How Often Should You Clean Solar Panels in Seattle?

Almost every Seattle solar owner asks the same thing: doesn't all this rain wash my panels for me? Short answer — no. Rain rinses dust but leaves behind the residue that actually costs you watts: pollen film, evergreen sap, moss spores, and the gritty mineral deposits left when soft rainwater evaporates on warm glass.

The short answer

For most homes in the Greater Seattle area, plan on a professional clean once a year, ideally in late spring after pollen season. Add a second cleaning if any of the following apply.

• Trees overhang or shade the array (sap, needles, bird traffic)
• You're within 5 miles of I-5 or another freeway (road grime is real)
• Panels sit at a low tilt (under 15°) — debris doesn't slide off
• You've noticed visible green tint or moss creeping under the frame

Why rain isn't enough

Rainwater is a solvent for water-soluble dirt, but it's an active deposit mechanism for everything else. As a drop dries, it concentrates whatever it picked up — pollen, pollution, hard-water minerals — into a ring on the glass. After dozens of cycles, that ring becomes a haze that scatters incoming light before it ever reaches the cell.

What dirty panels actually cost

Field studies and our own before/after meter readings put production loss in the Pacific Northwest at 8-15% on neglected residential arrays, with worst-case rooftop systems near treeline losing 20%+. On a typical 8 kW Seattle system, that's roughly $150-$300 of lost generation per year — every year — until cleaned.

Why you shouldn't DIY

1. Tap water leaves mineral spots that bake on within hours.
2. Most household soaps void panel warranties (manufacturers require pH-neutral, non-abrasive cleaners).
3. Walking on or around panels risks micro-cracks that don't show up until production drops months later.
4. Wet glass on a sloped roof is a serious fall hazard — most homeowner insurance won't cover roof falls during DIY work.

How we do it

We use pure de-ionized water through soft-bristle, telescopic brushes — no chemicals, no pressure washing, no walking on the array. The water dries spot-free because there are no minerals left to leave a ring. Every clean includes a quick visual inspection of mounts, junction boxes, and conduit.

Bottom line

If your panels haven't been cleaned in over 12 months, you're almost certainly leaving money on the roof. Get a free quote and we'll tell you straight whether you actually need it yet — we won't sell you a clean you don't need.