Gotcha.
Thermocouple effect.......
Most definitly an option.
In fact no law says that both processes couldnt be used at the same time
Steam that comes off the process could be condensed and part of it recycled, other part by using electricity could be converted to hydrogen viA electrolosis. Compress and liquify the hydrogen and you have the perfect motor fuel.
I found this information that seems interesting.
[The thermoelectric generator
While the Seebeck voltage is very small (in the order of 10-70µV/°C), if the circuit's electrical resistance is low (thick, short wires), then large currents are possible (e.g. many amperes). An efficiency trade-off of electrical resistance (as small as possible) and thermal resistance (as large as possible) between the junctions is the major issue. Generally, electrical and thermal resistances trend together with different materials. The output voltage can be increased by wiring as a thermopile.
The thermoelectric generator has found its best-known application as the power source in some spacecraft. A radioactive material, such as plutonium, generates heat and cooling is provided by heat radiation into space. Such an atomic power source can reliably provide many tens of watts of power for years. The fact that atomic generators are highly radioactive prevents their wider application.]
This leads me to believe that the efficiency of using this effect to generate electricity wouldn't be practical for a hole drilled in the Earth due to the fact that the length of wire would be many miles long (high resistance) and the difference in temperature insufficient.