The Earth’s heat balance has contributions from two significant sources of input; radiation from the Sun and heat radiating out of the Earth itself. Putting one’s hand on the ground will not detect the heat from the Earth; about 100 milliwatts per square metre. But stand near an active volcano and you will quickly detect the vast amounts of energy at play. All that ready energy could be accessible if we can figure out how.
Thor in Iceland may be showing the way. This experimental deep drilling project has pierced the Earth’s crust down 4659 metres. That’s down to where the Atlantic Ocean’s mid-ocean ridge is apparent. At that depth and location there’s a very high pressure and a very high heat. Plans are to draw 20 megawatts of energy from the well to provide for much of the requirements of the local population. Of course Iceland has a very unique geology and a very small population so Thor is a practical solution. If it all works out.
Energy from the Earth is already a specialty of Iceland. All of its electrical power comes from either dams or geothermal vents. No non-renewable fossil fuels for their power production. Similarly photovoltaic farms grace amenable deserts in other countries. Still, worldwide, 86% of primary energy comes from fossil fuels. Humans have to be a lot more inventive if we want to keep civilization at its current high level and possibly grow it.