Monocrystalline solar cells are made from thin wafers of silicon, sliced from large crystals that have been grown under carefully controlled conditions. The cells are typically a few inches across, and a number of cells are laid out in a grid to create a panel . Relative to the other types they have a high efficiency, meaning you will get more electricity from a given area of panel - useful if you only have a limited area for mounting your panels, or want to keep the installation small for aesthetic reasons. However, growing large crystals of silicon is a difficult and very energy-intensive process, and so the production costs of this type of panel have historically been very high. Production methods have improved though, and prices have fallen a great deal over the years, partly driven by competition as other types of panel have been produced.
It is rather cheaper to produce silicon wafers in polycrystalline form, as the conditions can be less tightly controlled. In this form a number of interlocking silicon crystals grow together. Panels based on these cells are cheaper per unit area than monocrystalline panels - but they are also less efficient, and in terms of pounds-per-watt there is not a great deal of difference.
The newest type of panel is based on amorphous silicon. Here the silicon atoms are not ordered in a crystal lattice at all. The production methods are quite different - instead of growing crystals, the silicon is deposited in a very thin layer on some kind of backing substrate. Sometimes several layers of silicon doped in slightly different ways to respond to different wavelengths of light are laid on top of one another to improve the efficiency. The production methods are complex, but less energy intensive than crystalline panels, and prices should come down as panels are mass produced using this process.
One advantage of the very thin layers used is that the panels can be made flexible. Types are available that can be curved to the bend in a roof for example, or even attached to a flexible backing sheet so that they can be rolled up and put away when they are not needed! The disadvantage of amorphous panels is that they are not as efficient per unit area as monocrystalline panels - typically you will need nearly double the area for the same power output. Having said that, for a given power rating they do perform better at low light levels than crystalline panels - which is worth having on a dismal winters day.
At least one manufacturer now produces a hybrid panel, where a layer
of amorphous silicon is deposited on top of single crystal wafers. This
gives some of the advantages (high power, but still efficient at low light
levels) - and some of the disadvantages (not flexible and relatively high
price) of the different panels.
|
|
|
|
|