Terrestrial heat

The earth has a temperature around 7000 degrees Celsius in inner the core, on an average the temperature increases by 25-35 deg. C. per kilometer measured from the earth surface and inwards. The temperature potential can be exploited as heat by pumping a fluid around in a circuit which takes the medium to depths of 2-5 kilometers. Depending on the depth and temperature profile, it is possible to achieve exit temperatures around 200 deg. C.
 
Due to variations of the earth’s crust thickness there will be different temperature profiles form place to place. Some areas are known to have hot springs and the like and volcanic activities, such areas will also be well suited for geothermal utilization. Japan and Iceland are examples of this, in Iceland geothermal energy is used for the bulk of the power and heat production.

At present there is no large scale geothermal energy utilization in Norway, but household heat pumps with geothermal utilization are becoming more widespread.
An area of interest with a particular potential for Norway is the abandoned or empty oil and gas fields. Geothermal projects are often troubled by the costs of drilling to great depths, for oil – and gas fields these structures are in place and costs much less to convert to heat extraction. By pumping a fluid in a loop to extract the earth’s heat from these fields a potential of up to 175 deg. C has been revealed in studies performed by SINTEF earch in co-operation with external interests. Net power production efficiencies of 6-10% can be achived dependent on the power cycle and medium that is used. Due to saved fuel costs and saved CO₂ tax, such systems can provide power at very competitive prices. SINTEF conducts studies of such systems and processes in co-operation with NTNU with a special emphasis on combined heat and power utilization.