What wildfire smoke does to your solar output

Distant smoke trims less from your solar than the orange sky suggests. The ash it drops on the glass is what lingers after the haze has gone.

Does smoke really cut your output?

A little, and usually less than it looks. A Colorado State University study published in Nature Communications in January 2025 found that transported wildfire smoke reduced solar resources by only about 5%, and in some places by less than 2%.

“Transported” is the key word. That is smoke that has travelled from fires hundreds of miles away, the kind that turns Front Range sunsets red for a week in August. The same study found larger losses near active fires, where smoke is thick and close to the ground.

“Solar resources” is the other key phrase. It means the sunlight reaching the ground, not the output of any one array. Your panels follow that light closely, but not exactly.

Why does the sky look worse than the numbers?

Because your eyes and your panels see light differently. Smoke scatters the direct beam of the sun, which is why the sun looks dim and the sky turns white or orange. A lot of that scattered light still reaches the panels from every direction.

So a hazy afternoon that feels gloomy on the deck can still produce a respectable day. Your app will show it as a slightly flatter, slightly lower curve, not a collapse.

When it does collapse, look for another cause: thick smoke from a close fire, cloud along with the smoke, or a problem unrelated to the weather.

When is it more than haze?

When the fire is close. Foothill and mountain fires west of Denver can put heavy smoke straight over Golden, Evergreen and the western suburbs. On those days the sky goes brown, the light at noon looks like dusk, and output falls much further than on a distant-haze day.

Close fires also drop ash. That is the part that outlasts the smoke, and it is the part a wash can do something about.

What is ash doing on the glass?

Sitting there. Fine wildfire ash falls as grey flakes and powder, often too light to notice until it gathers on a car windshield. On a panel, it settles evenly across the glass and collects thickest at the bottom frame.

Smoke passes in days. Ash stays until something moves it. A heavy rain can rinse some of it off steep glass. Dew and light showers tend to do the opposite, turning the powder into a paste that dries hard in the sun.

We cover why light rain can glue dust in place in does rain clean solar panels? Ash behaves much the same way, and it arrives in the driest part of the Front Range year.

How do you read smoky days in your app?

Compare like with like. A smoky day should be judged against clear days, not against the sunniest day of June.

• Pick clear days before the smoke: a few cloudless days from the weeks before.
• Pick clear days after it clears: once the sky is blue and the air smells normal.
• Compare daily energy: total kilowatt-hours for the day, not the peak power reading.
• Allow for the season: a September day makes less than a July one regardless.

If clear-day output after the smoke matches clear-day output before it, nothing stayed behind. If it sits lower and stays lower, ash or dust is on the glass.

Our guide to reading your solar app shows where to find those daily figures in most monitoring apps, and how to set up a quick before and after view.

Will smoke ever show as a fault?

No. Smoke and haze change how much light arrives, and the inverter simply makes less power from it. They do not trip an error code or take a panel offline.

So if your app shows a fault, a panel reporting zero, or an inverter warning during a smoky week, treat it as a separate problem. It is a question for your installer, not for the weather. We look and photograph, but we do not open electrical boxes or reset equipment, and neither should anyone on a ladder without the training.

What if the fire came close?

Then the ash is the least of it. When a fire burns near a neighborhood, heat, embers and firefighting water can all reach a roof. Panels, wiring and the roof under them deserve a proper look before anyone switches anything back on or climbs up.

• Your installer: wiring, inverters, and whether the system is safe to run.
• A roofer: the roof surface, flashing and any ember or heat damage around the mounts.
• Your insurer: anything you may claim, ideally before repairs begin.
• Us: a visual solar inspection with photos of every module, from the glass side only.

We will tell you plainly what we can see and who should handle it. We will not guess at what we cannot see.

Should you wash during smoke season?

Usually not. Washing while ash is still falling just resets the glass for the next smoky day. It also puts a crew on a roof in poor air for a result that may last a week.

We wait. On our two-season plan, the late-summer wash is booked for September, and if smoke is still heavy we move the date at no charge. On most years, the first cold fronts of autumn clear the air and bring the dry months to a close at about the same time.

The exception is a close fire that leaves a visible grey coat on the glass. Once the fire is out and the ash has stopped falling, that is worth a look sooner.

Can you just brush the ash off?

Please do not dry-brush it. Ash and the dust mixed into it are fine grit. Rubbed across glass without water, grit is how coatings get scratched.

Panel makers are specific about this. Panasonic’s EverVolt manual asks for deionized water free of grit, at ambient temperature, with a sponge, microfiber cloth or soft brush. The order matters: water first, so the grit floats, then a soft tool.

For a ground mount, a gentle rinse from the ground on cool glass is fine. For a roof, leave it for the crew, and stay off the ladder on smoky days anyway.

What does a smoke-season wash look like?

It follows the same four passes as any visit:

• Read: the monitoring desk pulls 30 days from your app, so the smoky stretch is on record.
• Look: photos of every row before anything gets wet, including the ash line.
• Rinse: pure water at air temperature, soft brushes, top row down, early morning.
• Prove: after photos and a comparison of the next clear days against the baseline.

The glass-level check matters more after a fire summer. Hot, dry months are when we most often find cracked sealant, browning and nests settled in under the bottom row.

Should someone watch the numbers for you?

If smoky summers leave you second-guessing your app, it can help. Our performance monitoring service reads your production data with read-only access and flags a slide that outlasts the weather.

That way a smoky week reads as a smoky week, and an ash film reads as a film, without you comparing graphs at night.

What is the short version?

• Distant smoke: a small, temporary dip; nothing to do.
• Close fire smoke: a bigger dip, and possibly ash on the glass.
• Ash that stays: shows as lower clear-day output after the sky clears.
• The fix: a pure-water wash once the season ends, not during it.

Where to go from here

When the sky turns blue again, check a few clear days in your app. If output has come back, the smoke took its share and left. If it has not, put your figures into the output check to see what the film is costing, and book an autumn wash when the air is clean.