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Solar Panel Cleaner Formulation: Up to 5.6% Output Loss for Pros

October 13, 2026
Solar Panel Cleaner Formulation: Up to 5.6% Output Loss for Pros

Deionized, reverse-osmosis, or distilled water is the safest cleaning fluid for any photovoltaic module, and a mild, pH-neutral detergent earns a place in the bucket only when the panel manufacturer specifically permits it, followed by a thorough rinse. Independent lab testing from Fraunhofer CSP found some commercial cleaners permanently degraded anti-reflective coatings, cutting module performance by as much as 5.6%. Check your module's datasheet for its approved pH range and water-quality limits before you mix anything.

TL;DR:

  • First Solar specifies pH 6.5 to 8.5, but check your module’s approved range and water limits before adding detergent.
  • Fraunhofer CSP found three of five tested commercial cleaners measurably degraded coatings; the worst permanently cut module output by up to 5.6%.
  • Avoid ammonia, bleach, citrus solvents, strong acids or bases, and abrasives, which can etch coatings, soften seals, corrode frames, or scratch glass.
  • Wash early morning or late evening, use manufacturer approved pressure and a soft nonabrasive brush, then rinse thoroughly with purified water.
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Table of Contents

Water quality and pH: why your base liquid matters

Tap water carries dissolved minerals that plain purified water does not. Those minerals show up as calcium and silica spots baked onto hot glass, and over seasons they build a haze that cuts light transmission and gives dirt something to cling to. Deionized, reverse-osmosis, or distilled water sidesteps that problem entirely because it leaves nothing behind to crystallize.

pH matters just as much as mineral content. First Solar's module cleaning guidelines call for cleaning agents in the 6.5 to 8.5 range, with purified water as the default and only mild, non-caustic detergents permitted beyond that. Push past either end of that range and you risk etching glass, corroding frame metal, or breaking down the sealants that keep moisture out of the junction box.

A pH meter or a $15 TDS meter tells you in seconds whether your water is safe to use, and that single reading shapes independent testing that found a 5.6% performance loss tied to the wrong cleaning chemistry, not the dirt itself.

Before any field job, we recommend checking water quality and pH carefully according to manufacturer guidance to avoid damage.

Skipping that last step is how a perfectly safe cleaning session still leaves a cloudy film that looks like damage but is really just leftover calcium.

Chemistries and household ingredients to avoid

Most coating damage traces back to a handful of ingredients that seem harmless in a kitchen cabinet but behave very differently on photovoltaic glass. Ammonia and bleach attack anti-reflective coatings chemically, etching microscopic pits that scatter light instead of transmitting it. D-limonene, a common citrus-based degreaser, softens certain polymer encapsulants and gasket materials over repeated exposure. Strong acids like hydrochloric acid and strong bases like sodium hydroxide sit far outside any manufacturer's approved pH range and corrode aluminum frames and edge seals.

Abrasive powders and scouring pads cause a different kind of harm: physical scratching that roughens the glass surface so dust and pollen stick more easily on the next soiling cycle, creating a cycle of worsening performance.

Fraunhofer CSP's testing put real numbers behind this risk: three of five commercial cleaners tested caused measurable degradation of the anti-reflective coating, with the worst performer cutting module output by up to 5.6%. That loss is permanent, not a temporary haze that clears with the next rain.

Avoid these in any solar cleaning formulation:

  • Ammonia-based glass cleaners, which attack anti-reflective coatings chemically.
  • Chlorine bleach, which corrodes metal components and degrades sealants.
  • D-limonene and other citrus solvents, which soften polymer gaskets over time.
  • Hydrochloric acid, sodium hydroxide, and other strong acids or bases outside the approved pH range.
  • Abrasive powders, scouring pads, or any gritty cleaner that scratches glass.

Manufacturer warranties typically name approved cleaning methods explicitly, and using an excluded chemical can void coverage if damage shows up later.

Formulation patterns and dilution guidance for safer cleaners

A sound solar panel cleaner formulation starts with the same base every time: RO or DI water, built up with a small amount of surfactant chosen for low residue rather than maximum foam. Patent filings covering PV glass cleaners describe a common pattern: amphoteric or anionic surfactants at roughly 1 to 10% by weight, paired with benign salts such as potassium phosphates, bicarbonates, or urea making up the bulk of the formula. Those benign salts do double duty, buffering pH near neutral while discouraging dirt from re-adhering after the rinse.

