Over the life of a solar module, it is common for dust and dirt particles to accumulate on the surface of it. This build-up can reduce the performance of the module. Normally, the build-up of dust particles will be washed away by periodic rainfall if the panels are tilted, but if significant dust particles appear on the module surface, cleaning – the way it is done and the frequency also will have to be done accordingly.

What are the key factors you need to look at when it comes to the cleaning practices for the solar panels?

  • Cleaning frequency in the plant should be in accordance with the on-site dust and atmospheric conditions

The frequency of module cleaning will depend on local site conditions and the time of year. As the level of module soiling is site-specific, the duration between cleans will vary significantly between sites. The frequency to clean modules will be dictated by factors such as site and surrounding area ground covering (dusty and arid sites will result in more soiling) and local rainfall patterns (drier areas will result in more soiling).

Evaluate the cleaning regimen followed by the O&M personnel. Ensure that the cleaning practices are effective and the frequency of it is in accordance with the rainfall availability and atmospheric conditions of the site. A region with a relatively high amount of rainfall, when left uncleaned for even a year may lose only up to 5% of the total generation. On the other hand, it has been observed that a plant in Saudi Arabia, in desert conditions, has lost up to 30% of generation after having been left uncleaned for about a year. At Solar Mango, we would suggest a cleaning frequency   of about once in three weeks for a region that has a moderate amount of rainfall

  • Cleaning procedures employed

Clean, low mineral content water is preferred for cleaning modules. A main water supply, ground water, stored water or access to a mobile water tank may be required for this. The water used should be not too cold as well as not too hot. Its temperature should be lukewarm water. It is usually advisable to clean the panels during the late evening night or early morning hours in order to avoid thermal expansion and cracks because of the temperature difference between the water and module surface temperature. Usually, the module cleaning is done by water spray jets. The pressure of the water spray should not be very high in order to avoid damage on the glass surface.

  • Compliance with module manufacturer’s instructions

Make sure that the cleaning practices are in accordance with the maintenance practices prescribed by the manufacturer. In most cases,  it is advised that the water used should be free from dirt and mud. Typically, the water used should be de-mineralized. Salt water may also lead to corrosion on module frame as well as the mounting structures. Nowadays, establishing a RO plant for the cleaning water requirement is becoming a common practice in order to not void any panel warranty claims.

  • Manual cleaning against automatic cleaning

After a thorough cost-benefit analysis with your O&M contractor, you might want to explore the idea of automatic cleaning for your panels. This makes use of a self-cleaning system that works by using a low volume nozzle to spray water and soap onto the solar panels and wipes them clean like a windshield wiper. This idea could be favoured in the case of utility-scale projects in remote locations and also sometimes in the case of rooftop power plants which pose a danger to seasoned rooftop professionals.

But manual cleaning, using a hose pipe and brush is mostly used. In these cases, the O&M personnel should oversee the actual cleaning work done by local labourers.

Over and above the points mentioned above, you should also check with your O&M contractor on the cost estimate to clean the PV modules and compare it with the potential increase in revenue. The agreed O&M contract should detail an agreed number of cleans per annum and their frequency. It should also outline the labour rate or unit price at which the owner may request an additional plant-wide clean of modules.

You might want to check these questions on Solar Power Plant Evaluation – Plant Performance

  • What is the average CUF (Capacity Utilisation Factor) of the power plant?-Here
  • What are the performance guarantees provided by the installer?-Here
  • What is the generation data from the power plant? Is it according to the industry standards?-Here
  • What are the O&M practices followed?-Here
  • How do you check the quality of the  O&M company and personnel? – Here
  • What are the innovations employed in the power plant? How can they impact your  financial returns?-Here
  • Is there scope for expansion of the power plant, in terms of scale?-Here
  • What were the key problems the power plant had faced and what were the causes for these?-Here