The deposition of dust and other micro particles over the PV modules is termed as Soiling. Furthermore, soiling is counted as one of the major causative factors hampering the PV power performance. Soiling loss is defined as the power loss resulting from the accumulation of dust, snow, dirt, and other particles that form a layer on the PV module surface. The various sources of Soiling can be categorized as due to:
The growth of lichens
Particulate matter that accompanies the wind
Dust from agricultural activities and from construction works
Dust from pedestrian and vehicular traffic
What Happens due to Soling
The soil accumulation on panel surface hampers the solar irradiance that has to penetrate the module. Consequently, this leads to reduction in energy output from the solar module. Till the module cleans well, the reduction in output might continue. So, to avoid incurring losses in investment in such solar projects because of reduced output, it is important to monitor panels for soling and clean them at regular intervals.
Factors affecting Soiling
The factors affecting soiling are as follows:
Climatic conditions and location characteristics
The local climatic condition and the geographical location of the solar power plant can have significant effect on soiling. Extremely dry/humid weather delivers soil and dust particles on the solar module. Due to repeated dry & humid weather cycle these particles can get stubborn and accumulate along the module frame, which is known as cementing.
Tilt angle and Orientation
The dust particles settle more on horizontal surfaces than the tilted surfaces and effect of gravity in dust accumulation increases with the tilt angle.
Ambient temperature, Pressure and humidity
At high ambient temperature and low relative humidity, wind carries the dust easily. The water vapor will condense and form water drops at low temperature. In addition, high relative humidity leads to greater soiling and forms a sticky surface over the solar panels. These sticky panels attract more dust from surroundings. When the airspeed is higher and there is low pressure, less soil accumulation occurs and vice-versa.
Dust has different properties like chemical, biological, electro-static and physical properties. The small dust particles settle down more than that of the larger dust particles on the PV panel.
The dust accumulation on PV panels varies with the property of panel surface. Certainly, plane panels have lesser dust accumulation while textured panels have rough and irregular surfaces increase the soiling on panel surface.
Any probability of dust storm or strong local winds or the occurrence of dew, rainfall, volcanic eruptions, etc. contributes to soiling of PV panels.
PV technology and cell configuration
Soiling affects the different PV technologies differently based on the spectral transmittance. Performance wise, the PV technologies like mono-crystalline and poly-crystalline PV panels have a different impact.