It gets pretty hot in the middle of the Earth. Imagine if we could harness that heat and use it ourselves? Well great news! We can, and it's called geothermal power. Our clever little guide is here to help you get to the bottom of this hot topic.
What is geothermal energy?
To break it down 'geo' means earth and 'thermal' means heat. So, geothermal power is quite literally just energy generated using the Earth's heat. But where does that heat come from? There are two key ways the Earth generates heat. It absorbs the heat from the sun, and also radiates heat from its molten core. We can then access these geothermal resources by digging beneath the planet's surface at depths ranging from several kilometres to just a few metres!
The geothermal energy generated this way is often also thermal (simply the heat itself), but geothermal technologies can be used to convert it into electricity too. We are then able to use that heat and electricity to keep our buildings warm and the power on.
How does geothermal energy work?
There are a few different geothermal technologies that allow us to generate energy from the Earth's heat. The technologies each operate at different depths and in different types of subsurface material (e.g rock and sediment). This means we can make use of a wide variety of geothermal resources around the UK.
Shallow depth technologies include ground source heat pumps (which can be used to heat homes) and repurposing unused mines. Deep geothermal technologies are used for larger scale energy projects, such as geothermal power plants and district heating systems for entire communities.
Ground source heat pumps. These heat pumps are an efficient home heating alternative to traditional gas boilers. They work at shallow depths by drawing heat from the ground water via boreholes, underground pipes, and pumps. Ground source heat pumps can also be used for home cooling by drawing heat away and into the groundwater. There are two main varieties of ground source heat pump: open loop systems and closed loop systems. Open loop systems pump up ground water to extract the heat. Closed loop systems run liquid through a sealed pipe system that absorbs heat underground and delivers it through a heat exchanger.
Hydrothermal systems. Also called aquifers, hydrothermal systems operate at depths of 1-3km1. An aquifer is a naturally occurring permeable rock or sediment, meaning groundwater can pass through it. They are able to store hot water at high enough temperatures for direct use as part of district heating systems. The hydrothermal system is normally set up by digging two boreholes down to the natural aquifer - one to draw up hot water and a second to flow back the cooled water.
Petrothermal systems. This geothermal system also uses wells to access underground heat. However, it targets rock types that are not permeable and so do not allow water to pass through them, such as granite. These are often even deeper than hydrothermal systems, operating at depths of around 5km2. Rocks of this type often have a higher than average amount of radioactive elements inside. Additional heat is produced by the radioactive decay of these elements, causing this system to operate at much higher temperatures - and therefore produce greater amounts of geothermal energy. It's no wonder then, that petrothermal systems are the most common form of geothermal technology used for generating electricity in power plants.
What is a geothermal power plant?
Geothermal power plants are a large-scale way to harness geothermal energy and use it to generate electricity. There are three different ways to generate electricity in a geothermal power plant, but they all work by using steam to rotate a turbine and generate power.
Dry steam. This uses naturally occurring underground steam, such as from geysers.
Flash steam. This uses natural reservoirs of high temperature groundwater, which turns into steam as it de-pressurises from being piped to the surface.
Binary steam. This cycles hot groundwater through a heat exchanger in a closed pipe system. The heat exchanger transfers the heat to a different liquid with a low boiling point, which vaporises and is used to turn the turbine. This method is used where the groundwater is not hot enough to become steam naturally.
5 geothermal energy advantages.
Geothermal energy is renewable. That means it can be naturally replenished as fast as we use it. Unlike fossil fuels, which are a limited resource that takes millions of years to form naturally. Investing in renewable energy helps to improve our national energy security, making us less vulnerable to changes in the energy market. Learn more about renewable energy.
Whatever the weather, we can count on geothermal energy. Unlike some other popular renewable energy sources, such as wind turbines and solar panels, geothermal energy isn't dependent on the weather. This makes it a reliable energy source all year round.
Save on space. Geothermal energy has a low surface footprint, meaning it doesn't take up much space to generate energy. This is especially significant for the UK, being an island we need to be conscious that we use land efficiently.
Low greenhouse gas emissions. Geothermal power produces significantly less greenhouse emissions than fossil fuels3. In fact, when used in direct heating applications (such as heating homes) emissions are usually negligible4.
Creating job opportunities. Another benefit of investing in this growing industry is the creation of jobs. This can be directly in building and maintaining the geothermal technologies, or through indirect opportunities in supporting industries. The Netherlands has reported that for every direct job created by geothermal energy, 2-3 more were indirectly created as well5.
Heating homes with geothermal energy.
20% of UK CO2 emissions come from home energy6. If you're looking to lower your carbon footprint at home, installing a ground source heat pump could be a great option. In fact, the Energy Saving Trust estimates that a well-insulated 4 bedroom home could avoid 3000 - 4500 kg of CO2 per year by upgrading from a gas boiler to a ground source heat pump7.
There are two types of ground source heat pumps that can be installed in homes.
Horizontal heat pumps. They are a closed loop of underground pipes installed in shallow trenches that cover a large surface area. This means they are very disruptive to the land. However, they are cheaper to install and best for properties with large outdoor spaces.
Vertical heat pumps. They are also a closed loop of underground pipes, but they are installed deep into the ground using vertical bore holes. This means they don't require as much land, but the installation is more expensive8. Best for properties with small outdoor spaces.
Is a ground source heat pump right for me?
There are a few things to be aware of if you are considering installing a ground source heat pump to use geothermal energy at home.
Firstly, whilst geothermal energy is relatively space saving on a large scale compared to other alternatives, it does still require land to set up. In some cases you may also need to apply for planning permission, although installation is usually included within your permitted developments. The area will also need to be accessible for digging machinery. For further advice on whether a heat pump could be right for you, reach out to an accredited installer.
The second thing to bear in mind is that heat pump installations are not always the most cost-effective option for households. They could save you money on annual heating bills, but this depends on the efficiency of your current heating system. Due to the work required in installation, ground source heat pumps have high upfront costs. On average a horizontal system costs around £28,000 and a vertical system around £57,0009. This barrier to access is currently one of the biggest disadvantages of geothermal energy for UK homes.
Although, the good news is, residents living in England or Wales can receive up to £7,500 towards the costs as part of the government's Boiler Upgrade Scheme.
If you'd like to make your home energy more renewable, but aren't sure if a ground source heat pump would work for you, there are other great renewable technologies to choose from.
Air source heat pumps are lower cost heating alternatives10 that don't need as much space for installation. Even better, they are still eligible for the Boiler Upgrade Scheme grant. Learn more about air source heat pumps.
Solar panels can help you generate your own renewable electricity, and they can be installed to provide solar water heating as well - providing you with renewable power and heating. Check out the benefits of solar power. Plus, as an E.ON Next customer, you can get up to £150 off a solar panel installation from E.ON.
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