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Cornish deep hot rock developments
19/7/2023
6 min read
Feature
Geothermal resources have the potential to produce renewable, constant (24/7) power and heat from natural resources and could play a pivotal role as the UK’s energy supply is decarbonised. Ryan Law, CEO of Geothermal Engineering, describes the company’s first Cornish developments.
Geothermal developments are associated with tectonically active regions where the Earth’s crust is thin and the surface heat flow is high. With current drilling techniques, only certain parts of the UK, mainly in Cornwall, are currently suitable for geothermal power extraction. However, as drilling and power plant technology becomes more specialised and efficient, new geothermal prospects at greater depths or lower temperatures have potential for commercial development.
Key benefits
There are numerous benefits to geothermal power production:
- Low carbon: Geothermal resources offer low-carbon, sustainable energy, generating less than 3% of the CO2/kWh compared to fossil fuel alternatives. This equates to a saving of more than 713,000 tonnes of CO2 equivalent (CO2e) per 5MWe power project.
- Small surface footprint: Geothermal power production has a very small surface footprint. It features the smallest surface footprint in terms of land use based on acres/1 GW of any onshore energy source.
- Baseload power with minimal waste: Geothermal also has minimal waste production, and can provide 24/7 baseload power, independent of weather or time-of-day factors, making it extremely reliable.
- Versatile heat energy: Geothermal energy can be used for heating or cooling. The efficiency of the various processes is dependent on the temperature, so one can determine the best use of a particular pocket of geothermal energy according to the temperature at which certain processes need to operate.
- Local community benefit: The heat energy from geothermal sources cannot be exported. So, this heat source will provide benefit to the local community through local heat networks directly into homes or businesses, or attract inward investment by companies or industries that need large amounts of cheap heat or cooling.
Geothermal resources offer low-carbon, sustainable energy, generating less than 3% of the CO2/kWh compared to fossil fuel alternatives.
Grid access
As with any renewable power source, a critical aspect for the successful rollout of geothermal power in the UK will be ensuring access to the National Grid. To be able to supply baseload renewable electricity to the National Grid, each geothermal power plant will need an access point nearby. Current limitations to the grid mean that there are many sites in Cornwall that would be suitable for the production of geothermal energy but are currently unsuitable for development because the power cannot be exported.
Landmark geothermal developments
Geothermal Engineering (GEL) aims to deliver 25 MW of renewable baseload electricity and 100 MW of renewable heat across its portfolio from deep geothermal resources in the UK by 2028.
The company currently has three sites under development in Cornwall, at United Downs, Penhallow and Manhay (see Box).
United Downs – deep geothermal power plant in the UK
The United Downs project was first conceived in 2009. Drilling of the wells commenced in 2018. The project will start generating power and heat from the hot granite rocks beneath Cornwall in 2024.
Two wells have been drilled and tested, including a production well drilled to 5,275 metres measured depth, which is the deepest well ever drilled on UK soil, and an injection well of 2,393 metres measured depth. A smaller rig was used to complete the wellhead and enable test equipment to be used to take core samples, temperature and core test. The first geothermal steam was produced in July 2021.
This pioneering test plant will deliver around 2 MW of baseload electricity and up to 10 MW of zero-carbon heat to be used in a large housing development at Langarth Garden Village near Truro, being developed by Cornwall Council. It aims to provide power for 3,800 homes and up to 10,000 people.
The heat network is estimated to save approximately 5,000 t/y of CO2e for Langarth Garden Village alone, compared to the alternative low-carbon option of using an air source heat pump for each home. Heat from the network will also be supplied to the Royal Cornwall Hospital, local schools and a leisure centre.
Penhallow geothermal project
GEL’s second geothermal power project is located at Penhallow, in the parish of Perranzabuloe, and was granted planning permission in September 2022. Works are scheduled to begin in late 2023. GEL has made a commitment to protect the local environment at all project sites, and the initiative at Penhallow intends to see the site’s biodiversity increase by more than 40%.
