank digestion system. NNFCC (2011) have examined the use of purpose grown crops along similar lines, but by considering waste-crop systems that can be applied within the confines of individual farms. They examined the technical and economic benefits of allowing a gradual increase of purpose grown crops in the feedstock to allow use of the continuously stirred (CSTR) digester. Essentially, this maximises the use of purpose grown crops without significant increase in capital cost and mirrors the most likely farmer model in that purpose grown crop is used to improve the economies of scale. The NNFCC model of AD was developed to examine the use of purpose grown crops in proportions of up to 50% fresh weight in the input mix to the farm-based AD plant. Their model allows the incorporation of crop production variables, for different areas of the country:

Climate

Soil type

Slope

Farming type – e.g. an arable based meat industry and cereals in east vs. dairy and grass/ some cereals in west (wholecrop wheat vs. maize/ grass).

When there are dominant inputs of food waste from households and commercial or industrial premises, i.e. a dominant single stream food waste, it may be necessary to restrict the purpose grown crop use to ensure an efficient digestion system and to not exceed ~15% DM in feedstocks needed for conventional CSTR AD systems. The AEA/ADAS tool has been modified to examine the effects of gradually increasing the proportion of purpose grown crops up to the limit covered in the NNFCC report for DECC; however there are major differences that should be highlighted. The scenarios examined by the NNFCC work were for „farm-based‟ or closed systems; i.e. for an individual farm business scenario; whereas, our tool deals with an


AEA / ADAS 25

open system that could be applied on a local area basis in E&W (i.e. through use of the 10x10km gridded data). Figure 2 illustrates 10 sets of feedstocks covering the full range of the compositions found in viable AD plants (taken from the April 2011 AEA/ADAS tool output). It shows that there are some areas with a large proportion of food waste and, at the other extreme, there are some areas with a large proportion of livestock waste or agricultural residues. Food waste is a rich feedstock, which in conventional AD systems could require anything between 30 and 90 days as residence time to ensure maximisation of energy generation. This feedstock is available throughout the year, generally without much seasonal variation. In contrast the agricultural waste and feedstocks vary with season, particularly with respect to quantity, but also composition. To address this we have pegged the percentage purpose grown crops to the agricultural feedstock. Consequently all percentages of purpose grown crop(s) in the feedstock are expressed independently of the food and garden waste.

Figure 2 Range of feedstock compositions found in viable AD plants

3.2 AD Tool Modifications

In summary the primary elements of the MCDS tool are as before. The AD plant is based on the conventional CSTR system. Correlations developed for capital cost of AD plants, whether Type 1 or 2, and that for the annual operation cost are virtually the same. The key differences are highlighted below.

Dairy and beef cattle are assumed to be housed only in winter and the consequent drop in slurry is assumed to be 50%, which is made up by either wheat silage, maize silage or grass silage, depending on the priorities set by the user and their availability within the locality (i.e. within the 10x10 km cell area). The same quantity of dairy and beef cattle slurry are taken (i.e. from 50% of the year when housed) but they can be added with a specified proportion of purpose grown crop (i.e. up to 50% within the agricultural feedstock).

The Feed-in-Tariff was based on two bands: 9p/kWh for AD/CHP generating greater than 500 kWe; and 11.5 p/kWh for those generating less. This has now been changed to allow the three bands under the revised FIT scheme. The impact of this change alone, for the scope of AD in E&W is given in the next section.


26 AEA / ADAS

As before, some of the key system and operating parameters as well as key prices used in the analyses are given as default values, but the user of the tool will be able to change these; see Table 6.

Table 6 Technical and economic input parameters (changeable by user)

3.3 Impact of the Changes in Feed in Tariff

Since the Feed in Tariff (FiT) scheme started in April 2010, a set of rates existed for anaerobic digestion installations. These were used in our earlier tool (delivered in April 2011). However, in June 2011 the Government announced new FiT levels for AD installations, to be effective from 1

st August

2011 (DECC, June 2011). Both the old and the new rates are set out in Table 7 below.

Table 7. The old and new FiT rates

Generation capacity Old FiT rates New FiT rates

>500 kWe 9 p/kWh 9 p/kWh

>250 kWe – ≤ 500 kWe 11.5 p/kWh

13.0p/ kWh

≤ 250 kWe 14.0p/ kWh


AEA / ADAS 27

We have used the earlier MCDS tool, which accounts for „supplementary use of purpose grown crops‟, to determine the effect of the new FiT when all other conditions are kept the same. Figure 3 shows changes in the number of economically attractive (IRR>15%) as well as „viable‟ (IRR>0%) AD plants under the old and the new FiT bands. These have been further divided into Type 1 and Type 2 AD plants as earlier defined

10 to illustrate the impact of FiT on agricultural feedstock.

Relative comparisons of overall resource utilisation, energy generation and GHG savings are summarized in Table 8.

Figure 3 Changes in economic viability of AD plants due to FIT changes

Table 8 Resource utilisation, energy generation and GHG saving for economically attractive plants (IRR>15%)

Old FIT New FIT % change

Waste utilisation

Food waste (Mt/y) 9.8 9.9 1.0%

Livestock waste (Mt/y) 7.1 7.8 10.0%

Other agricultural waste (Mt/y) 0.8 0.8 0.0%

Energy generation

Net methane produced (TWh/y) 10.04 10.30 2.6%

GHG saving Greenhouse gas emission savings (ktCO2eq/y) 3,148 3,128 -0.64%

This comparative assessment shows that:

10

Defined as:

Type 1 being food waste driven (defined as having ≥15% food and garden waste)

Type 2: agricultural AD plants (defined as having <15% food and garden waste)


28 AEA / ADAS

The changes in FiT lead to a rise in overall viable AD plants and economically attractive plants. Viable AD plants increase from 855 to 903 (i.e. by 48 AD plants); whereas those economically attractive (IRR > 15%) increase from 333 to 372 (i.e. by 39).

The new FiT bands lead to 10% increase in agricultural feedstock utilisation; whereas that of food waste is only 1% increase. The analysis also shows that there is likely to be a marginal increase in energy generation but a marginal reduction in GHG saving. Care should be taken when interpreting such data and analysis, as they represent a form of estimation based on geographical approximation of the waste. In practice, however, it is possible that AD project developers will, where possible, make small adjustments to the plants they build to take economic advantage from the new FiT rate bands. For instance, if it looks feasible to develop an AD plant between 500kWe and 1000 kWe within a locality (10km grid area), there may be a temptation to install two plants – thereby gaining higher FiT rates for the renewable electricity generation. As such the numbers of AD plants would be higher than those predicted by this tool.

3.4 Using the MCDS Tool for Purpose Grown Crops As mentioned above the multi-criteria decision support (MCDS) tool consists of an Excel workbook with underlying code plus a GEO database. The user should not need to open the database directly, as it is handled by the underlying code in the Excel workbook. This section provides the steps involved in using the overall tool. In comparison with the original tool delivered in April 2011, this extension has an extra capability to analyse purpose grown crop related scenarios in addition to the originally modelled examination based on 10x10km areas in England and Wales. Model Inputs There are several types of input that the model deals with:

1. The data in the GEO database. The user of the model should not access this database directly to prevent corrupting the data. The model reads these data into Excel through VBA code. This is then used alongside other inputs.

2. Predetermined parameters in the model. These are global parameters that do not vary from cell to cell. They are fixed throughout the model runs and stored in an excel spreadsheet. These include: conversion factors for CH4 production, dry matter percentages, N content and plant operational parameters. They cannot be accessed or changed by the tool user.

3. User inputs. The user can choose waste streams, key input parameters related to electricity production and economics as well as the criteria weights.

As before, most of the actions described in this section have to be carried out through the “User” worksheet, to which the user is directed after accepting the conditions of use. Figure 4 shows the typical steps involved in analysing purpose grown crops using the Tool.


AEA / ADAS 29

Figure 4 Steps to run the model

This provides spreadsheet output containing a summary of values of purpose grown crop related variables. The output table contains the key variable values related to purpose grown crops, such as feedstock usage, crop displacement, energy recovery and GHG emissions. The output also includes three key charts illustrating the results: Resource utilisation, crop availability, utilisation and energy recovery.

Plotting The user can choose to plot any of the available data or results variables. This will appear in the “Plot” sheet and the user will be redirected there automatically.

Detailed information and ordering of areas by priorities

Provides (spreadsheet) outputs such as those of the original tool and additional purpose grown crop related variables.

Criteria values and AD scores for each grid cell

Tables of feedstock used, energy and material balance, GHG emissions, and capital and operating costs by (10x10 km) grid cells

Total values for resources used and outputs used in all plants above 0% IRR and economically attractive (IRR >15%) plants

Step 1 As in the original tool, in step 1 the user can select economic and technical input parameters and desired waste feedstocks. Any combination of livestock slurries, agricultural waste, food wastes and garden waste may be obtained by ticking the relevant boxes, as illustrated in Figure 5 below. If the user wants to go back to the original technical and economic parameters that were set when this product was created, this can be done by pressing “Restore Defaults” button in the Key Input Parameter area (they are also shown in Figure 5 below).

Step 1: Select Primary Data

Feedstocks and Technical & Economic Input Parameters

Step 2: Select Scenarios (Purpose Grown Crop choice, allowance and displaced crop

priorities)

Detailed Run

Step 4: Further analysis

Step 3: Press the button to execute calculations


30 AEA / ADAS

Figure 5. Feedstock and technical parameter selection

Step 2 and Step 3 To set a Scenario in the current tool, the user has to define three factors (see Figure 6):

1. Purpose grown crop: Choose between Maize silage, Grass silage and Wheat silage.

2. Purpose grown crops feedstock allowance: this is the maximum allowed proportion of purpose

grown crop in overall agricultural feedstock, expressed as a percentage.

