Whenever only a small amount of space is available, use is generally made of monocrystalline modules. Because the silicon content of the cells is purer, their efficiency is particularly high. Around 15 % less surface area is needed than with other modules for the same output. The cell voltage is normally also slightly higher. Monocrystalline modules currently have a life expectancy of over 30 years, with the manufacturers giving a performance guarantee of over 20 years. The cells of monocrystalline modules are generally black.
Polycrystalline modules have a somewhat lower silicon content, but are more environmentally friendly to manufacture. They therefore have a lower level of efficiency and need a greater surface area for the same output. Because the price per Watt often turns out lower, they are nevertheless frequently used for large installations. In terms of their service life and reliability, polycrystalline modules are in no way inferior to the others. The cells generally have a bluish colour with a glittery effect.
Various chemical elements are used in the production of amorphous modules. The original output decreases heavily in the first 1,000 hours of service, but this degradation has already been taken into account in their manufacture, which is why amorphous modules have a higher output when first delivered. After the initial aging period, the output remains stable. Thanks to the new thin-layer technology, amorphous modules can nowadays be manufactured extremely cheaply and in an environmentally friendly manner. This technology is used in most small-scale applications (pocket calculators, clocks etc.), but it is also being increasingly used for larger systems. The service life is nowadays more or less the same as with the silicon modules. They generally have a homogenous, reddish black, slightly transparent appearance. Because amorphous modules are often considerably cheaper than the others, their price per Watt is particularly favourable. The two disadvantages in terms of cost are the more complicated assembly and the need for a larger frame.