You only need 60 degree C to provide a building with heating and hot tap water and there are huge energy CO2 neutral energy resources at 70 degree C or more in the underground!

Therefore it is worth to consider how to utilize this resource.

In some countries there are even warm springs and in Iceland the geothermal energy is used for power production and for heating almost all buildings, mainly through large one-pipe open district heating systems.

In other countries like Denmark the 70 degree C hot water resources are around two kilometer below the surface. Therefore it can only be explored in large scale in district heating systems. Two test plants are in operation, two are in the pipeline.

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In the Danish case it is expensive to explore geothermal energy, however compared to many other zero carbon solutions it is not expensive. However you need to consider the following:

• It is very expensive to drill 2 km holes in the underground and to establish the necessary facilities. Therefore the plant should always be in a certain scale and with long utilization period, e.g.as base load in a large district heating system
• There is always a risk that well will be dry due to low permeability. Therefore detailed seismic investigations are important before the decision is taken
• The salinity is very high. Therefore special precautions shall be taken with the heat exchangers.
• The geothermal water can utilized more efficient with low temperature heating, e.g. if the buildings use floor heating, and with a heat pump.

Ramboll has provided seismic analysis for the geothermal projects in Copenhagen and in Sønderborg for Ørsted and Ramboll is currently was undertaking a feasibility study for Viborg district heating company for a new geothermal plant with a total capacity of 16-32 MW geothermal.