Geothermal energy has a great potential to supply electricity, heating and cooling in cities. Nevertheless, it is very important to know exactly where can we do the installation. A detailed study of the type of ground is required. But, as you can imagine, it means taking samples from different places, analysing them, etc. A study developed by the Karlsruhe Insitute of Technology has made use of satellites to search for underground heat islands suitable for geothermal energy generation.
Searching for heat islands with satellites
Several studies have shown that underground water is warmer in cities than in rural areas. The reasons of this fact are diverse: population density, surface sealing, thermal radiation of buildings, industry, and transport as well as lacking vegetation. Then, why don’t we make use of it? It can be helpful to provide heating in winter and cooling in summer. Just an installation of geothermal or groundwater pumps is enough.
Up to now, the relationship between above-ground and underground temperatures was not clear. Researchers from several institutions (Institute of Applied Geosciences, KIT and ETH Zurich) has analysed heat islands in four cities in Germany. Satellites were used to measure surface temperatures. However, description of underground heat islands is much more difficult and other methods are still required.
Researchers compared the results of above-ground and underground temperatures. They found a spatial correlation of 80%. It was interesting that the older the city (like Cologne), the bigger the correlation. Scientists found that 95% of the areas studied had higher underground temperatures than above-ground ones. This may happen because of other factors such as cellars of buildings, sewers, etc.
As satellites were not a good method, researchers decided to include population density and cellars temperature in their calculations. The results were much more accurate: only a difference of 0.9º K was achieved. Philipp Blum claims that the study is promising and a good approach:
This method can be applied for a first assessment of underground heat islands and, hence, of ecological conditions in the groundwater and of the geothermal potential. No complex groundwater temperature measurements and interpolations are required.
You can find the whole study in a paper published in Environmental Science and Technology.