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View Diary: Solar Energy Vs. Mountaintop Removal (50 comments)

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  •  Continuingon what Lib Dem FoP said (6+ / 0-)

    I doubt that water will be the working fluid, for physics reasons.  

    If you're making electricity by heating something up and turning generators, you're dealing with heat engines. And heat engines work better the greater the difference between the hot and cold sides, and the hotter the hot side is in absolute measure.

    You can indeed make turbines that run off the boiling of very volatile liquids, with a fairly cool 'hot' side. But their efficiency is low, a greater percentage of the energy put into them comes out as waste heat and a lower percentage as useful power.  You can cascade such units, but each one in turn is running an increasingly low efficiency.  On top of that the issue of keeping the cold side cool enough becomes a problem, even if you can tap ocean water the limit on the cold side is about 4 degrees Centigrade.

    Photovoltaics are not heat engines, and don't have the same sort of limitation. But they have no intrinsic energy storage, unlike heat-driven systems that can store their heat in thermal mass to extend their productive time period.  The thermal mass can be fluids, masses of concrete, or even broken rock.

    •  Much Work On Maintennance Free Stirling Engines (1+ / 0-)
      Recommended by:
      DaleA

      Even though they have traditionally been rather finicky. But they would have a lot of applications, like home AC.

      •  Stirling engines are heat engines (3+ / 0-)
        Recommended by:
        badger, DaleA, bernardpliers

        and can't break the Carnot limit.  While a Stirling engine is theoretically able to reach the Carnot limit, real world implementations fall short of that. And that's still the Carnot limit, the lower the hot-cold difference the lower the efficiency, and the cooler the hot side the lower the efficiency.

        Engineers in the 19th century were near terminally depressed when it was realized what the limits on heat engines were.

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