Geothermal power at Eden

We have plans to generate power from deep inside the Cornish granite.

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In partnership with Cornwall-based EGS Energy, we have planning permission for a 5-7MW geothermal power plant on the Eden Project site, taking energy from the heat in underground granite rocks.

Geothermal energy is the heat in the rock beneath our feet. Worldwide, natural spas have been enjoyed for millenia, and in active volcanic and tectonic areas, like Italy, hot rocks have been producing power for a hundred years.

Advances in engineering mean that lower temperature resources in geologically stable regions are now usable.

About Eden's proposed geothermal power plant

On a site the size of a football pitch, the geothermal power plant would produce enough power for the Eden Project and around 7,000 houses, plus all the heat we can use, and more.

EGS Energy is part-owned by the team who have already built three engineered geothermal plants in Europe, including one in Landau, Germany.

Engineered geothermal system

The power plant at the north end of our site would be an 'engineered geothermal system' (EGS). Here's how they work:

In construction

  1. Two boreholes, each around 25cm wide, are drilled into the rock to a depth of about 4.5km. Water is pumped down one borehole into the natural fractures in the rock to create an engineered heat exchanger between the two boreholes. 
  2. A heat exchanger is engineered between the two boreholes. 

In operation

  1. Cold water is injected down one borehole, picks up heat from the rock and is pumped back up to the surface at about 180°C.
  2. This hot water runs through a binary cycle turbine to make electricity.

Advantages of geothermal energy

  • Geothermal power is the only renewable energy resource not affected by the weather; it is 'on' 24 hours a day, with plants typically running over 90% of the time.
  • The surface area of the plant is the smallest of any power source, and with buildings no higher than 10m, geothermal energy has a low impact on the landscape.
  • Recent research has shown that geothermal energy could provide up to 20% of the UK's current electricity demand, and a vast amount of heating. 

For more information on geothermal energy, please visit the EGS Energy website, or take a look at our Understanding geothermal power infographic.

Frequently asked questions

How noisy will it be?

Rigs are hired from the oil industry, so drilling will take place 24 hours a day to minimise the cost. It will take around 20 weeks per well. The rig will be one specifically for use in a populated area and heavily soundproofed, producing up to 45dBA at 200m. During operation, the generator will make a constant noise: a maximum of 30dBA at a distance of 200m. But because buildings are low, the noise can be tempered by landscaping.

Will drilling the rock cause problems at the surface?

In December 2006 in Basel, Switzerland, earth tremors were felt in an area where geothermal development was taking place. Cornwall’s geology is far more stable than that in Basel, which is in a tectonic region with a long history of earthquakes. Many years of geothermal development and reservoir stimulation were carried out at the Rosemanowes research project in south Cornwall with only one tremor felt at the surface and no damage recorded. Nevertheless a full seismic risk report has been carried out. Seismic sensors and accelerometers will be installed to make sure that in the highly unlikely event of any increase in the level of seismic activity, work would be stopped and the matter investigated.

Creating a geothermal heat exchanger is not the same as fracturing the rock to extract shale gas. Our purpose is to create a supply of renewable energy rather than release fossil fuels for burning. We will be working with natural fractures in the rock, and as the whole development will be enclosed in steel casing to ~4km, water table contamination is not an issue. We have no plans to use proppants or associated viscous chemical fluids to keep the circulation open. 

Will it affect the water supply?

Water will be needed to set up the system, but the wells are totally encased with steel to a depth of 4km. This means that the water will circulate in a closed loop and will have no impact on local aquifers or present any risk of flooding at the surface. Any water released from the wells during maintenance or normal running will be contained in lagoons and treated.

What about radiation?

Radon and background radiation is naturally produced by the granites and clays of Cornwall. The chemical composition of the water and all waste streams will be monitored and dealt with throughout the drilling of the wells. During operation, all water will circulate in a closed circuit.

Is geothermal electricity expensive?

Geothermal costs are largely up front: drilling is expensive, and not every well will work. In countries with an established industry, conventional geothermal plants are cost competitive already. DECC’s own figures show that on a levelised cost basis, geothermal electricity from the lower temperature resources we have in the UK would be the same price as onshore wind electricity, and cheaper than solar or biomass. If the heat can be used, it is cheaper still, and the technology is still at a phase where substantial improvements are expected.

Will it cool the Earth?

No. The heat extracted from the rock is a minute fraction of the vast heat available in the Earth’s crust. The design life of the plant is 25 years, and after it has closed the heat in the rock will recover, possibly allowing the well to be reused after some decades.