Herlev, Denmark

Real estate | 1,385 sqm installation


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Project Summary

Social housing association Herlev Kommunes Boligselskab/KAB realised a 1,025 m² collective solar thermal system on a field and 8 times 45 m² solar thermal systems on the roofs on individual houses. A 3,000 m³ insulated season storage basin is located 6 metres below the field panels. The residential complex comprises apartment building with a total area of 6,710 m². The system was installed during the initial construction of the buildings. I was the first solar thermal systems in Denmark with seasonal heat storage. A central gas fired boiler, a gas engine/generator and a heat pump for heat recovery is also a part of the energy supply system. The total energy system has decreased the emissions by 80 % compared with conventional energy supply – without extra cost for the users. In total the system reduces the natural gas consumption to 35 kWh/(m²·a).



Type of building

Real estate

Number of users / dwellings, floors

80 dwellings
2 floors

Year of construction


Total effective area (heated)

6,710 m2

Hot tap water consumption

4,672 m3/a (calculated)

Whole energy consumption for tapwater heating purpose after CSTS implementation

523,267 kWh/a

System engineering

Year of construction of CSTS


Type of collectors

Flat plate collectors

Thermal power

970 kWtherm.

Aperture area of collectors*)

1,025 m2

Buffer storage (seasonal)

3,000 m3

Hot tap water storage

20 m3 (8 × 2.5 m3)

Total capacity of boilers with energy source

450 kW, natural gas

Type of hot tap water heating


Type of heating system



Total cost solar system

1,270,000 Euro

Cost of the CSTS / gross area of collectors

917 Euro/m2


49 %


Output of solar heat**)

623,250 kWh/a

Reduction of final energy***)

700,000 kWh/a

CO2-emissions avoided

143 t CO2/a

Solar performance guarantee


*) Aperture area = light transmitting area of the front glass
**) measured, between storage and piping to taps (solar system output)
***) related to the measured output mentioned before