For anybody who is interested in this stuff, I was the CTO of a Canadian geothermal company, and I became convinced that it was folly to dig 4km down to get hot water when we are surrounded by waste heat in large industrial plants that is largely untapped.

By way of example, I was working on a geothermal plant in Alberta that would generate 5MW and cost $60 million (CDN) to build. Similar heat can be found everywhere at surface, especially in Alberta which has a heavy industrial base. Harnessing the heat from industrial sources is exactly the same as a geothermal plant: only the source of heat is different.

For example, I scoped a project on a natural gas pipeline compressor station. It used a RB211 gas turbine to drive the compressor. Capturing the waste heat from the exhaust stack of that engine gave us 7MW of net generation, at a cost of $30 million, and much lower operating expenses to boot.

58% of the energy we generate each year is lost, much of it (upwards of 20%) as industrial waste heat. That's terajoules of electrical generation potential globally, just from the easily captured stuff.

It's not exactly like geothermal energy, because you have counterparty risk in that the cement factory (or whatever) might close. But the tech is identical to geothermal, and there's no exploration risk or digging expense.