PV performance

Solar photovoltaics perform differently depending on the area of the country, their orientation, pitch and any shading issues:

The map below shows the variation in irradiation across the UK in kWh/m²

The table below shows the percentage of the irradiation you can expect at varying orientations and pitches.

What are the effects of shade?
Shading is critical. Minor shading can result in significant loss of energy. This is because the cell with the lowest illumination determines the operating current of the series string in which it is connected. Many modern modules use bypass diodes to minimise shade effects; but these effects must still be considered, preferably in the first stages of building design. Watch for landscaping, trees and even handrails.

If shading is unavoidable, or poor light is expected on a regular basis, the best types of PV to use are amorphous thin-film (eg Kaneka/Unisolar products), or hybrid (mixing monocrystalline and amorphous technology - eg Sanyo HIT modules).