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Life cycle assessment of a solar thermal collector

Fulvio Ardente, Giorgio Beccali,Maurizio Cellura*, Valerio Lo Brano

Dipartimento di Ricerche Energetiche ed Ambientali (DREAM),

Universita di Palermo, Viale delle Scienze, 90128 Palermo, Italy

Received 9 March 2004; accepted 13 September 2004

Available online 23 November 2004

Abstract

The renewable energy sources are often presented as ‘clean’ sources, not considering the

environmental impacts related to their manufacture. The production of the renewable plants, like

every production process, entails a consumption of energy and raw materials as well as the release of

pollutants. Furthermore, the impacts related to some life cycle phases (as maintenance or

installation) are sometimes neglected or not adequately investigated.

The energy and the environmental performances of one of the most common renewable

technologies have been studied: the solar thermal collector for sanitary warm water demand. A life

cycle assessment (LCA) has been performed following the international standards of series ISO

14040. The aim is to trace the product’s eco-profile that synthesises the main energy and

environmental impacts related to the whole product’s life cycle. The following phases have been

investigated: production and deliver of energy and raw materials, production process, installation,

maintenance, disposal and transports occurring during each step. The analysis is carried out on the

basis of data directly collected in an Italian factory.

q 2004 Elsevier Ltd. All rights reserved.

Keywords: Life cycle assessment (LCA); Renewable energy; Solar thermal collector

1. Introduction

All goods and services have an environmental impact along their life cycle. On this concept

the European countries have focused their attention, considering the improvement of

Renewable Energy 30 (2005) 1031–1054

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doi:10.1016/j.renene.2004.09.009

* Corresponding author. Tel.: C39 91 236 131; fax: C39 91 484 425.

E-mail address: [email protected] (M. Cellura).

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F. Ardente et al. / Renewable Energy 30 (2005) 1031–10541032

the eco-performances of products/services as a key point of the European environmental

programme [1]. In other words, global environmental problems can be met only if the use of

the energy and the raw materials per product unit will be reduced, i.e. eco-efficiency increased.

The need to strengthen the ‘green market’ has been successively confirmed in another

official document named ‘the green paper on Integrated Product Policy (IPP)’ [2]. Once a

product is put on the market, there is relatively little that can be done to improve its

environmental characteristics. The IPP approach seeks to reduce the environmental

impacts occurring throughout the entire life cycle of the product since the early stages

of product design and development. Furthermore, the diffusion of the ‘green public

procurement’ should induce the producers to investigate the environmental impacts of

their production and to disseminate the environmental information adopting scientific data

format as the environmental product declaration (EPD) [3].

For IPP to be effective, life cycle thinking needs to become second nature for all those

who come into contact with products [4]. The cognitive process is at the basis of the

environmental performances improving. It is necessary to have detailed and reliable data

on which to base assessments regarding each life cycle step. Life cycle assessment (LCA)

represents an important support tool for IPP and the ‘the best framework for assessing the

potential environmental impacts of products currently available’ [4]. To obtain reliable

results, data should be collected and managed following standardised procedures. The

international standards of series ISO 14040 represent a widespread accepted methodology

[5–7]. The best way to demonstrate the advantage of the life cycle thinking concept is by

demonstrating its practical application. The present paper focuses the attention upon one

of the most common renewable technologies: the solar thermal collectors for warm

sanitary water demand. Renewable energy sources are often presented as ‘clean’ energy,

not considering the environmental impacts related to their manufacture. The production of

the renewable plants, like every production process, entails a consumption of energy and

natural resources as well as the release of pollutants [8].

Many authors have deeply investigated the benefits related to the employment of solar

systems [9–13] including studies regarding LCA of solar collectors and comparative

analyses of different collector’s typologies [14–19]. However, the study’s assumptions or

data references are often not clearly shown. In addition, results are often presented as

aggregated indexes [15–17] making difficult the comparison among different studies or the

dominance analysis of each life cycle step are difficult. Furthermore, some life cycle steps

(as, for example, installation or maintenance processes) are generally not investigated in

detail or are simply neglected. Some studies, in fact, consider the full LCA of a solar

collectors as too much expensive and time consuming [17] or suppose as significant only

the impacts related to materials processing and collector’s assembling [18,19].

On the other hand, the principles of eco-design suggest to employ disaggregated

information to identify the steps with the greatest impacts and with the largest

improvements potentials [20,21]. The aims of this paper are:

–
to trace an eco-balance of an exemplary equipment, referring to a passive thermal. The
research refers to a passive thermal solar collector produced in Italy

–
to grant transparency of assumptions, system boundaries and data sources in order to
allow comparability to other studies

F. Ardente et al. / Renewable Energy 30 (2005) 1031–1054 1033

–
to present results as much disaggregated as possible, in order to show the incidence of
each component and life cycle step and to avoid uncertainties related to weighting

processes and impacts assessment

The presented results are extracted from the case study ‘CS2’ performed within the

works of Task 27—Subtask C of IEA (International Energy Agency) about ‘Performance,

durability and sustainability of advanced windows and solar components for buildings’.

