• CO2-free supplement to district heating
• Wells access underground water reservoirs
• Geothermal plant

In some parts of the world there are extensive underground reservoirs of water interlaced with heat-conducting layers of sandstone. This creates hot water, which can be extracted to become a CO2-free supplement to district heating. This is called geothermal heating. 

Geothermal energy
Today, geothermal energy (site is only in Danish) is one of the cleanest energy sources for heating. In itself, geothermal energy is CO2-free. However, transferring geothermal heat into the district heating pipeline system requires power plant-generated power. But this is a modest tradeoff, as ten units of CO2-free geothermal energy are produced for each unit of power employed.

An underground circulation system
In order to extract the energy, wells are built to access the water reservoirs. Hot water is pumped up from one well and the heat is extracted from the water via heat pumps and heat exchangers. The heat is then distributed through the local district heating system – which is why geothermal plants should preferably be situated close to thermal power stations.

The cooled water is led back into the reservoir through a second well. This keeps the pressure in the reservoir high and stable, as underground pressure pushes the hot water close to the earth’s surface.

Expanding our expertise
DONG Energy is currently involved in two geothermal plants, one of which was originally built back in 1984 as a pilot project for research and development. In addition, DONG Energy is planning to develop a third geothermal plant together with a partner. From 2012, this plant will be an important element in Sønderborg's vision to become CO2-neutral.