Mechanism of photovoltaic panels rotating with the sun

Sunlight has two components: the "direct beam" that carries about 90% of the solar energy and the "diffuse sunlight" that carries the remainder – the diffuse portion is the blue sky on a clear day, and is a larger proportion of the total on cloudy days. As the majority of the energy is in the direct beam, maximizing collection requires the Sun to be visible to the panels for as long as possible.. [pdf]
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