Data regarding the production, the installation and maintenance phases have been directly

collected; thanks to the collaboration of an Italian firm [22]. The data collection has been

also referred to the Environmental Management System active in the production site. Data

regarding raw materials and energy sources have been referred, when possible, to Italian

mean values. When not available, data of other European databases have been employed.

2. The choice of the functional unit (FU)

The first phase of the LCA is the goal and scope definition. It includes an important

step: the clear statement of the functional unit (FU). The FU is defined as the ‘reference

unit expressed as quantified performance of the product system’ [5]. The FU is important

as basis for data collection and for the comparability of different studies referred to the

same product category. The choice of the FU is not always immediate. In our case study

three different alternatives were checked [3]:

1.

1

wat

mo

FU equal to the entire equipment. The results are presented as global quantities

concerning the whole collector. Probably, this is the most intuitive choice but it could

cause misunderstanding. In fact, there are various typologies of collectors, which can

be roughly divided in two main categories: collectors with forced circulating flow and

collectors with natural circulating flow.1 Performing the LCA related to these two

collector’s types, the results could be not comparable.

2.
Impacts per unit of collector area. This alternative may be misleading. Enlarging the
collector surface S, the specific environmental impacts (as, for example, the ‘CO2/S’)

could decrease. So, two collectors with the same total impacts could have different

specific ones. In fact, the collector with the greater surface would be considered as more

‘ecological’ not necessarily being. Furthermore, a greater extension does not imply a

proportional growth of the energy harvest, due to the non-linear relationship between

the collector surface and the collected energy.

3.
Impact per unit of energy output. This alternative is generally chosen for energy
systems [23,24], because it refers to the environmental impacts of the energy

performances of the plant. However, it is difficult to apply this FU to the LCA of solar

collectors. The output of this system is an extremely variable data, depending on

The first one represents the normal flat collector whose thermal fluid is moved by a pump towards a separate

er tank. The second is a compact collector strictly connected to a smaller water tank, and the fluid is naturally

ved by the difference of density caused by the solar heating.


the solar energy input. Confusion could arise referring the impacts to the energy output

because the same collector could have a different eco-profile depending on the location.

Our LCA case study refers to the first FU alternative, and the environmental impacts are

related to the whole collector.

2.1. The studied system

The studied FU is one solar thermal collector (dimensions: 2.005!1.165!0.91 m)

with a total net surface of 2.13 m2. The FU is constituted by three main components:

–
The absorbing collector (including the main framework, the absorbing plate and the
pipes for the thermal fluid flow);

–
The water tank (including the heat exchanger, the coverage, the electrical resistance
and the inner pipes for the sanitary water flow);

–
The external support (employed to fasten the system on the houses roof).
The collector belongs to the category of passive solar device. The water tank and the

absorbing surface are strictly connected, constituting a unique unit, and the thermal fluid

circulation occurs with the natural convection. The internal fluid circuit does not need

pumps and it does not cause power energy consumption. This typology of collector is

particularly recommended for small domestic plants with a medium–low demand of

sanitary warm water.

The water tank and the collector can be directly installed on sloping roofs. The

producing company also furnishes an optional steel support that allows the installation on

flat roofs. This constructive typology being common in Italy, the external support has also

been included into the FU (see Fig. 1).

Fig. 1. Solar thermal collector with water tank and support.


Impacts related to the three components have been disaggregated to grant the

transparency of the study and to define a dominance analysis referring to the main

components of the plant.

2.2. Technical peculiarities and mass detail

The collector framework is made of painted galvanised steel (0.003 m width). A black-

painted copper plate, welded with pipes for the thermal fluid flow, constitutes the

absorbing surface. An aluminium frame with high-reflectance coefficient to increase the

collector’s efficiency protects the plate. The thermal insulation is granted by high-density

polyurethane-PUR foam (0.03 m width).

The collector is covered by high-transparent tempered single glass with low iron-oxides

percentage. The glass (0.004 m width) is shock-proof and it is hermetically fastened to the

framework. To reduce heat losses, vacuum is created inside the collector.

The water tank has 0.16 m3 of capacity and it mainly consists of a galvanised steel

framework. It is protected by the stainless steel coverage, and it is placed on the top of the

collector. The space within the water tank and the external coverage is filled with high-

density PUR foam. There are two circuits for the fluid flows: the heat carrier circuit and the

sanitary water circuit. The thermal fluid is a mixture of water (50–80%) and propylene–

glycol (20–50%) that avoids freezing problems during the cold season. It has been

supposed to use a 50% mixture. The fluid mixture flows along a cylindrical interstice that

works as heat exchanger. The water tank encloses a magnesium anode (to reduce the

corrosion) and an electrical resistance. In the studied FU, this auxiliary resistance is not

computed as a water tank’s part but it is considered separately (in the section ‘other

components’). So, it is easier to state the incidence of this component on the global eco-

profile.

