I would call solar energy "Free Energy" that is an unlimited source of energy that requires not only next to no maintenance but even better it requires no maintenance at all. How about gravity? I would put it in the same category. The energy is "Free", it is the engineering and application that cost. Using water converted in to hydrogen and oxygen as an energy source is another almost "Free" energy source that the cost is in the engineering and not the "Free energy" source.
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