So I'm thinking why we don't do geothermal. And it occurs to me that the opportunity to go that deep into the earth is limited. I may have just answered my own question but let's keep going.
Imagine you've got a river and a very deep hole. A hole so deep that in fact that when you get down a mile or two it's hot enough to make steam. The original question was a kind of open query as to if the energy of steam off the hot rock is enough to be exothermic. How hot does the rock have to be as a ratio to depth of the hole so that there is recoverable energy if you dump a river down it and drive steam turbines?
But it occurs to me that the earth just doesn't get hot close enough to the surface to make any of that work on a general basis. You'd have to be somewhere the magma and other hots were close otherwise simple kinetic energy would be more efficient. Obviously hydroelectric only needs water to fall a few hundred feet to make serious amounts of electricity, why drill a hole a mile deep? Besides, oilwells go miles deep and they don't hit the heat. So geothermal is limited to very specific geographical locations.
And so I defer to Wikipedia:
The United States of America is the country with the greatest geothermal energy production.[31]
The largest dry steam field in the world is The Geysers, 72 miles (116 km) north of San Francisco. The Geysers began in 1960, has 1360 MW of installed capacity and produces over 750 MW net. Calpine Corporation now owns 19 of the 21 plants in The Geysers and is currently the United States' largest producer of geothermal energy. The other two plants are owned jointly by the Northern California Power Agency and the City of Santa Clara's municipal Electric Utility (now called Silicon Valley Power). Since the activities of one geothermal plant affects those nearby, the consolidation plant ownership at The Geysers has been beneficial because the plants operate cooperatively instead of in their own short-term interest. The Geysers is now recharged by injecting treated sewage effluent from the City of Santa Rosa and the Lake County sewage treatment plant. This sewage effluent used to be dumped into rivers and streams and is now piped to the geothermal field where it replenishes the steam produced for power generation.
Another major geothermal area is located in south central California, on the southeast side of the Salton Sea, near the cities of Niland and Calipatria, California. As of 2001, there were 15 geothermal plants producing electricity in the area. CalEnergy owns about half of them and the rest are owned by various companies. Combined the plants have a capacity of about 570 MW.
The Basin and Range geologic province in Nevada, southeastern Oregon, southwestern Idaho, Arizona and western Utah is now an area of rapid geothermal development. Several small power plants were built during the late 1980s during times of high power prices. Rising energy costs have spurred new development. Plants in Nevada at Steamboat near Reno, Brady/Desert Peak, Dixie Valley, Soda Lake, Stillwater and Beowawe now produce about 235 MW.
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