Biomass domestic micro-cogeneration, the last step towards sustainable development for private houses?

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1 Biomass domestic micro-cogeneration, the last step towards sustainable development for private houses? Ismael Daoud Facilitateur en Cogénération de la Région wallonne et bruxelloise COGENSUD asbl & ICEDD asbl In order to be able to produce, on-site, about 100% of its energetic needs through renewable sources, a residential building will be obliged to opt for a mix of different and quite expensive technologies. A solar water-heater could cover between 40 and 60% of the sanitary water needs, as 5% of a household s total energy consumption. Photovoltaic cells or a micro-wind installation could cover 50% of electrical needs, as 5% of total energy consumption. An automatic boiler provided with wood pellets could cover all the heating needs, as 60% of total energy consumption. Residential energy consumption and renewable productions 50% PV or Wind Transport Biofuels 20% Wood boiler Electric appliances Domestic hot water 50% Solar thermal Space heating 60% Micro-CHP The main asset of «domestic micro-cogeneration is given by its capacity to provide all the heating and electrical needs, trough the use of ONE SINGLE technology, provided with a fossil fuel or, even better, a renewable fuel (bio-diesel, vegetal oil, wood pellets or biogas). Many manufacturers propose nowadays products which are able to adapt properly on private house scale. This is the case of internal combustion engines or Stirling engines. Fuel cells, on the contrary, are still the object of research and development in an effort to reduce costs significantly (at the moment amounting at /kw) and improve the life duration of components. Technologies using the Rankine organic cycle still have to be developed before they can enter the market. Simultaneous production of heat and power implies simultaneous use of this heat and this power. In practice, this simultaneousness will rarely be achieved. It will be consequently necessary to store the heat in a heat storage device (between 150 and 800 litres). With regards to electricity, the ideal solution would be use virtual storage provided by the grid. This process starts to be admitted by Belgian legislation. And, why not, one day, it could also be possible to charge the batteries of a car, of a motorcycle or of an electric bike using biomass domestic micro-cogeneration.

2 More topics: technology comparison, profitability assessment, sensitivity analysis of energy and CO2 savings, specific supports in Belgium, district heating VS micro-cogeneration. Conference paper On average 1, 60% of energy private house consumption is used by the domestic heating systems, for the production of sanitary hot water, of power supply for electrical devices and 20% by car transportation. The best solution would be to produce these different kinds of energy in an efficient way, preferably through renewable sources. Moreover, if possible, this should be done locally in order to reduce losses in the electricity transmission and distribution lines, compensate the absence of investment in new centralized power plants and create new jobs. Different techniques exist to achieve this. A solar water heater can cover between 40 and 60% of sanitary hot water needs, as 5% of household total energy consumption. This is mainly negligible Photovoltaic cells or a micro-wind installation could cover 50% of electrical needs, as 5% of total consumption. An automatic boiler provided with wood could cover every heating need, as 60% of total energy consumption, which starts to be more interesting. Only power supply for car transport is missing to reach a global renewable solution close to 90%. Residential energy consumption and renewable productions 50% PV or Wind Transport Biofuels 20% Wood boiler Electric appliances Domestic hot water 50% Solar thermal Space heating 60% Micro-CHP The idea of being able to add up, in the way explained above, the different technologies used to reach a reduction of environmental impact of a private house is seductive, but remains, however, very complex and expensive. We should also not forget the consumption of raw materials for the production of these different equipments. The principle of rationality leads us to opt for a SINGLE local energy production technology which should be able, moreover, to cover the TOTAL demand of a private house. Since a house needs heat and power at the same time, won t it be more adequate to produce this heat and this electricity simultaneously? 1 Rounded up figures extracted from 2041 Walloon region (Belgium) energy budget in the domestic sector.

3 The answer is given by the cogeneration, which consists in the recuperation of heat losses released by a technology producing electricity (gas turbine, gas engine, steam turbine...). In order to match private houses special needs, we ll speak about «domestic microcogeneration», able to be provided with fossil fuels (natural gas, oil fuel, propane...) and, more recently, with renewable fuels (bio-diesel, vegetal oil, wood pellets ). On a domestic scale, it will be necessary to reduce the size of cogeneration units in order to reach electrical capacities of 1 to 10 kw and thermal capacities of between 10 to 25 kw. As a consequence, it then becomes possible for a house to cover the total amount of electric and thermal needs with the same piece of equipment. While this may sound utopian, it remains nonetheless the announced ambition of Honda that launched 2, back in March 2003, the first domestic micro-cogeneration unit, the Ecowill GE160V, which runs on a natural gas engine and is characterized by its very small size (1 kw electric and 3.25 kw thermal). More than units have already been sold on the Japanese market 3. The price of the unit, without installation costs, is approximately excluding VAT. Honda Ecowill Unit 1 kw é & 3.5 kw th Other manufacturers have, in the same way, developed this kind of domestic cogeneration systems based on a combustion engine: Senertec 4 (over units sold as of October 2006), Ecopower 5, EC Power 6 and Cogengreen 7, among others. Even if all these engines work with fossil fuels (natural gas or oil fuel), some models can, on the other hand, run on renewable fuels (bio-diesel, rapeseed oil or biogas). This would constitute a rational way of using a renewable fuel, even if of limited availability. At the Jon Slowe March/April 2006 :

