The eco-village will cover an area the size of 500 football pitches
A system to harness hot natural waters for renewable energy is to be created in County Durham.
Newcastle University is leading plans to develop a "huge central heating system" deep below the site of a proposed eco village in Weardale.
Scientists and engineers want to drill a twin borehole system to continually cycle groundwater through rocks as deep as 1,000m (3,280ft).
They hope the prototype will be used as a model to tap other UK "hot spots".
The team plans to drill a borehole to "re-inject" water which will be brought to the surface at a temperature of about 30C (86F) by a pumping borehole, originally drilled three years ago.
Energy will be generated by passing the hot water through a heat exchange device.
Project lead Professor Paul Younger said using a twin set of boreholes solved problems which had hindered other attempts to use deep-seated hot water, which is heated by naturally-occurring low-level radiation found in all rocks.
He said: "Water from such depths is twice as salty as seawater, so unless you happen to be on the coast, you can't let the spent water flow away at surface.
"By re-injecting water using a second borehole we are able to maintain the natural water pressures in the rocks and allow pumping to continue for many decades to come."
Used water will be reintroduced to the granite at a depth of about 420m (1,377ft) and will heat up again as it flows through a complicated maze of fractures on its way back to the pumping borehole.
The project will provide renewable energy for homes and businesses in the planned Eastgate eco-village in Weardale.
Some of the water will also be used for a natural hot water spa, thought to be the first in the UK since the Romans tapped the hot springs at bath.