Geothermal energy is a sustainable energy source produced by tapping into the natural heat that exists within the Earth. It’s considered a reliable energy source given the heat generated within the Earth is constant.
How is geothermal energy made?
Geothermal energy can be accessed from a few metres to a few kilometres below ground and extracted using either shallow or deep geothermal technologies.
Shallow geothermal energy
Shallow geothermal energy is stored at depths of up to 500m and requires the use of ground source heat pumps to extract heat. The temperatures accessed by shallow geothermal technologies range from 10 to 25C and is stored within soil and rocks, aquifers (known as groundwater), and flooded mines.
Ground source heat pumps (GSHPs) can only extract heat from soil or water stored under the Earth’s surface up to depths of around 200m. This heat doesn’t come from the Earth’s core, but rather from the sun heating the Earth’s surface. However, geothermal energy is broadly defined as heat emanating from the Earth’s core, so it is inaccurate to say that heat pumps use geothermal energy to heat buildings.
Mine water energy
Given the UK’s legacy of mining, there are now over 2,000 abandoned mines across the UK. Once flooded, water within these mines can be used for geothermal heating, colling, and as underground energy storage. Water temperatures within these mines sit between 10 to 15C, but deeper mines could reach higher temperatures.
Open-loop configurations are used to abstract and discharge water from different zones within a mine. Using this water for geothermal energy adds value to otherwise dormant mines.
According to research from The Coal Authority, roughly 25 per cent of UK homes are situated in former coalfield areas with mine water offering decarbonised heat opportunities.
Deep geothermal energy
Deep geothermal energy is accessed by drilling wells and boreholes to reach heat supplies deep within the earth. The heat accessed through these processes is used for commercial and domestic purposes, industrial processes, agriculture, and power generation. The two systems used to access deep geothermal energy include:
- Hydrothermal – accesses heat from deep aquifer up to depths of around 1 to 3km and temperatures of 40 to 80C.
- Petrothermal – accesses heat from granite infusion where temperatures can reach up to 200C at depths of about 5km.
