Micro CHP units meeting tomorrow’s

power/heat demands and improving the

integration of renewables

Jan de Wit, Danish Gas Technology Centre,

Denmark

Laila G. Madsen, IRD Fuel Cell Technology, Denmark

Morten Karlsen, Mads Møller Melchiors, Dantherm

Power®, Denmark

Kristina F. Juelsgaard, Jens Jakobsen, SEAS-NVE,

Denmark

Aksel Hauge Pedersen, DONG Energy Renewables,

Denmark

Allan Jørgensen, DONG Energy, Denmark

Michael Byllemos, Sydenergi, Denmark

Introduction

Future houses will need more electricity and less heat than today’s houses. Statistics show this

development already, and improved insulation standards will significantly contribute to this.

The development will lead to increasing power-to-heat consumption ratios, which should also

be reflected in the production portfolio. Heat-only should only be produced for peak supply,

while the majority of heat should be produced as cogeneration, large, medium and small-

scale. Technologies for all power ratios are available if gas is used as fuel.

To increase security of supply and to minimise transmission and distribution losses mini- and

micro-cogeneration can be implemented along with larger-scale cogeneration. Costly power

grid expansions can also be avoided by distributed power production. The very small units

might be fleet operated as virtual power plants enabling power balancing and the best

integration of renewables.

The importance of the power production efficiency

Gas and oil fired domestic heating appliances have undergone several technology steps and

have now reached very high efficiencies. So has power generation. Highly efficient gas

engines and combined-cycle production units are in the range of some 46-59% power

production efficiency when operating in CHP mode. In power mode only, latest-technology,

large combined power units can achieve even higher power production efficiency. However,

also older production power units are in operation in all countries and despite widespread

CHP and renewables much power is still produced as power-only based on fossil fuels.

When installing micro CHP units, power and heat are produced as close to the end-user as

possible. Power and heat transmission losses are minimised as much as possible. By

substituting a heating device in the house and producing both heat and power primary fuel is

saved due to the general advantage of combined heat and power production. However, the

micro CHP product will often compete with highly efficient condensing gas heating

appliances and with efficient centralised power production units. Therefore, the overall

efficiency of the micro CHP unit is important and the electricity production efficiency even

more important to obtain primary fuel savings.

In Figure 1 this primary fuel saving of mini- and microcogeneration units is taken into

account for the heating efficiency of the appliance to make it comparable with other

traditional appliances. Traditional non-condensing gas boilers have an efficiency of some 85-

90% and condensing appliances have a fuel utilisation efficiency (heating efficiency) of some

95-103% with a Lower Calorific Value (LCV) reference. Figure 1 shows that the power

production efficiency of the micro CHP appliance should be above some 15% to compete

with the heating efficiency of condensing appliances, thus giving true primary fuel savings.

Figure 1 Heating efficiency of micro CHP devices. The primary fuel saved elsewhere is

taken into account and benefits the heating efficiency of the micro CHP unit. The

primary fuel savings will depend on the power production efficiency of the

centralised plant; here 45% power production efficiency of a power-only plant is

used. For the micro CHP unit a total efficiency of 80% is assumed.

Demonstration project with fuel cell based micro CHP units

A Danish development and demonstration project with micro CHP based on various types of

fuel cells and different fuels was launched in 2006. Micro CHP is of particular interest as

mini-, medium- and large-scale CHP are largely built out. Some 45% of the Danish electricity

production is based on CHP and some 80% of the heating supplied via district heating

networks is already CHP based.

The project was divided into three phases. In the first phase the most promising fuel cell types

and appliances were pointed out and lab tested. In the second phase micro CHP units for

third-party installation were produced and tested at a limited number of sites. Phase 3 consists

of field tests at numerous sites of improved versions based on the phase 2 works and testing.

The project developed micro CHP units with different fuel cell technologies such as low-

temperature PEM, high-temperature PEM and Solid Oxide Fuel Cells (SOFC). These

technologies were lab tested and, if ready, brought to field tests.

microCHP Heating Efficiency

(incl. benefit for fuel saved elsewhere at power-only plant)

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40

microCHP Electrical Efficiency

%

Heating efficiency

%

Stirling Tech.

ICE Engines

engines

Fuel Cell based Tech

Hydrogen fuelled micro CHP units are being tested in the town of Vestenskov at Lolland.

