| By :
Aaron Dicks
Copyright (c) 2010 Aaron Dicks Solar Photovoltaic (Solar PV) systems are significantly impacted by shading as it can reduce the output of the PV array. Ideally the Solar PV systems should be located in a shade-free area. However most grid-connected systems are often located on-roofs in built locations, where shading is largely inevitable. There are many forms of temporary shading that can affect the performance of the Solar Panels including: snow, fallen leaves and general dirt. Nonetheless generally this loss of efficiency amounts to between 2 per cent and 5 per cent and can be overcome by paying careful attention to the arrangement and angle of the panels. A tilt of 12 degrees or more allows for the solar panel to self-clean, as greater tilts increase the flow of rain and thus helps to get rid of any potential shading blockages. By arranging the Solar PV modules horizontally this enables losses made by the shading to be reduced by half (in comparison to if it was positioned vertically). The snow on Solar PV arrays melts faster than the surrounding snow so the temporary shading effect should not last for a long period of time. Generally the shading arising from shading factors such as: air pollution, fallen leaves and dirt can be managed by regular cleaning; this can significantly improve the effects of shading on the solar yield. A good cleaning method is to simply clean the Soar PV array with water, avoiding powerful detergents and cleaning tools that could scratch and damage the PV array. The most common forms shading can derive from the location of the Solar PV array, the building itself, self-shadings from the Solar Panels and Direct Shading. Shading resulting from the location can be caused by the buildings surroundings. This can range from tall trees to neighbouring buildings. Shading resulting from the building should be strongly considered, special attention could be paid to satellite dishes and offset building structures. Once you have identified if there are any obstructions, shading can be avoided by moving these obstacles. However if this is not possible the shading effect can be minimised if taken into account during the initial stage of deciding the type of system being installed (stand-alone and grid-connected systems). When installing a rack-mounting system potential self-shading can arise from the rows of Solar Panels in front of each other. A good Solar PV system will minimise this effect by optimizing the tilt and distance between the panels, in the design process of the system. In instances of direct shading, it can cause high losses of energy although the intensity of the energy loss is largely dependent on how close the she shadow is from the obstructing object to the Solar PV array. The larger the distance to the shadow- casting object from the Solar PV system, the brighter the shadow is and the more shading losses are reduced.
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