Earth's Heat to Power 10,000 Homes

The UK's first geothermal power plant has been turned on, providing a completely new type of renewable electricity using hot water from underground.

On Thursday morning, the Cornish plant will be switched on after nearly two decades in development which required Geothermal Engineering Ltd (GEL) to drill the deepest on-shore well in the UK.

The water, super-heated by rocks, will help drive turbines to generate electricity for 10,000 homes, but will also provide the UK's first domestic supply of lithium - a critical mineral used in green technology.

The British Geological Survey said it was a "major step forward" for geothermal but high drilling costs could make replicating the project difficult.

The Earth generates heat which can be harnessed by drilling down below the surface to provide a renewable, and continuous source of energy to heat and power our homes – known as geothermal energy.

The further down you go the hotter it gets. At shallow depths the heat is enough to warm our homes and businesses. This is already done in some parts of the UK – for example, ground source heat pumps are a form of geothermal technology, and in places like Southampton, heating is provided to hundreds of homes via a local network.

But this project has drilled to far greater depths - three miles below the surface - where temperatures climb to nearly 200C, and this is enough heat to generate electricity.

"You drill deep boreholes into the ground, and then fractures within the granite rock are used to circulate the water that pick up the heat [that is] used for electricity production," explained Dr Monaghan, head of geothermal at the British Geological Survey (BGS).

Granite is particularly ideal for this technology as it is very effective at holding and conducting the Earth's heat.

This is the first time the feat has been achieved in the UK because drilling this far down is a technically and financially costly endeavour. The project has cost £50m to date, funded through private investors and the EU.

Ryan Law, CEO of GEL, told the BBC: "[I'm] tremendously excited after 15 years of hard graft, difficulties, we're finally there."

He said geothermal power was "really important" for the UK because there are no price fluctuations like with gas.

"And unlike other renewable sources like wind and solar we are constantly on, 24/7 electricity," he added.

- Authors: Esme Stallard and Kate Stephens, BBC