Manhay – granted planning permission in February 2023
The third of GEL’s geothermal sites is the Manhay project – located within the parish of Wendro and granted planning permission in February 2023. For this site, GEL plans to increase local biodiversity by around 70% through encouraging more wildlife to the area, planting hedgerows around the site and working with the community to support sustainable projects.
GEL estimates it will take around three years of preparation to begin electricity generation at both Penhallow and Manhay. Two deep wells will be drilled at each site, with the deeper well estimated to reach around 4,500 metres in depth. Natural hot geothermal fluid will be brought to the surface, whilst the second (at 3,000 metres) will deposit the cool fluid back underground after the heat has been extracted to produce electricity.
When up and running, both power plants are each expected to generate around 5 MW of green, baseload electrical energy 24/7, and around 20 MW of thermal energy. The combined output from these plants will generate enough power and heat for the equivalent of up to 22,000 UK homes and save over 1.4mn tonnes of CO2 emissions compared to a gas-fired power station of the same power output.
Both the Penhallow and Manhay sites will be provided with a £40,000 community fund, with more than £1mn to be spent on local businesses during construction.
Drilling rig at United Downs geothermal project site in Cornwall
Photo: Geothermal Engineering
How GEL is funded
The United Downs project has received a total investment of more than £35mn from Kerogen Capital and Thrive Renewables as well as the European Regional Development Fund and Cornwall Council. GEL announced its most recent funding round in March 2023, with £12mn from Kerogen Capital and £3mn from Thrive Renewables. These funds will be used to complete power production at the United Downs plant by 2024, as well as for further development across its wider portfolio in Cornwall.
In addition, £22mn was recently awarded to develop a geothermal district heating network at Langarth Garden Village, as part of a wider round of £91mn granted by the Department of Energy Security and Net Zero (DESNZ) to seven heat network projects across England. This is an important investment by government given that about 50% of all energy in the UK is used for heating, but most of this currently comes from gas. The funds will allow Cornwall Council to work with GEL to develop a new heat network using hot water from the deep geothermal well at United Downs.
The allocations from DESNZ in turn form part of a larger £288mn government package, the Green Heat Network Fund, rolling out heat networks across the nation and providing a cut to carbon emissions equivalent to taking 5.6mn cars off the road for a year.
Lithium extraction opportunity
In 2021 GEL discovered very high levels of lithium in the geothermal waters at United Downs. Third-party tests showed that there are more than 250 mg/l in the fluid extracted from around 5 km below the ground. Subsequently, GEL trialled sustainable, zero-carbon methods of extracting the lithium, which has so far resulted in a 90% recovery rate.
Tests have also shown that magnesium concentration in the fluid is low. This is a positive sign as the presence of magnesium can often hinder the lithium extraction process. Based on the findings of tests conducted in 2021, GEL is looking at the potential to produce 4,000 t/y of lithium from its sites by 2026 using direct lithium extraction (DLE), an environmentally-friendly practice where the geothermal fluid is deposited back underground after the lithium has been extracted.
With lithium being used in multiple electronic devices, and a widespread shift to electric vehicles, it is in extremely high demand. The UK currently produces no lithium and the carbon footprint of manufacturing lithium-ion batteries is substantial.
The Faraday Institution, a government-backed body promoting the battery industry, estimates that UK demand for lithium could reach 75,000 t/y of lithium carbonate equivalent by 2035, based on projected growth in domestic battery demand. For this reason, it is vital that the UK focuses on harnessing its domestic sources of lithium, which will be key to the UK’s journey to net zero, as well as offering an exciting opportunity for the development of south-west England as a new UK sustainability hub.
Looking forward
According to the Deep Geothermal Energy review by Arup and the Renewable Energy Association in 2022, there is the potential for 222 GWe of electricity supply from geothermal resources in the UK, which equates to around six times UK annual electricity demand.
Developing geothermal resources in the UK will play a critical role in our energy security and independence. Alongside this, the potential of projects like Langarth are increasingly important, especially due to the recent news that the UK is set to miss out on climate targets across almost every front, according to the Climate Change Committee.
Until recently, investment in the UK’s deep geothermal resources has been overlooked, so GEL is excited to see this sector start to realise its potential as it switches on power next year.
More news about geothermal developments in Cornwall can be found here.
