The impracticality of "alternative energy" has been spelled out in the past. It's just basic mathematics, in fact just simple arithmetic. It's a matter of determining the capability of solar power, for example, and then comparing that to the needs of the population. But even if it was possible to stave off famine by fastening solar panels onto all our roofs, there would still be the question of what to do next. Solar-panel construction for a thousand years? Perhaps the impasse is more psychological than technological.
Solar power has many problems, none of which can be solved. The biggest problem is scale. Solar arrays for 7 to 12 billion people could be found only in a Hollywood movie. The raw materials would be largely inaccessible: not only would vast quantities of fossil fuels and metals, including rare ones, be needed to build and maintain these arrays, but one would need to explain how a solar-energy collector is going to enable people to dig mines half a mile into the ground and extract the ore. And one would then have to explain, once all of the world's 500+ exajoules of annual energy production have been switched to solely electric, how it would be possible to use electric-only as a means of providing airplanes, fertilizer, plastics, and so on.
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