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Friday, 22 May 2015

Washing of Solar PV Arrays

A solar PV array is a set of solar PV modules mounted together and connected in series, parallel or series-parallel combination to get the desired electrical output i.e. voltage, current and hence the DC power.

Why washing of Solar PV arrays is important?

Solar PV arrays are usually called maintenance free, but they require regular cleaning and washing to maintain the rated power output. The glass covers are cleaned regularly to remove dirt and other deposits such as bird droppings. Cleaning of Solar PV system is regular and a natural process during the rainy season, but in other seasons, regular washing of the same with simple water is needed to enhance the system performance. Figure 1 shows the manual cleaning of a small roof top solar PV system.

Fig.1: Manual cleaning of a small roof top solar PV system.

Wrong cleaning practices, bad quality water and use of in-appropriate cleaning agents may damage the PV modules or other components. It may also reduce the system performance. Certain Solar PV sites require specific cleaning procedures. Procedure also depends on the water quality and the cleaning mechanism used.

What precautions to be taken while cleaning of Solar PV system?

The water used for cleaning of PV panels should be clean, soft and low in mineral content. If the water is comparatively harder, the water must be squeezed off to avoid building up of scale. In any case, the water hardness should not be more than 200 ppm. 

One can use lukewarm water and soft sponge or micro-fibre cloth also if the deposits are thick and stubborn. If necessary, a mild, non-abrasive, non-caustic detergent may be used. Situations, more prone to diesel fumes and deposits, may require a mild de-greaser agent along with the soap.

Cleaning of solar PV arrays should be carried out when they are not excessively hot i.e. the arrays should preferably be cleaned in the morning or evening time. Thus, cleaning of small solar PV arrays is similar to cleaning of any ordinary glass window. 

But in large Solar PV systems, several PV modules are connected in series, producing enormous DC voltage. In PV systems having higher DC voltages, cracks in modules, cables or joints may pose dangerous conditions to cleaning personnel. Hence, it is adviced to inspect the modules and cables thoroughly for any cracks or other damages before the commencement of cleaning. Workers engaged in cleaning should wear proper protective equipments while working with larger and higher voltage PV plants.  

Visual inspection of the PV modules should also be done after washing to check for any cracks, chips or discolouration. If any defect is observed, it should be monitored regularly for any further deterioration. During the inspection, condition of the mounting frame should be noted for any loose nut/bolt or rusting.