Solar heating plant


Symbiosis combining large scale solar heating, gas fuelled CHP and absorption heat pump.

Silkeborg municipal-owned district heating company in Denmark, supplies most of the city Silkeborg with heat. The 400 GWh annual heat production has for 20 years been provided with a gas fuelled CC plant and gas boilers. Due to lower electricity prices, this production has been less cost effective recent years.

Therefore, the company and the city looked for better solutions. The  result of a detailed feasibility studies was to use the symbiosis of combining large-scale solar water heating and a more efficient gas CC plant by sharing a new absorption heat pump and larger heat storages.

The symbiosis between large scale solar and the CHP plant comprises the following:

The storage is mainly used for solar in three summer months and for CHP optimization the rest of the year

The heat pump increases the production of solar heat autumn and spring and increases the efficiency of the CHP plant with flue gas condensation the rest of the year, thereby improving the competitiveness of the plant in the electricity market and its operation hours

The total investment has been around 230 mill DKK for the solar heating plant and 450 mill DKK for heat pump, the flue gas condensation and the tanks.


Gas fuelled CC plant: 108 MW elec./85 MW heat

Total efficiency of the plant: 87%

Heat storage tank: 2*16.000 m3 = 32.000 m3

Heat production from CHP: 80 GWh

Heat production boilers: 320 GWh


Gas fuelled CC plant: 106 MW elec./120 MW heat

Total efficiency of the plant: 102%

Heat storage tanks: 4 x 16.000 m3 = 64.000 m3

Large-scale solar heating: 156.000 m2

Absorption heat pumps: 25 MW cooling capacity

Heat production solar: 70 GWh

Heat pump from solar: 10 GWh

Heat production CHP: 210 GWh

Heat pump condensation: 30 GWh

Heat production boilers: 80 GWh

Date of release