How commercial solar owners can keep panel cleaning consistent with module warranties, based on NREL O&M best practices: methods, water quality and records.
Module Manufacturers' Instructions Come First. This Paper Summarizes NREL's PV O&M Best Practices On Approved Cleaning Methods, Water Quality, Methods To Avoid And The Records Commercial Solar Owners Should Keep.
Download PDFExecutive Summary
Owners of commercial solar arrays often ask whether cleaning can void a warranty. The governing document is always the module manufacturer's own installation and maintenance manual, which varies by product. What does not vary is the industry baseline: the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) publishes O&M best practices that tell operators to follow the manufacturer and set out which cleaning methods to avoid.
Key Points
- Manufacturer Rules Come First: "Follow the PV module manufacturer's recommendations with any array cleaning." NREL/TP-7A40-73822 §5.7.1
- Gentle Methods Only: Clean "with plain demineralized water and mild detergent recommended by the manufacturer." §5.7.1
- Methods To Avoid: "Do not use high-pressure water, brushes, or any types of solvents, abrasives, or harsh detergents." §5.7.1
- Warranties Shape Maintenance: Scheduled maintenance is often carried out to conform to manufacturers' recommendations "as required by the equipment warranties." NREL/TP-7A40-73822
- Keep Records: Record keeping and enforcement of warranties are core O&M functions. NREL/TP-7A40-73822
What Warranties Typically Say About Cleaning
Module warranty and maintenance terms differ by manufacturer, so this paper does not summarize any one brand. NREL's guidance is the practical rule: read the manual for the installed modules and follow it. NREL notes that preventive maintenance frequency is influenced by equipment type, site conditions and warranty terms, and is "often carried out at intervals to conform to the manufacturers' recommendations, as required by the equipment warranties." NREL/TP-7A40-73822, O&M functions
On rooftop systems there is a second warranty to protect: the roof. NREL states that roofs under warranty require annual preventive roof maintenance to maintain the roof warranty, and recommends identifying roof-warranty conditions, "including the selection of cleaning agents." NREL/TP-7A40-73822, roof considerations
NREL O&M Best Practices
NREL's Best Practices for Operation and Maintenance of Photovoltaic and Energy Storage Systems, 3rd Edition (NREL/TP-7A40-73822, December 2018) explains why cleaning matters: "Soiling reduces the energy output of the PV array and can lead to localized hot-spot failures if the soiling is uneven," so uneven soiling such as bird droppings should be addressed. §5.7.1
Cleaning "may be on a defined interval or 'condition based,'" with soiling measured by instruments to trigger a cleaning. Frequency may be seasonal, depending on local rainfall and dust. §5.7.1 The report lists sources that may call for a cleaning regimen, including construction dust, pollen, bird populations, diesel soot in cities and industrial sources such as kitchen exhaust. §5.7.1
Approved Methods And Water Quality
| Method | NREL Guidance |
|---|---|
| Water | Plain demineralized water |
| Detergent | Mild detergent recommended by the manufacturer; no harsh detergents |
| Tools | Bucket, strip cleaner and squeegee with overlapping vertical strokes, "in the same way window glass is cleaned on commercial buildings" |
| High-Pressure Water | Do not use |
| Brushes, Solvents, Abrasives | Do not use |
| Robotic Systems | Available for large systems; many require the system design to accommodate them |
Source: NREL/TP-7A40-73822 §5.7.1
Documentation To Keep
- The Module Manufacturer's Installation And Maintenance Manual For Your Exact Model
- Cleaning Dates, Method, Water Type And Any Detergent Used
- Before And After Photos, Especially Of Uneven Soiling Or Damage
- Roof Warranty Terms And Any Roof Maintenance Records For Rooftop Arrays
- Production Data Around Each Cleaning, If Monitoring Is Available
NREL lists record keeping and enforcement of warranties among the core operations functions of a PV O&M program. NREL/TP-7A40-73822 A cleaning log built around the manufacturer's manual is the simplest evidence that the array was maintained as the warranty expects.
Sources
- NREL, Sandia National Laboratory, SunSpec Alliance And SuNLaMP PV O&M Best Practices Working Group, Best Practices For Operation And Maintenance Of Photovoltaic And Energy Storage Systems, 3rd Edition, NREL/TP-7A40-73822, December 2018 (OSTI ID 1489002). osti.gov/servlets/purl/1489002
This paper summarizes published technical guidance for general information and is not legal advice. Requirements may change and vary by city; consult the current text, your local agency and qualified professionals.
