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Micro-Cogeneration – I

Introduction

Kari Alanne

University Lecturer, D.Sc (Tech.)

© Kari Alanne

Session outline

1. Background

2. What is micro-cogeneration?

3. Micro-cogeneration technologies

4. Domestic micro-cogeneration

5. Micro-cogeneration system

6. Operational strategies

7. Energy excess, shortage and storage

8. Future trends

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Background –

Key phrases of sustainable development

• Scarcity of natural resources

• Efficiency in terms of the use of energy and raw materials

• Utilization of local resources

• Decentralization – ”not all the eggs in the same basket”

• Networking

• Flexibility and scalability

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Background – Different energy supplies

In the past

• Furnace in every single house

• Wooden fuel from the surroundings

• No electrical devices – no demand of electricity

Now

• Large power plants

• District heating

• Increasing demand of

electricity

In the future (?)

• Every single house consumes

and produces its own thermal and

electrical energy

• Thermal demand

minimized, strong dependency on electricity

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Definitions – what is micro-cogeneration?

• Also known as micro-CHP: Combined Heat and Power

• ”Simultaneous production of electricity and thermal energy in small units close to consumers”

• ”A direct replacement for a boiler in a hydronic heating system, which simultaneously produces heat & electrical power”

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Definitions – technical

• EU Directive on micro-cogeneration:– electrical power less than 50 kWe

– ”Mini-CHP”: electrical power > 50 kWe

• European Committee for Standardization (EN50438):– 16 A per phase in three phase (25 A single phase)

• Domestic scale micro-cogeneration (DCHP):– “one unit per home”

– practically: less than 5 kWe

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Micro-CHP technologies

• Fuel cells

• Stirling engines

• Internal Combustion engines

• Microturbines

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Micro-CHP technologies – fuel cells (FC)

• Operational principle: – inverse electrolysis (details on separate slide)

– operational temperatures 60…100ºC (Poly-Electrolyte Membrane, PEM), 600…1000ºC (Solid-Oxide Fuel Cells, SOFC)

• Fuel:– hydrogen, reformed natural gas

• Efficiency:– electrical efficiency 40 % – overall efficiency 65-75 %

– electrical power / heat flow ~ 1.0 (PEM)

• Market status: – emerging technology

• Estimated installed costs: – 2700…4200 EUR/kWe (10…100 kWe plants, full market)

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Fuel Cells – operational principle

Source: Center for Fuel Cell &

Hydrogen Research

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Micro-CHP technologies – Stirling engines (SE)

• Operational principle:

– reciprocating engine, combustion outside the cylinder

– operational temperature 60…80ºC

• Fuel:

– natural or biogas, gasoline, diesel, LPG, various liquid or solid fuels

• Efficiency:

– electrical efficiency 20-30 %

– overall efficiency 80-90 %

– electrical power / heat flow ~ 0.3

• Market status:

– emerging technology

• Estimated installed costs:

– 1100…2500 EUR/kWe (5…10 kWe plants, full market)

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Stirling engines – operational principle

• 2 cylinders (expansion and compression) containing the working gas combined with a passage

• a high temperature is maintained in the expansion cylinder (red) and the compression cylinder (blue) is cooled

• classified into i) alpha, ii) beta and iii) gamma types according to how the pistons are arranged

Alpha type Stirling engine

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Micro-CHP technologies – internal

combustion engines (ICE)• Operational principle:

– conventional reciprocating engine, combustion inside the cylinder– operational temperature 85…100ºC

• Fuel:– natural or biogas, diesel, gasoline

• Efficiency:– electrical efficiency 25-30 % – overall efficiency 75-85 %– electrical power / heat flow ~ 0.5

• Market status: – on the market

• Installed costs: – 847…1020 EUR/kWe (5.5-30 kWe plants)

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Micro-CHP technologies – microturbines (MT)

• Operational principle: – conventional gas turbine process– operational temperature 85…100ºC

• Fuel:– natural or biogas, diesel, gasoline, alcohols

• Efficiency:– electrical efficiency 25-30 % – overall efficiency 60-70 %– electrical power / heat flow ~ 0.5

• Market status: – on the market

• Installed costs: – 800…1000 EUR/kWe (> 25 kWe plant)

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Images of micro-CHP products - I

Honda Ecowill ICE Whispergen SE

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Images of micro-CHP products - II

Acumentrics AHEAD SOFC Turbec T100 MT

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Domestic micro-CHP (DCHP) concept

micro

CHP

plantFuel

100%

ELECTRICITY

IMPORT/EXPORT

EXHAUST

5-15%

Heat

70%

ELECTRICITY

15-25%

• lighting

• appliances

• building services

• space heating

• domestic hot water

(DHW)