3. Potential displaced crops and their priorities. Select boxes next to the crops you wish to

include in analysis. Then assign them a priority from 1 to 5 – this is used by the model to

determine which land areas to pick first for growing the purpose grown crop. It is assumed that

only if there is not sufficient land of the first priority crop in an area, the purpose grown crop

will then be grown on the second priority land and so on.

Figure 6: Choosing Purpose Grown Crop and Displaced Crops

When the user has decided on all the inputs, the way to get an overview of the effects of purpose grown crops is to click the “Create PG Crop Summary” button. This will take the user to the “Purpose Grown Crops” sheet and provide an output of the form seen in Figure 7.


AEA / ADAS 31

Figure 7: Example Output

Step 4 Apart from the results seen in the purpose grown crop summary, the user can view purpose grown crop related data and result variables visualised on a GIS based plot. This will appear in the “Plot” sheet and the user will be redirected there automatically.

Figure 8: Snapshot of plotting options area of the Tool

This version of the model also allows the user to obtain the same format of detailed output as was available in the original model – but with details of purpose grown crops included.

To do this, in addition to the normal Step 1 and Step 2 inputs, the user should select the criteria weights to define their priorities, or leave it as it is if not interested in arranging the cells based on particular priorities (Figure 9).

Figure 9: Criteria selection


32 AEA / ADAS

After doing this, pressing the “Detailed Run” button will produce (within about five minutes) the detailed output, containing tables of criteria values, energy, material variables, greenhouse gas related outputs and so on. Model outputs Overall, the model produces 3 types of output:

1. Database updates. After running the model calculations, all result variables are added to the Access database. The results are associated with grid cells in the same way as the input data. For each 10x10 km square, this includes: criteria values; normalised criteria values; AD Score, as well as purpose grown crop related variables. Once again, as with inputs, the user should not access this form of output directly. The following two types of output are available for the model user.

2. Tabular form of results and charts on an Excel spreadsheet. These results are shown as tables in Excel.

3. Graphical output – plot – on Excel spreadsheet. The user can see the model outputs as well as input data visualised in a form of GIS based plot. The plotting is done on an Excel spreadsheet by accessing and analysing GIS data in the Access database.

In the pink area titled “Scenarios” there is a drop-down box that allows the user to pick from one of the set scenarios or create a new one. There are 5 predefined scenarios. The weightings corresponding to the selected scenario will appear in the purple box titled “Weights”. Structure Please note there are five visible worksheets in the Excel workbook (“Tool”):

The “Information” sheet contains the key project information.

The “User” sheet contains the main user interface with the model. All input parameters and weights are selected in this sheet. The running mode and plotting options are also selected by the user on this sheet. For that purpose, this sheet contains several clearly separated sections for inputs and a section with buttons for choosing the model running mode and plotting the results.

The remaining three sheets contain output. On opening the Tool they will display the outputs of the last runs and will be updated each time the model is run again. “Purpose Grown Crops” sheet shows the compact output – the Purpose Grown Crops summary. It contains core values of material usage, energy output and crop displacement obtained from the selected purpose grown crop scenario.

The “Details” sheet displays criteria and AD Score values for grid cells. In addition to that, it contains detailed information about waste usage, electricity production, purpose grown crop usage and costs of a potential AD plant in each 10x10 km grid square.

“Plot” is the graphical output sheet. It displays an Excel generated England and Wales map showing a chosen data or result variable.

In general, the “User” sheet will be used for any user interaction with the model, the three output sheets will be used for analysing results, while “Information” sheet is designed to provide the MCDS tool description.


AEA / ADAS 33

4 Results for Selected Scenarios and Discussion

This section demonstrates the use of the MCDS tool by examining the five different scenarios of purpose grown crops (maize, wheat, grass) displacing selected food or feed crops. The basis of selecting the scenarios was given earlier in Section 2.5 and the actual scenarios are listed in Table 9.

Table 9 The five scenarios used for illustrating use of the MCDS tool

Scenario no. Purpose grown crop

Displaced area/crops**

1 Maize silage Temporary grass (best economic case)

2 Maize silage Premium wheat land (worst economic case)

3 Maize silage Permanent pastures (worst environmental case)

4 Grass silage Permanent pastures (best environmental case)

5 Wheat silage Premium wheat land (worst possibility)

** Note the way the model is designed; it will choose secondary displacement areas too, in cases where the chosen crop area is insufficient. Below results are presented for (a) for the use of agricultural feedstock alone and then (b) for all feedstocks, including the food and garden waste; in both of these we illustrate Scenario 1 - the best economic case (see Section 2.5) as well as comparative assessment of the five scenarios. Subsequently, sensitivity analysis is carried out to test overall impacts on AD if (1) no food waste were available, (2) if the gate fee for food and garden waste was to fall to zero and (3) consequences of using purpose grown crops beyond 50% in the agricultural mix. Appendix 1 gives the full tabulated results for the five scenarios.

4.1 Agricultural Wastes with Purpose Grown Crops

4.1.1 Scenario 1: Maize silage grown on temporary grass land (excluding food waste)

In this section we explore the use of agricultural wastes alone (i.e. excluding food waste) alongside purpose grown crops in AD, so as to provide a perspective on those based on farm-based systems only. Such AD plants would not be subjected to the rigorous permitting requirements, as those using food wastes are, and therefore would be the natural choice for some farmers in England and Wales. Table 13 summarises resource use, land use change, energy generation and GHG savings based on Scenario 1 for those AD plants considered to be economically attractive (i.e. IRR>15%); this is further illustrated in Figure 11. This is then followed by Table 11 and Error! Reference source not found. for all economically viable plants (IRR>0%).


34 AEA / ADAS

Table 10 Summary statistics of economically attractive AD plants (i.e. IRR>15%) based on Scenario 1 with agricultural wastes only

Note: the fugitive emissions rate for the AD plant is included in the “Net GHG emissions” line and the rate is set at 1% of the methane production, for the purposes of this analysis (although previous Defra studies have indicated this could be up to 3% for small scale farm digesters).

0% 10% 20% 30% 40% 50%

Materials

Quantity of agricultural w aste Mt/y 1.1 0.7 0.2 0.1 0.0 0.0

Quantity of municipal w aste Mt/y 0.0 0.0 0.0 0.0 0.0 0.0

Quantity of PG crop in feedstock Mt/y 0.0 0.1 0.0 0.0 0.0 0.0

Total area displaced ha 0.0 1,990.5 997.7 995.6 586.6 0.0

Quantity of w aste Mt/y 1.1 0.8 0.2 0.1 0.1 0.0

Crops Displaced

Wheat ha 0.0 0.0 0.0 104.8 279.8 0.0

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0

Temporary grass ha 0.0 1,990.5 997.7 890.8 306.9 0.0

Permanent pastures ha 0.0 0.0 0.0 0.0 0.0 0.0

% Crop Area Displaced

% Wheat displaced 0.00% 0.00% 0.00% 0.01% 0.02% 0.00%

% Barley displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

% Temporary grass displaced 0.00% 0.28% 0.14% 0.12% 0.04% 0.00%

% Permanent pastures displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%

Energy

Methane from digester M m3/y 97.5 74.9 22.5 15.1 7.0 0.0

Net methane produced GWh 987.2 758.5 227.7 152.5 71.0 0.0

Generation capacity MW 39.4 30.3 9.1 6.1 2.8 0.0

Electricity produced GWh 345.5 265.5 79.7 53.4 24.8 0.0

GHG Balance

GHG emissions from PG crop tCO2/y 0.0 7,962.0 3,990.7 3,982.5 2,346.5 0.0

GHG saving due to displaced crops tCO2/y 0.0 -8,151.1 -4,085.5 -4,041.5 -2,307.3 0.0

PG crop effect on GHG balance tCO2/y 0.0 -189.1 -94.8 -59.0 39.2 0.0

Net GHG Emissions (all inclusive) ktCO2/y -151.5 -118.5 -32.2 -22.0 -10.2 0.0

Costs and numbers of plants

Number of potential plants in

10x10km areas 81 58 14 7 2 0

Of these Type 1 (large) 1 2 4 2 1 0

Of these Type 2 (small) 80 56 10 5 1 0

Total capital cost M £ 157.0 129.9 45.2 29.8 14.0 0.0

Purpose grown crops (% in agricultural

feedstock)


AEA / ADAS 35

Figure 10 Graphical representation of results for economically attractive AD plants in scenario 1 with agricultural wastes only

0.0

500.0

1,000.0

1,500.0

2,000.0

2,500.0

10% 20% 30% 40% 50%

Are

a d

isp

lace

d,

he

ctar

es

Proportion of purpose grown crops in feedstock

Crop displacement (ha)

Wheat Barley

OSR Temporary grass

Permanent pastures

81

58

147

2 0

0

10

20

30

40

50

60

70

80

90

0% 10% 20% 30% 40% 50%

Nu

mb

er

of

pla

nts

Proportion of purpose grown crop in feedstock

Economically attractive AD plants

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0% 10% 20% 30% 40% 50%

Ag

ric

ult

ura

l w

aste

, M

t/

y


Resource utilisation (Mt/y)

0.0

200.0

400.0

600.0

800.0

1,000.0

1,200.0

0% 10% 20% 30% 40% 50%Me

th

an

e p

ro

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ctio

n,

GW

h/

y


Net methane produced (GWh)

-160.0

-140.0

-120.0

-100.0

-80.0

-60.0

-40.0

-20.0

0.0

0% 10% 20% 30% 40% 50%

GH

G E

mis

sio

ns,

k

tCO

2/

ye

ar


Net GHG emissions (ktCO2/y)


36 AEA / ADAS

Table 11 Summary of resource use, land use change, energy generation and GHG savings based on economically viable AD plants (i.e. IRR>0%), based on Scenario 1 with agricultural wastes only

