According to composition, the result can be either a transparent, translucent or non-transparent module. Light transmission through transparent and translucent modules can be set from 4% to 30% according to the choice of spacing. Polycrystalline silicon cells were used in 1991 in Aachen by the architect Georg Feinhals for the renovation of the glass façade of the Stawag administration building. Special light-scattering and insulating glass elements were developed in order to meet both the needs in terms of lighting and insulation, as welI as the desire to maintain and exploit the corporate image as protected through the façade.

In the exterior laminated glass the PV cells have a gap of 5mm between them (SGG Optisol Façade). On the inside a laminated glass with an opaque interlayer was used. The glazing lets through approx. 0.08 of the incident light and provides an even illumination of the interior space.

Amorphous solar cells are attracting great interest at present, because of their potentially lower costs. Thanks to thin-film technology they can be manufactured using less material and at lower temperatures. The films can be applied to various carriers such as glass, plastics or steelfoils. Unfortunatelv the efficiency is still relatively low, values of 5 - 7% are typical. Large areas of amorphous silicon cells are mostly red-brown-ish, or, when transparent, slightly reddish.

Also available are semi transparent amorphous solar cells They are produced by removing partial areas of the thin film by means of a laser separation process, in order to create narrow transparent strips between the opaque surfaces, which allow up to 12% of the incident light to pass through. The impression gained is that of looking through a half-open louvre blind (Asi-Glass).

As alternatives to amorphous silicon solar cells other materials are attracting increasing interest - materials such as CdTe and CuInSe2. These cells can be built using established thin film technologies or even by a dipping process. In smaller areas up to l6% efficiency has been reached under laboratory conditions. Production values, however, do not exceed 8% so far.

Optimised exploitation of solar energy can be achieved by combining several thin film layers with different spectral responses. So-called tandem cells have reached up to 12% efficiency under laboratory conditions, slightly higher values seem possible. Further possibilities are offered by triple cells which consist of a succession of three thin film layers Efficiencies of 10% in production quantities are becoming realistic.

Although PV cells cannot yet compete economically with other ways of generating energy, they are gaining ground due to a generally increasing concern for the environment, supportive regulations and financial help from public funding.