A corrosion inhibitor protects aluminum frames and fasteners, and a low-foam wetting agent helps the solution sheet off cleanly instead of pooling in cell gaps where it can dry into streaks.

Before any mixture touches a customer's array, professionals should work through a short validation sequence:

  1. Mix a small test batch and confirm pH lands inside the manufacturer's approved window, typically 6.5 to 8.5.
  2. Check conductivity or TDS of the finished solution, not just the water you started with, since additives change the reading.
  3. Record specific gravity so every future batch matches the tested formula exactly.
  4. Apply the test batch to a spare panel or a hidden corner of an installed module, then inspect after drying for streaking, spotting, or haze.
  5. Document the module manufacturer's written approval, or lack of restriction, for the chemistry you intend to use.

Keep a safety data sheet and batch record for every formulation you field, including lot numbers and test results. That paper trail matters if a warranty claim ever hinges on what touched the glass.

Pro Tip: Treat any homemade mixture as a prototype, not a finished product. A commercial PV-specific concentrate that has already been through compatibility testing removes the guesswork that a one-off kitchen-sink blend cannot.

For operators who would rather start from a formula that has already cleared these checks, a PV panel cleaner concentrate built for private label gives a tested starting point instead of a trial-and-error mix.

Safe application: timing, pressure, and brush choice

Technician brushing a ground-mounted solar panel

Clean early morning or late evening, when module and water temperatures are close together. Splashing cold water on hot glass is the fastest way to induce thermal shock, and module cleaning guidance warns against cleaning during peak heat for exactly that reason.

Pressure matters as much as temperature. Stick to the nozzle pressure your module manufacturer specifies, and skip high-pressure washers entirely unless the equipment is explicitly rated for PV glass. A jet that strips dirt can just as easily strip the anti-reflective layer underneath it.

  • Use soft-bristle, non-abrasive brushes with non-conductive handles, and test any new brush on a spare panel first.
  • Rinse thoroughly with purified water after any detergent contact, leaving nothing behind to dry into a film.
  • Squeegee the surface dry rather than letting water evaporate on its own, especially if your water source has any hardness.
  • Walk and kneel only where the installer's layout permits foot traffic, since glass that looks sturdy can still crack under uneven weight.

Pro Tip: Keep a second bucket of clean rinse water on hand so your wash water never gets reused for the final pass, which is how streaks and residue sneak back onto a panel you just cleaned.

How a contract formulator develops PV-safe cleaners at scale

We built our in-house lab around exactly this kind of problem: a chemistry that has to be gentle on coatings, effective on real dirt, and consistent batch after batch. Our chemists work from a large library of proprietary formulas, which means a PV-safe cleaner rarely starts from zero.

Our development workflow runs in a straight line: a technical brief, a lab prototype built to match it, compatibility testing against pH targets and extended coating exposure, a pilot batch sized for real-world trial, then full-scale production once the pilot checks out.

What clients walk away with:

  • A safety data sheet and dosing instructions ready for field crews.
  • Documented QC parameters, including pH, conductivity, and specific gravity targets for every batch.
  • Pilot samples sized for compatibility testing on live installations before committing to a full run.

Brands ready to move past DIY mixing can request a formulation brief through our contract chemical manufacturing services and get a pilot batch moving quickly.

Shelf life and storage conditions for solar panel cleaner formulations

A pH-neutral, low-residue cleaner is only as good as the bottle it is still in on the day you use it. Surfactant-based formulas drift over time: separation, cloudiness, or a shift in pH are all signs that a batch has started to break down, and a cleaner that has drifted outside its tested pH window can damage coatings just as surely as the wrong chemistry from day one.

Store concentrates and ready-to-use solutions in sealed, opaque containers away from direct sunlight and temperature swings. Heat accelerates surfactant breakdown, and freeze-thaw cycles can cause some formulations to separate permanently. A cool, stable storage room, not a truck bed baking in summer sun, keeps the chemistry intact.