0% 10% 20% 30% 40% 50%

Materials




Total area displaced ha 0.0 13,308.3 20,980.8 35,854.7 59,886.8 115,900.4


Crops Displaced

Wheat ha 0.0 2.2 97.6 852.1 3,131.7 10,228.3

Barley ha 0.0 0.0 0.0 0.0 0.0 45.0

OSR ha 0.0 0.0 0.0 0.0 0.0 2.2

Temporary grass ha 0.0 13,306.0 20,883.2 35,002.7 56,755.2 105,534.6



% Wheat displaced 0.00% 0.00% 0.01% 0.05% 0.18% 0.60%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy


Net methane produced GWh 2,326.7 3,082.2 2,933.7 3,546.5 4,600.1 7,281.4


Electricity produced GWh 814.4 1,078.8 1,026.8 1,241.3 1,610.0 2,548.5

GHG Balance

GHG emissions from PG crop tCO2/y 0.0 53,233.1 83,923.3 143,418.9 239,547.3 464,094.1

GHG saving due to displaced crops tCO2/y 0.0 -54,496.7 -85,883.7 -146,542.6 -244,187.2 -470,666.2

PG crop effect on GHG balance tCO2/y 0.0 -1,263.5 -1,960.5 -3,123.7 -4,639.9 -6,572.1

Net GHG Emissions (all inclusive) ktCO2/y -590.0 -764.1 -606.8 -711.4 -929.3 -1,487.1



10x10km areas 309 372 311 320 360 451



Total capital cost M £ 568.3 828.1 1,053.0 1,244.1 1,577.9 2,427.5


feedstock)


AEA / ADAS 37

Figure 11 Economically viable AD plants (i.e. IRR>0%) based on Scenario 1 with agricultural wastes only

0.0

20,000.0

40,000.0

60,000.0

80,000.0

100,000.0

120,000.0

140,000.0

10% 20% 30% 40% 50%

Are

a d

isp

lace

d,

he

ctar

es



Wheat Barley

OSR Temporary grass

Permanent pastures

309

372

311 320360

451

0

50

100

150

200

250

300

350

400

450

500

0% 10% 20% 30% 40% 50%

Nu

mb

er

of

pla

nts


Number of viable AD plants

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0% 10% 20% 30% 40% 50%

Ag

ric

ult

ura

l w

aste

, M

t/

y



0.0

2,000.0

4,000.0

6,000.0

8,000.0

0% 10% 20% 30% 40% 50%Me

th

an

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ro

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ctio

n,

GW

h/

y



-1,600.0

-1,400.0

-1,200.0

-1,000.0

-800.0

-600.0

-400.0

-200.0

0.0

0% 10% 20% 30% 40% 50%

GH

G E

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tCO

2/

ye

ar




38 AEA / ADAS

Figure 12 Maps showing suitable locations of AD plants and strains of displacing temporary grass for growing maize silage, based on Scenario 1 considering agricultural wastes (i.e. excluding food waste)

The left hand graph shows the location of AD plants: the areas in white – yellow are those where AD can be used; black represents „no-go‟ areas and light grey those areas where there is no potential for AD. The right hand graph shows the scenario results: the more yellow the square is, the greater the proportion of area subject to change due to purpose grown crops.

The above two sets of results (for economically attractive and viable AD plants) show remarkably different trends as the proportion of maize silage is increased from 0% to 50%:

The number of economically attractive AD plants decrease from 81 with no silage to virtually

no plants if 50% maize silage is taken; whereas the corresponding increase in economically

viable AD plant from 309 to 451.


agricultural waste to nothing (as AD plants are likely to show IRR >15%); whereas it is quite

variable with the viable AD plants – going through a form of maximum at 10% crop use and a

possible minimum at ~20% crop use but then rising to around 4.6 Mt/y with 50% purpose

grown crop in the feedstock.

Crop displacement areas rise to around 2,000ha at 10% crop feed but then declines to nothing

at 50% crop feed as no plants remain economically attractive. As far as viable AD plants are

concerned, crop displacement area rises gradually to 116,000ha with 50% purpose grown

crops.





These differences stem from the fact that the addition of purpose grown crops reduces returns on investment of those considered to be economically attractive (IRR>15%) but it has the opposite effect on plants that are barely viable and generally smaller scale based on agricultural wastes. Similar differences can be observed between economically attractive and viable plants within scenarios 2-5, when only agricultural wastes are considered. Given that farmers traditionally have

IRR (AD plant locations) - agri waste - 50% PG crop allowed


AEA / ADAS 39

tended to settle for lower than 15% returns on their investment, it is prudent to examine the impact of purpose grown crops on all economically viable plants (i.e. IRR>0%). As such the following sections will comment mainly on the economically viable AD plants.

4.1.2 Comparison of five runs (excluding food waste)

Table 15 compares all economically viable plants for the five scenarios. It shows that power generation increases with the rising percentage of purpose grown crops. In particular, energy generation rises from ~2.3 TWh to 13.5 TWh, wheat silage providing the highest value of energy generation. GHG savings also rise from ~0.6 MtCO2/y to ~ 2.9 MtCO2/y, while the number of viable AD plants rise from 309 to ~655 with 50% purpose grown crops.

Table 12 Comparison of economically viable AD plants (i.e. IRR>0%) based on agricultural wastes for the chosen five runs

% Purpose grown crops in agricultural feedstock 0% 10% 20% 30% 40% 50%

Land use change

Run 1-MS on Grass Total ha 0 13,308 20,981 35,855 59,887 115,900

Run 2-MS on Wheat Total ha 0 13,308 20,980 35,855 59,887 115,900

Run 3-MS on Pgrass Total ha 0 13,308 20,980 35,855 59,887 115,900

Run 4-GS on Pgrass Total ha 0 12,254 20,311 38,655 80,758 160,265

Run 5-WS on Wheat Total ha 0 23,073 41,004 83,892 147,901 244,389

Energy recovery

Run 1-MS on Grass GWh 2,326 3,082 2,933 3,546 4,600 7,281

Run 2-MS on Wheat GWh 2,326 3,082 2,933 3,546 4,600 7,281

Run 3-MS on Pgrass GWh 2,326 3,082 2,933 3,546 4,600 7,281

Run 4-GS on Pgrass GWh 2,326 3,141 3,097 4,052 6,409 10,574

Run 5-WS on Wheat GWh 2,326 3,808 4,264 6,390 9,324 13,508

GHG saving

Run 1-MS on Grass ktCO2/y -590 -764 -607 -711 -929 -1,487

Run 2-MS on Wheat ktCO2/y -590 -757 -597 -693 -896 -1,422

Run 3-MS on Pgrass ktCO2/y -590 -670 -459 -459 -511 -683

Run 4-GS on Pgrass ktCO2/y -590 -764 -617 -780 -1,229 -1,950

Run 5-WS on Wheat ktCO2/y -590 -983 -965 -1,432 -2,040 -2,890


Run 1-MS on Grass 309 372 311 320 360 451

Run 2-MS on Wheat 309 372 311 320 360 451

Run 3-MS on Pgrass 309 372 311 320 360 451

Run 4-GS on Pgrass 309 383 330 374 514 655

Run 5-WS on Wheat 309 450 425 512 598 649

4.2 All wastes with Purpose Grown Crops

4.2.1 Scenario 1: Maize silage grown on temporary grass land – all wastes

Table 13 summarises resource use, land use change, energy generation and GHG savings based on Scenario 1 for those AD plants considered to be economically attractive (i.e. IRR>15%); this is further illustrated in Figure 13. This is then followed by Table 14 and Figure 14 for all economically viable plants (IRR>0%).


40 AEA / ADAS

Table 13 Summary statistics of economically attractive AD plants (i.e. IRR>15%), based on Scenario 1 considering all wastes

Note: the fugitive emissions rate for the AD plant is included in the “GHG emissions from AD plant operations” line and the rate is set at 1% of the methane production, for the purposes of this analysis (although previous Defra studies have indicated this could be up to 3% for small scale farm digesters).

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 58.3 663.4 1,200.6 2,313.1

Barley ha 0.0 0.0 0.0 0.0 1.2 19.4

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0




% Wheat displaced 0.00% 0.00% 0.00% 0.04% 0.07% 0.14%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy




Electricity produced GWh 2,421.7 2,308.1 2,298.7 2,274.6 2,164.9 2,069.4

GHG Balance



PG crop effect on GHG balance tCO2/y 0.0 -579.1 -1,138.9 -1,499.6 -1,685.9 -1,422.6

Net GHG Emissions (all inclusive) ktCO2/y -3,310.0 -3,172.6 -3,127.7 -3,054.8 -2,891.3 -2,722.4



10x10km areas 429 375 346 311 269 220



Total capital cost M £ 1,956.0 1,877.8 1,862.3 1,825.8 1,718.5 1,616.1


feedstock)


AEA / ADAS 41

Figure 13 Graphical representation of results for economically attractive AD plants in scenario 1 considering all wastes

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429

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Economically attractive AD plants

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Municipal waste Agricultural waste

5,000.0

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42 AEA / ADAS

Table 14 Summary of resource use, land use change, energy generation and GHG savings based on economically viable AD plants (i.e. IRR>0%) - Scenario 1

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 2.2 153.3 1,500.7 5,502.9 16,428.8

Barley ha 0.0 0.0 0.0 0.0 42.3 452.1

OSR ha 0.0 0.0 0.0 0.0 0.0 12.1


Permanent pastures ha 0.0 0.0 0.0 6.5 81.1 1,476.5


% Wheat displaced 0.00% 0.00% 0.01% 0.09% 0.32% 0.97%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy

Methane from digester M m3/y 1,091.5 1,180.2 1,327.6 1,522.5 1,783.8 2,217.9




GHG Balance

GHG emissions from PG crop tCO2/y 0.0 106,982.1 243,201.3 423,749.2 668,757.6 1,070,947.3

GHG saving due to displaced crops tCO2/y 0.0 -109,522.2 -248,926.3 -433,271.9 -682,170.2 -1,079,259.5





10x10km areas 1020 987 1009 1033 1054 1095





feedstock)


AEA / ADAS 43

Figure 14 Economically viable AD plants (i.e. IRR>0%) - Scenario 1: impacts of increasing purpose grown crops in feedstock

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44 AEA / ADAS

Figure 15 Maps showing suitable locations of AD plants and strains of displacing temporary grass for growing maize silage, based on Scenario 1 considering all wastes

The left hand graph shows the location of AD plants: the areas in white – yellow are those where AD can be used; black represents „no-go‟ areas and light grey those areas where there is no potential for AD. The right hand graph shows the scenario results: the more yellow the square is, the greater the proportion of area subject to change due to purpose grown crops.

