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Tim Smit on geothermal at Eden

Hear our co-founder talk about our exciting plans.

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About Eden's proposed geothermal power plant

Located close to the main gate, we will drill a single 4.5km well into the rock. This first phase of the geothermal plant will produce enough heat for Eden’s Biomes, offices and nursery greenhouses.  The £16.8m project has been funded by the European Union, Cornwall Council and an institutional investor.  Its success will pave the way for a second well and electricity plant, so that by 2023 Eden should be exporting enough renewable electricity and heat to wipe out its carbon footprint.

Engineered geothermal system

When we have completed the second phase, 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 and the first phase project, please visit the Eden Geothermal 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?

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. 

  • There are two companies developing deep geothermal resources in Cornwall; Geothermal Engineering Ltd (GEL) and Eden Geothermal Ltd (EGL). GEL has drilled two deep wells from its United Downs site near Redruth, EGL hopes to be drilling a well from the Eden Project site in 2020.
  • These are renewable energy projects and do not involve fracking. They are not covered under the same regulatory framework as shale gas exploration projects and are not subject to the same limits on induced seismicity. Rather, they are regulated by the Local Authority and are monitored and managed using protocols based on a combination of magnitude and measured surface ground vibration, which has been used to control and monitor mining and quarrying activity in the county for many years.
  • Small natural earthquakes happen in Cornwall all the time. GEL has installed a network of seismometers and has been monitoring since May 2018. In that time more than 20 natural events have been detected, with magnitudes ranging from 0.8 to 2.3. The most recent was on the 7th August 2019 near Helston, which reached 2.2 on the Richter scale. No damage was reported.
  • To date, neither deep geothermal project has induced any seismic events of any size.

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. BEIS’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 35 years, and after it has closed the heat in the rock will recover, possibly allowing the well to be reused after some decades.