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Micro-CHP plant

Pre-handling of fuel and air

Fuel Air

Energy conversion module

Power conditioning module

Electricity

output (AC)

Electricity

(AC) for

ancillaries

Auxiliary burner

Heat

recovery

Exhaust gasExhaust

gas out

Water out Water

in

Mechanical power

or electricity (DC)

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Integration of micro-CHP plant into

building services

Buffer

storage

60…80ºC*

µCHP

plant

>80ºC

Hydronic

radiators

network or

floor

heating

40…70/

20…40ºC

Controller Circulating

pumpElectricity to

HVAC,

lighting and

appliancesElectricity to

grid

Fuel

and

air

Exhaust

gasesDomestic

hot water

55ºC

Cold

water* The storage temperature is

controlled using heat sink and

auxiliary burner, when needed.

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Operational strategies

• Aim:– to find optimal match between electrical

and thermal demand and supply

• Methods:– power control

– load management

– electrical and thermal storages

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Power control

1. Electrical load following mode, thermal excess is stored or dumped, thermal shortage generated by auxiliary burner and/or discharging the thermal storage

2. Thermal load following mode, electrical excess is stored or fed into the grid, electrical shortage satisfied by grid electricity or by discharging the storage

3. Operation at constant power (base load), the employment of thermal and electrical storages, heat sink, auxiliary burner and grid, when needed

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Temperature control of buffer storage

• The purpose of the buffer storage:

– to deliver heat to the hydronic heating system

– to shave the peak thermal demands

• Preset threshold values for storage

temperatures determine the on/off-

operation of the micro-CHP plant.

• The temperature of supply water to

the radiator network is controlled by

mixing supply and return water

according to the outdoor

temperature.

0

10

20

30

40

50

60

70

80

16

12 8 4 0 -4 -8

-12

-16

-20

-24

-28

Outdoor temperature [C]

Su

pp

ly w

ate

r te

mp

era

ture

[C

]

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Power control - challenges

• Only on/off operation available the usual present day micro-cogeneration technologies

• Long start-up and shutdown periods may be required (Stirling engines)

• Substantial fuel demand at start-up phase• Limited dP/dt (Solid-Oxide Fuel Cells)

• Low part-load efficiency

The above challenges are technology-specific.

In general: steady demand close to specific power output is preferable in the sense of micro-cogeneration.

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Load management

• A procedure to adjust electrical demands rather than the output of the plant

• Examples:

– Forced switch-off of ”power-eaters” such as sauna stoves and ovens

– Limited simultaneous use of electrical appliances

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Seasonal (long-term) thermal storages

• Thermal surplus during warm season commonly occurs in the case of micro-CHP, when the plant can be operated close to constant power only and shutdowns are not preferred (e.g. SOFC plant)

�Significant thermal losses, poor annual efficiency

�Solution: seasonal thermal storage

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Thermal storage technologies

• Mass storages

• Phase change materials (PCM)

• Thermo chemical energy storage

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Applicability of seasonal thermal storages

• Operational environment:

– climatic conditions, e.g. ground temperature, snow-covered ground

– geological structure of the building site

• Inlet temperatures of the heating system:

– 40ºC (low temperature heating system)

– 70ºC (conventional radiator heating in Finland)

• Trade-off between storage capacity and storage

losses must be found!

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Integration of seasonal thermal storage

into residential micro-CHP plant

Seasonal heat storage (5…45ºC)

Heat pump

Buffer storage

(45…50ºC)

Floor heating system (25…30ºC)

µCHP plant

(>100ºC)

Heat exchanger

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About electrical storages for micro-CHP

• Basic requirements:

– large charge-discharge

quantities

– must tolerate high discharge

power

– minor service requirements

– safety

– longevity

– high energy density

• Selected alternatives– Lead-acid- battery

• good availability at low price (4-6 Wh/€)

• low energy density 60-75 Wh/L

– NiMH- battery

• in the market, high price (1 Wh/€)

• high energy density 140-300 Wh/L

• high self-discharge

– LiFePO4- battery

• emerging, high price (< 1Wh/€)

• high energy density 170 Wh/L

• low service requirement

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Electricity to the grid?

• Monetary compensation for the electricity fed into the grid may

be based on:

– Feed-in tariffs

• the utilities are obliged to buy electricity from small producers at rates set by the government (buyback rate)

• a two-directional electricity metering required

• applied in many European countries

– Net-metering

• the deduction of energy outflows from metered energy inflows and compensated through a retail credit by a utility

– Time-of use metering

• Two-directional metering strategy that allows rate schedule depending on the peak demand hours

• The stability of the grid limits the amount of grid-connected

small-scale producers

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Energy saving houses – challenge for the future

• Thermal demand decreases significantly due to forthcoming low energy and passive construction standards.

