The power output delivered from a photovoltaic module highly depends on the amount of irradiance which reaches the solar cells. Many factors determine the ideal output or optimum yield in a photovoltaic module. However, the environment is one of the main contributing parameters which directly affect the photovoltaic performance.
The dust accumulated on the front transparent substrate of a PV panel may reduce the power output and may even cause a hot-spot effect. The industrial effluents or bird drops may be severe factors for affecting output, and the extent of the severity depends on the transparency of the foreign objects. In general, when PV modules work, ideally no environmental influencing factors should affect their operation, as these may distinctly reduce the power output. Overall, there should be no obstructed object over the modules surface at any time.
Shading due to soiling is divided in two categories, namely, soft shading such as air pollution, and hard shading which occurs when a solid such as accumulated dust blocks the sunlight. Studies show that soft shading affects the current provided by the PV module, but the voltage remains the same as the light intensity is still homogeneous on the dusty surface. In hard shading, the performance of the PV module depends on whether some cells are shaded, or all cells of the PV module are shaded. If some cells are shaded, then as long as the unshaded cells receive solar irradiance, there will be some output although there will be a decrease in the voltage output of the PV module.
Solar PV panels have been designed for easy maintenance. However, cleaning solar panels can assist in optimizing electricity output. The need for cleaning will vary dependent on the accumulating velocity of the fouling, location, rainfall, pollution levels and the angle of installation – the lower the angle of installation, the more cleaning will be required. To optimize electrical output, it is recommended to clean the panels when dirt can clearly be seen on the glass surface.
‘Normal’ rainfall will naturally clean the panels if installed at a sufficient angle to ensure water runs off the surface. Nonetheless, even though rainfalls are free of charge, still there are seasonally volatile. Therefore, the reliability of this cleaning method is questionable especially when soiling is intensive, and rainfall is not enough either in quantity or in intensity to wash off the soil. It is observed that sharp declines in performance have been noticed in various cases after a light rainfall. Wind can also assist to reduce or eliminate soiling to a certain extent, but there is a need of water to clean the surface for optimum power generation.
Eventually, the benefit of cleaning dirt and debris from the PV modules is a trade-off between the cost of cleaning, the increased energy production as a result of this cleaning, and the inevitable re-soiling of the PV modules over a period of time once they have been cleaned. It is also a necessary part of the system maintenance as most PV manufacturers require the cleaning of the PV modules in frequent intervals to maintain product and performance warranties.