The above two sets of results (for economically attractive and viable AD plants) show remarkably different trends as the proportion of maize silage is increased from 0% to 50% as part of the agricultural feedstock mix:

The number of economically attractive AD plants decrease from 429 with no silage to around

220 plants with 50% maize silage; whereas there is an increase in economically viable AD

plant from 1020 to 1095.

Waste utilisation decreases within the economically attractive AD plants; whereas it is fairly

constant with the viable AD plants.


but up to around 270,000ha for viable AD plants.




are considered they increase from ~5 MtCO2/y saving to ~7 MtCO2/y.

These differences stem from the fact that the addition of purpose grown crops reduces economic viability of AD plants, especially of those driven by large quantities of food wastes. However, the use of crops in AD has a greater and positive influence on plants which are largely based on agricultural waste feedstock. Similar differences can be observed between economically attractive and viable plants, within scenarios 2-5. Given that farmers traditionally have tended to settle for lower than 15% returns on their investment, it is prudent to examine the impact of purpose grown crops on all economically viable plants (i.e. IRR>0%). As such the following sections will comment mainly on the economically viable AD plants.

IRR (AD plant locations) - all wastes - 50% PG crop allowed


AEA / ADAS 45

4.2.2 Comparison of five runs (all wastes)

Table 15 compares all economically viable plants for the five scenarios. These show that for all scenarios power generation increases with the rising percentage of purpose grown crops. In particular, energy generation rises from ~11 TWh to 28 TWh - notably, wheat silage providing the highest value of energy generation. GHG savings also rise from ~5.3 MtCO2/y to ~ 8.6 MtCO2/y while the number of viable AD plants rise from 1020 to ~1180 with 50% purpose grown crops.

Table 15 Comparison of economically viable AD plants (i.e. IRR>0%) for the chosen five runs

% Purpose grown crops in agricultural feedstock 0% 10% 20% 30% 40% 50%

Land use change

Run 1-MS on Grass Total ha 0 26,746 60,800 105,928 167,079 265,725

Run 2-MS on Wheat Total ha 0 26,746 60,800 105,928 167,079 265,725

Run 3-MS on Pgrass Total ha 0 26,746 60,800 105,928 167,079 265,725

Run 4-GS on Pgrass Total ha 0 24,084 55,843 100,021 162,610 261,375

Run 5-WS on Wheat Total ha 0 41,146 92,012 159,544 260,044 403,618

Energy recovery

Run 1-MS on Grass GWh 11,047 11,945 13,437 15,410 18,054 22,447

Run 2-MS on Wheat GWh 11,047 11,945 13,437 15,410 18,054 22,447

Run 3-MS on Pgrass GWh 11,047 11,945 13,437 15,410 18,054 22,447

Run 4-GS on Pgrass GWh 11,047 11,973 13,570 15,770 18,833 23,669

Run 5-WS on Wheat GWh 11,047 12,813 15,011 17,956 22,344 28,489

GHG saving

Run 1-MS on Grass ktCO2/y -5,262 -5,315 -5,594 -5,954 -6,420 -7,239

Run 2-MS on Wheat ktCO2/y -5,262 -5,299 -5,558 -5,891 -6,320 -7,083

Run 3-MS on Pgrass ktCO2/y -5,262 -5,127 -5,166 -5,208 -5,248 -5,393

Run 4-GS on Pgrass ktCO2/y -5,262 -5,286 -5,543 -5,883 -6,342 -7,067

Run 5-WS on Wheat ktCO2/y -5,262 -5,584 -5,990 -6,552 -7,419 -8,580


Run 1-MS on Grass 1020 987 1009 1033 1054 1095

Run 2-MS on Wheat 1020 987 1009 1033 1054 1095

Run 3-MS on Pgrass 1020 987 1009 1033 1054 1095

Run 4-GS on Pgrass 1020 995 1032 1077 1119 1177

Run 5-WS on Wheat 1020 1036 1060 1083 1128 1156

4.3 Constraints on AD Implementation

4.3.1 Limited FiT Budget

In March 2011 a fast-track review of the FiTs scheme was launched by DECC, since the original target Internal Rate of Return (IRR) for solar PV of 5% was being exceeded and a huge demand for larger PV schemes (i.e. schemes that fall into the new band of >250 kW to 5 MW) was envisaged. In contrast there was almost a complete lack of activity in the AD field. The overall budget is relatively fixed (although it may be subject to review), and so the implementation of such solar projects would threaten the amount available for AD plants, as they are generally smaller and slower to implement. As such the number of plants that would be supported is likely to be less than the analysis here suggests.

4.3.2 Impact food waste and falling gate fees

As was reported in the previous report (Defra, April 2011), the gate fees linked to the food wastes improve the economic attractiveness of AD plants and consequently lead to much higher utilisation of all feedstock – agricultural waste feedstocks as well as food waste. Comparing results obtained by


46 AEA / ADAS

including and excluding food and garden wastes from the feedstocks clearly show their importance in making more AD plants economically attractive. The modelling adopted in the MCDS tool assumes that all food waste is potentially available to AD. Undoubtedly some food waste will be committed to other disposal routes, depending on the local authority contracts with waste management companies. These variations are not taken into account and as a result it is likely that the actual implementation of AD would be lower than suggested here. (There is, however, evidence that even where the local authorities had previously adopted composting, they are considering adopting AD where it is seen to be financially and environmentally attractive). WRAP‟s Gate Fees Report 2011 shows that the AD plant gate fee for food waste is gradually decreasing. The 2010 gate fee was £13 per tonne lower than that in 2009 (currently the median is reported to be £43 per tonne with the range between £36 and £64 per tonne). We believe that the trend is likely to continue downwards. Key factors behind this (cited in the Gate Fee report) are the increasing number of AD facilities based on food waste (some of which are very large scale) that earn additional revenue from electricity and heat generation. To assess this trend, we undertook additional runs based on Scenario 1, with and without gate fees (but without considering any supply-demand effects that would normally ensue). The results show that when the food waste gate fee is zero, not only is there a decrease in the use of food waste, but there is a significant decline in agricultural waste utilisation. This reflects the importance of the gate fee linked with food waste. To understand how the decline in agricultural feedstock comes about, we examined AD plant specific information, for the run based on Scenario 1 using 50% maize silage. These have shown that there is a significant decline in returns, which lead to lower utilisation of all wastes, including dairy, beef cattle and pig slurry.

4.3.3 Finance and Regulatory Issues

Apart from those given above, there are other significant barriers to the adoption of AD:

Capital costs are considered to be too high to provide reasonable returns on investment,

particularly with the agricultural AD schemes. As a result, it is difficult to raise bank funding.

Build Operate and Transfer (BOT) finance mechanisms appear to be available where there is

a clear case for merchant AD plants, which are invariably based on food waste. Such a

mechanism is not available to agricultural AD schemes, as there is a perceived high risk by

banks, investors and the farm owners.

AD plants that use food waste in farm based digesters find the process of acquiring planning

consent particularly difficult. During the recent fast-track FIT review (March 2011), there was a

specific comment that the paperwork required to comply with the Animal By-Product

Regulations (requiring all feedstocks to be pasteurised) and to meet the PAS 110 standard

added £600,000 to the capital cost on an AD plant. Some farm owners also cited lack of clear

policy or guidance on the use of purpose grown crops as a barrier to implementing AD plants.

There are other barriers related to project implementation and replication across scales, which compound on the smaller scale plants particularly. These factors are likely to fewer AD plants being implemented than the analysis here suggests.

4.4 Using Greater Proportion of Purpose Grown Crops

The project team undertook a visit to Stoke Bardolph AD plant, which is based solely on the purpose grown crop from its 750ha estate. It was hosted by Severn Trent Greenpower Ltd, who own and operate the plant. The host provided a great deal of information and insight into the design, engineering, operation as well as the growing of crops and the economics of the plant. Appendix 2 gives the summary of the visit and key information acquired. The estate on which the plant is based cannot grow food crops for human consumption, so it is dedicated to providing feedstock for the AD plant. It has the capacity to provide around 35,000 t/y of maize and around 2,000 t/y of wheat – after ensiling the whole crops. We have used this plant‟s data


AEA / ADAS 47

to check how close our tool comes, particularly to the AD plant calculations. There is a remarkable closeness with respect to the energy output, GHG balance and capital cost of the plant.

For illustration in this report only, and at the request of Defra, we have extended the use of this model up to 90% crop feed. It should be noted that the model is based on AD plants designed for low solids systems, based on CSTR type reactors. As the content of purpose grown crop in the feedstock increases, the solids level also increases. It is likely that alternative designs, based on high solids system, might be more appropriate to the digestion of such feedstock. Any impact of the change of solids content to the design of the plants is not considered by the MCDS tool. It is however a vital area to be considered if significant proportions of crops are to be used in AD plants.