• Electrical demand may decrease, remain the same or even increase in the future

� Electrical demand increases vis-à-vis thermal

demand, whereas the electricity/heat ratio of micro-

cogeneration plants (excluding fuel cells) is small.

• Zero energy / plus energy houses / autonomous houses aim at meeting the electrical demand by local generation.

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Example: demand profiles

Standard house, Helsinki

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

1 652 1303 1954 2605 3256 3907 4558 5209 5860 6511 7162 7813 8464

Time [h]

Ele

ctr

icit

y/h

eat

[W]

Electricity [W] Heat (standard house) [W]

Passive house, Helsinki

0

1000

2000

3000

4000

5000

6000

1 639 1277 1915 2553 3191 3829 4467 5105 5743 6381 7019 7657 8295

Time [h]

Ele

ctr

icit

y/h

eat

[W]

Electricity [W] Heat (standard house) [W]

© Kari Alanne

Trends of development

• Polygeneration– simultaneous production of electricity, heat

and cooling energy (at various enthalpy levels), fuel synthesis (e.g. hydrogen)

• Hybrid systems– micro-cogeneration +

• solar and micro-wind

• heat pump

• energy storage

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Micro-Cogeneration – II

Research on micro-cogeneration at Aalto University

Kari Alanne

University Lecturer, D.Sc (Tech.)

© Kari Alanne

Session outline

1. Baselines for the micro-CHP research at Aalto

2. Current research efforts

– SOFC micro-cogeneration

• economic assessment (break-even costs)

• seasonal thermal storages

• cost-optimized operation

– Combustion engines

• calibration and validation of SE simulation model

• performance assessment of SE-micro-cogeneration in single buildings and communitites

3. Future research

4. Discussion

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General baselines

• Computational study by IDA-ICE whole-building

simulation program

• Target building: single-family house (131 m2, 4

occupants) located in Helsinki area

• Annual electricity consumption: 6100 kWh/a

• Annual thermal energy consumption: 11200

kWh/a

• Reference system: hydronic heating system with

condensing gas boiler (η=93 %)

© Kari AlanneIDA Simulation Environment

• Simulation environment with different applications– IDA Indoor Climate and Energy (ICE)– IDA Road Tunnel Ventilation (RTV)– IDA Tunnel

• Developed at the Swedish Institute of applied mathematics and at KTH• Owned by Equa Simulation, www.equa.se

• Features– Possibility to write user defined models – Support of either NMF or Modelica models– Adaptive time step– Very flexible data input possibilities– Easy data export (to Excel, Matlab, etc)– Unique 3D visualization and animation of inputs and results for quality

control and presentation capabilities– A model version handling system for easy comparison between different

runs– Plenty of result presentation possibilities– Location and climate downloads– Internet and email support

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Economic premises for SOFC micro-

cogeneration in Finnish households

Presented in Clima 2007 conference in Helsinki

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Objective and methods

• Objective:– To evaluate the financial viability of SOFC-based micro-

cogeneration for residential applications in terms of

• break-even prices for plant investment and buyback prices of electricity

• sensitivity of break-even prices to electrical power, operational strategy and overall efficiency

• Methods:– Computational study by IDA-Indoor Climate and Energy (IDA-ICE)

– Estimation of hourly energy consumptions

– SOFC-”blackbox” model developed by VTT on the basis of the model specification by Beausoleil-Morrison et al. (2005)

– Estimation of SOFC operation

– Post-processing of simulation results

• financial analysis

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Results

What should the buyback price be to

create annual savings when SOFC is

compared with the reference system?

0

2

4

6

8

10

12

0,5 0,6 0,7 0,8 0,9 1

Overall efficiency

Bre

ak-e

ven

bu

yb

ack

pri

ce (

sn

t/kW

h)

1 kWe 2 kWe 3 kWe

Overall efficiency 80 %,

2 % escalation of electricity price

0

1000

2000

3000

4000

5000

5 7 9

Buyback price snt/kWhP

ayb

ack p

rice (

EU

R)

5 a 10 a 15 a 20 a

How much may an SOFC plant cost

in order to be feasible within

payback periods of 5-20 years?

© Kari Alanne

Conclusions

• Preferred operation: constant run of 1 kWe

SOFC (efficient heat recovery necessary)

• Investment support is required to make SOFC micro-cogeneration financially viable.

• Computational results cannot be generalized.

