Despite all its potential to power the future, solar produces only around 2 percent of the energy in the U.S. Some of that is because of the high cost of the panels, but most of it is due to their low efficiency. Solar panels can only absorb a fraction of the sunlight that hits them, and that's in the best of conditions.

But what about in the worst of conditions? New research from Duke University and the Indian Institute of Technology in Gandhinagar points a finger at airborne dust and pollution as a major reason why solar power isn't as good as it could be: Their research shows pollution can reduce the efficiency of solar panels by up to 25 percent.

"My colleagues in India were showing off some of their rooftop solar installations, and I was blown away by how dirty the panels were," said lead study author Michael Bergin in a press release. "I thought the dirt had to affect their efficiencies, but there weren't any studies out there estimating the losses. So we put together a comprehensive model to do just that."

The researchers measured the efficiency of the solar panels over time as they got dirtier. They found that only a few weeks of buildup was sufficient to block much of the sunlight from reaching the panels. After cleaning, the study's solar panels saw a 50 percent jump in efficiency.

Most of the stuff caked on the panels was ordinary dirt and dust. But a small percentage—around 8 percent—was from human pollution. These particles can have a much greater impact on panel efficiency because they're much better at blocking the light. "We always knew these pollutants were bad for human health and climate change, but now we've shown how bad they are for solar energy as well," said Bergin. "It's yet another reason for policymakers worldwide to adopt emissions controls."

Professor Michael Bergin and colleague Chinmay Ghoroi stand next to their dirty solar panels. Duke University

Pollution in the atmosphere also plays a role. The researchers used NASA atmospheric data to estimate how much sunlight was being blocked by particles in the atmosphere. They found that solar panels in very dirty environments saw a 25 percent drop in efficiency from atmospheric pollution alone.

Combining these two effects, a solar panel located in a heavily polluted environment that hasn't been cleaned in a month or more might see a total efficiency drop of 35 percent or more. This is bad news for countries like China and India as they ramp up in solar power.

"China is already looking at tens of billions of dollars being lost each year, with more than 80 percent of that coming from losses due to pollution," said Bergin. "With the explosion of renewables taking place in China and their recent commitment to expanding their solar power capacity, that number is only going to go up."

Source: Duke University via New Atlas

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