Question by Prof. Roy Hinkley: Would a solar powered microwave generator warm the planet?
Assume that the albedo of the solar panel is equal to the albedo of the surrounding land, and that the generator is not a blackbody, so that 100% of its power output falls within the microwave band.
Will this device warm the planet more than if it did not exist at all? Or would the visible light converted into electricity by the solar panel equally and exactly offset the energy contribution to the atmosphere from the microwaves, thus keeping total energy (and thus temperature) constant?
Answer by Paul B
If the solar panel has an albedo equal to the surrounding land, the total energy it is absorbing is equal to what the land would have absorbed. One way or another, that energy will be converted into heat, so the overall effect on the planet is zero.
Contrast coal-powered electricity. Here the heat generated directly, including the heat that ends up powering your microwave, is equal to the heat of combustion of the fuel and contributes to global warming. The same, of course, would be true of a nuclear power station. However, for the coal powered station, the real problem is not the heat generated by burning the fuel, but the heat subsequently trapped in the atmosphere by the emitted carbon dioxide.
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