For a little background on geothermal, keep in mind that while the amount of energy stored in heat within the Earth is indeed vast, it's also extremely hard to

For a little background on geothermal, keep in mind that while the amount of energy stored in heat within the Earth is indeed vast, it's also extremely hard to make use of generally. One of the things that I find interesting about physical science is how many similarities there are between things that flow of very different types. In this way, making power from heat is very much like making power from water. We cannot make power from water just sitting around somewhere, no matter how high or low; we can only make power by allowing it to flow from somewhere high to somewhere low and tapping that flow. And for practical purposes, we need flow that has a certain minimum pressure and volume to be able to convert it electrical power in a cost-effective way. Heat works the same way. There may be a tremendous amount of energy in something very hot, but the only way to use it, convert it into power, is to allow it to flow to somewhere cooler, and tap that flow in a way similar in concept to a water turbine. And just like the water turbine, the heat flow must have a certain temperature difference and rate of flow to be converted into electrical power in a cost-effective way. Unfortunately, geothermal is terrible at this over most of the Earth's surface. The heat gradient between the hot lower levels of the crust and the surface is so long and gradual that it's effectively impossible to make electrical power from it. It's kind of like trying to extract energy from a flowing stream that's thousands of miles wide, but only a centimeter deep and flowing at barely a trickle. The total amount of energy associated with that flow is enormous, but it's so diffuse that it's difficult to tap. Note that these guys are planning to use it for heating buildings. That's much easier, as water coming out at 120-150 degrees F is perfectly fine for that. It could potentially save a bunch of energy versus electrical or gas heating, assuming they can pipe it around without losing too much heat. But making electricity effectively requires getting the water hot enough at moderately high pressure to make steam to turn a turbine with. You can play games with exotic working fluids and such to try and get something from lower temperature differences, but it's probably impossible to run a plant at market electricity rates like that. If we ever want to make really big amounts of energy from geothermal, I haven't really run the numbers on it, but I suspect we'd need to tap into heat below the actual crust, just to get the heat replenishment rate from the mantle high enough. We'd definitely need to be able to drill and maintain holes that deep, and then run some sort of working fluid down to the bottom, let it pick up heat at a multi-gigawatt rate, then pipe it back up to the surface without losing too much of the heat. If we ever figure out how to do that, then we'll have essentially all the power we could ever use in about the safest and least-interfering way I can imagine.