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Ecotricity explains: Geothermal energy

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By Olly Rose
2 Nov 2021

In 2022, we’ll be helping to bring geothermal energy to Britain for the very first time, powering homes with renewable energy generated from steam more than three miles beneath Cornwall.

The site will produce at least 3 megawatts of electricity (enough to power 10,000 homes a year) which will be distributed via the National Grid.

We spoke to Hazel Farndale, Project Geologist from our partners, Geothermal Engineering, to find out more about geothermal energy, how it works and how it can help create a green Britain.

What is geothermal energy?
Geothermal energy is taking the heat from deep within the earth and using it at the surface, either directly as heat or to produce electricity.

How does geothermal energy work?
Here at the United Downs site in Cornwall, geothermal energy works by drawing fluid up from a depth of about five kilometres from a really deep well. We then use that fluid at the surface to generate steam, which can be used to turn a turbine and generate electricity.

We then put the fluid back underground, through our injection well and let it percolate back down through the hot granite to restart the process.

What are the benefits of adding geothermal to Britain’s energy mix?
It's a renewable, sustainable source of energy and a baseload provider, which means it produces energy 24/7 almost 365 days of the year. Also, it has the smallest surface footprint of any type of energy generation.

What’s the potential for geothermal energy in Britain?
There’s huge geothermal potential here. In theory, we can get geothermal energy anywhere in the country, we just have to drill deep enough. With current drilling technology, it's best to do this in Cornwall and Devon because here we have a granite body that naturally produces heat.

A recent independent report by the Renewable Energy Association estimated that there's a potential geothermal resource of 220 gigawatts beneath our feet here in Britain, enough to power all the UK's homes more than 18 times over. This is far more than we need. It has really exciting potential.

Is geothermal energy safe?
Understandably, there’s a lot of concern around drilling technologies associated with getting energy from under our feet. Geothermal is a really safe way of harnessing the natural heat under the ground – all we're doing is injecting fresh water.

This can be drinking water quality, so there's no contamination of anything under the ground. We're also heavily regulated by the likes of the Environment Agency and the Health and Safety Executive.

Can we repurpose existing oil and gas wells for new geothermal sites?
There are a number of possibilities for geothermal around Britain, not just drilling deep into granite down here in Cornwall. We can also do what we call repurposing of oil and gas wells. All over the country, we have these wells drilled to one or two-kilometre depths.

These won't get enough heat out for generating power with the current technology but they can be used to provide a source of heat at under a hundred degrees Celsius. The infrastructure is already there, we’d just be repurposing the existing wells which would reduce upfront costs tremendously.

What impact does a geothermal site have on the local community?
Each geothermal development site can produce tens of jobs directly. It also has potential to attract a lot of heat intensive businesses, because of the heat associated with the electricity production. So there’s potential for hundreds of indirect jobs as well in local communities.

As far as the site goes, we want to be a good neighbour and minimise the impact on the local area. We keep our noise levels down, make sure our light pollution is minimal and ensure we have a solid traffic management plan in place.

What impact does a geothermal site have on the environment?
It's really important to minimise the environmental impact of developing a new geothermal site.

Before we even apply for planning permission for a site, we undertake hundreds of different surveys. These can be with ecologists looking at the numbers of dormice, slow worms and bats, as well as helping us to understand how much biodiversity there is on a site. We also look at the heritage that's there, making sure that we preserve it, all of which then moves forward into the development itself.

Once it’s operational, we rewild the parts of the site that we no longer need. And we also only use the water that is already within the granite, so there's a closed loop and it will stay within the granite.

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