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Transparency and efficiency


Solar modules can be opaque or semitransparent. In mono- or polycrystalline modules, the spacing between cells and to the edge can be varied so as to allow variation of shadowing and transparency. In thin-film modules, additional cuts perpendicular to the cell strips create a semitransparent effect. Because semitransparent modules absorb less light, they are less efficient per unit of area. Therefore, performance diminishes with increasing translucency.

Figure 1: Possible combinations of cell types and cell spacing

Source: ertex solar 2009

Figure 2: Semitransparent crystalline solar cell

Source: sunways 2009

Figure 3: Shading by means of transparent PV modules, Ludesch municipal centre, Vorarlberg

Source: ertex solar 2009

Figure 4: Semitransparent thin-film module, Constance University

Source: cluster_energietechnik 2009


Efficiency is given as a percentage and is the ratio of electrical energy generated and the amount of incident light. We distinguish between cell and module efficiency. Module efficiency pertains to total module area and is therefore always slightly lower than cell efficiency. This is due to some extent to the unusable spaces between the solar cells lined up in the module (source: bp_ 2009). According to the “2009 Solar module market overview” drawn up by the German Photon magazine, current average and maximum module efficiencies are as follows:

Table 1: Module efficiencies
Module Average efficiency (%) Maximum efficiency (%)
monocrystalline 13,3 19,6
polycrystalline 12,9 18,5
approx. 6 11,3
The nominal power of a PV module is derived from efficiency and is given in watt-peak (Wp). It is the power output under laboratory conditions (vertical illumination of 1000 W/m² in a standardised solar spectrum AM (Air Mass) 1.5 and module temperature 25 °C) in order to allow comparison of modules. In real conditions, annual yield depends greatly on the degree of latitude and the installation situation.

Last page update: 04.02.2011