Wednesday, April 05, 2006

What's the importance of cogeneration?

By Eckhard Schulz 

In partnership with Energie-Fakten

Mature technologies are now available for the combined production of electricity and heat (cogeneration). They can use fossil or nuclear energy carriers, as well as biomass.

In a proper comparison (serving the same energy needs through both alternatives), cogeneration uses 15-20% less energy, and contributes an equivalent amount of emission reductions, compared to the production of electricity and heat in separate facilities, i.e. a thermal power plant and a modern boiler. In this case, the comparison needs to be based on the same fuel. When cogeneration is combined with a fuel switch -- from coal to gas, the impact of switching fuel is more important than the impact of cogeneration, due to the favourable characteristics of gas compared to coal. The advantage of cogeneration also decreases with higher efficiency of future power plants.

Cogeneration is above all meaningful for applications where there is a large and continuous (not just seasonal) demand for heat close to the cogeneration facility. If there is no demand for heat from a cogeneration facility, its efficiency for the production of electricity will be lower than for optimised thermal power stations. Larger cogeneration facilities have in general lower production costs than smaller units. But on the other hand, transport of heat to users takes longer and is more expensive.

Cogeneration provides 6% of heat in Germany. Each year, about 55 TWh (1 TWh = 1 billion kWH) is produced. German cogeneration facilities operate less frequently in condensation regimefootnote{i.e. without simultaneous use of heat}, in comparison to other European countries. With a market share of 10% electricity produced from cogeneration facilities, Germany's performance is about average. Denmark is leading. But in Denmark, cogeneration facilities operate a considerable amount of time in the condensation regime. Moreover, the development of individual heat supply on the basis of gas has been inhibited in Denmark by regulation for a long time.

Government supports the further development of cogeneration. In case of district heating, this will not be possible, due to the reducing heat demand for dwellings, based on more stringent regulations for isolation and energy performance. For local heat production, there are growing possibilities if technology further develops (e.g. fuel cells). The already significant portion of cogeneration in industrial energy supply (electricity and steam) can increase further. Above all, the power to heat ratio (more electricity and less heat produced by cogeneration) increases significantly, compared to older facilities.

This contribution was originally published on July 21, 2005 by Energie-Fakten.

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