The section ‘other components’ also includes the materials for packaging (cardboard

and the low density polyethylene, ‘LDPE’) and the external high-density polyethylene

(HDPE) pipes used to connect the collector to the water tank.

Galvanised steel bars, together assembled and fastened to the collector by means of

bolts and screws, constitute the support. Table 1 shows the details of employed materials

and masses.

3. Analysis of life cycle phases

The following sections describe the study’s assumptions and the related energy and

environmental impacts occurring during the collector’s life cycle. The following phases

have been investigated: production and delivery of energy and raw materials, production

process, installation, maintenance, disposal and transports occurring during each step.

3.1. Transports

As mentioned above, the FU is mainly composed of metallic and plastic

components.

Table 1

Details of employed materials and masses

Absorbing collector Water tank Support Other parts

Material Mass (kg) Material Mass (kg) Material Mass (kg) Material Mass (kg)

Galvanised

steel

33.9 Galvanised

steel

49.6 Galvanised

steel

27 Card-

board

3.0

Glass 10.5 Stainless

steel

21.0 Stainless

steel

0.5 LDPE 0.8

Copper 8.2 Rigid PUR 4.8 HDPE 0.87

Stainless steel 6.1 Thermal

fluid

5.4 Copper 0.46

Rigid PUR 4.2 Copper 3.8

Aluminium 4 Epoxy dust 0.7

Thermal fluid 0.9 Steel 0.4

Epoxy dust 0.3 Welding rod 0.2

Welding rod 0.1 Brass 0.1

Brass 0.04 Magnesium 0.2

Flexible PUR 0.01

PVC 0.01

Total 68.2 86.2 27.5 5.1


As it is not possible to determine the exact amount of travels for the production of

the solar collector, the ‘tkm’ is assumed as functional unit for truck’s transport.

It represents ‘the energy and environmental impacts referred to the transport of 1000 kg of

products for 1 km route’ [25]. The impacts are then calculated by means of the masses and

the distances.

It has been assumed that every transport occurs by means of trucks with 28,000 kg

capacity. A different assumption regards the glass transport, purchased from a foreign

company, that is supposed transported by medium and high-capacity trucks. Having not

further information, it has been supposed an averaged condition of half load transport for

double way. Specific impacts related to trucks have been referred to Italian studies

performed by the Italian Agency for the Environment Protection [25,26].

Regarding all the input materials employed during the life cycle steps and considering

the mean distance values, it has been estimated a global transport load of 154 tkm. Details

of estimated air emissions are shown in Table 2.

3.2. The production process

Data regarding the collector’s production process have been collected; thanks to a field

analysis. The production process concerns mainly in metals transformation and in

assembling them with other externally worked parts (generally, little plastic or metal

auxiliary parts). The three main components (absorbing collector, water tank and support)

are produced in different periods, then packed and stored in warehouses (Fig. 2).

Successively, external companies sell the collectors, attending to transport and install

them to final users.

Table 2

Estimated transport’s air emissions

Transport’s air emissions

C6H6 (mg) 5.9

C20H12 (mg) 0.03

CO2 (kg) 20

Cd (mg) 0.3

NMVOC (g) 27.4

CH4 (mg) 890.4

CO (g) 56.4

NOx (g) 259.7

SO2 (g) 16.9

Pb (mg) 2.1

Particulate (g) 14.2

N2O (g) 2.8

Zn (g) 0.9


3.2.1. Production of the absorbing collector

The absorbing collector consists mainly of three parts: the framework, the absorbing

plate (including the pipes for the thermal fluid flow) and the glass.

The framework is obtained using a zinc steel plate. After cutting and bending, it is

glazed with epoxy powders. Both the absorber plate and pipes are copper made. The pipes

are separately worked and then welded to the plate by acetylene welding. Having no

available data about acetylene welding, air emissions have been not computed. However,

little quantities of acetylene are used and consequently air emissions can be neglected.

Absorber and pipes are then black painted to increase their absorbance. The absorbing

plate, the framework and the glass are successively assembled together. Finally, PUR

insulation is blown and the external framework is painted with epoxy powders.

Fig. 3 shows the production process flow-sheet with the succession of employed

materials and numbered sub-processes. Each sub-process has been analysed to state the

energy and mass flows (Fig. 4 shows the details of the process number C.1 representing the

production of the external collector’s framework).

3.2.2. Production of the water tank

The water tank mainly consists of three parts: the framework, the interstice and the

external covering. The water tank is made using a galvanised steel sheet cylindrical shaped

(diameter 0.444 m). The side parts are welded to this cylinder. A flange is annexed to one

Fig. 2. Solar collector production flow.

Fig. 3. Collector manufacture, process flow-sheet.


side: this flange works as support for the electrical resistance, the magnesium anode and

the coil copper pipe. Successively, another cylindrical steel sheet is externally welded to

the water tank. The thermal fluid flows inside this interstice and exchanges heat with water

tank.

The external covering is separately produced and painted. Finally, the water tank parts

are assembled together and PUR is injected into empty spaces.

