I would appreciate it if someone could chime in here who knows what they're talking about on the physics of this:
My intuition is that there are a number of big problems:
1) power that a power station could supply is limited to the thermal conduction within the earth's crust that the power plant has access to. Instantaneous power can be high, but it would cool down the rocks. I don't think rocks are good conductors. It seems one needs to somehow access a large surface area (facing down) of rocks but a drill hole is vertical.
2) getting heated steam from inside the crust to the surface for electricity conversion faces losses by way of heat conduction to the drill hole. What are the losses there per km, for instance? Does this make some depth infeasible?
Separately, has anyone done a calculation of the actual energy that is released from the inside of the earth through the surface? It seem extremely small for most parts of the world and so would need a massive surface area. I am sceptical that there are many areas which would provide consistent long term energy (over just cooling the rocks too far).
1. Fracking tech allows us to drill horizontally, and enhanced geothermal systems rely on this to get that surface area exposure at 7+ km below the surface
2. The steam's extremely (225C+) hot, so there are losses but doesn't make it infeasible.
Below a certain depth, the earth gets 1º hotter per 40m of depth.
Fracking has nothing to do with horizontal drilling. Fracking is used to increase the connectivity of the reservoir to the wellbore, in the case of low permeability reservoir. For geothermal applications there is no reason to pick the low perm and increase the cost of well completion.
Horizontal directional drilling is a very established field, which is very technologically intensive and some of the things we can do in this area are nothing short of amazing. Basically any trajectory can be executed, including some smart things like underground loops. Couple this with electric submersible pumps (ESP), which help to increase the flow and potentially run water through several cycles to maximize the contact with hot payzone before getting it to surface and you can do many interesting things.
My intuition is that there are a number of big problems: 1) power that a power station could supply is limited to the thermal conduction within the earth's crust that the power plant has access to. Instantaneous power can be high, but it would cool down the rocks. I don't think rocks are good conductors. It seems one needs to somehow access a large surface area (facing down) of rocks but a drill hole is vertical.
2) getting heated steam from inside the crust to the surface for electricity conversion faces losses by way of heat conduction to the drill hole. What are the losses there per km, for instance? Does this make some depth infeasible?
Separately, has anyone done a calculation of the actual energy that is released from the inside of the earth through the surface? It seem extremely small for most parts of the world and so would need a massive surface area. I am sceptical that there are many areas which would provide consistent long term energy (over just cooling the rocks too far).