Most well-formulated, pH-balanced cleaners hold their performance for twelve to eighteen months when stored properly, though the exact window depends on the specific surfactant package and preservative system in the formula. Label every container with a manufacture date and a retest date, and treat any batch that has passed its retest point as suspect until you confirm pH and clarity again.

For crews running multiple trucks or warehouses, batch tracking matters as much as the formula itself. A cleaner that tested safe in the lab six months ago is only still safe if nothing changed in storage between then and the day it goes on a customer's roof.

Regulatory considerations and safety data requirements

Any cleaning chemical sold or used commercially needs a safety data sheet that spells out its ingredients, handling precautions, and disposal requirements. That document is not paperwork for its own sake. It is what a crew references if a worker gets splashed, what a fire marshal asks for during an inspection, and what a customer's insurer wants on file before signing off on a maintenance contract.

Formulators also need to track ingredient restrictions that vary by state and by end use, since a surfactant or inhibitor that is fine in an industrial cleaner can face different labeling or disposal rules depending on where it is sold. Wastewater runoff from cleaning operations is a separate consideration: a formula that is gentle on glass still needs to be safe to rinse into a storm drain or onto the ground beneath a ground-mount array.

Biodegradability is worth asking about directly. A cleaner built on readily biodegradable surfactants and benign salts, the kind of composition patent literature on PV glass cleaners describes, breaks down in the environment faster than formulas built on harsher solvents, which matters for large-scale solar farms where runoff reaches open ground or nearby water.

Keeping a complete batch record, safety data sheet, and compatibility test result on file for every formulation is the simplest way to answer a regulator's or a customer's question before it becomes a problem.

Regulatory considerations and safety data requirements — overview diagram

Prioritize coating health over cosmetic cleanliness

A panel that looks streaky but still tests within its rated output is in better shape than one that looks showroom-clean after a cleaner quietly etched its coating. We think the industry's obsession with spotless glass gets the priority backwards: long-term energy yield and warranty standing matter more than how a module looks from the ground.

Test before you scale, get manufacturer sign-off when you can, and treat a vetted formulation as the safer bet over a confident guess.

— Faisal Mansur

Custom formulation and pilot manufacturing for PV-safe cleaners

We build pH-neutral, low-residue cleaner formulations to spec, run compatibility testing against the coating types you actually service, and hand you a pilot batch before committing to a full production run. Whether you need a private-label product carrying your own brand or a wholesale supply for a fleet of maintenance crews, in-house chemists adapt an existing base from a formula library or build something new around your technical brief.

Sarawest USA

Getting started means telling us what you need cleaned and what you are cleaning it for. Submit a formulation brief through our private label cleaning products page and we will walk you through pilot sizing from there.

FAQ

How do I clean solar panels myself safely?

Rinse with deionized, reverse-osmosis, or distilled water and a soft, non-abrasive brush, scheduling the job for early morning or evening to avoid thermal shock. Only add a mild, pH-neutral detergent if your panel manufacturer's documentation permits it, and rinse completely afterward.

What is the 33% rule in solar panels?

This phrase does not correspond to a standard cleaning or maintenance specification from panel manufacturers or independent test labs. If you encountered it referencing a specific product or program, check that source directly rather than treating it as an industry-wide standard.

Will WD-40 clean solar panels?

No. WD-40 is a petroleum-based lubricant and solvent, not a cleaning agent designed for photovoltaic glass, and its chemistry falls well outside the mild, pH-neutral range that module manufacturers recommend. Using it risks leaving an oily residue that attracts dust and can interfere with coatings.

Can I use Dawn dish soap to clean solar panels?

Dish soap is not formulated for PV glass and can leave a film that attracts dust after it dries, which is the opposite of what a low-residue cleaner is supposed to do. Purified water with a manufacturer-approved, pH-neutral detergent is the safer choice when soap and water alone will not cut through soiling.

Why do some cleaners damage solar panel coatings?

Chemicals outside the roughly 6.5 to 8.5 pH range that most manufacturers approve can chemically etch anti-reflective coatings or corrode frame metal. Fraunhofer CSP testing confirmed this with real numbers, finding that some commercial cleaners permanently reduced module output by as much as 5.6%.

Sources