Fig. 5 shows the production process flow-sheet with the details of masses and sub-

processes.

3.2.3. Production of the support

The support consists of various steel bars. These are cut, drilled and finally fastened

together with bolts. Fig. 6 shows the production process flow-sheet with the details of

masses and sub-processes.

Fig. 4. Details of collector’s framework production.

Fig. 5. Water tank manufacture, process flow-sheet.


3.3. Air emissions in the factory

Power energy being the only energy source directly employed during the production

process, there are not direct emissions from fossil fuels combustion. The production

(mainly concerning with cutting and drilling processes) causes the production of scraps

and metallic dusts. However, it has not been possible to state the exact quantities of

released dusts. On the basis of data coming from the Environmental Management System,

dusts have been indirectly estimated as percentage (about 1.5%) of the process scraps

mass. Particular emissions are produced during the plasma cutting, the coating and

Fig. 6. Support manufacture, process flow-sheet.

Table 3

Main air-emissions due to welding

Collector Water tank

Used electrode (kg) 0.1 0.2

Air emissions

Cr (mg) 0.3 0.6

Cr (VI) (mg) 0.1 0.2

Mn (mg) 99.1 198.2

Ni (mg) 0.4 0.8


the welding. These processes are described in the following paragraphs. No water

emissions have been detected.

3.3.1. Shielded metal arc welding

Shielded metal arc welding (SMAW) is employed to weld together various collector’s

parts with welding rods. The elemental composition of the fumes varies with the electrode

type and with the work-piece composition. Hazardous metals have been recorded in

welding [27].

Following the US welding classification, it has been assumed to use the welding rod

class E6010. The specific air pollutants, produced consuming 1 kg of rod E6010, mainly

include: Mn (9.91!10K1 g/kg); Ni (0.04!10K1 g/kg); total Cr (0.04!10K1 g/kg) [27].

Table 3 shows welding emissions related to the water tank and the collector production.

3.3.2. Plasma cutting

Regarding dry plasma cutting of 0.008 m plate we estimate, for stainless steel, the

global release of 30–40!10K3 kg of fumes per cutting minute and, concerning mild steel,

the release of 20–26!10K3 kg of fumes per cutting minute [28]. Table 4 shows the main

components of fumes in dry plasma cutting [28].

Dry plasma cutting is used in the water tank production to cut and drill some stainless

and mild steel plates. As the amount of emission increases increasing the plate thickness

[28], a linear variation of fumes with thickness has been supposed. The used plates have a

thickness of 0.003 m. Concerning the composition of fumes, average values of Table 4

have been chosen. Calculated emissions are summarised in Table 5.

3.3.3. Surface coating

The production process includes the application of epoxy powders. The coating is

applied by melting the powder on the surfaces. The employed epoxy powders had

Table 4

Composition emission in plasma cutting [18]

Main components of fumes in dry plasma cutting

Fe (%) Mn (%) Cr (%) Ni (%) Cu (%) Mo (%)

Mild steel (0.008 m) 67–73 2–10 – – 0–1.4 –

Stainless steel (0.008 m) 38–44 4–10 12–20 4–8 2–6 0–1

Table 5

Plasma cutting—global air emissions

Mild steel Stainless steel

Cutting time (min) 16.5 4.5

Pollutant Mild steel Stainless steel Total (g)

NOx (g) 42.6 26.6 69.2

Fe (g) 99.6 24.2 123.8

Mn (g) 8.5 4.1 12.7

Ni (g) 3.5 3.5

Cr (g) 9.5 9.5

Cu (g) 1.0 2.4 3.4

Mo (g) 0.6 0.6


a content of about 7 g of volatile organic compounds per kilogram. Emissions from surface

coating for an uncontrolled facility could be estimated by assuming that all the VOC are

emitted [29]. The coating air emissions are summarised in Table 6.

3.4. Installation

The installation consists of the following steps:

–

Tab

Air

Use

CO

Air

Est

Transport of the FU from the factory to storehouses for the sale by retail;

–
Transport from storehouse to the user place;
–
Installation of FU’s parts.
Transports from factory to storehouses employ various trucks. Also the destinations are

variable (depending on the selling companies places). For these reasons, the following

average conditions have been assumed:

–
Functional unit: 1 tkm of 28,000 kg capacity truck;
–
Covered distance (double way): 100 km.
The FU is transported from storehouse to the user place by van of 3500 kg capacity.

Generally, the company makes one travel for each collector. The average covered distance

(double way) is 30 km. The installation consists of:

–
To fasten the support on the roof;
–
To fasten the water tank and the collector to the support.
le 6

emissions of epoxy dust coating

Collector Water tank

d epoxy dust (kg) 0.350 0.730

V content (g/kg) 7 7

emissions

imated COV emission (g) 2.45 5.11

Table 7

Installation — transport’s air emissions

Transport’s air emissions

C6H6 (mg) 0.72

Benzopirene (mg) 0.004

CO2 (kg) 10.17

Cd (mg) 0.06

NMVOC (g) 12.79

CH4 (mg) 318

CO (g) 46.24

NOx (g) 61.23

SO2 (g) 4.44

Pb (mg) 0.25


N2O (g) 0.87

Zn (g) 0.11


Specific impacts related to transports refer to Italian studies [25,26]. Table 7

shows the calculated transport’s air emissions. Regarding the drilling operations during

the fastening, it has been measured the consumption of 0.5 MJ of low voltage

electricity.