Natural gas fuelled units of another design and make are being tested in the Varde region in

western Jutland.

The Lolland hydrogen fuelled sites

The units installed in the town of Vestenskov are hydrogen fuelled. The hydrogen is produced

in two electrolysers feeding the hydrogen grid of Vestenskov, see Figure 2. The basic idea

behind electrolysers and the connected hydrogen storage tank is to use surplus wind power

electricity for the hydrogen production.

Figure 2 The electrolyser used in Vestenskov for hydrogen production and the 6 bar

storage tank

Figure 3 The hydrogen grid of Vestenskov during construction works

The hydrogen grid was built in two phases. The grid for the first field test houses was made in

coated stainless steel. The piping for the succeeding grid in Vestenskov was made with PE-80

tubing.

The overall conceptual idea of the Vestenskov grid is shown in Figure 4. It can be seen that

sustainable energy resources are predominant in the concept.

Figure 4 An overall plan for hydrogen production, storage and utilisation in combination

with other fuels of sustainable origin

In the field test installations the fuel cell based micro CHP units are connected via a heat

storage facility. For additional peak heating during the coldest part of the heating season an

electrical cartridge heater is integrated in the heat storage.

All the hydrogen fuelled micro CHP units at Vestenskov are connected to the internet; this

enables remote control, if needed, and data transmission.

During the complete project period 3-4 versions of the IRD unit were developed. The

improvements were based on general research and technology improvements over time and

due to technical feedback from the third-party laboratory tests and field tests during the field

testing in Phase 2 and 3. In every new version of the units significant reductions in volume

(typically 33% for each step) and cost (typically half cost for next version) were achieved.

Figure 5 shows the two versions of the IRD micro CHP units used for field testing in

Vestenskov. By using hydrogen directly as fuel, the units have excellent load response and

fast start and stops.

Figure 5 The hydrogen fuelled IRD fuel cell based microcogeneration unit (LT-PEM

technology). The photo to the left shows the unit developed for field test in Phase

2. The photo to the right shows the unit developed for field test in Phase 3. Both

photos were taken during testing at DGC and both show the volume reductions

achieved going from one phase to the next.

The graphs in Figure 6 show operation results of one of the hydrogen fuelled Vestenskov

units.

Figure 6 Results from operation of a hydrogen fired micro CHP unit in Vestenskov during

the heating season 2011-2012. These units are available for both full-load and

part-load operation.

The Varde natural gas fuelled sites

The first Dantherm Power units (Phase 3 testing) were installed and started January/February

2012 in Varde. Some 20 units in total were installed in the Varde region of Jutland during

spring 2012. Most houses are inhabited by private consumers; a few installations were made

in office buildings, business centres etc., see examples in Figure 7 and 8.

Figure 7 A Varde field test site; a private

house. The only outside sign of

the micro CHP unit installed is

the extra balanced flue on the

roof.

Figure 8 Another Varde test site. This

installation is made at a

municipality service centre.

The units operated as much as possible depending on and controlled by the heat demand of

the houses. They were stopped during the summer period due to the low and very fluctuating

heat load in this period. They were started again around week 36 of 2012 and are expected to

operate until the end of the heating season early summer 2013.

The fuel used for the Varde sites is natural gas from the Danish natural gas distribution grid.

The natural gas has its origin from offshore production sites in the North Sea (high heating

value) or it is imported gas coming via Germany, mostly with a lover heating value. The

Danish natural gas grid includes two underground natural gas storage facilities for securing

stability of supply and for balancing seasonal production patterns. In the Varde region, gas

will predominantly be based on the North Sea supplies. The fuel reformers used at present in

the units do not favour the presence of nitrogen, which may be the case in imported gas.

The Varde units are installed as shown in Figure 9. The units operate as the primary heat

production unit to obtain as many operating hours as possible. If more heat is needed for the

house, there is a secondary standby heat producing unit in the houses.

Originally, the use of heat storage was intended; due to space considerations and to avoid

year-round heat losses from such a device this was omitted in the final house configuration.

Figure 9 System layout for connecting the Dantherm Power units to the existing heating

systems of the private-house test sites in the Varde region. No heating storage is

used.

All the natural gas fuelled micro CHP units in the field test fleet of the Varde region are

connected to the internet; this enables remote control, if needed, as well as data transmission.

