Electrostatic cleaning of Solar Modules

Proper operations and maintenance (O&M) of solar systems is important in order to ensure effective generation. One of the crucial ways in this process is to regularly remove dust and soil from solar panels, which accounts for 25 – 35% of the total O&M cost. Uncleaned solar panels result in substantial loss in power generation. A 2019 study on solar photovoltaic (SPV) modules in Doha estimates that the lack of module cleaning could affect in a 12- 24% loss in power outputs per month. Solar module cleaning is a very important factor to get optimum yield from a solar project. About 5 litres of water is required to clean a solar panel and a typical 1 MW solar plant annually consumes about 24,000 litres of water. In an uncleaned solar plant yield can be lowered as much as 30% as compared to a cleaned solar power plant in just a month.

Watered cleaning system

In India, where solar capacities are increasingly being developed in desert areas, these modules need to be washed once a week. The amount of water needed to clean a single solar panel is 3-5 litres per panel in normal areas and 7-8 litres in arid areas. This means that for a 1 MW solar park with about 3,000 panels, up to 24,000 litres of water would be required.

Water requirement for cleaning panels (and its frequency) mainly depends on the cost which a developer is willing to pay. The cost scale can be huge because the location of the site and its surroundings plays a crucial role.

Let’s say a site is located in a desert location. It may require more water to clean such panels and also its frequency will be higher than other plants that are located in less dusty locations. Also, the cost of transporting water to the site and using labour force to clean the modules will add up to the total O&M cost as the sites located in the deserts are far away from the cities. Usually, the cleaning frequency may be 2 times a month. But all this comes with a cost and hence again, this depends on the cost which a developer is willing to pay per month.

States that house a large part of the country’s solar capacity, such as Rajasthan, Gujarat and Karnataka, consume very high amounts of water. As per a recent report by the World Resource Institute, 79 per cent of new renewable capacity is set to be built in areas that are already facing severe water shortages.

While there has been a sharp decline in solar tariffs over the past few years, the cost of water has been increasing. A case in point is Rajasthan, which has seen a doubling in its water costs over the past five years. In Karnataka, the price of water rose nearly a hundred times in 2018.

Water-less cleaning systems

To reduce the labour costs associated with module cleaning and use less water for O&M of solar projects, developers have made attempts to install robotic cleaning systems in larger solar parks such as Bhadla in Rajasthan and Rewa in Madhya Pradesh.

Active methods entail labourers using fixed brushes or microfibre-based cloth to clean the solar panels. The most common waterless method for cleaning solar panels is the use of mechanical brushes. These panel-cleaning brushes are designed to rotate and remove soil from the panels. Although this method uses some amount of water, it is still far less than that used in traditional wet clean methods. In larger solar parks, mechanical brushes have also been fixed on to robotic cleaning systems, which are even more water efficient. These active cleaning methods are sometimes also combined with vacuum cleaners for better results.

Electrostatic cleaning of Solar Modules

In recent years there have been initiatives to go for cleaning of solar pv modules using automatic robotic cleaning systems. However, there are concerns for scratches on SPV modules due to the brushes used in the robotic cleaning systems.

To overcome these concerns a new system has been developed by researchers at MIT using electrostatic repulsion to cause dust particles to detach and virtually leap off the panel surface, without the need for water or brushes. An electrostatic charge is applied on panel surface and the dust particles will slide down.  

The new system developed only requires an electrode, which can be a simple metal bar, to pass over the panel, producing an electric field that imparts a charge to the dust particles as it goes. An opposite charge applied to a transparent conductive layer just a few nanometers thick deposited on the glass covering of the solar panel then repels the particles, and by calculating the right voltage to apply, the researchers were able to find a voltage range sufficient to overcome the pull of gravity and adhesion forces, and cause the dust to lift away. The system can be operated automatically using a simple electric motor and guide rails along the side of the panel.