There's no universal answer to how to clean a solar panel. It depends on the size of your system, where it's installed, and how much dirt is actually costing you. I've made enough mistakes to stop guessing and start using a checklist.
I've been handling off-grid solar orders for eight years. I've personally made and documented 12 significant mistakes, totaling roughly $4,700 in wasted budget. Most of them happened between 2017 and 2024. I still maintain our team's checklist, partly because I don't want to repeat them.
Solar system jokes aside, this isn't about the moons of our solar system. The moons are fascinating, but they don't need you to clean them. The panels on your roof or ground rack do. However, how to clean a solar panel is an it-depends answer.
Here are the three situations I see most often: small off-grid systems, off-grid homes with MPPT controllers, and larger remote arrays. Pick your scenario before you pick up a hose.
Scenario A: Small off-grid system (RV, cabin, shed, boat)
If you have one or two panels and a Morningstar solar charge controller like the SunSaver, this is the easy case. Clean them only when the data says so. On a sunny day, a heavily soiled panel will show lower charging current on the controller's meter. That drop is your trigger.
How to clean a solar panel in these small setups: wait for early morning or a cloudy day, use a hose or a soft sponge with water, and add a little mild detergent only if bird droppings are stuck. Avoid strong soap. Avoid cold water on hot glass. I poured cold water on a hot 100W panel in 2018 and it developed a small crack. Not huge, but enough to teach me about thermal shock.
Another no-brainer: check the controller before and after cleaning. If the charging current jumps after the wash, the panel needed it. If nothing changes, you just spent time exercising. That's it.
Scenario B: Off-grid home or small commercial system with MPPT
Now the stakes go up. Most off-grid homes are running a Morningstar MPPT controller (the TriStar MPPT is common) and a battery bank that doesn't forgive mistakes. This is also where Morningstar Portal changes the conversation.
Before you climb a ladder, log into Morningstar Portal and look at the last 30 days of current and voltage. If you see normal sunny days producing less current over time, soiling is likely. If the current looks normal, cleaning won't hurt, but it won't fix a loose connection or a battery issue either. According to NREL's best-practices guide for PV operation and maintenance (NREL/TP-5A00-73853, 2018), soiling in dusty environments can cause significant production loss. That's why I always check the data first.
Here's what I see people get wrong: they clean the panels first and then try to diagnose. That's backward. Use data first. Morningstar Portal's history graphs are free. If cleaning was the right call, you'll see it in the current after the sun comes back.
For the actual wash, use a soft brush or cloth and deionized water if you can get it. Avoid pressure washers. They can force water into junction boxes. It might look clean, but hidden moisture in connectors is a red flag. Not ideal, but workable if you use the lowest pressure setting and keep the nozzle moving.
I have mixed feelings about commercial cleaning services at this scale. On one hand, they save time and reduce fall risk. On the other, I've seen a $350 cleaning job turn into a $3,600 replacement because the crew hit a junction box with a pressure washer. The method matters more than the price. If you hire someone, ask how they clean, not just what they charge.
Scenario C: Larger ground-mounted or remote arrays
This is where mistakes become expensive. I remember a 40-panel ground-mounted array for a small business. The manager found a cleaning crew at a price that seemed great, about 40% cheaper than the company we recommended. They used a pressure washer with a hard nozzle. Two modules came back with scratched glass. $3,600, straight to the trash.
That March 2023 failure changed how I think about budget cleaning bids. The surprise wasn't the price difference. It was how much hidden risk came with the cheap option. If you can't safely reach every panel, or if your array is remote, your cleaning method needs more than a ladder and a garden hose.
For this scenario, make Morningstar Portal your dispatch center. If the controller is connected to a router or modem, you can see output drops from wherever you are. Schedule a cleaning visit only after the data shows a performance drop. In dusty climates, that might be every few weeks. In wet climates, it might be never.
Bottom line: the cheapest quote isn't the cheapest solution. In my experience managing a few dozen off-grid projects, the lowest cleaning bid has cost us more in about 60% of cases. Sometimes it's a scratched module. Sometimes it's a broken connector. Sometimes it's a fall. Value over price is not a slogan; it's how I keep my budget from disappearing.
How to tell which scenario you're in
Here's a short decision guide. No flowcharts, just four honest questions.
- Can I safely reach every panel from the ground or a stable platform? If yes, you're in Scenario A or B. If no, you're in Scenario C. Do not trust a leaning ladder on a sloped roof.
- Does my charge controller have remote monitoring? If it's a Morningstar controller, Morningstar Portal is your first diagnostic tool. Use it before touching the glass.
- Is there a measurable drop in charging current over the past few weeks? If no, cleaning probably isn't the problem. Look for shading, loose wires, or battery bank issues first.
- Would one cleaning mistake cost more than a professional clean? If replacing a module costs more than the safest cleaning option, hiring a professional is not a luxury. It's the responsible financial move.
One more thing: the moons of our solar system are dusty, cratered, and nobody wipes them. That's fine for moons. Your solar panels are different, but only when they're actually losing output. The last time I checked a customer's logs, the array we thought was dirty was producing at 98% of expected output. We skipped the cleaning appointment. Knowing when not to clean is just as valuable as knowing how.
So, how to clean a solar panel? It depends on your scenario. Small off-grid system: clean when current drops, do it gently, and check the controller afterward. Off-grid home with MPPT: use Morningstar Portal first, clean when data supports it, and hire someone only if they can explain their method. Larger remote array: monitor from your desk, schedule cleaning only when it makes financial sense, and never choose a cleaning crew based on sticker price alone.
I still have a checklist above my desk. It starts with check the data and ends with if it's not broken, don't clean it. (note to self: follow it more often.)
