Water plays an important role in keeping the panels dust-free, but it’s a precious resource that’s better utilized elsewhere. In their quest for better alternatives, MIT researchers have devised a new solar panel cleaning method that uses electrical charges to repel the dust particles, essentially making them jump off the panels. “The research paper is useful for continued progress on the problem of PV (photovoltaic) soiling,” Matthew Muller, Engineer in the PV Performance and Reliability Group at the National Renewable Energy Laboratory (NREL), told Lifewire over email. “The paper is well written, is a useful step in the long term work to address PV soiling, and therefore some of the experiments described are very useful to the community.”
Bite the Dust
In their paper, MIT graduate student Sreedath Panat and professor of mechanical engineering Kripa Varanasi cite projections that estimate solar power will amount to 10 percent of global electricity generation by 2030. They argue that despite recent improvements in PV technology to help improve the efficiency of solar panels, dust accumulation is one of the biggest operational challenges for the industry. Dust, explains Muller, lands on the solar panel due to gravitational and other deposition methods. “The dust particles then block the transmission of light into the solar cell, hence causing a power reduction for the given external irradiance. We see losses from PV soiling in the US range from 0-7% where 7% losses are for dusty regions in the southwest,” explained Muller. Furthermore, the researchers state that in harsh environments like in the middle of a desert, dust accumulates at rates close to 1 g/m2 per day and, if not cleaned, can pile up to 3 mg/cm2 in under a month. To put that into perspective, dust accumulation of 5 mg/cm2 corresponds to almost 50 percent loss in power output, share the researchers. To put that in monetary terms, they say that an average power loss of 3-4 percent on a global scale amounts to an economic loss of $3.3 to $5.5 billion. No surprise, then, that huge amounts of resources are spent to clean the solar panels, sometimes even several times a month, depending on the severity of soiling conditions. The most common cleaning method is using pressurized water jets and sprays, which the researchers estimate can contribute up to 10 percent of the operation and maintenance cost of solar farms. Other researchers have calculated that solar power plants consume about one to five million gallons of water for cleaning per 100 MW of generated electricity per year. Scaled up, that translates to up to 10 billion gallons of water for solar panel cleaning purposes, which is estimated to be enough to satisfy the annual water needs of up to 2 million people.
Clean Getaway?
Dry scrubbing is one alternative to water-based cleaning, but this isn’t as effective and runs the risk of scratching the panels and causing an irreversible reduction in their effectiveness. Electrostatic solar panel cleaning, which doesn’t use water, nor has the risks of contact scrubbing, has emerged as an exciting alternative. Electrodynamic screens (EDS) are the most popular electrostatic dust removal systems, and these are used on the Mars rover, Muller points out. However, the researchers argue that there are several challenges for implementing EDS in solar panels on Earth, such as moisture intrusion and accumulation, which could eventually lead to electrical shorting of the electrodes. Their proposed mechanism builds on top of the existing electrostatic cleaning method and uses electrical charges to cause dust particles to detach and leap from the surface of the panels. The system can be operated automatically using a simple electric motor and guide rails along the side of the panel. The technology is exciting, but is only at a research level and therefore a long way from being commercially viable, reminds Muller. Furthermore, he adds that the researchers conducted tests with road dust, which is an ideal case. “In [the] real world, soil can be much more complex… and hence the device might not work in a number of environments.”