For scenario 1, based on the use of purpose grown maize silage (grown on temporary grass land), four additional runs were set up with 60%, 70%, 80% and 90% crop.

The results presented in The results for GHG reflect the interaction between two systems: the agricultural crops displaced and the crops grown for AD. Essentially large GHG savings from displacement of crops is matched by the GHG emissions from those crops grown for AD. Therefore the increased GHG savings reflect the increased biogas use from the system.

Table 16 and Figure 16 show the figures for economically viable AD plants (IRR>0%). These show that for England and Wales, there would be

A rise in land use change of up to 2.7 Mha

The number of AD plants would be ~1000

A total energy recovery of up to ~118 TWh.


48 AEA / ADAS

The results for GHG reflect the interaction between two systems: the agricultural crops displaced and the crops grown for AD. Essentially large GHG savings from displacement of crops is matched by the GHG emissions from those crops grown for AD. Therefore the increased GHG savings reflect the increased biogas use from the system.

Table 16 Summary of resource use, land use change, energy generation and GHG savings based on economically viable AD plants (IRR>0%)


AEA / ADAS 49

60% 70% 80% 90%

Materials

Quantity of agricultural w aste Mt/y 6.3 8.9 10.8 12.0

Quantity of municipal w aste Mt/y 0.0 0.0 0.0 0.0

Quantity of PG crop in feedstock Mt/y 9.4 20.7 43.2 106.7

Total area displaced ha 235,586.3 517,938.4 1,080,744.6 2,667,451.8

Quantity of w aste Mt/y 15.7 29.6 54.0 118.7

Crops Displaced

Wheat ha 37,031.9 132,690.0 361,664.2 816,899.6

Barley ha 1,398.0 17,695.5 75,555.0 261,137.4

OSR ha 111.8 1,312.3 7,570.5 59,847.5

Temporary grass ha 194,892.7 333,690.2 463,064.6 564,119.2

Permanent pastures ha 2,152.1 32,550.4 172,890.4 965,448.0


% Wheat displaced 2.18% 7.81% 21.30% 48.11%

% Barley displaced 0.18% 2.24% 9.57% 33.08%

% OSR displaced 0.02% 0.24% 1.38% 10.92%

% Temporary grass displaced 26.99% 46.22% 64.14% 78.14%

% Permanent pastures displaced 0.05% 0.73% 3.89% 21.73%

Energy

Methane from digester M m3/y 1,266.8 2,513.3 4,932.5 11,656.8

Net methane produced GWh 12,821.7 25,437.1 49,921.9 117,978.7

Generation capacity MW 512.3 1,016.3 1,994.6 4,713.8

Electricity produced GWh 4,487.6 8,903.0 17,472.7 41,292.6

GHG Balance

GHG emissions from PG crop tCO2/y 954,074.0 2,249,153.6 5,265,231.0 15,931,498.8

GHG saving due to displaced

crops tCO2/y -943,167.8 -1,973,459.5 -3,850,147.8 -8,589,428.1

PG crop effect on GHG balance tCO2/y 10,906.2 275,694.1 1,415,083.2 7,342,070.8

Net GHG Emissions (all inclusive) ktCO2/y -2,566.5 -4,736.4 -7,954.8 -13,703.4



10x10km areas 565 719 887 1059

Of these Type 1 (large) 335 505 743 1009

Of these Type 2 (small) 230 214 144 50

Total capital cost M £ 4,161.3 7,937.2 14,792.7 32,372.8

Purpose grown crops (% in

agricultural feedstock)


50 AEA / ADAS

Figure 16 Operating data for AD plants with increasing percentage of purpose grown crops in feedstock

4.5 Other Comments

At present milk producing farms are finding it difficult to stay in business and some see the opportunity of expanding maize growing as a crop for AD. The cost-benefit of this has been examined by NNFCC at individual farm level where changes in the total number of livestock animals leads to the prospect of growing maize silage for AD; they have also examined the GHG balance (NNFCC, 2011).

The datasets used in the development of the AEA/ADAS tool are based on data at one point in time (2009/10) and it does not lend itself to studying varying livestock in any one particular region.

A shift in land use of more than 10% is likely to have some impact on production potential and market supply. It is normal to have up to 10% variation between years, due to weather and market fluctuations, and sometimes more. This level of change would be triggered for wheat at just above

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AEA / ADAS 51

70% energy crops, and for barley 80%. There is unlikely to be an issue for oilseed rape. The largest changes are impacting on the displacement of grassland, which is significant, even at 60%, with over 50% of the temporary grassland being displaced to maize. At this level the number and/or intensity of current livestock numbers could not be sustained.

There are also environmental implications of growing maize. There are potential benefits to biodiversity due to spring cropping, but these may be diluted if large blocks of land are put into continuous maize, without mitigation measures. The cultivation of maize can also lead to increased soil erosion risk and nutrient loss due to the later harvesting in wet conditions, and the open stubble left over winter. These issues are also discussed in Section 2.2.


52 AEA / ADAS

5 Conclusions

A multi-criteria decision support (MCDS, comprising Excel Model and a database) tool that facilitated policy and strategy based examination of anaerobic digestion (AD) plants across England and Wales (E&W) was delivered to Defra in April 2011. This tool was based on waste arisings for feedstocks and allowed the use of purpose grown crops to be able to smooth out seasonal variation in dairy/beef farm slurries.

The same tool has now been modified to study the effects of increasing the use of purpose grown crops in AD up to 50%. This percentage is quoted for the overall agricultural feedstock; any presence of food or garden waste will be additional to these. FiT bands have changed from August 2011, and this too has been incorporated. The tool will allow the user to study policy based impacts related to the use of purpose grown crops in AD plants within England and Wales and discern key trends with respect to land use and energy generation, alongside some of the environmental impacts. It should not be used to „read specific outputs‟ on a plant by plant or area by area basis.

The three crops that are most likely to be grown for purpose grown energy crops for AD are grass, forage maize and forage wheat. The choice will depend on soil type and climate, production economics and market prices, and agronomic issues. There are some geographical limitations to current forage maize production which means it is more suited to light and medium soils and more southerly latitudes. There are no limits on grass and wheat production in terms of soil type and latitude, but yields do vary significantly in different situations. These crops will become attractive to grow if the price for AD is equal to or greater than the value in other markets. For grassland, the comparison is the value of livestock produced from the land. The decisions could be quite localised depending on yield potential and costs of production. The agronomic considerations will include how the crop fits into current production systems. Growing maize may be an attractive option for some as it can be grown continuously, it is spring planted so spreads workload and it has lower inputs of fertiliser and sprays, but it can be late to harvest which can cause problems with soil and following crops, and there is a need for specialist machinery. Grass will be attractive for those already in a grass based system, but it may be that some could switch to growing grass. Forage wheat will be an option for many farmers who will already have suitable machinery and skills, but there are agronomic limitations in that it usually needs to be grown in rotation for best yields, and growing for a feedstock may not be competitive with other markets such as milling.

Increasing cropping for use as energy crops will result in changes in land use and/or changes in end use of the output. The impact that this will have on food security is complex and needs to take into account global commodity supply for products such as wheat. Crop land use varies on an annual basis due to weather and crop economics in any case with wheat area ranging by over 200,000ha (2.0%) in recent years for example, and other crops have had larger swings in area. It is therefore possible that energy crops could be accommodated without major impacts up to certain levels.

The environmental impacts of changing to crops for AD primarily arise if there is a switch from permanent grassland to cropping, as this will release sequestered carbon. There may also be other impacts, such as possible soil erosion from increased maize production; and impacts on biodiversity if there are large areas of monoculture such as continuous maize.

Use of purpose grown crops benefit the AD system as it helps to improve the overall „volumetric‟ and „operational‟ efficiency of the AD process.

The changes in FiT lead to a rise in overall viable AD plants and economically attractive plants. Viable AD plants increase from 855 to 903 (i.e. by 48 AD plants); whereas those economically attractive (IRR > 15%) increase from 333 to 372 (i.e. by 39). There is also a 10% increase in agricultural feedstock utilisation but only 1% increase in food waste. The analysis also shows that there is likely to be a small increase in energy generation but only a marginal reduction in GHG saving.

Care should be taken when interpreting such data and analysis, as they represent a form of estimation based on geographical approximation of the waste. In practice, however, it is possible that AD project developers will make adjustments to the AD plants to take economic advantage from the new FiT rate bands and thereby lead to a greater number of AD plants. The MCDS tool use has also been demonstrated with selective outputs in this report, together with their discussion based on a select five scenarios:


AEA / ADAS 53

Scenario 1: Maize silage grown on temporary grass land Scenario 2: Maize silage grown on wheat land Scenario 3: Maize silage grown on permanent pastures Scenario 4: Grass silage grown on permanent pasture land Scenario 5: Wheat silage from premium wheat land

The tool has been designed to study outputs for economically attractive AD plants (with IRR>15%) and viable AD plants (with IRR>0%). Scenario 1 has been illustrated fully in Section 4, with agricultural waste and then with all waste included. In each case this then followed by comparative assessments of all five scenarios. The key conclusions from Scenario 1 based on agricultural waste and as the proportion of maize silage is increased from 0% to 50%, are as follows:

The number of economically attractive AD plants decrease from 81 with no silage to virtually

no plants if 50% maize silage is taken; whereas the corresponding increase in economically

viable AD plant from 309 to 451.


agricultural waste to nothing (as AD plants are likely to show IRR >15%); whereas it is quite

variable with the viable AD plants – going through a form of maximum at 10% crop use and a

possible minimum at ~20% crop use but then rising to around 4.6 Mt/y with 50% purpose

grown crop in the feedstock.

The area of crop displacement rises to around 2,000ha at 10% crop feed but then declines to

nothing at 50% crop feed as no plants remain economically attractive. As far as viable AD

plants are concerned, crop displacement area rises gradually to 116,000ha with 50% purpose

grown crops.

