Classification of photovoltaic glass: solar-cell substrates include ultra-thin glass, coated glass, and low-iron (ultra-white) glass. By function and manufacturing method, photovoltaic glass falls into 3 product categories: covers for flat-panel solar cells, generally made from rolled glass; conductive substrates for thin-film solar cells, with semiconductor layers only a few microns thick deposited on flat glass; and lenses or mirrors used in photovoltaic systems. These categories have different properties, functions, and added value.

The most widely used photovoltaic glass is high-transmittance, low-iron glass, also known as ultra-clear glass. Iron is generally an impurity in glass, except in heat-absorbing glass. Iron impurities color the glass, increase heat absorption, and reduce light transmittance.

Iron enters glass through its raw materials, refractories, and metal production equipment and cannot be eliminated completely. Production controls can minimize its content. The source gives an iron-content range of 0.008% ~ 0.02% for solar-cell glass, compared with more than 0.7% for ordinary float glass. For glass thicknesses of 3.2 mm and 4 mm used in China, solar visible-light transmittance is generally 90% ~ 92%.

As one of the most important components of solar photovoltaics, glass panels must be highly transparent. Therefore, the iron content of silicon materials used in the production of solar glass is very strict, the content of FE2O3 is 140-150 ppm.

Applications of photovoltaic glass: Germany has long used transparent flat glass as a substrate for solar cells. German researchers installed panel-shaped solar cells as building window panes, supplying electricity directly to households and feeding surplus energy into the grid. This application soon attracted interest in the United States and Japan, accelerating the development of low-iron and ultra-thin glass for solar energy.