There are three basic types of solar cell
Crystalline solar cells are wired in series to produce solar panels. As each cell produces a voltage of between 0.5 and 0.6 Volts, 36 cells are needed to produce an open-circuit voltage of about 20 Volts. This is sufficient to charge a 12 Volt battery under most conditions.
– made from a single large crystal, cut from ingots. Most efficient, but also the most expensive. Somewhat better in low light conditions than other types.
– basically cast blocks of silicon which may contain many small crystals. This is probably the most common type right now. Slightly less efficient than single crystal cells, but once set into a frame with 36 or so other cells, the actual difference in watts per square metre is low.
Although the theoretical efficiency of monocrystalline cells is slightly higher than that of polycrystalline cells, there is little practical difference in performance. Crystalline cells generally have a longer lifetime than the amorphous variety.
- technology is most often seen in small solar panels, such as those in calculators or garden lamps, although amorphous panels are increasingly used in larger applications. They are made by depositing a thin film of silicon onto a sheet of another material such as steel. The panel is formed as one piece and the individual cells are not as visible as in other types.
The efficiency of amorphous solar panels is not as high as those made from individual solar cells, although this has improved over recent years to the point where they can be seen as a practical alternative to panels made with crystalline cells. Their great advantage lies in their relatively low cost per Watt of power generated. This is offset, however, by their lower power density; more panels are needed for the same power output and therefore more space is taken up. As a result they are probably the least common of the three types of solar cell.