3.5. Maintenance

As suggested by the selling company we have supposed that the FU would have an

average useful life of 15 years. In absence of rare external damages (as the glass break), the

FU does not necessitate frequent maintenance. The ordinary cycles consist of one

operation every 4–5 years (in all 2–3 operations during the FU’s useful life). Regarding the

maintenance phase, main assumptions are:

–
Two maintenance operations (after 5 and 10 years from the purchasing);
–
Travels of maintenance technicians (overall distance 80 km by diesel car);
–
Each operation includes the substitution of the following components:
– PVC gaskets;

– Sealing;

– Magnesium anode;

– Electrical resistance;

– Thermal fluid (50% water; 50% propylene–glycol)

Air emissions produced during the transports are summarised in Table 8.

3.6. Disposal

The FU’s manufacture causes the production of scraps and wastes (the amount is

4.4 kg, excluding the packagings that wrap raw materials). The company periodically

deliver the wastes to a company that takes care about disposal.

Table 8

Maintenance phases— transport’s air emissions

Global distance 80 (km)

NH3 (mg) 80.0

Cd (mg) 0.03

CO (g) 28.0

CO2 (kg) 9.2

Cr (mg) 0.14


SO2 (g) 2.88

Zn (g) 0.003

CH4 (mg) 480.0

N2O (g) 0.80

Ni (mg) 0.20

COV (g) 4.40

NOx (g) 22.0

Cu (g) 0.005

Se (mg) 0.03


Regarding the FU’s disposal, no data are available. In fact, the company started the

production of solar collectors few years ago and, consequently, the sold collectors have not

yet reached their end-life. Furthermore the producing company have not started any

project regarding the collector’s recycling (for example, the users could return the

collectors to the factory and the collectors could be successively disassembled in their

components). In particular the metallic components (representing more than 80% of the

total mass) could be potentially recycled.

Having no further information, the recycling of materials has been neglected. It is only

supposed that solar collectors would be collected and disposed to the nearest landfill by

truck (50 km double way). Suppose the transports occur by 28,000 kg truck, the release of

1.4 kgCO2 and few quantities of other pollutants has been estimated. Impacts related to the

landifill management have not been considered.

4. Energy analysis

The energy analysis concerns with the energy flows occurring during the life cycle of

the product. The energy consumption could be split into ‘direct energy’ and ‘embodied

energy’. ‘Direct’ is the energy directly used during a life cycle step (for example, it

includes the electricity or heat energy employed during the production, the fuel for

transports, etc.). ‘Embodied’ is the energy consumed by all the processes associated with

the production of the materials employed as FU’s inputs.

Besides, it is necessary to state how much of the energy consumption is related to the

‘feedstock’ rate. This is defined as ‘heat of combustion of raw material inputs, which are

not used as an energy source, to a product system’ [6]. The feedstock quantifies the

potential of materials (as wood or plastics) to deliver energy when they are burned with

heat recovery after their useful life. The overall energy consumption can be obtained

Table 9

Direct energy consumption

Direct energy consumption

End-energy Primary energy

Electricity MV

Absorbing collector 66.6 MJ 191.0 MJPrim

Water tank 113.0 MJ 324.0 MJPrim

Support 9.6 MJ 27.6 MJPrim

Total 542.6 MJPrim

Electricity LV

Installation 0.56 MJ 1.8 MJPrim

Total 1.8 MJPrim

Diesel (for transports)

Materials (process input) 6.62 kg 346.5 MJPrim

Installation 3.30 kg 172.7 MJPrim

Maintenance 2.96 kg 155.1 MJPrim

Disposal 0.45 kg 23.6 MJPrim

Total 697.9 MJPrim


multiplying the used energy quantities by the calorific value. Following the suggestions of

the Italian Environment Protection Agency (ANPA), all the energy calculations refer to

the gross calorific value for fuels [30]. The following paragraphs show in detail the energy

consumption during all the life cycle phases.

4.1. Direct energy consumption

The FU’s LCA has involved two direct energy consumptions: the electricity used for

the production (medium voltage) and installation (low voltage) and the diesel oil used for

transports (during every life cycle phase).

However, the energy quantities described in the previous paragraphs are end-energy

quantities, meaning the energy quantities consumed by final users. All these quantities

have to be valued as primary, defined as the energy embodied in natural resources (e.g.

coal, crude oil, sunlight, uranium) that has not undergone any anthropogenic conversion or

transformation [31]. The secondary sources can be transformed into primary quantities by

means of specific conversion factors. They represent the effective MJs of energy that are

necessary to deliver one MJ of energy to users, including all the energy losses occurring

during the energy source life cycle.2 Table 9 summarises direct energy consumption in

terms of end-energy and primary-energy.