The field test hosts can follow production etc. from their units via a Man-Machine-Interface

(MMI).

In early spring 2013, the natural gas fuelled Varde units reached 100.000 operating hours all

together. The unit with the highest number of operating hours will reach some 7000 operating

hours by February 2013. A Dantherm Power unit is shown in Figure 10.

Figure 10 The natural gas fuelled fuel cell micro CHP unit used for the field test sites in the

Varde region (LT-PEM technology). These units are made by Dantherm Power®.

The micro CHP unit is at front; the appliance at the back is a heat storage unit

connected to solar heat collectors.

Presentations on the operation of selected units are shown in Figure 11 and 12. The diagrams

show the key values for each two-week period of the field test site operation until now. It can

be seen that availability above 90% is obtained in most periods for the unit shown in the

figures. The electricity production efficiency from natural gas to 230 V AC power is in the

range of some 32-36% and the total efficiency in the range of 95-102% for 20 units.

The number of faults seen does not necessarily lead to a complete stop of the units until

service has been made. Many of these faults are addressed automatically by the units’ own

control systems, or they can be solved through remote service.

The power production efficiency is significantly higher than technologies available for CHP

production in the 1.5 kWe power range (stirling and reciprocating engines).

Figure 11 Operation of a test house during the first part of the heating season 2012/2013.

Natural gas fired micro CHP in the Varde region.

Figure 12 Operation of another test house during the first part of the heating season

2012/2013. Natural gas fired micro CHP in the Varde region.

The units were installed in both private houses and service centres. In the latter case, all

electricity produced is used in-house with no export taking place as only one unit has been

installed. In the Varde test sites, preliminary analyses have shown that the micro CHP units

cover from approx. 10 and up to 50-60% of the electricity consumption of the house and from

5-45% of the heating demand.

In the private houses import and export of electricity take place as the electricity consumption

profile does not necessarily fully match the production profile of the (mostly heat controlled)

micro CHP unit.

A few preliminary examples are shown in Table 1 below.

Table 1 Power production of the micro CHP units, imports and exports of power in the

same period, examples

Period 1/4 - 27/8 2012

Electricity Exports

House# Power Prod.

µCHP Electricity Imported

Electricity consumption

Electricity Exported

µCHP electricity coverage

of the µCHP production

compared to house consumption

# kWh kWh kWh kWh % % %

2 1247 12453 13700 0 9 0 0

5 1294 2102 2864,87 531 45 41 19

6 1314 1290 2161,6 442 61 34 20

7 943 1450 1872,11 521 50 55 28

8 1402 1641 2715,08 328 52 23 12

12 1252 1667 2738,14 181 46 14 7

13 983 8287 9128,83 141 11 14 2

14 807 1620 1932,94 494 42 61 26

20 1162 1717 2419,19 460 48 40 19

Biogas fuelled installations

Two biogas fuelled LT-PEM based micro CHP units were installed in the southern Jutland

region for a period. The units were basically of the same design as the natural gas fuelled field

test units in the Varde region.

The biogas fuelled units were installed at a technical road service centre in Sønderborg

Municipality and at the airport. The gas was upgraded biogas, i.e. biogas where CO2 was

removed. These units were operated for approx. 1250 and 1600 hours, respectively, in 2012.

This equals some 45-58% of the total time available in the period. Sulphur removal is

necessary when using biogas.

Business models

There are multiple business models for ownership and operation of such micro CHP units.

Private ownership: The owners themselves invest, operate and call for (or contracts) the

service and repairs needed. This business model leaves significant financial risks on the

shoulders of the private consumer. Service and repairs might be costly as large-scale logistic

benefits for service providers cannot be obtained if no other units are situated in the same

geographical area.

Equipment lease: This kind of lease lowers the initial investment costs.

Professional ownership: Third-party ownership (energy distributors, suppliers, ESCOs etc.)

and operation in designated areas will give the private consumer less investment and

economic risk for such first-generation appliance. To a larger extent, it will provide a basis for

optimal power production based on the actual needs of the grid etc. It will also mean a

significant potential for lower service and repair cost as logistics can be optimised in respect

to both service and repairs. If remotely operated, a number of units can act as a virtual power

plant. En example can be seen in Figure 13.

Figure 13 Data transmission and interconnection between the micro CHP unit and parties

active for micro CHP test in DONG Energy POWER-HUB. The purpose of these

tests was to make the units respond to price signals and/or to make them ready for

TSO system services.

