Underworld Heat & Geothermal Power Plant

We already have a boiler now we can use the heat from the under ground to boiled the water to a steam for 0 pollution.

Speaking shorlty - "Just add Volcano"

I think it could be similar to how ground water works. It is an underground liquid deposit of heat that you build this building on. It consumes some monthly, and it replenishes passively every month, but if you consume too much it will empty over time.