The generation of almost limitless power from the seething mass of magma that our continents float lazily upon.
It's the no lose renewable option. No house price depressing windmills or car melting solar panels; no worry about off shore wind farms scything migrating birds out of the sky, or tidal power generators interfering with the movement of fish. You just dig a pipe a few thousand metres into the ground, pour some water down it, and wait for it to flash off into steam and rise up some other pipes to drive a turbine. Nothing to see. Nothing to crash into. Nothing to make your "As seen on Escape to the Country" posh village home lose a few quid off its value.
Geo-Thermal energy is essentially nuclear in origin; fission reactions in Earth's core heat the molten mantle and drive things like volcanoes and hot springs. But this is a clean form of energy, water goes in, steam comes out. No carbon production or geiger clacking waste to dispose of. And the energies involved are so much higher than other renewables.
All this is for the future of course, reliable sources of shallow depth geo-thermal heat are not common. But imagine what could happen when we develop the technology to drill twenty miles down? The power is virtually without end. The science fiction writer Olaf Stapledon foresaw this as the future of the Earth in his classic "Last and First Men" where he wrote of the evolution of humanity over trillions of years.
The potential is there. As a science fiction lover, and writer myself I love wondering where it could end up. I suppose there are hazards too, relating to seismic activity and instabilities in the Earth's crust. People might fear that somewhere like Basildon will end up under ten feet of bubbling lava. But in the end, it will be worth it.
The Pros and Cons