Energy from cherry stones in CHP system

Energy from cherry stones

Gas CHP engine supports biomass and fossil fuel boilers

In 2006, our German office encouraged the town council of Sasbachwalden, Germany, to look into the use of biomass district heating for public buildings. The company subsequently took responsibility for developing the district heating system which supplies six public buildings under different ownership. Due to careful system design, the wood-chip boiler rarely has to modulate its output, which leads to an exceptionally high seasonal efficiency. The project was delivered 7% below budget costs.

The town council was so delighted with the system that a larger follow-on contract was awarded in 2007: a district heating network supplying the local swimming pool, spa and 22 private dwellings. Our design was awarded government support to the tune of 100,000 Euro for our innovative concept of deriving energy from a plentiful local resource: the stones of cherries, a waste product of the local Black Forest kirsch distilleries!

Three sub-systems produce a total output of around 1MW:

  • A 400kW biomass boiler is used for space heating in winter
  • A 600kW fossil-fuel boiler provides redundancy and tops up heat output from the biomass boiler during peak periods; this boiler runs for around 5% of the time
  • A gas CHP engine (12kWth, 6kWe) produces electricity all-year-round. The waste heat from the engine provides hot water during the summer. The year-round use of heat leads to an overall seasonal efficiency of the CHP system of around 80%
  • In addition, heat for the swimming pool is derived from the existing solar thermal system