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At a maximal deepness of about 20 km
Then the steam rises up in the sloped tunnel as in a chimney, cools down, condensate to water and starts the entire process again.
runs down again a long pipe and feeds first the water turbines again
Quote from: Wolfhart WillimczikAt a maximal deepness of about 20 kmI understand that the typical temperature rise with depth is about 25C per km.So as you say, a very deep tunnel is needed to obtain high temperatures for electricity generation (ie expensive).So it is usually more economical to find locations where there is a magma body at shallower depths, so the thermal gradient is greater (eg Iceland or New Zealand).
Shallower rocks start off at a lower temperature than deep rocks. But rocks have fairly poor thermal conductivity, so as soon as you try and put heat into them, they heat up; when the temperature matches the heat source, you generate no more power. - It is more efficient to have your cold sink on the surface - eg evaporation towers or the ocean
But operating costs are radically different between the surface and deep underground. - At elevated temperatures and dripping water deep underground, the generators will always be breaking down - the electrical conductors will be arcing over - Engineers and Technicians can't easily reach the equipment to service it, because the access tunnel is full of hot water. - It's much better to put the active equipment on the surface, where it can be air-cooled, and accessible for maintenance