Your guide to geothermal energy and how it works

With renewable energy sources in high demand, we look into the different types in more detail to find out how geothermal energy works.

Disclaimer: The information on this page was last updated on 23/12/2022, 13:21:48

With the need for renewable energy on the rise, we’re learning more and more about the benefits of different sources. While geothermal energy is one of the less accessible sources, it is a great way to generate heat and electricity where you can.

How does geothermal energy work?

Geothermal energy uses heat derived from beneath the Earth’s surface. You’ll likely find geothermal power plants in an area with a lot of hot springs, geysers, or volcanic activity, where the Earth can reach over 120C under the surface.

There are a few different ways geothermal energy is used in areas with high volcanic activity. It’s used to generate electricity in the most opportune locations, but can also be used to heat homes where less heat is available.

Below are the most common ways geothermal energy is used and how it works.

Geothermal power plants

Geothermal power plants convert the heat from 1500m under the surface into electricity.

Firstly, hot water is pumped from deep underground under extremely high pressure and through a well. When the water reaches the surface, the pressure drops which turns the water into steam. This steam spins a turbine which is connected to a generator to convert this into electricity.

Once the steam has spun and gone through the turbine, a cooling tower cools the steam back into water which is pumped back into the Earth. Some of the water droplets are lost throughout the process, however, thanks to the water cycle, we can continue to use this for years to come.

Geothermal heating

Geothermal heat pumps use the heat directly from the Earth’s core to heat homes and businesses. They’re most often and most effectively used in areas with high volcanic activity. This is because the temperatures of underground water sources have extremely high temperatures, also heating the ground massively.

When it’s cold, these heat the water running through the geothermal system. Due to the almost uniform heat through the system, no pumps or turbines are needed to transfer the heat. Geothermal heat cools as it reaches the surface, transferring the heat into the building and back underground to be re-heated.

Ground source heat pumps

Ground source heat is often confused with geothermal energy. While both take temperatures from underground, geothermal energy takes the heat from close to the Earth’s core and ground source heat takes it from much closer to the surface.

Ground source heat pumps are also used to heat and cool water in our homes, however, these heat pumps use the sun’s ability to heat the shallow ground (less than 200m deep). This process uses the soil and underground water to cool the condenser. It uses electricity to transfer heat through underground pipes rather than turbines.

When the weather is cold, the water heats up as it travels through the pipe deep underground where the temperature is warmest. Once it reaches back above ground, the heat is transferred into the building, cooling the water again. It’s then pumped back underground where the process starts all over again.

When the weather is warm, this process can run in reverse: the water cools the building and the heat is transferred back around the underground pipes.

Advantages of geothermal energy

For both power and heat generation, geothermal is a great renewable energy source to consider if you can. It comes with a huge number of benefits, including:

  • Reliability - Geothermal energy doesn’t fluctuate as solar and wind do as the source is steady and doesn’t change with the weather
  • Rapid evolution - There are an increasing number of new technologies and explorations taking place around geothermal energy in order to improve it and make it more readily available
  • Sustainability - The heat from under the ground will always be there to be tapped into. While it’s likely that some locations perfect for geothermal energy could cool down, there will be magma to heat water for billions of years
  • Very little maintenance required - Because geothermal systems have very few moving parts, all of which are sheltered in a building, their lifespan is relatively high (up to 50 years) and don’t need servicing as often
  • Financial grants available - While a geothermal heat pump comes with high installation costs, there are Government grants available to help cover some of these costs, such as the Renewable Heat Incentive and Green Homes Grant

Disadvantages of geothermal energy

Just like any other renewable energy source, while it’s more environmentally friendly than some other fuel sources, geothermal energy comes with its disadvantages too.