2 The production of electricity refers to the Italian energy mix during the period 1990–1994 [26]. Data include

all the energy losses occurring in the following phases: extraction, treatment and transport of fuels, production and

distribution of electricity, construction and disposal of structures. It has been assumed the following conversion

factors: low voltage electricity (3.21 MJPrim/MJEnd) and medium voltage electricity (2.87 MJPrim/MJEnd).

Regarding diesel oil for transport, it has been assumed a conversion factor of 1.16 MJPrim/MJEnd. It includes all

the energy losses occurring for extraction, refining and transport of diesel up to the filling station [32].

Table 10

Embodied energy consumption

Embodied energy of materials

Fuel (MJprim) Feedstock (MJprim) Total (MJprim)

Collector 3297.1 215.3 3512.5

Water tank 3641.0 485.9 4126.9

Support 1066.4 – 1066.4

Other

(HDPE pipes-resistance)

64.9 41.7 106.7

Other (packaging) 147.0 141.9 289.0

Maintenance 544.1 627.2 1171.3

Total (MJprim) 8760.6 1512.1 10,272.7


4.2. Embodied energy consumption

Analogous to the direct energy consumptions, also the embodied energy consumptions

have to be computed as primary. Table 10 summarises the primary energy demand for all

the employed raw materials. Data regarding the embodied energy of materials refers to

the Italian official environmental database [26]. Missing data are taken from other sources

[32,33]. General assumptions are:

–
Missing information about Italian stainless steel, it has been referred to average steel
data;

–
The producing company employs glass with low iron oxides. Missing information
about this glass, it has been referred to common float glass for windows;

–
The company uses epoxy powders as coating. Missing information about these
powders, data have been referred to epoxy resin. However, epoxy powders are about

0.6% of the overall empty mass and they could be neglected, following 1% cut-off

criteria [5].

–
No information is available about the eco-profile of welding rods. However, the rod
mass is very low (less than 0.2% of the overall mass) and it has been neglected in the

calculations.

4.3. Global energy consumption

The global energy consumption is obtained by adding embodied and direct

contributions (Figs. 7 and 8). Table 11 shows the energy consumption (split in the

energy carriers). It is possible to point out that:

–
The global energy consumption is 11.5 GJPrim. The direct energy consumption is only
11%, while the indirect is 89%.

–
The energy consumption for the production (542.6 MJPrim of electricity) is less than 5%
of the global consumption. This value shows the low incidence of the factory process on

the global energy balance.

Fig. 7. Global energy consumption (feedstock and fuel energy demands).


–
The energy consumption (direct and indirect) related to the water tank manufacture is
about 4.4 GJPrim (38.6% of the global). The production of the collector has a similar

energy demand (3.7 GJPrim and 32% of the global) while the support involves a lower

consumption (about 1.1 GJprim).

–
Installation and disposal have a low incidence. The computed impacts are mainly
related to transports. About the installation, it is possible to observe that the support is

used for flat-roof installation (and it is the most common case in our region). If the

support is considered as belonging to the installation, its contribution will be about

11.5% of the global consumption.

Fig. 8. Global energy consumption (direct and embodied contributions).

Table 11

Main energy and resource consumption

Primary energy consumption

Not renewable sources

Coal (kg) 193.7

Natural gas (N m3) 42.8

Coke (kg) 1.5

Wood (kg) 7.6

Lignite (kg) 39.2

Oil (kg) 88.8

Uranium (kg) 0.001

Renewable sources (MJ) 673.8

Fuel energy (GJ) 10.0

Feedstock energy (GJ) 1.5

Total primary energy (GJ) 11.5


–
The inclusion of other parts (copper resistance and HDPE-pipes) needs of a further
0.2 GJPrim (0.9% of the global). The packaging has, instead, a greater influence

(0.6 GJPrim and 2.5% of global).

–
Maintenance involves a significant energy consumption (about 11.5% of the global). This
is caused by the use of spare parts (and, in particular, by the substitution of thermal fluid).

–
The propylene–glycol is an oil-derived fluid and it involves a primary consumption of
77.4 MJprim/kg. Furthermore, this fluid is largely employed in the collector (about 19 kg

all over the life cycle). Consequently, the global use of this fluid has a great incidence

on the results (about 13% of the global consumption).

–
Transports cause the consumption of about 700 MJprim (6.1% of the global).
–
Feedstock consumption is about 13% of the global (and about 15% of the indirect
contribution). This energy could be theoretically recovered when materials are burnt

(with heat recovery) after their end-life. Actually, about 60% of feedstock is related to

the use of propylene–glycol; this fluid is mixed to water in the thermal fluid and,

generally, it is wasted without any treatment.