As the micro CHP unit can be switched off during periods with sufficient sustainable power

(or low electricity prices) in the electrical grid, heating of the house must be secured by 100%

backup. This can be done via an electric heating element or via heating based on a gas burner.

This device might also owned by the third-party owner. In principle, the house owner can

simply buy the heat needed, independently of its origin at an agreed price. This leaves the

house owners with little investment, little risk and a well-known price for the heating needed.

Such a business model could be offered by energy distributors/suppliers, appliance suppliers,

ESCOs etc.

The 20 field test units installed in the Varde region are equipped with a Man-Machine-

Interface (MMI), where the hosts can follow the operation status and production numbers of

“their” unit. Experience has shown that this is rarely used. So even among these first-mover

hosts/clients there is limited interest in such real-time updates.

Challenges

The following sections describe the challenges revealed during this project for successful

market introduction of competitive fuel cell based micro CHP units.

Price: The production costs of these units must be further reduced. Inevitably, to some extent,

there will be benchmarked on price against more traditional gas boilers, which are produced

in millions of items each year reaching sales prices of some 3-4000 Euro. Micro CHP units

based on engine technology (more traditional gas engines or stirling engines) are being

introduced on the market at a price level of some 6-7000 Euro each.

Lifetime: There is a lifetime aspect regarding the core component of the unit: the fuel cell

stack. Very few stacks have been tested beyond a lifetime of 10.000 hours. This might be

equal to only approx. two years of operation as a heating appliance. Gas boilers often have a

lifetime of some 15 years; although heat exchangers and other relatively low-cost components

might be exchanged during this lifetime.

Limitations regarding water temperatures: LT-PEM cell stacks have limitations as regards

acceptable working - and thus cooling - temperatures. The LT-PEM units used in this project

did not accept higher inlet temperatures than approx. 45 °C and were not able to produce

forward water temperatures higher than approx. 65 °C for the connected heating system.

In principle, fuel cell stacks have excellent load response characteristics. At operating

temperature they can go from idle to full load within seconds and vice versa. However, if the

units are fuelled with other fuels than hydrogen they need to be fitted with a fuel reformer,

and this component will usually be the bottleneck in regard to load response.

If SOFC based units are used, they need to be at operating temperature before current can be

drawn. To avoid thermal stress and breakdowns, heating up from cold start should be made

with a controlled (programmed) process, which may take hours. Field tests with SOFC units

are planned at the end of 2013.

A heat storage unit might prove useful for the optimal operation of the micro CHP units.

However, despite the fact that water has the highest storage capacity per volume compared to

most other fluids, such a component will need space and might be an undesirable component

in the domestic sector. If a storage unit is needed, reductions in space requirement are most

welcome; this may be obtained by using phase-shift mediums, but such mediums are not yet

fully developed.

If not supplied with pure hydrogen, the natural gas or biogas preparation/conversion is a key

issue if a fuel processor/reformer lifetime of some 40.000 hours is to be reached. Imports and

exports of natural gas in Europe increase and larger variations in gas composition are seen.

For cost efficient layout and/or due to operational aspects of the micro CHP units, some sort

of peak-load or supplementary heating is needed. This should preferably be integrated in the

micro CHP unit to avoid further space requirements for the heating appliance.

Achievements

Through its three phases the project showed significant unit improvements regarding unit cost

reductions, unit volume reductions and improved unit reliability etc.

The electrical efficiency of the hydrogen and the natural gas fuelled units is second to none

compared to other CHP units in this power range (1 kWe).

During the third phase of the project units were developed and demonstrated to operate

without a need for heat storage.

Remote operation was demonstrated; so was data transmission via the internet.

Units for three different fuels were demonstrated: hydrogen, natural gas and upgraded biogas.

The hydrogen fuelled LT-PEM based units showed excellent load response and very short

start and stop times.

Acknowledgements

The demonstration and testing activities were partly supported from the Danish Energy

Research programmes via the government’s Finance Acts, the Danish Energy Agency and

EUDP.

References

1. Smart Power Generation; Jacob Klimstra, Wärtsilä “Energy/In Detail” Wärtsilä

Technical Journal 02.2011

2. PEM Fuel Cell Power for Stationary Applications, IRD/DGC, Conference and Trade

Show, Vancouver 2007