Interesting. Nothing is free. The heat deep in the Earth is largely due to the Moon’s tidal influences. If a system of tapping that energy is feasible and put into use it will to some tiny extent begin to slow the Moon’s orbital velocity.
Personally hate wiki but this one is pretty well written and has solid references.
https://en.m.wikipedia.org/wiki/Earth%27s_internal_heat_budget
https://phys.org/news/2011-10-vast-amounts-solar-energy-earth.html
Lunar tidal heating is minimal compared to radioactive decay and primordial gravitational collapse energy. The outward flow of geothermal heat is tiny compared to the incoming solar flux.
37 TW geothermal vs 117,000+ TW solar not even a rounding error. Humans could power our entire race with geothermal and not touch the heat balance of the planet. These are Terawatt seconds not hours so you have to convert to terawatt hours then multiplied to a full day to have an accurate comparison.
In kilowatt hours geothermal flows are
3,196,800 terawatt hours per day and solar is a mind boggling 14,947,200,000 terawatt hours per day.
Humans use on avg 58kWh per day when averaged over 7.7 billion people that’s
58kWh times all 7.7 billion of us is
446,600,000,000 kilowatt hours per day or 446.6 terawatt hours per day. There is zero way we could even hope to alter the heat balance of the planet powering our species with geothermal energy. The sun dwarfs anything humans will ever do.
https://home.uni-leipzig.de/energy/energy-fundamentals/04.htm