A silly controversy has arisen concerning the color of photovoltaic solar panels. Apparently a new book "SuperFreakonomics" contains the following (quoted here):
As an example he points to solar power. “The problem with solar cells is that they’re black, because they are designed to absorb light from the sun. But only about 12 percent gets turned into electricity, and the rest is reradiated as heat — which contributes to global warming.
Yglesias (among others) jumps on this statement (here and here) posting a photo of solar panels that appear to be dark blue and claiming:
... Still, it is worth dwelling a moment on the fact that their critique of photovoltaic literally rests on the idea that PV cells are black whereas in reality they’re usually blue:
First their critique depends on solar cells being dark (low albedo) not black. Perhaps they should have said "dark" instead of "black" but this is not a serious error. Especially since, Yglesias to the contrary, many cells are black. It is hard to judge color from photos because the cells are often reflecting the blue sky. See for instance this photo where the cells appear to be blue except at the upper right where they appear to be brown because they are reflecting brown branches instead of blue sky.
Anyway the critique is because solar cells are dark they may absorb more sunlight than whatever background they are replacing thus heating the earth. This can occur whether the cells are black or dark blue in appearance. However this effect is not important. Coal power plants also generate considerable waste heat as their thermal efficiency is only about 33%. It is doubtful that solar cells produce more excess heating per unit of electricity generated than the waste heat from coal power plants. And in any case the global warming concern with coal power plants is not their waste heat (which is not significant globally compared to solar heating) but the much greater long term heating effect from the CO2 emitted when coal is burned.
Does this mean photovoltaic solar cells make sense? Not really, they are inferior to wind turbines which also don't emit CO2 and are much cheaper .
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