Solar cells

Solar cell types

There are various types of solar cells. Monocrystalline and polycrystalline solar cells are typically used for photovoltaic systems installed on roofs. The difference between the two types is mainly in appearance, with the structure of polycrystalline cells giving them a variable blue/bluish colour. This is due to the production process, in which the cells are made from fragments, unlike monocrystalline cells, which are made from continuous single pieces. Crystalline cells utilise approximately 16%-20% of the light energy from the sun. The technology is around 40 years old and therefore "safe". There are also thin film modules, which are less efficient and typically require a larger area.

Solar cells are usually produced in 156 x 156 mm format. They are connected in series in a panel containing 60 or 72 cells, for example. The panel usually has a silver or black aluminium frame.

Positioning

The best position for solar cells is at 25-45 degrees facing south with no shadows from trees, buildings, masts, etc. The pitch is generally less important in terms of power than often assumed.

Solar cells generate electricity from light, so it is the amount of light that is key to success. A slightly overcast day with diffuse light is actually excellent for solar cells.

Although the optimum position is facing south, the output of solar cells that face between east and west at a lower pitch is typically between 80% and 90% of the power generated in the best possible position. Solarglas is happy to supply documentation for the anticipated output from a given installation.

Maintenance

Photovoltaic installations are largely maintenance free. You need to reckon with full or partial replacement of the inverter every 15-20 years, however.

Service life

A photovoltaic installation has an expected service life of 30-50 years. The solar cells degenerate by approximately 0.5% per annum, so the installation will have an expected output of around 85% after 30 years. The most recent experience shows degeneration of less than 0.5% and therefore a slightly longer service life of 40-50 years, provided the module is well made.

Photovoltaic modules

A nominal maximum power, e.g. 250 Wp, is quoted for photovoltaic panels. The nominal maximum power indicates maximum production at a given time (e.g. 250 watts) and must not be confused with how many kilowatt hours (kWh) the panel is expected to generate per annum.

The various manufacturers have different power tolerances, e.g. +/- 5%. All SOLARWATT panels have a positive tolerance, which means that the nominal power is a minimum figure: -0/+5 watts. Our panels have by-pass diodes, which stop shaded areas affecting entire modules or strings. All the glass used for framed modules is frosted, so light is refracted diffusely, i.e. thrown in different directions to minimise reflection.

SOLARWATT manufactures the strongest modules on the market. They are tested for Danish climatic conditions (snow load, wind load, etc.) in accordance with IEC 61215 Ed. 2 and IEC 61730 and a wide range of other tests for hail, salt and ammonia - see under Products.