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Solar cell
Photovoltaics allows direct conversion of sunlight into electrical energy. Conversion takes place without any emissions and material flows inside the solar cell. The efficiency of solar cells is given as a percentage. Efficiency is the ratio of electrical energy generated and the amount of incident light.
Solar cells are distinguished by their substrate material: crystalline solar cells and thin-film cells. Crystalline cells (currently) consist of monocrystalline (mc-Si) or polycrystalline (pc-Si) silicon and have the highest level of efficiency. The cells can be contacted on the front or back. Applying the contact on the back reduces or completely eliminates the contact grid on the front, thus reducing shadowing effects and thereby increasing efficiency (idw-online 2009).
Currently there are three different thin-film cell technologies available on the market: silicon-based (amorphous silicon: a-Si; a combination of a-Si and microcrystalline silicon a-Si/µc-Si), cadmium telluride (CdTe), and copper indium diselenide (CIS, CIGS). Research is also ongoing on a host of other thin-film cells and organic or dye-sensitised cells, that will come onto the market in the next few years with the promise of major cost reductions for PV systems.
Both types – crystalline cells and thin-film cells – have their merits:
Table 1: Comparison of crystalline cells and thin-film cells
| Cell type | Advantages | Disadvantages |
|---|---|---|
| Crystalline | High, stable cell efficiency mature cell technology (years of experience) Variety of colours and forms |
Limited flexibility (cell grid) Inhomogeneous appearance No homogeneous transparency Complex, time-consuming cell/module production |
| Thin film | Lower system costs homogeneous appearance Variety of colours and forms semitransparent |
(As yet) lower levels of efficiency Less experience with regard to long-term stability |
Table 2: Typical solar cell characteristics
| Cell | monocrystalline | polycrystalline | thin-film |
|---|---|---|---|
| Size | commonly: 125 x 125 mm, 156 x 156 mm |
commonly: 125 x 125 mm, 156 x 156 mm |
almost any substrate format |
| Form | rectangular, square, pseudo-square (with rounded corners) | rectangular, square |
any substrate format |
| Colour | usually black |
usually crystal-blue | black, reddish-brown or dark-green |
| Efficiency | currently up to approx. 21% | currently up to approx. 16% | currently up to approx. 13% |
Figure 1: Examples of monocrystalline solar cells
Figure 2: Example of monocrystalline back-contact cell
Source: solar-designs 2009, ecn.nl 2009
Figure 3: Examples of polycrystalline solar cells
Figure 4: Polycrystalline back-contact solar cell (example)
Figure 5: Examples of thin-film cells
Last page update: 04.02.2011
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