Photovoltaic PV Collectors

Sunlight is composed of photons with energy corresponding to the range of wavelengths within the solar spectrum. When photons strike the collector cell, they may be reflected, pass through, or be absorbed, but only the absorbed photons generate electricity. This is because the construction material (the silicon atoms in the crystal) has to receive 1.1 eV to cause its valence electron (electron in the outermost shell) to move into the conduction zone. 

A typical silicon PV cell is composed of a wafer consisting of an ultra-thin layer of phosphorus-doped silicon (N-layer with a negative character). 

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This layer is placed on top of a thicker layer of boron-doped silicon (P-layer with positive character). These layers are connected by the P-N junction. When sunlight strikes the surface of the PV cell, an electric field is generated, which provides momentum and direction to the light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electric load. 

Presently, the availability of solar-grade silicon is limited, and its cost is over 30/kg and rising. The largest supplier of polycrystalline silicon (Hemlock Semiconductor Corp.) is building new production facilities, and users such as Sharp Corporation and BP Solar are working on designing thinner panels requiring less silicon. 

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National Renewable Energy Lahoratory internal report) Flatplate photovoltaic (PV) collector modules are typically... 

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