5. Environmental impacts

The main environmental impacts can be included in the following classes:

–
Resources consumption;
–
Air emissions;
–
Water emissions;
–
Wastes and solid pollutants.
Environmental impacts have been divided into direct and indirect. Direct impacts are

those directly related to the production process and to transports. Indirect are the impacts

related to the production of process inputs (as raw materials and energy sources). The FU’s

manufacture caused the direct emission of some air pollutants and the production of

Table 12

Resource consumption

Main resources consumption

Ferrous minerals (kg) 293.5

Water (m3) 31.6

Iron scraps (kg) 47.3

Bauxite (kg) 14.9

CaCO3 (kg) 14.3

Copper minerals (kg) 8.2

NaCl (kg) 7.7

Zinc (kg) 6.8

Sand (kg) 6.4

Copper scraps (kg) 5.4

Lime (kg) 2.0

Clay (kg) 1.3

Nitrogen (kg) 1.2


a small quantity of wastes. Emissions related to the production of diesel fuel have been

neglected: these emissions are very low with respect to those related to the fuel

combustion [26].

5.1. Resources consumption

The life cycle analysis has shown an overall consumption of about 415 kg of resources.

The employed materials are summarised in Table 12. It is possible to observe that they are

mainly constituted by ferrous minerals: it reflects the FU’s composition mainly made by

steel parts.

5.2. Air emissions

Table 13 shows the direct and indirect air emissions. In detail, we could observe that

–
The overall CO2 emission is about 650 kg;
–
Indirect emissions are generally dominant and they are mainly related to the raw
materials production (with an incidence of about 80–90%). The other emissions

(related to the production and transports) have an overall incidence of 10–20%.

–
Direct emissions of some metal pollutants (as Fe, Mn, Mo, Cr) related to the
production process are dominant. These emissions are mainly due to cutting and

welding phases.

5.3. Water emissions

Water emissions are only indirect (in fact, neither the production process nor the

transports have water contact). Table 14 shows the main pollutants. Organic releases

amount to 18 kg of chemical oxygen demand (COD); other emission are mainly little

quantities of metallic ions.

Table 13

Direct and indirect air emissions

Indirect Direct Total

Raw materials Electricity Transports Production

process

CO2 (kg) 580.4 35.8 40.8 657.0

CO (kg) 4.4 0.01 0.1 4.5

SO2 (kg) 3.3 0.2 0.03 3.6

CH4 (kg) 2.1 0.05 0.002 2.2

NOx (kg) 1.3 0.1 0.4 0.1 1.8

Dust (kg) 0.5 0.02 0.03 0.07 0.6

NMCOV (kg) 0.2 0.05 0.03 0.01 0.3

Mn (kg) 0.0001 0.3 0.3

Fe (kg) 0.0004 5.6!10K7 0.1 0.1

N2O (g) 20.9 1.5 1.9 24.3

HCl (g) 35.0 1.1 36.1

Cr (total) (g) 0.01 0.004 0.0003 10.7 10.7

Ni (g) 0.3 0.0004 4.7 5.1

Cu (g) 0.01 0.005 3.4 3.4

Zn (g) 2.3 1.0 3.3

HF (g) 2.5 0.2 2.6

NH3 (g) 2.5 0.03 2.5

Mo (g) 0.003 0.6 0.6

Pb (g) 0.5 0.012 0.003 0.5

PAH (g) 0.2 0.001 0.2

Benzene (mg) 529.0 87.3 7.1 623.4

Cd (mg) 125.4 1.3 0.1 126.9


5.4. Wastes

Wastes directly produced by company are about 4.4 kg. The overall produced wastes

are summarised in Table 15.

Table 14

Water emissions

Water pollutants

COD (kg) 18.1

Fe (g) 49.8

Mg (g) 16.4

K (g) 7.8

NH3 (g) 4.8

Phosphorus (g) 1.4

Cr (g) 1.1

Pb (g) 0.5

Na (g) 0.4

Ni (g) 0.4

Mn (g) 0.3

Cd (mg) 5.4

Hg (mg) 4.0

Table 15

Wastes production

Wastes production

Normal wastes (kg) 59.5

Special wastes (kg) 5.2

Ashes (kg) 6.8


5.5. Potential environmental impacts

The eco-profile of the collectors can be summarised employing the following potential

environmental indexes:

–

Tab

Pot

Pot

GW

AP

OD

NP

PO

Global warming potential (GWP);

–
acidification potential (AP)
–
ozone depleting potential (ODP);
–
nutrification potential (NP)
–
photochemical ozone creation potential (POPC)
These indexes have been calculated employing the characterisation factors regarding

the compilation of the Italian Environmental Product Declaration (EPD) [30]. Results are

summarised in Table 16.

