You can go deeper, but in most regions you'll be into impermeable rock by the time you get usable temperatures. You need the rock to be permeable so brine can flow from your injection site to the extraction well.
Companies like Eavor claim a closed loop in impermeable rock will work, but then you're limited by the thermal conductivity of the rock around your pipe. You can only pull out as much heat as can flow through the rock around the pipe. Our simulations on Eavor's system showed they would work for about a couple months before they started dropping off.
Fracking seems like a more promising avenue, and it might work. A ton of political challenges there though.
Companies like Eavor claim a closed loop in impermeable rock will work, but then you're limited by the thermal conductivity of the rock around your pipe. You can only pull out as much heat as can flow through the rock around the pipe. Our simulations on Eavor's system showed they would work for about a couple months before they started dropping off.
Fracking seems like a more promising avenue, and it might work. A ton of political challenges there though.