It is well known that atmospheric dust and soiling can reduce the performance of solar modules. The lack of module cleaning could lead to power output losses of 12-24 per cent per month. Furthermore, if the soiling contains salt, it may also cause potential induced degradation in PV modules. This underscores the importance of timely and proper cleaning of PV modules, especially in dry, arid areas where panels need to be cleaned at least once a week. In this article, Renewable Watch compares various types of cleaning technologies being employed in India…
Manual cleaning
This is the most commonly used method for cleaning solar PV modules. Based on water availability, dry or wet cleaning may be used. Dry cleaning involves the use of brushes/microfibre/vacuum cleaners with minimal water usage, while manual cleaning mostly involves extensive water usage. This was the norm in conventional solar PV projects, as it did not necessitate any upfront investment for routine maintenance through the manual method. However, it is a slow and less effective technique as compared to automated technologies. The water requirement in manual cleaning can go as high as 24,000 litres per MW for a single cycle of cleaning. Additionally, the labour requirement for cleaning also adds to the overall operational cost, driving annual cleaning costs up to Rs 750,000 per MW per year.
Sprinkler systems
These systems perform routine cleaning to prevent the accumulation of dirt. The high-velocity spray from the nozzles ensures effective cleaning of the modules and the wash-rinse cycles of the sprinklers can be custom programmed, providing an autonomation option. The cost of installing these systems is quite low compared to other autonomous options. However, the extremely high water usage of sprinkler systems makes them viable only for smaller-sized power plants, where water availability is not a constraint and water costs are low. Another downside to the sprinkler system is that the nozzles require routine cleaning and frequent replacement due to salt formation.
Truck-mounted cleaning systems
Truck-mounted cleaning systems consist of a brush connected to the hydraulic arm of a truck or other vehicles, which drives between the PV module rows. The arm can cover large module areas and enable faster cleaning, making it a viable option for utility-scale plants where there are large distances between rows (2.5 to 3 m). However, this is also a downside as most projects are designed to utilise the maximum land area for energy generation, limiting the applicability of such systems. The deployment of large trucks in solar fields also poses a high probability of damage to modules in case of operator errors. The cost of such systems can range from Rs 10 million to Rs 15 million.
Semi-automated systems/portable robots
These are small, battery-operated cleaning devices (up to 1 square metre in size) that are positioned manually on PV tables and perform automated cleaning. They are optimal solutions for large rooftop and small-scale installations because of their size. Each robot costs between Rs 1 million and Rs 1.5 million. However, their application is limited to simple arrays without gaps, relative tilt angles or steps between PV modules as these devices have to be placed manually, thereby increasing the time required and the overall cleaning cost.
Fully automated systems
Fully automated cleaning robots are installed on each row of a PV system and are stored at a parking station on one side of each row. These systems are completely automated and use separate rails for their movement. They can even operate at night without affecting the operations of the plant during the day. The initial cost of installation of these systems is high (up to Rs 4 million per MW), but since operational costs and water usage are extremely low, it is an attractive option for large utility-scale power plants. Evidently, most greenfield projects in India are now incorporating designs with provisions for robotic cleaning.
Drone cleaning
The process of the overall operations and maintenance becomes faster and cheaper with unmanned aerial vehicles, especially in developing countries. These drones are equipped with a brush that sweeps dry dust and dirt from PV module surfaces. Single drones can simultaneously perform cleaning as well as check-ups of PV panels.
Outlook
Conventionally, developers used to rely on manual cleaning to ensure the performance of modules. However, as the size and number of utility-scale solar PV plants grow in the country, achieving the same efficiency becomes increasingly difficult and costly. Moreover, the added constraint of water availability near power plant areas further adds to the woes of maintenance crews. To this end, in 2019, the Ministry of New and Renewable Energy issued a letter recommending the prudent usage of water for cleaning utility-scale solar projects and also recommended the adoption of robotic cleaning technology, which uses less water for cleaning solar projects. Such government initiatives backed by the entry of efficient cleaning solutions will lead to greater uptake of waterless and robotic technologies going forward.
