Is the reason they have to drill down 20 km to 500C rather than say 7 km to 175C (presumably a far simpler task) is the equilibrium heat flow?
That is, the water/steam cycle is extracting heat from the surrounding rock. That can only be extracted at a rate that matches the heat inflow, or ideally, ever so slightly less, so as to maintain equilibrium over decades over cubic miles of rock.
Yes, I understand that larger temperature differences increase thermodynamic efficiency. But if the energy produced is constant, efficiency may not matter as much as ease of construction etc.
Interesting point, what would explain it is non linearity. If you get 20% efficiency at 5 but 35% at 7km depth it might still be worth it. Would still have to outperform exponential drill cost with depth
That is, the water/steam cycle is extracting heat from the surrounding rock. That can only be extracted at a rate that matches the heat inflow, or ideally, ever so slightly less, so as to maintain equilibrium over decades over cubic miles of rock.
Yes, I understand that larger temperature differences increase thermodynamic efficiency. But if the energy produced is constant, efficiency may not matter as much as ease of construction etc.