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Theoretical maximum for energy from direct and diffuse sunlight


SCHEMES for the conversion of sunlight to useful (electrical, mechanical, chemical) energy all make use of the high spectral temperature of solar radiation relative to the terrestrial ambiance. Some schemes, but not others, also make use of the high directivity of the solar flux. For example, focusing mirror arrays require direct sunlight, while photovoltaic devices are indifferent to the directness or diffuseness of light of a given intensity. In biological systems, photosynthesis evidently makes little use of sunlight directivity, since it is not observed to depend strongly on plant orientation on angular scales as small as half a degree (the size of the Sun); on the other hand, Kevan1 reports some heliotropic, arctic flowers whose corollas are nearly paraboloidal and focus direct (but not diffuse) radiation on the sporophylls.

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PRESS, W. Theoretical maximum for energy from direct and diffuse sunlight. Nature 264, 734–735 (1976).

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