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Seasonal heat storages and residential

micro-cogeneration

Presented in MICRO-COGEN 2008 conference in Ottawa

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Objective and methods

• Objective:

– to find the optimal shape and size of a seasonal mass thermal

storage in a simulated residential SOFC plant located in

Finland

– to find break-even price for storage investment

• Methods:

– IDA-Indoor Climate and Energy (IDA-ICE) – estimation of

hourly energy consumptions

– Post-processing the simulation results in a spreadsheet

application

• polynomial expression to predict the thermal production of an SOFC plant

• financial analysis to find out the economic value of accumulated energy savings and the break-even price

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Results and conclusions

• Optimal storage size: 150 m3, semi-spherical shape

• Optimum operational conditions:

– constant operation of 3 kWe

– annual fuel savings of 5342 kWh a-1

– annual cost savings of 194 EUR a-1

– total savings of 2483 EUR (20 a)

• Computational results cannot be generalized (e.g. optimal storage size).

• The financial viability of the storage was not evaluated in the computational study, but on the basis of experience the present configuration is hardly feasible.

© Kari Alanne

Cost-Optimized Operation of a Residential

SOFC Plant

Presented in MICRO-COGEN 2008 conference in Ottawa

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© Kari AlanneObjective, methods and results

• Objective:

– to evaluate the potential to improve the energy efficiency of a simulated residential SOFC plant located in Finland applying a simple cost-optimization algorithm

• Methods:

– IDA-Indoor Climate and Energy (IDA-ICE) – estimation of hourly energy consumptions

– Post-processing the simulation results in a spreadsheet application

• polynomial expression to depict the thermal production of an SOFC plant

• optimization algorithm to find out the control parameter (20%…100% of the specific power) that results in minimum costs at given time step

• Results:

– Annual savings of 65 EUR compared to constant operation of 1 kWe were obtained using the optimization algorithm � feasible in all probability

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Implementation and Validation of

Combustion Engine Micro-cogeneration

Routine for the Simulation Program IDA-ICE

Presented in Building Simulation 2009 in Glasgow

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Background

• The original combustion engine model

– was developed in the IEA/ECBCS Annex 42 for whole-

building simulation programs

– is a ”grey-box” model that circumvents the exact

thermochemical modelling of combustion process

– addresses the dynamic effects of micro-CHP devices

– had been so far implemented in ESP-r, TRNSYS and

EnergyPlus

• The novelty of the IDA-ICE implentation:

– thermal exhaust gas heat recovery

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Model validation

• Method:

– inter-program comparison with ESP-r, TRNSYS and EnergyPlus

– Annex 42 test program entailing 9 test series and total 44 separate cases

• An excellent agreement was obtained

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SE micro-CHP in a single-family house –

performance assessment

• 3 – 5 % cut to primary energy consumption and CO2

emission compared to hydronic heating based on

natural gas boiler and grid electricity depending on

building type (standard vs. passive) and climate

(Helsinki, Jyväskylä)

• The effect of exhaust heat recovery ~ 1 %

• Cumulative savings €3000-4000 (10 years, interest rate 2 %, electricity price 5-15 c)

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SE micro-CHP in small communities –

performance assessment

• ”District micro-cogeneration”: 9.5 kWe pellet burning SE micro-cogeneration plant

• 70 % of annual electricity consumption can be covered by local micro-cogeneration, when the

number of houses < 10

• Annual primary energy consumption curbed by 25 % and CO2 emission by 19 % in comparison with pellet-

fuelled district heating without CHP

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Research trends at Aalto university

• Commercialization of a Rotary Steam Engine (RSE)

micro-polygeneration (electricity + heat +

desalination) system (technical development and

experimental research)

• Hybrid systems (solar + micro-cogeneration)

• Zero and plus energy buildings, autonomous buildings

• The application of micro-co-/polygeneration in small communities

• Contribution to IEA/ECBCS Annex 54

© Kari AlanneRotary Steam Engine (RSE)

• Ongoing pilot project for a 4 kWe / 30 kWth pellet-fuelled Novoro2, funded by Tekes

• Novoro Inc. collaboration with Applied thermodynamics research group since 2006 (-2010)

• Good applicability to biofuels, solar energy and thermal energy in desalination processes

• Estimated installed cost of a similar magnitude as for micro-CHP plants based on internal combustion engines

4 kWe / 30 kWth NOVO2 - RSEExample: RSE and solar-powered desalination

Source : Novoro Inc. / Heikki Pohjola and Aalto University / Applied Thermodynamics

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RSE micro-cogeneration plant

© Kari Alanne

Evaporator

RSE Generator

Condenser

Water container

Source : Novoro Inc. / Heikki Pohjola

© Kari Alanne

Collaboration opportunities?

Current research themes:

• Micro co-/polygeneration

• Zero and plus energy buildings, autonomous buildings– Definitions – connection to life-cycle economy

– Applicability to• various building types

• climates

– Simulation / optimization studies