Advantages of Plexiglas Panels
Plexiglas panels are made of acrylic material, which means that they can be cut easily with a band saw. Plexiglas allows about 90 percent of light rays to pass through it to the solar cells.
Despite allowing this much light through to the solar cells, Plexiglas protects the solar cells very well from wear, ensuring that they last as long as possible.
Advantages of Tempered Glass Panels
Tempered glass panels are more durable than Plexiglas -- this is important to consider in residential neighborhoods, as a stray ball can hit a solar panel. A crack in a tempered glass panel will not impede the solar cells from working properly.
Tempered glass is also easy to cut -- this makes it easier to fit on panels of all shapes.
Disadvantages of Plexiglas Panels
Plexiglas has a softer outer surface than tempered glass and can crack or scratch easily, leading to solar cells being blocked from receiving solar rays. Plexiglas does not bend easily, which requires that it be supported on the solar panel -- failure to provide proper support can result in the Plexiglas panel cracking.
Disadvantages of Tempered Glass Panels
The cost of tempered glass is typically higher than that of Plexiglas (tempered glass can cost up to $150 per sheet as of 2011) and does not allow as much light to penetrate to the solar panels, reducing the efficiency of the cells. Although tempered glass sheets are durable, there exists the risk that they may shatter, which could block the solar cells from receiving light.
A sheet of shattered tempered glass will also allow moisture into the panel, which will eventually ruin the solar cells.