Increasing air pollution levels can affect the energy generation capabilities of installed solar projects and can be a deterrent in utilizing the full solar potential. The scattering and extinction of light caused by air pollution reduces the available solar resource and increases the fraction of diffused light. These effects, if not taken into consideration, can make solar powered applications underperform and become unreliable, threatening widespread adoption of solar.

Per a study published in the journal Energy & Environmental Science, fine particulate matter in the air affects the energy yield of photovoltaic (PV) installations. Fine particulate matter is predominantly anthropogenic and is a main contributor to haze events. Reduced insolation results in lost revenue for system operators and investors in PV systems.

While correlating the measured particulate concentrations and solar insolation in Delhi, it was found that 12.5 percent of the incoming light is extinct for every 100 mg m3 particle concentration. Using this relation, the study projected that total sunlight reaching the ground in Delhi for one year is reduced by more than one ninth due to air pollution. This amount corresponds to 40 kWh m2  of annual energy generated for a 20 percent efficient silicon solar panel. Even higher relative losses must be expected for solar cells with a band gap greater than that of silicon.

Ian Marius Peters, now an MIT research scientist, was working on solar energy research in Singapore in 2013 when he encountered an extraordinary cloud of pollution. “The city was suddenly engulfed in a foul-smelling cloud of haze so thick that you couldn’t see the buildings on the other side of the street, and the air had the acrid smell of burning,” Peters said. “The event, triggered by forest fires in Indonesia and concentrated by unusual wind patterns, lasted two weeks, quickly causing stores to run out of face masks as citizens snapped them up to aid their breathing.”

While others were addressing the public health issues of the thick air pollution, Peters’ co-worker Andre Nobre from Cleantech Energy Corp., whose field is also solar energy, wondered what impact such hazes might have on the output of solar panels in the area. That led to a years-long project to quantify how urban-based solar installations are affected by hazes, which tend to be concentrated in dense cities.

The study found that there’s never a day without pollution in Delhi, and the effects of that pollution are indeed substantial. In some cases, it can mean the difference between a successful solar power installation and one that fails to meet expected production levels, possibly even operating at a loss.

For example, study results showed the annual average level of attenuation of the solar panel output was about 12 percent, a margin that is larger than the profit margins for some solar installations. This reduced solar panel output not only impacts that project, but also potentially causes a ripple effect by deterring others from investing in solar projects.

Typically, the size of a solar installation is determined by the expected levels of sunlight reaching the ground in that area. Failing to factor in the effects of haze on solar panel output could result in the project falling short of meeting its intended output and expected revenues.

“When you’re doing project planning, if you haven’t considered air pollution, you’re going to undersize, and get a wrong estimate of your return on investment,” said Peters

After their detailed Delhi study, the team examined preliminary data from 16 other cities around the world, and found impacts ranging from 2 percent attenuation in Singapore to over 9 percent in Beijing, Dhaka, Ulan Bator, and Kolkata. In addition,  the researchers looked at how different types of solar cells — gallium arsenide, cadmium telluride, and perovskite — are affected by haze, because of their different spectral responses. All of these solar cells were affected even more strongly than the standard silicon panels initially studied. Perovskite, a highly promising newer solar cell material, was affected the most, with over 17 percent attenuation in Delhi.

Many countries around the world have been moving toward expansive installation of urban solar panels, with India aiming for 40 GW of rooftop solar installations. So, the impact of these reductions in output could be quite severe, the researchers say.

In Delhi alone, the lost revenue from power generation could amount to as much as $20 million annually; for Kolkata about $16 million; and for Beijing and Shanghai it’s about $10 million annually, the team estimates. In the United States, planned installations in Los Angeles could lose between $6 million and $9 million.

Overall, the potential losses “could easily amount to hundreds of millions, if not billions of dollars annually,” the study notes. And if systems are under-designed because of a failure to take haze into account, that could also affect overall system reliability.

Per the study, the situation is slightly different for bifacial modules which use proportionally more diffuse light. “As haze increases the ratio of diffuse to direct light, bifacial modules will likely experience smaller losses than their mono-facial counterparts,” the study states.

Meanwhile, in a significant move towards curbing the menace of air pollution in the national capital, Delhi chief minister Arvind Kejriwal recently announced that his government has approved the hiring of a consultant to run 1,000 electric buses.