Net methane (or biogas) production from economically attractive AD plants decreases from




The key conclusions from Scenario 1 based on all wastes and as the proportion of maize silage is increased from 0% to 50%, are:

The number of economically attractive AD plants decrease from 429 with no silage to around

220 plants with 50% maize silage; whereas the corresponding increase in economically viable

AD plants is from 1020 to 1095.

Waste utilisation decreases within the economically attractive AD plants (due to fall in their

number); whereas it is fairly constant with the economically viable AD plants.


and up to around 270,000ha for viable AD plants.

Net methane (or biogas) production in economically attractive AD plants decreases from



are considered they increase from ~5 MtCO2/y saving to ~7 MtCO2/y.

These differences, whether with agricultural wastes or with all wastes, stem from the fact that the addition of purpose grown crops reduces economic viability some of the large AD plants and hence their number. However, the use of crops in AD has a greater and positive influence on plants which are largely based on agricultural waste feedstock. Similar differences can be observed for scenarios 2-5. Given that farmers traditionally have tended to settle for lower than 15% returns on their investment, it is prudent to examine the impact of purpose grown crops on all economically viable plants (i.e. IRR>0%).

As was reported in the previous report (Defra, April 2011), the gate fees linked to the food wastes improve the economic attractiveness of AD plants and consequently lead to much higher utilisation of all feedstock – agricultural waste feedstocks as well as food waste. When the food waste gate fee is


54 AEA / ADAS

zero, not only is there a decrease in the use of food waste, but there is a significant decline in agricultural waste utilisation. This reflects the importance of the gate fee linked with food waste.

Overall, the use of purpose grown crops improves the economic viability of AD plants, resulting in the potential for the development of more plants. This is related to the increased methane production from the co-digestion of purpose grown crops.

In scenario 1 we carried out a limited number of runs with purpose grown crop ranging from 50% to 90%. One important result from this analysis is that for agricultural waste based systems: as the proportion of purpose grown crops increases above 70% the land use begins to impact permanent pasture, i.e. there is significant land use change. This has other important implications in terms of environmental impact and GHG emission savings, a consequence which should be investigated further. It must also be noted that the model was not designed for the types of AD system that might be used for the high dry matter content feedstocks. This may have an impact on the analysis and the conclusion that can be drawn for such high levels of purpose grown crops in AD.

The analysis showed that at lower percentages of purpose grown crops there was no displacement of permanent pasture. However, as the percentages are increased other arable and grass land area would also be required.

NFU, in association with CLA, have estimated that for their predicted 1000 on-farm AD plants, there will be some 100,000 to 125,000 hectares that will provide purpose grown crops, mostly in rotation with other crops. We cannot verify or compare this here as their estimation appears to be based on a standard design and scale of operation.

The analysis reported using the MCDS tool shows that the use of purpose grown crops alters the economic viability of AD plants. But this effect varies depending on the size and type of AD plants. For AD plants with significant food waste (Type 1), it depresses the economic viability; whereas for those primarily based on agricultural feedstock (Type 2) it increases economic viability, especially at the smaller scale end.

AD plants that use mainly (or only) energy crop(s) will remain „special cases‟ where the land cannot be used for food production. For illustration, we tested the use of this model for up to 90% crop feed, also under scenario 1. It showed for England and Wales, this would require up to 2.7 Mha, leading to around ~1000 AD plants which would be capable of providing up to ~118 TWh of biogas, without a significant change in the GHG savings.

The outline assessment presented in this report suggests that this level of land take will not have any great impact on food security. Further research may be required to properly assess where land may be taken out of food production, which crops or livestock might be displaced.

The subject of the wider impacts is fraught with scientific and technical uncertainties, particularly regarding the GHG emissions related to the cultivation of purpose grown crops. This includes a lack of understanding of indirect land use change and how to account for it. In addition, there is a degree of uncertainty around technology, economics and environmental issues related to AD plants. For instance, it should be noted that the model is based on AD plants designed for low solids systems, based on CSTR type reactors. As the content of purpose grown crop in the feedstock increases, the solids level also increases. It is likely that alternative designs, based on high solids system are needed. This is a vital area to be investigated, especially with respect to their potential use in England and Wales, if significant proportions of crops are to be used in AD plants.


AEA / ADAS 55

5.2 References

Anon (2010) Fertiliser Manual (RB209). 8th Edition, June 2010. Defra, London

Baggott, S., Brown, L.M.R., Murrells, T., Passant, N., and Watterson, J. (2004) UK Greenhouse Gas Inventory, 1990 to 2002. Annual Report for submission under the Framework Convention on Climate Change, AEA Technology plc, Culham Science Centre, Abingdon, Oxon., OX14 3ED, UK.

Brockman, J.S. and Gwynn, P.E.J. (1988) Journal of the British Grassland Society, 19, 169-155.

Croezen H J et al (2010). Biofuels: Indirect land use change and climate impact; report by Delft, June 2010, CE Publication (www.ce.nl)

DECC (June, 2011); New Feed-in Tariff levels for large-scale solar and anaerobic digestion announcement, Press release: 11/046, 09 June 2011; http://www.decc.gov.uk/en/content/cms/news/pn11_046/pn11_046.aspx

DEFRA (2011); Implementation of AD in E&W: Balancing optimal outputs with minimal environmental impacts; final report, AEAT/ENV/R/3162, April 2011.

DEFRA report -'European experience with small-scale and on-farm anaerobic digestion (WR1119).

Defra Farming and Food Brief (September 2011), which includes balance sheet analysis and farming performance. See http://www.defra.gov.uk/statistics/2011/10/03/foodfarmbrief-sep11/

Encrop (2009) energy from field energy crops – a handbook for energy producers www.encrop.net

IEA Bioenergy Report on Biogas from Energy Crop Digestion (2010), produced under Task 37 on Energy from Biogas and Landfill Gas. Authors: Rudolf Braun, Peter Weiland and Arthur Wellinger.

IEA Bioenergy Task 37. Germany country report on biomass (2011). www.iea-biogas.net

Murphy Bokern (2011) pers. communications between Luke Spadavecchia and Donal Murphy-Bokern, August 2011

NNFCC (2011); Farm-Scale Anaerobic Digestion Plant Efficiency; report produced by Lucy Hopwood of NNFCC for DECC; March 2011.

RB209 Fertiliser manual Guidelines – Defra (2010) http://archive.defra.gov.uk/foodfarm/landmanage/land-soil/nutrient/documents/rb209-rev-100609.pdf

Wilkinson, J.M., Newman, G. and Allen, D.M. (1999) Maize: producing and feeding maize silage, Chalcombe, Lincoln, pp. 73.

Williams, A.G., Audsley, E. and Sandars, D.L. (2006) Determining the environmental burdens and resource use in the production of agricultural and horticultural commodities. Main Report. Defra Research Project IS0205. Bedford: Cranfield University and Defra. Available on www.silsoe.cranfield.ac.uk, and www.defra.gov.uk

Williams, A.G., Audsley, E. and Sandars, D.L. (2010). Environmental burdens of producing bread wheat, oilseed rape and potatoes in E&W using simulation and system modelling; Int J Life Cycle Assessment, 2010, 15:855-868.

WRAP Gate Fees Report, 2011. Comparing the cost of alternative waste treatment options.

http://www.ce.nl/

http://www.decc.gov.uk/en/content/cms/news/pn11_046/pn11_046.aspx

http://www.defra.gov.uk/statistics/2011/10/03/foodfarmbrief-sep11/

http://www.encrop.net/

http://www.iea-biogas.net/

http://archive.defra.gov.uk/foodfarm/landmanage/land-soil/nutrient/documents/rb209-rev-100609.pdf

http://www.silsoe.cranfield.ac.uk/

http://www.defra.gov.uk/


56 AEA / ADAS


AEA / ADAS 57

Appendices

Appendix 1: Outputs for Scenarios 1-5: Agricultural Wastes only

Scenario 1: Maize Silage to Temporary Grass as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 2.2 97.6 852.1 3,131.7 10,228.3

Barley ha 0.0 0.0 0.0 0.0 0.0 45.0

OSR ha 0.0 0.0 0.0 0.0 0.0 2.2




% Wheat displaced 0.00% 0.00% 0.01% 0.05% 0.18% 0.60%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance







10x10km areas 309 372 311 320 360 451





feedstock)


58 AEA / ADAS

Scenario 1: Maize Silage to Temporary Grass as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 104.8 279.8 0.0

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0

Temporary grass ha 0.0 1,990.5 997.7 890.8 306.9 0.0



% Wheat displaced 0.00% 0.00% 0.00% 0.01% 0.02% 0.00%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance



PG crop effect on GHG balance tCO2/y 0.0 -189.1 -94.8 -59.0 39.2 0.0




10x10km areas 81 58 14 7 2 0





feedstock)


AEA / ADAS 59

Scenario 2: Maize Silage to Wheat as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 13,236.1 20,626.9 34,156.0 55,051.8 96,639.5

Barley ha 0.0 58.3 231.8 1,411.5 4,078.3 11,802.7

OSR ha 0.0 0.0 9.8 23.7 106.2 566.0

Temporary grass ha 0.0 13.9 112.3 263.6 650.5 6,801.9



% Wheat displaced 0.00% 0.78% 1.21% 2.01% 3.24% 5.69%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.02% 0.10%



Energy





GHG Balance



PG crop effect on GHG balance tCO2/y 0.0 6,161.9 8,089.3 15,112.9 28,538.6 58,806.8




10x10km areas 309 372 311 320 360 451





feedstock)


60 AEA / ADAS

Scenario 2: Maize Silage to Wheat as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 1,990.5 997.7 995.6 586.6 0.0

