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It seems to me that the advantage of solar thermal is that it uses mirrors to concentrate solar energy, whereas the advantage of photovoltaic is that its direct energy conversion is simpler and more efficient.
Isn't there a case for using mirrors to concentrate solar power onto PV cells? I'm assuming that mirrors are cheaper (per unit area) than PV cells. Is there a problem with this - perhaps that the cells would overheat? Has it been done?