Approximate sun elevation curves; the earth is assumed to be spherical, and its orbit circular.
Approximate insolation curves; the earth is assumed to be spherical, and its orbit circular.
Betz's law asserts a maximum limit to the energy that can be extracted from a moving body of air. The air leaving a wind turbine has to be able to escape; it cannot simply pile up behind the turbine at zero energy. Real turbines are able to capture even less energy than the hard limit of Betz's law would seem to allow.
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