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0

Temporary grass ha 0.0 0.0 0.0 0.0 0.0 0.0



% Wheat displaced 0.00% 0.12% 0.06% 0.06% 0.03% 0.00%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance



PG crop effect on GHG balance tCO2/y 0.0 701.9 292.5 340.4 140.7 0.0




10x10km areas 81 58 14 7 2 0






AEA / ADAS 61

Scenario 3: Maize Silage to Permanent Pastures as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 310.7 1,222.0

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0


Permanent pastures ha 0.0 13,308.3 20,980.8 35,854.7 59,576.1 114,678.5


% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.02% 0.07%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance




Net GHG Emissions (all inclusive) ktCO2/y -590.0 -670.3 -459.0 -459.2 -510.6 -683.3



10x10km areas 309 372 311 320 360 451





feedstock)


62 AEA / ADAS

Scenario 3: Maize Silage to Permanent Pastures as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 109.8 0.0

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0


Permanent pastures ha 0.0 1,990.5 997.7 995.6 476.8 0.0


% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.01% 0.00%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance



PG crop effect on GHG balance tCO2/y 0.0 13,832.0 6,932.8 6,918.6 3,340.3 0.0




10x10km areas 81 58 14 7 2 0





feedstock)


AEA / ADAS 63

Scenario 4: Grass Silage to Permanent Grass as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 168.3 856.2

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0




% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.01% 0.05%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy

Methane from digester M m3/y 229.9 310.4 306.0 400.4 633.3 1,044.8




GHG Balance




Net GHG Emissions (all inclusive) ktCO2/y -590.0 -763.6 -617.0 -780.0 -1,229.4 -1,950.1



10x10km areas 309 383 330 374 514 655





feedstock)


64 AEA / ADAS

Scenario 4: Grass Silage to Permanent Grass as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 55.4 0.0

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0


Permanent pastures ha 0.0 1,884.6 951.3 983.7 466.1 0.0


% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance



PG crop effect on GHG balance tCO2/y 0.0 3,767.3 1,901.7 1,966.5 972.9 0.0




10x10km areas 81 62 16 9 2 0





feedstock)


AEA / ADAS 65

Scenario 5: Wheat Silage to Wheat as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 22,704.6 39,770.3 78,502.2 133,055.9 206,135.1

Barley ha 0.0 220.5 995.1 4,305.4 10,170.4 18,673.7

OSR ha 0.0 15.3 13.9 135.6 321.7 2,203.0

Temporary grass ha 0.0 132.8 225.1 948.9 4,322.4 16,821.4



% Wheat displaced 0.00% 1.34% 2.34% 4.62% 7.84% 12.14%


% OSR displaced 0.00% 0.00% 0.00% 0.02% 0.06% 0.40%



Energy

Methane from digester M m3/y 229.9 376.2 421.3 631.3 921.3 1,334.6




GHG Balance




Net GHG Emissions (all inclusive) ktCO2/y -590.0 -983.0 -964.8 -1,432.0 -2,039.9 -2,889.8



10x10km areas 309 450 425 512 598 649



Total capital cost M £ 568.3 1,036.2 1,451.8 2,074.6 2,821.7 3,787.6


feedstock)


66 AEA / ADAS

Scenario 5: Wheat Silage to Wheat as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 3,398.7 2,652.1 3,894.7 5,387.1 8,879.1

Barley ha 0.0 0.0 19.7 25.2 25.2 0.0

OSR ha 0.0 0.0 0.0 10.6 10.6 0.0




% Wheat displaced 0.00% 0.20% 0.16% 0.23% 0.32% 0.52%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance




Net GHG Emissions (all inclusive) ktCO2/y -151.5 -153.4 -68.0 -73.7 -83.1 -115.5



10x10km areas 81 70 28 26 24 31





feedstock)


AEA / ADAS 67

Appendix 2: Outputs for Scenarios 1-5: all wastes

Scenario 1: Maize Silage to Temporary Grass as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 2.2 153.3 1,500.7 5,502.9 16,428.8

Barley ha 0.0 0.0 0.0 0.0 42.3 452.1

OSR ha 0.0 0.0 0.0 0.0 0.0 12.1




% Wheat displaced 0.00% 0.00% 0.01% 0.09% 0.32% 0.97%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance







10x10km areas 1020 987 1009 1033 1054 1095





feedstock)


68 AEA / ADAS

Scenario 1: Maize Silage to Temporary Grass as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 58.3 663.4 1,200.6 2,313.1

Barley ha 0.0 0.0 0.0 0.0 1.2 19.4

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0




% Wheat displaced 0.00% 0.00% 0.00% 0.04% 0.07% 0.14%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance



PG crop effect on GHG balance tCO2/y 0.0 -579.1 -1,138.9 -1,499.6 -1,685.9 -1,422.6




10x10km areas 429 375 346 311 269 220





feedstock)


AEA / ADAS 69

Scenario 2: Maize Silage to Wheat as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 25,537.7 56,184.0 94,360.3 141,162.0 207,627.5

Barley ha 0.0 517.3 1,924.5 5,736.7 13,970.3 30,512.7

OSR ha 0.0 23.4 61.6 133.5 420.0 1,081.0

Temporary grass ha 0.0 667.1 2,630.3 5,691.4 11,445.4 25,027.4



% Wheat displaced 0.00% 1.50% 3.31% 5.56% 8.31% 12.23%


% OSR displaced 0.00% 0.00% 0.01% 0.02% 0.08% 0.20%



Energy





GHG Balance







10x10km areas 1020 987 1009 1033 1054 1095





feedstock)


70 AEA / ADAS

Scenario 2: Maize Silage to Wheat as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 5,735.5 11,193.7 16,355.3 20,080.1 23,299.0

Barley ha 0.0 106.6 218.2 277.3 430.2 566.7

OSR ha 0.0 4.9 15.1 21.3 38.5 62.1

Temporary grass ha 0.0 248.8 766.6 1,476.9 1,791.3 2,187.2



% Wheat displaced 0.00% 0.34% 0.66% 0.96% 1.18% 1.37%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.01% 0.01%



Energy





GHG Balance







10x10km areas 429 375 346 311 269 220





feedstock)


AEA / ADAS 71

Scenario 3: Maize Silage to Permanent Pastures as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 310.7 1,286.1

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0




% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.02% 0.08%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance

GHG emissions from PG crop tCO2/y 0.0 252,745.2 574,563.1 1,001,023.3 1,577,201.7 2,504,092.9


PG crop effect on GHG balance tCO2/y 0.0 185,854.6 422,501.5 736,096.4 1,158,947.6 1,837,894.3




10x10km areas 1020 987 1009 1033 1054 1095





feedstock)


72 AEA / ADAS

Scenario 3: Maize Silage to Permanent Pastures as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 230.5 680.4

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0




% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.01% 0.04%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance







10x10km areas 429 375 346 311 269 220





feedstock)


AEA / ADAS 73

Scenario 4: Grass Silage to Permanent Grass as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 168.3 856.2

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0



% Crop Area Displaced 24,083.5 55,843.1 100,021.0 162,610.2 261,374.7

% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.01% 0.05%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance







10x10km areas 1020 995 1032 1077 1119 1177





feedstock)


74 AEA / ADAS

Scenario 4: Grass Silage to Permanent Grass as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 0.0 0.0 0.0 138.0 508.0

Barley ha 0.0 0.0 0.0 0.0 0.0 0.0

OSR ha 0.0 0.0 0.0 0.0 0.0 0.0




% Wheat displaced 0.00% 0.00% 0.00% 0.00% 0.01% 0.03%


% OSR displaced 0.00% 0.00% 0.00% 0.00% 0.00% 0.00%



Energy





GHG Balance







10x10km areas 429 380 352 322 283 240





feedstock)


AEA / ADAS 75

Scenario 5: Wheat Silage to Wheat as main choice; economically viable plants (IRR>0%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 38,956.1 83,071.6 136,451.4 205,206.0 292,321.9

Barley ha 0.0 983.5 4,032.9 11,911.9 29,090.4 52,637.5

OSR ha 0.0 35.5 100.9 358.6 975.6 3,421.7


Permanent pastures ha 0.0 0.0 1.7 45.8 1,225.8 6,395.9


% Wheat displaced 0.00% 2.29% 4.89% 8.04% 12.08% 17.21%


% OSR displaced 0.00% 0.01% 0.02% 0.07% 0.18% 0.62%



Energy



Generation capacity MW 441.4 511.9 599.8 717.4 892.7 1,138.3


GHG Balance







10x10km areas 1020 1036 1060 1083 1128 1156





feedstock)


76 AEA / ADAS

Scenario 5: Wheat Silage to Wheat as main choice; economically attractive plants (IRR>15%)

0% 10% 20% 30% 40% 50%

Materials






Crops Displaced

Wheat ha 0.0 8,765.7 18,193.8 29,374.8 42,225.4 57,315.9

Barley ha 0.0 210.5 463.3 953.0 1,904.5 2,964.3

OSR ha 0.0 10.1 22.2 60.5 99.6 237.9

Temporary grass ha 0.0 420.6 1,230.6 2,387.9 3,802.1 5,492.4



% Wheat displaced 0.00% 0.52% 1.07% 1.73% 2.49% 3.38%


% OSR displaced 0.00% 0.00% 0.00% 0.01% 0.02% 0.04%



Energy





GHG Balance







10x10km areas 429 398 381 369 345 310





feedstock)


AEA / ADAS 77

Appendix 3: Stoke Bardolph AD plant based on purpose grown crops

Summary

Construction: May 2009

Commissioning: May 2010

Development costs: £15m, including plant design, construction and commissioning (but excluding land cost)

Technology supplier: Schmack Biogas GmbH

Feedstock: 35,000t/a maize silage and 2,000t/a whole wheat silage

Land use: 750ha dedicated land, contaminated with elevated levels of heavy metals from historic waste recycling activities.