4 same time these systems help meet all the heating and electricity needs of a private house, with one single device and one single renewable source. The use of wood implies conditioning it in the form of pellets in order to allow an automated management of the supply to the cogeneration unit. This implies the use of another technology: the external combustion engine or Stirling engine. Indeed, the combustion of a solid fuel such as wood pellets cannot be done inside an explosion engine cylinder. There lies the attractiveness of an external combustion engine: the use of continuous combustion flame, serving as heat source for the thermodynamic cycle. Heater Expansion space Expansion cylinder Generator Regenerator Cooling water Cooler Compression space Compression cylinder SOLO Stirling 161 Solo Stirling 161 Unit kw é & 8 22 kw th This is the principle which has been developed by Sunmachine 8, whose first wood fired model has been presented to the public at the Renewable Energies Fair in Lyon on February This constitutes a future technology for the domestic sector. Developing an electric power modulating between 1.5 and 3 kw for a thermal power between 4.5 and 10.5 kw, such a technology shows good electric conversion efficiency of between 20 and 25%. However the Sunmachine unit with wood pellets costs, without installation costs, excluding VAT. For the moment, the company is testing 50 units and has the ambition of making it commercially available by July

5 Sunmachine unit, running on wood pellets 1.5 à 3 kw é & 4.5 à 10.5 kw th Other manufacturers, at a less advanced stage, are developing domestic micro-cogeneration units on the basis of Stirling principle, and can also run with wood pellets: Otag 9, SPM 10, among others. When it comes to Stirling units running on natural gas, the Whispergen unit 11 rated 1kWe and 14 kwth (including an additional and optional burner of 6 kwth) is probably the most advanced the kind. More than 500 units have been installed in Great Britain and in the Netherlands and Powergen, the UK subsidiary of E-ON has ordered, back in August 2004, units to be delivered by The model Solo , which develops a maximum electric power of 7.5 kw, remains directed to larger buildings only. We can also quote, for domestic-level applications: Sigma Elektroteknisk (acquired by Disenco 13 ), Microgen 14 (based on the SunPower model), Enatee 15, among others. Fuel Cells, on the contrary, still have to be object of research and development in order to reduce costs significantly (at the moment amounting to /kwe!) and in order to improve the life duration of components. Technologies which use Rankine organic cycle still have to be developed before they are ready to enter the market (Energetix de Baxi, Enginion, Cogen Miero ). Commercialisation of many of these units is planned for An important limitation of cogeneration comes directly from its very principle: combined production of heat and power implies the fact that heat and power have to be consumed at

6 the same time and in the same given proportion. One solution, which is necessary if the user wants to replace his boiler with a domestic micro-cogeneration unit 16, is to be able to store the extra heat in a storage device, in order to make use of it at a later stage. Moreover, the addition of this heating water storage device allows a more regular functioning of the cogeneration unit. As underlined by the November 2005 report the Carbon Trust s small scale CHP field trial update 17, it is absolutely essential to reduce the number of rampup/shutdown cycles in order to attain enough savings in primary energy and, consequently, avoided CO 2 emissions. Indeed, the electrical consumption of auxiliaries at the moment of shutdown of the cogeneration unit (fans for example) or at the moment of ramp-up tends to reduce net electricity production. In the same way, thermal losses (due to chimney convection, for example) of the unit at the moment of shutdowns reduce the quantity of useful heat available in the home. There lies the importance of considering the unit as functioning on a base load basis when making the key decisions on the sizing of the microcogeneration unit and the capacity of the heat storage device. The decisions will be determined by the thermal points guaranteed by the discharge of heat storage. In the same manner, for the electricity, it is very unlikely that domestic electricity needs correspond exactly to the amount of power produced by the cogeneration unit. In addition, when it is not necessary to heat the house (summer time), micro-cogeneration will be shut down and it will not produce the necessary electricity for domestic needs. Consequently, storage (seasonal!) will be necessary. To improve rationality, it is recommended to use the grid as an electrical energy storage device. This principle starts to be admitted in Belgium: when micro-cogeneration electricity production is greater than on-site electricity needs, the energy meter inverts, allowing a valorisation of electricity which is physically sold to the grid at network prices. The latest financial stimulations allow domestic micro-cogeneration to be profitable and to finally blossom The only constraint is that the yearly electricity production by the micro-cogeneration unit cannot be greater than the domestic annual electricity consumption; in other words, difference in meter indexes cannot be negative. Thereby, the energy in the sustainable 21 st century house will be produced on-site by a single domestic co-generation unit, preferably running on biomass. Every electricity need, thanks to grid storage and every heating need, thanks to a heating water storage device, will be covered by this single, clean and, thanks to different supporting measures, profitable technology. The final step would be the possibility to produce, through domestic microcogeneration, the electricity necessary to recharge the batteries of a vehicle, of a motorcycle or of an electric bicycle. A dream that will soon be reality More topics presented during the conference: Technology comparison (power, efficiency, investment, maintenance) Profitability assessment for different types of houses in Belgium Impact of reference values on energy and CO 2 savings Specific supports to residential micro-cogeneration in Belgium District heating VS micro-cogeneration. 16 See «Analyse des systèmes de micro-cogénérations» - Mémoire de Ismaël Daoud et Nicolas Pierreux June Site :