  • Restricted by location - Geothermal energy is only accessible in select areas across the globe as it relies on having enough heat below the surface due to volcanic activity and hot springs
  • Gas from below the surface is released - While the generation of geothermal electricity doesn’t release greenhouse gases, many found underground are released when extracting the energy
  • High start-up costs - It can cost anywhere between £2 million and £7 million to set up a geothermal energy plant with a 1mw capacity. However, Governments in countries that are perfect for geothermal plants often offer grants to lower the costs and increase the use of renewable energy
  • Increased earthquake risk - Digging for a geothermal power plant can disrupt the structure of the Earth, especially if water is being forced underground to exploit the resources further. This means that there is a much higher risk of triggering earthquakes than other energy sources
  • Large surface area - Geothermal power plants and heat pumps and ground source heat pumps are quite large and take up a lot of space. Large areas will need to be dug in order to take advantage of geothermal energy, whether that’s downwards or longways

Where is the best location for a geothermal power plant?

Geothermal energy requires hot temperatures below the Earth’s surface, which occur around geothermal reservoirs underground. These reservoirs are naturally occurring and find their way to the surface in three different ways:

  • Volcanoes and fumaroles
  • Hot springs
  • Geysers

Because of this, the best locations for geothermal energy are near the boundaries of the Earth’s tectonic plates. These are where most volcanoes form and the most likely places for geothermal reservoirs to be found.

Geothermal energy in the UK

Unfortunately, here in the UK, even our temperature 500m underground averages around 39C. Which is far too low when it comes to geothermal electricity generation. We probably wouldn’t see temperatures high enough to generate geothermal electricity in the UK until at least 2500m below the surface, if not further.

With further research taking place around the world, it is possible that the right technology could come along which will allow us to effectively harness the power of geothermal energy to generate electricity in the UK. The most likely places to be able to generate geothermal electricity are:

  • South West England
  • The Lake District
  • Weardale
  • Eastern Highlands of Scotland

However, we are able to use ground source energy to heat homes. This is similar to geothermal energy, however, relies on the sun’s ability to heat the ground and requires a lot lower temperatures and shallow ground.

The heat stored just under the surface (200m) is largely derived from solar radiation absorbed by the ground and distributed by natural groundwater systems and man-made structures such as flooded coal mines. The ground then acts as a kind of ‘solar battery’, allowing us to heat and cool our homes.

Geothermal energy around the world

Luckily, many other countries are the perfect source for geothermal energy as they have much higher sub-surface temperatures due to high volcanic activity, multiple hot springs, and geysers.

Geothermal energy is generated in over 20 countries with the largest producers being:

  • USA
  • Indonesia
  • Philippines
  • Turkey
  • New Zealand
  • Mexico
  • Italy
  • Iceland

Geothermal energy for businesses

If your business is lucky enough to be able to take advantage of geothermal energy, you should definitely consider it.

With the increase in popularity of environmentally friendly businesses, you can use your use of a carbon-free, renewable, and sustainable energy source as a selling point. People are more likely to have a positive view of your business and become new, loyal customers when they see your green credentials.

Geothermal energy could also be a much cheaper way to control the temperature at your business premises, from offices to stores. Geothermal heat pumps can easily heat buildings in the winter and also work in reverse to cool you down in the summer months. Find out more about heating and cooling your workspace here.

What help is available?

If you think you could benefit from a geothermal or ground source heat pump, there are a number of different Government-led schemes in place to help homes and businesses move over to renewable energy sources.

The Renewable Heat Incentive is a scheme set up to financially support people who use renewable energy sources to heat their homes and businesses, helping cover the installation and running costs. There are two versions of the scheme - one for business and one for domestic renewable energy users.

You can apply for the Renewable Heat Incentive if you generate your own heat using renewable energy sources and you’re:

  • A homeowner
  • A landlord
  • A self-builder

Or you provide heat to:

  • An indoor swimming pool
  • A garage/outbuilding
  • A shed
  • A commercially used building

The Green Homes Grant offered to pay at least two-thirds of the cost (up to £5,000) of energy-saving home improvements, including ground source heat pumps. Unfortunately, the application deadline for this scheme was in March 2021, but if you’ve already been accepted into the scheme or your application is being processed, you’ll still be able to get your vouchers to cover the costs.

The Green Deal helps you find the best way to pay for energy-saving home improvements. Energy improvements can be expensive so the Green Deal offers you a finance plan. The Government will lend you the money to pay for the work which will be paid back through an extra charge on your electricity bill. If you move out before the work is fully paid for, you won’t have to pay it anymore as you won’t be benefitting from it. The new occupier will pay the remaining balance.

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