6. Energy and CO2 payback times

The energy payback-time (EPT) can be defined as the time necessary for a solar equipment

to collect the energy (valued as primary) equivalent to that used to produce it [34]

EPT ZLCAenergy

Euseful KEUse

(1)

where

LCAenergy

le 16

ential env

ential env

P (kgCO2

(kgSO2 eq

P (kgCFC-

(kgPO43K

eq

PC (kgC2H

primary energy consumed during all the life cycle phases (GJ);

Euseful
yearly useful saved energy (GJ per year);
Euse
energy employed during the use of the renewable system (GJ per year).
ironmental impacts

ironmental impacts

eq.) 721

.) 5

11 eq.) Negligible

.) 0.7

4 eq.) 0.4


In passive collector systems the water circulation occurs naturally and, consequently, the

‘Euse’ is null. The energy saving referred to the use of solar collector has been calculated

considering the average temperatures and solar inputs of the city of Palermo (Italy, 388

latitude) [3,9]. The useful primary energy saving ‘Euseful’ is estimated 6.6 GJ per year [34].

The payback-time related to the studied equipment results lower than 2 years. This value

shows the great energy convenience of such technology.

Knowing the yearly ‘Euseful’, we have also calculated the yearly emission saving (EMS–i).

It represents the emissions that the auxiliary system would produce to deliver as much

energy as that saved by means of the solar collector. The EMS depends on the typology of

the employed auxiliary heater. The global impacts during the life cycle and the emission

saving are summarised by the emission payback-time (EMPT). It is defined as the

time during which the avoided emissions due to the employment of the solar plant are equal

to those released during the production and use of the renewable plant itself. It is possible to

calculate the EMPT relatively to the pollutant ‘i’ as [34]

EMPTKi ZEMi

EMSKi KEMUSEKi

(2)

EMi
global emissions of generic pollutant i related to the production, assembly,
transport, maintenance and disposal of the solar plant (kgi);

EMS–i
yearly emission saving of generic pollutant ‘i’ (kgi/year);
EMUSE–i
yearly emission of pollutant ‘i’ related to the use of the renewable plant (kgi/year).
The EMuse could be caused by the use of the conventional energy that the plant needs to

work (mainly the electricity used by pumps). In passive collectors the EMuse term is null.

The global warming potential (GWP) related to the collector life cycle is 721 kgeq.CO2

(see Table 16). Considering a domestic gas boiler as auxiliary system, it is assumed a

specific global warming factor of 65.7!10K3 kgeq.CO2 per MJ of useful heat [26]. The

yearly CO2-eq. emission saving is estimated to be 407 kgeq.CO2 [34]. Similarly to the energy

payback-time, even the CO2 payback-time resulted lower than 2 years.

The positive judgements revealed by the low values of energy and CO2 payback times

substantially agree with the results of different studies [14,17–19].

7. Conclusions

The present report shows the results of an LCA performed upon a solar thermal collector.

Production process, installation, maintenance, transports and disposal are checked.

The collected information could become an important starting point to improve the

ecological performances of the product. It is important to carry out a database of FU’s

environmental performances as a powerful tool for the eco-oriented design. On the other

hand, we would like to point out that the life cycle thinking is basic in the design for

environment but the final decision regarding the product cannot be just ‘environmental

oriented’. Other aspects like cost, physical lifetime, and energy performances are important


factors underpinning customer’s preferences. To achieve a more realistic evaluation, it is

important to consider a set of core criteria in addition to the main function, keeping in mind

that designers generally do not give top priority to the environmental matters. In this respect,

design for environment means to take environmental issues into account without

compromising the other features of the product and to seek a balance among all the

competing requirements.

Regarding the studied FU, it has been estimated an overall primary energy consumption

of 11.5 GJ. However, the energy directly used during the production process and installation

is only the 5% of the overall consumption; another 6% is consumed for transports during the

various life cycle phases. The remaining percentage is employed for the production of raw

materials, used as process inputs. These results show that the direct energy requirement is

less important than the indirect one (in fact, the production processes consist mainly in

cutting, welding, bending and assembling steps with a low energy demand). Consequently,

including or neglecting some materials, the results will be sensibly modified. For example

excluding the collector’s support, the primary demand decreases of 1 GJ (10% of the overall

consumption). Furthermore, maintenance can involve a large primary energy consumption

related to the substitution of spare parts. Two maintenance cycles has been supposed with an

overall primary energy demand of 1.1 GJ.

The production of the solar collector causes mainly direct emissions of metals (Fe, Mn,

Mo, Cr, etc.) related to cutting and welding phases. Regarding the other pollutants, it is

possible to comment in a similar way as done in the energy analysis. In fact, the indirect

emissions (related to production of raw materials) are about the 80–90% of the overall

releases, and the results sensibly depend on the materials included in the calculations. Direct

emissions related to transports have an incidence of 10–15%. Water soil releases and wastes

are very low.

As previously shown, it is very important to clearly define the study’s boundaries and the

involved materials. To grant transparency of results, the study has been presented as much

disaggregated as possible and all the study’s assumptions have been described in detail. It is

possible to separate all the contributions and follow all the calculation steps, to modify the

initial hypothesis (e.g. excluding or adding some components) and to re-calculate the LCA

results.

The last part of the study focused on the calculation of energy and CO2 payback times.

According to the results of other authors, these indicators resulted very low (less than 2

years) showing the great environmental convenience of this technology.

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