Does geothermal energy only work in areas of volcanic activity?
If you were to take a sample of the population in most major countries and asked them to visually describe a geothermal energy plant, they might paint you a picture similar to the large steaming power plants near active volcanoes. Or they’d point you to pictures of geothermal activity in Iceland or New Zealand. However, geothermal energy can be found in many parts of the world, not associated with volcanic activity.
The term geothermal energy refers to any heat derived from the ground, whether that’s a few metres (shallow geothermal) or a few hundred kilometres (deep geothermal) below the surface. Let’s understand a little more about each of these concepts.
Shallow geothermal energy
Shallow geothermal energy, or low-grade ground-source energy, comes from heat absorbed from the sun by the earth. Developing shallow geothermal energy normally requires a heat pump to help increase temperatures to levels we can use to heat buildings. One example of shallow geothermal energy in the UK is the reuse of the country’s historical mine sites (that have long since been disused). Mines used to require constant draining of wastewater to avoid contamination of rivers and potable aquifers. This ‘waste’ water is warm and having absorbed heat from the surrounding rocks, is now ready for repurposing to warm buildings. It’s estimated that ¼ of the UK’s population lives above abandoned mines. These mines have the potential to generate 2.2 million GWh of heat which could keep approximately 18 million people warm and cosy with no associated greenhouse emissions.
Deep geothermal energy
Deep geothermal energy is defined by the UK government as sourced from more than 500m depth. The heat is generated partly from primordial heat left over from when the Earth was formed, and partly from heat generated from the normal decay of naturally occurring radioactive minerals. There are many forms of deep geothermal energy, some that produce water that is hot enough for heating and others that produce steam, which can be used to generate electricity and heat.
The UK has been using deep geothermal energy since the times of the Roman occupation, in areas such as Bath in Somerset where the water naturally flows to the surface at approximately 45oC. More recently (since 1986) heat and with the addition of biomass heating, electric power has also been produced in Southampton. This has helped to save 10,000 metric tonnes of CO2 emissions from the port and surrounding municipal buildings every year.
More excitingly, in 2020 steam was produced directly from deep well bores at the United Downs Industrial Estate, near Redruth in Cornwall. A power plant is currently being constructed that will generate 65 MW of electrical power, with hot water being used to supply heat to a rum distillery and the local community.
Geothermal energy is being explored across the UK and in many other parts of the world. As our understanding of the related/required geology and new technologies to extract heat evolve, the prospects for geothermal are definitely increasing.