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An analysis by the National Renewable Energy Laboratory (NREL) in North Carolina reveals that various types of tree pollen can reduce the efficiency of solar panels by more than 15%. Unlike the immediate improvements that are assumed to follow heavy rains, the recovery of yield after the pollen season is gradual. Manual cleaning after rain can increase performance by 5% to 11%.
A study carried out in collaboration with experts from the National Renewable Energy Laboratory (NREL) of the US Department of Energy, Duke University, Solar Unsoiled Inc, the University of Jaén (Spain) and the Sapienza University of Rome, has called into question the hypothesis that rain alone can effectively clean solar panels. Examining different pollens at five solar energy facilities in North Carolina, researchers found that pollen from tree species such as cypress, juniper, pine, and oak were especially tenacious at sticking to solar panels. .
During peak pollination seasons, variations in pollen types caused a decrease in solar panel efficiency of up to 15%. Despite rain “cleanings,” unwashed panels suffered an annual production loss of approximately 10%. Manual cleaning with a wet brush, after rain, showed an increase in yield from 5% to 11%.
The facilities studied, whose capacity ranges between 4 and 9 MW, are oriented towards the south with an angle of 20° and have been operating for approximately seven years.
Initially, researchers expected that fouling losses would be minimal, due to the areas relatively high average rainfall and short periods of drought. However, during the tests they found that the fouling losses and associated generation losses exceeded their expectations.
This data set is not universally applicable across the country, as pollen types and intensities vary across regions. Deserts mainly face dust, but agricultural areas in these regions also face pollen problems during certain seasons. East Coast facilities, characterized by a generally more humid climate and dense tree cover, consistently face pollen-related problems.
In this study, tree pollen was the predominant type affecting facilities during the spring, which had a significant impact on solar generation. The researchers observed that pollen from grasses and weeds, which peaks towards the end of summer, did not correlate with increased dirt losses on solar panels, unlike pollen from trees.
NREL and Solar Unsoiled will continue research to better understand the problem. They have observed that pollen particles from different trees have different levels of adhesion, influenced by factors such as the size and shape of the grains, the nature of the surfaces to which they adhere, their compositional properties and environmental conditions such as humidity. relative and wind patterns.
Carla Dawson of Soilar Tech, PV dirt mitigation consultants, suggests using a soft brush instead of a hard one to clean pollen from solar modules. She states: “Due to the high level of cementation generally associated with pollen compared to dust, it is common to clean with stiff bristle brushes.”
Although stiff bristles can remove pollen in a single pass, they can cause permanent damage to the anti-reflective coatings on solar panels, “creating a long-term permanent loss,” he said.
Dawson concluded that panels with high levels of pollen deposition are best cleaned with soft bristles, “and should have been tested in laboratories that measure levels of anti-reflective coating degradation and water with low levels of TDS.” |
