By Charles W. Thurston

Diversified 3M Corp. rolled out a new roll-on aftermarket Anti-Soiling Liquid for the glass covers of flat-mounted photovoltaic solar panels that deters soiling and helps the modules yield between five percent and 10 percent more energy in comparison testing, according to Carrie Ruby, a marketer for the St. Paul, Minn.-based company. Water beads up and runs off panels with the new liquid applied.

Unveiling the product at the Solar Power International 2012 show in Orlando in September, 3M says that the coating will either eliminate the need for PV module cleaning or diminish the number of cleanings necessary for optimal performance. The coating will sell for the equivalent of $1 per square meter, with coverage estimated at 20 square meters per liter, assuming a double roller pass.

The solution was tested for eight months in the Arizona desert against modules that did not receive any cleaning. “Down the road we also will be looking at an OEM product,” said Ruby. With a pH of 3.0, the product has a shelf life of only six months after manufacture, according to 3M. The company estimates that the liquid will last two years after appropriate application, which includes a de-ionized water rinse.

Some solar panel vendors require that owners perform minimal cleaning in order for the performance warranty for the panel to be valid. Conventional wisdom holds that the cost of cleaning solar panels outweighs the value of the power loss. In some cases, where a minimum generation level is required from the system, breach of contract can revoke power royalties, subsidies and other forms of revenue.

The alternative to using an anti-soiling agent or even cleaning is a dirty solar panel, which may generate 25 percent or 30 percent less energy if never cleaned, according to data from Heliotex, a provider of automated solar panel cleaning systems based in Palm Desert, Calif. One Heliotex system offered online cost $2,000. The Boston Solar Company predicts less extreme power losses from failure to clean, at around eight percent, but dirt occlusion is cumulative. Boston Solar recommends a yearly panel cleaning.

While the new 3M product can be used on residential systems, its application adopting is more likely with commercial or industrial solar arrays where the amount of power generated is usually guaranteed through a power purchase agreement, in cases of third-party owners of the solar system. Financiers often require a maintenance program for solar systems they lend to, and cleaning services would be included.

Residential solar panel cleaning services may charge a minimum of $150 for a service call and up to $30 per panel for cleaning with de-ionized water. Sears sells a telescoping squeegee package for homeowners for $475. Commercial and industrial panel cleaning services are likely to cost more, given that ancillary services are likely bundled. So the price point of the 3M liquid seems inexpensive compared with cleaning services, although only a module-specific monitoring system will help system owners know when system output has declined, signaling the potential need for a cleaning.