Geothermal from mines?

[AstroTurf]

That's why it's better to pump hot water up to the surface and drop that pressure at the surface, a process which will turn it into steam, and use it to drive a turbine.

I would rather do that bit 4km's down. It would create it's own closed system I think. No need to keep pumping water into the system.

 

[TooFastTim]

I would rather do that bit 4km's down. It would create it's own closed system I think. No need to keep pumping water into the system.

It would do but that would pose it's own problems: how do get the genset down 4km's? How do you build the generating hall that far down? What about geological instabilities down there and so on.

 

[agentrfr]

Approximate base load? How large is large enough? I doubt it, peak hours is outside the time that the sun shines. Until energy storage is economically viable, solar will not be supplying base load. Solar/wind is great for renewable, crappy for transmission control and load management.

I did a couple of Geothermal plants and it is great for base load, technologies also does not have to be expensive if you know what you're doing.

Specifically for wind if the geographical area of the farm is large enough (i.e along a coast line for 100s of km) then the power output of the farm is approximately stable (for the most part anyway unless there is a massive storm - but it is a more or less predictable base load power source). That's why I call it approximate base load

PV and CSP only generate power when the sun is shining yes, so they're only really useful for daytime operations or when you have some sort of energy storage system. I agree solar isnt useful for reliable / grid feed applications.

The thing is per watt, PVs are about 0.12 USD/watt currently and wind VAWTs not far behind that. While geothermal is ideal imo, nobody is going to fork out for the premium for it - remember gwavaments the world over want to be visibally green. A geothermal plant is "invisible" to the public.

Oh, that bit I'm pretty sure about. I'm not sure how much energy would be imparted to the superheated water vs how much would be needed to get that head of water back to the surface. I reckon it that it would take more to get it back to the surface.

The Kiwis use a lot of geothermal but that geothermal's quite close to the surface.

AFAIK most geothermal power plants these days use an organic rankine cycle, not a water based one. You can boil and superheat the refrigerants much easier than water can (4km down is 3869 atmospheres of head, and water only boils at about 332 C there - at those pressures life becomes very difficult...)

Pushing the fluid down and getting it up is trivial - the mass is stuck in a pipe so the mass must be conserved. Much like a siphon only the difference in entry and exit heights matter - not how far up or down the fluid path goes. (google Bernoulli's equation if it still doesnt make sense - lots of cool youtube videos on it)

I would rather do that bit 4km's down. It would create it's own closed system I think. No need to keep pumping water into the system.

Nope, you have to then get your equipment down there. That's expensive and unsafe for the people that need to maintain everything. As long as the return pipe has enough insulation, you can have it lose practically no heat irrispective of the length of the pipe. Some of the people at Wits when I was doing my Honours in ChemEng were insulating pipes and things with aerogel - fantastic stuff