Question

Why does a solar panel need a glass cover??

Answer 1

There are solutions also with plastics which allow for flexibility when used with thin film solar cells but either they are too expensive or not long lasting.About glass fiber, it is not used in commercial solar panels, the plastic commonly used below the glass sheet to encapsulate the cells is EVA (ethylen vinyl acetate) and a backsheet of Tedlar.
There is a relatively new development in the commercial market to use also the backside of the cells to capture light reflected by the surroundings of the panel and increase power generation (the bifacial cell), a second glass sheet is used in the back of these solar panels.

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