If you want to go deep enough for the system scale to be reasonable, you have to get a big drilling rig. You'll hit rock within a couple hundred feet or perhap

If you want to go deep enough for the system scale to be reasonable, you have to get a big drilling rig. You'll hit rock within a couple hundred feet or perhaps a thousand, but I'm not sure of anywhere in the world with 5,000-10,000 feet of dirt. The problem with going shallower is that the system capacity is directly proportional to depth and weight. Too shallow and you have to have huge weight and that means a large diameter hole and really big cables and such. But going deeper requires drilling through rock, and aquifers which are located within the rock. That means big regulatory hurdles because nobody wants to poison the aquifer on accident. Plus the large costs of drilling through rock. I really like the idea from a theoretical standpoint. It's very elegant. But it doesn't seem practical from an economic or regulatory standpoint. If there are places where you can get the diameter and depth for free, it's clearly genius. But I don't think purpose-drilled holes for this will become a thing -- at least barring some kind of immense breakthrough that I can't even imagine.