The benefits of having a solar panel roof have been proven, but there is a new pitfall homeowners should be aware of.
In a recent Reddit post, a Washington homeowner revealed a 20% drop in solar panel output during periods of wildfire smoke, even when it appeared sunny outside.
The reason behind this? The smoke’s fine particles likely scattered and weakened the sunlight before it hit the solar panels, reducing their electricity output.
“A 20% reduction from a supposedly sunny sky is not unusual. It happens all the time. People look up, see blue, check their app, and assume their inverter has fried. The sky is tricking them,” explains Greg Field, owner of PGT Home Energy Solutions in Tempe, AZ.
This story shows how wildfire smoke can affect solar systems, even without the presence of clouds, winter shadows, tree limbs, or debris buildup.
It also highlights the importance of monitoring solar production and cleaning your system properly when necessary.
Why wildfire smoke reduces solar production
Solar panels convert the light that actually reaches them.
“Wildfire smoke puts a layer of microscopic particles between the sun and the roof, and that layer scatters and absorbs sunlight before the panels ever see it,” says Nicole Tomasin, chief commercial officer at Energy Access Innovations in Dallas.
According to Tomasin, the 20% dip in solar panel output the Washington homeowner saw was likely the result of smoke in the air and particles on the panel.
Smoke suspends millions of particles overhead that block and scatter sunlight before it reaches the roof.
“The sky can look bright, even hazy-sunny, while the panels are receiving significantly less usable light. Brightness is not the same as intensity,” Tomasin explains.
A homeowner sits on his roof and watches an approaching fire to his home. (Mark Rightmire/Orange County Register via Getty Images) Smoke isn’t the only culprit. Ash and soot can settle on the panels and create a physical barrier.
“Air quality often clears days or weeks before the panels do, so production can stay low well after the smoke is gone, until rain or a cleaning takes care of it,” adds Tomasin.
Tomasin also points out that the production estimate on a solar contract is built with a small allowance for normal dirt, dust, and pollen. There is no line item for two weeks of wildfire smoke.
Wildfire smoke is just one of the many environmental factors that could affect solar output over time.
“Dust in the Southwest, pollen in the Southeast, salt air on the coast, and heavier storms nearly everywhere all move real production away from the brochure over a system's 25-year life,” Tomasin adds.
Tomasin believes that none of that changes whether solar is worth installing. However, it does change what you should expect solar alone to do for you on the worst days of the year.
How to monitor and maintain your solar panels
Fortunately, you don’t have to make wild guesses about the state of your solar panels. As long as your system was installed in the past decade, it likely came with a monitoring app that can help you determine what’s going on.
“Open it on a clear day and look at what a good week produces. That is your baseline.
"When smoke rolls in, put your production numbers next to your local air quality index (AQI),” says Tomasin.
If output falls as AQI climbs and recovers as it drops, you have your answer, and have saved yourself a service call. If production stays flat while the air clears, that is when you call your installer, because something else is going on.
If ash has settled on your panels, cleaning can restore lost production.
When doing so, use water and a soft brush, follow the manufacturer's instructions, and skip pressure washers and abrasives. Do it early in the morning or evening. And remember that cold water on hot glass can crack it.
“If your roof pitch is steep or higher than one story, skip the DIY route and hire an insured professional solar-cleaning service instead. Doing it incorrectly can damage anti-reflective glass coatings or you could get hurt,” explains Sequoya Cross, vice president of energy storage for Briggs & Stratton Energy Solutions in Wauwatosa, WI.
Michael Stadler, a former energy research scientist at Lawrence Berkeley National Laboratory and co-founder of energy modeling platform Xendee in San Diego, also recommends adding adding a battery, and possibly even a backup generator.
"If maintaining power during these periods is a major concern, consider a backup generator powered by diesel or natural gas. It may only need to run a few days a year, but it can provide another layer of protection when solar production and battery reserves aren't enough," Stadler says.