Greenhouse gas emissions could be cut sharply using micro combined heat and power systems (micro cogeneration), according to new research. The research suggests that micro cogeneration plants could contribute to the 20 per cent reductions in greenhouse gas emissions needed by 2020 to meet the targets set under the Kyoto agreement.

Meeting the Kyoto commitment to reduce greenhouse gas (GHG) emissions will mean significant changes in the way Europe generates power. Out-of-date power stations will be decommissioned and in Germany, for instance, 40 GWel of power plant capacity, approximately a third of Germany's total installed capacity, must be replaced by the year 2020.

An understanding of the environmental impact of alternatives to centralised sources of energy supply is crucial in terms of developing energy technologies and deciding policy. Research from the Institute for Energy and Environmental Research Heidelberg, Germany, explored the contribution of micro cogeneration systems to reductions in GHG emissions, savings in grid capacity and a move to renewable fuels. Life-cycle assessment and an analysis of emissions were conducted on a range of technologies, such as fuel cells, reciprocating and large or small Stirling engines, to evaluate their environmental impact.

The researchers studied systems with a capacity of 15 KW or less, and believe that the main market for these systems will be in replacing gas heating boilers in single buildings within existing housing stock. They compared these systems with the environmental impact of new power plants which would otherwise have to be installed, for a range of effects including emission of GHGs and acidification.

Most micro cogeneration systems were found to be superior as regards GHG emissions both to today's average electricity supply mix in Germany, and to separate production of electricity and heat using the latest gas operated power plants and condensing boilers, and comparable to district heating systems based on cogeneration. GHG reductions of 1 tonne per year (for a single family house) to 11 tonnes per year (for a hotel) could be achieved. When compared with coal-fired power plants, even greater reductions were achieved. From the point of view of local air quality in residential areas, reciprocating engines were found to produce insignificant levels of emissions, and the researchers recommend that low NO2 reciprocating engines should be further developed.

The likely consumers of these technologies are single family households, where peak demand in both heat and power are likely to coincide. Micro cogeneration would reduce consumer demand from high cost centralised peak-load power plants. This suggests that fuel cell technology, with its high power-to-heat ratio, could have a competitive advantage in the case of a single family house. The micro cogeneration systems investigated still relied on a fossil fuel, namely natural gas, so further developments would ideally be part of a strategy focusing on developing renewable energy technologies, combined with improvements in energy efficiency and energy saving.

Source: Pehnt, M. (2008). Environmental impacts of distributed energy systems - The case of micro cogeneration, Environmental Science & Policy. 11(1): 25-37.

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