Power generation capacity: 2.1 MWe

Introduction This visit was organized by Severn Trent Greenpower Ltd

11 at the request of the project manager

dealing with Defra‟s project „Implementation of Anaerobic Digestion in England and Wales: Balancing optimum outputs with Minimal Environmental Impacts‟, which includes examination of the use of purpose grown crops in AD.

For some 120 years, waste arisings from the City of Nottingham has been recycled to the farmland surrounding Severn Trent‟s sewage treatment works at Stoke Bardolph, Nottingham. As a consequence the land has become contaminated with elevated levels of heavy metals rendering it unsuitable for food crop production.

Severn Trent has been farming the land for many years growing crops for cattle fodder and industrial use but in 2007 Severn Trent began to examine alternative uses and particular for renewable energy generation.

A number of factors encouraged them to consider renewable energy generation for the site. In supplying over 2 billion litres of drinking water each day and treating all of the waste water from around 8 million customers, Severn Trent uses a huge amount of electricity, circa 900GWh each year.

The cost of this electricity at around £50million is a major component of the company‟s operating costs. The cost of energy, energy price volatility and the effects of climate change could have a significant impact on the Company and therefore they have set themselves a target to produce 30% of their own electricity needs from renewables by 2015.

The Stoke Bardolph estate is sufficient to produce 35,000 t/y of maize and around 2,000 t/y of wheat which is the feedstock for their new Energy Crop AD power plant. Site visits to established anaerobic digestion (AD) plants in Europe convinced them that there was a business case for the development of an AD plant using ensiled maize.

The Concept The concept involves the use of Severn Trent‟s own land for purpose-grown crops that can be used to produce an easy to store silage feedstock. The plant produces biogas that is used for combined heat and power (CHP) and digestate that is re-cycled to the land to provide fertiliser and soil conditioning. Currently the sewage works has a base load energy requirement of 3.5 MWe, some of this is already being met by generating electricity from sewage gas, but the remainder (around 1MW) is being

11

John Jackson, ST Farm Manager; Martin Dent, Renewable Energy Development Manager; and Justin Bailey, Biosolids sludge and C-strategy. Severn Trent Greenpower Ltd, Stoke Bardolph Sewage Works, Stoke Lane, Burton Joyce, Nottingham, NG14 5HL


78 AEA / ADAS

satisified from the Crop AD plant and a further 1MW is exported to the grid, to net off electricity imports elsewhere. The plant uses some of the heat produced to maintain the digestion process however a surplus amount of heat is produced which Severn Trent is considering options for using on the sewage works or for heating commercial glasshouses or as part of a community heating scheme

Feedstock Severn Trent is using its entire 750ha Stoke Bardolph estate to grow the maize and whole crop wheat feedstock. As the land is so fertile (from the historic recycling activities) the maize yield is generally high at around 50t/ha. Maize is a good energy crop as it yields a high amount of energy per hectare, it is pest and disease resistant and is suitable to be grown as a mono-crop. In the UK, maize is drilled in April and by harvest time in September/October the plants have grown to around 10 foot high. The harvesting process involves chopping up the entire leaves, stem and cobs of the plant into 6-8mm pieces which is then deposited, rolled and covered in purpose built storage clamps. Severn Trent is trialling around 50 alternative new maize varieties of maize to identify those which can produce higher biogas yields. When ensiled properly, the silage can be stored in clamps for many years without losing its energy potential. The digestate from the AD process contains good levels of NPK and is suitable for recycling to the land as a fertiliser replacement. The farm estate is quite flat and there are no problems from run-off pollution from the maize cultivation although it does lie within a nitrogen vulnerable zone (NVZ) which places some restrictions on the timing and quantity of digestate recycling. Severn Trent estimates that its maize production costs are around £17- £18/t (fresh weight) which compares to the market value of maize which could be more than double this figure. Each silage clamp is able to store 7,500 tonnes of maize silage (see photo). The use of the digestate liquor as fertiliser is saving around £100,000/y in fertiliser costs.

The AD process

The plant was supplied by Schmack Biogas GmbH, who were selected as the preferred process supplier due to their track record (with over 300 biogas plants worldwide), and having successfully scaled up this technology to a 10MW biogas plant, at the company‟s headquarters in Schwandorf, Bavaria. There are two parallel lines, each comprising a set of primary and secondary digesters. The primary digesters are fed with the maize silage at a dry matter content of 28-32% and is watered down with recycled digestate to produce a biomass slurry of ~10% solids, after 20 days retention the slurry is then fed to a secondary digester and retained for a further 70 days.


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Feedstock bins 25t/d silage feedstock is fed into feed bins twice a day using a front loader. These covered feed bins hold a total of 35t. The feedstock is automatically fed into the primary digester once an hour using a screw auger.

Primary digesters There are two „Euco‟ plug flow primary digesters. These are long, horizontal digesters, designed to achieve plug flow as they move forward at a steady rate, with a retention time of 20 days. These digesters decrease the solids content in the feedstock from 32% to 14%. Each primary digester has a capacity of 550 m

3. The maize slurry is agitated and heated by a horizontal paddle mixer driven by a

2.2 kWe motor. Hot water is pumped through the central spine of the paddle mixer at 60⁰C to keep

tank contents at 40-42⁰C. The design of this tank allows optimal mixing and distributes the heat evenly within the digester to provide ideal fermentation conditions for the digestion to take place. Approximately 30% of the overall biogas is produced at this stage of the plant (reflecting the hydrogen and CO assimilation by methanogenic bacteria).

Secondary digesters The feedstock and biogas produced in the primary digesters are fed into secondary stage digesters. These are „Coccus‟ digestion tanks, each with a 4,000 m

3 capacity. These reduce the dry solids

content from 10% to around 9% over some 70 days. The Coccus digesters are vertical cylindrical digestion tanks with a central column supporting the roof below the biogas storage section. They are heated by passing hot water through pipes encircling the inside tank walls. This system maintains the

digester temperature at 42⁰C. Three mechanical mixers are arranged at 120 degrees to other at

different heights to allow the forced mixing of the entire digester volume; optimised heat distribution allows greater volumetric loading and therefore greater efficiency of the digestion process. These secondary digesters produce 65% of the biogas (reflecting the acetate conversion routes, as mediated by methanogenic bacteria).

Digestate Separation Digestate produced at the end of the process is basically the digested plant silage. It retains a high NPK (nitrogen, phosphorous, potassium) content and is suitable for use as a natural fertiliser. It is separated into „liquor‟ and „fibre cake‟ fractions. Annual production of digestate is expected to be 26,000m

3 liquid and 5,000t of solids. The liquor is stored in tanks under a press before recycling to

land. A significant proportion is also recycled back to mix with the incoming feeds to the primary digesters; this is designed to retain and enhance the methanogenic bacteria population. The fibre cake is used as a soil conditioner and improver. It may be stored in a clamp bay to be aged before being ploughed in.

AD plant performance parameters

Process Parameters Comment

Feedstock: Whole crop maize and whole crop wheat silage: 35,000 t/y maize silage and 2,000 t/y whole crop wheat

Feedstock characteristics: DM = 28-30% of the total weight

VS = 80% of DM

Hydraulic Retention Time (HRT):

Approximately 90 days; 20 days in primary AD; 70 days in secondary

Temperature: 40-42 degrees C

Gas production: 850 - 900 m3/h

Digestate characteristics: Total solids are around 5 to 6 %, can be lower with longer retention within the digesters, Liquor fraction contains 2-6% DS; and cake 25% DS.

Overall carbon saving: 7,400 tCO2/y relative to the previous operation

Biogas treatment and Utilisation


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The biogas is treated in-situ (within the upper part of the AD process vessel) to decrease the H2S and moisture content. Desulphurisation is achieved using a non-woven fleece material containing bacteria that consume hydrogen sulphide to produce sulphate. To achieve this, air is introduced at a very low concentration (achieving 0.09ppm oxygen within the biogas). The biogas passes through this fleece and into the head space in the upper part of the digestion tank. Moisture in the biogas is removed using condensate traps situated strategically along the biogas pipeline. The biogas is fed into two Jenbacher CHP engines, rated at 1.064MWe. Heat output is rated at 1.122 MWth. The load factor was estimated to be 90%. The aim is to generate 15GWh electricity and 16GWh heat annually. The parasitic load on the AD plant is 4-6% of the power generation and heat use varies between 1% in summer to around 5% in winter. A proportion of the heat is used to maintain the temperature of the digesters at around 42oC and the remainder does not have a use at present. The power is used within the sewage treatment works and is registered under the Feed-In-Tariff scheme.

Plant costs The IRR for the plant was set to be >10% as a condition of finance by Severn Trent. The overall cost of development was £15 million for the overall plant development, excluding the land. This included around £1 million for the CHP set and £1 million for the plant design costs. The costs of grid connection were low because of the existing infrastructure.

Operating costs of around £1m p.a are dominated by the cost of the feedstock production (60%). The AD plant is automated and the labour requirement is low, at around 1.5 full time staff equivalent.

Other Issues Since commissioning Severn Trent have experienced very few problems with the plant extending only to minor mechanical breakdowns. The biology of the plant has remained stable and is constantly being monitored by the specialist process supplier in Germany.

There was not a need for Severn Trent to apply for an Environmental Permit (EP) because the feedstock is 100% crop based although the Environment Agency did grant an Exemption Certificate during the early start up of the biological commissioning phase.

Figure 17 Primary digester design (source: Schmack web site)


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Figure 18 Secondary digester (Source: Schmack web site)

Photos of the plant

Storage of maize silage

The feedstock - maize silage

Digestate storage

CHP plant

Documents

Implementation of AD in E&W