How often should you clean rooftop solar panels and check the inverter?

The short answer

There is no single interval. LONGi's panel manual says to clean a module whenever dirt covers the colour of the cells, and suggests at least every 40-50 days in rainy areas and every 20-30 days in dry areas with little rain. SMA's inverter manual has a qualified person check the inverter for dust every 6 to 12 months, depending on how dusty the site is, and check the fans every 12 months. Both are manufacturer guidance for their own products, not a legal requirement. Your own manuals come first.

Panels: when to clean

The LONGi operation and maintenance manual (written for all LONGi modules, and framed largely around power stations) says dust, bird droppings, ice and snow reduce output, and that partial shading can cause hot spots. Its rules:

• A module must be cleaned when dirt partly obscures the cells or covers their primary colour.
• The customer should judge the cleaning cycle from the actual site. For reference it gives at least once every 40-50 days in rainy areas and at least once every 20-30 days in dry areas with little rain.
• On bifacial modules, it recommends cleaning the back at least once every half year. It does not recommend cleaning the back of a mono-facial module.

That large-site framing means a home roof may not need to follow the day counts, but the "clean when visibly dirty or shaded" rule applies to any LONGi module. Other makers' manuals were not read for this guide.

Panels: how to clean

From the same manual:

• Ordinary mains water can be used. Avoid hard water, because minerals deposit on the glass over time.
• The water and the module should not differ in temperature by more than 10 °C, and the manual says not to clean when the ambient temperature is below 5 °C, to avoid freezing and cracking the glass.
• Clean in the early morning, at dusk or on a rainy day, not in strong sun. The manual recommends irradiation of 200 W/m² or less, and warns about electric shock because modules still produce voltage on cloudy days.
• Start dry: sweep with a dry duster or soft cloth. Only if deposits remain, use water with a soft brush or non-woven cloth.
• If you use pressurised water, the pressure at the module surface must not exceed 0.7 MPa.
• Use glass cleaner or alcohol only where water cannot do the job, then rinse.

It also lists what not to do: do not use blades, metal scouring tools or abrasives; do not use steam, acids, alkalis or strong solvents; do not step on the modules; do not splash water on cables or connectors; do not clean modules with broken glass or exposed cables; and do not work in strong wind, heavy rain or heavy snow. For snow, it says to use a soft tool and remove it evenly, never to pour hot water on the modules, and never to force off frozen snow or ice.

Panels: a thermal check

The LONGi manual suggests an infrared thermal-imager check once every half year for stations that have the equipment, in irradiation of at least 600 W/m² and wind of 2 m/s or less. A temperature gap of 30 °C or more between the hottest and coolest cells of one module is flagged as abnormal. First rule out shade or dirt; if the module still overheats, the manual says to mark it and contact the manufacturer. This is a job for your installer, not a DIY step.

The inverter

SMA's servicing schedule (the page does not name the model; its address suggests a Sunny Tripower series) lists, for a qualified person:

• Check the temperature and dust contamination, and clean the enclosure if needed: every 6 to 12 months, depending on the site's dust content.
• Check that the air inlet and outlet are clear: every 6 to 12 months.
• Check for fan event messages or unusual fan noise, and clean or replace the external fans if needed: every 12 months.
• Check cable glands are sealed: every 12 months. Check cable connections are secure and undamaged: every 6 to 12 months.

On a separate SMA page for a storage inverter, reduced fan performance can be restored by cleaning with a soft brush, a paint brush or a damp cloth, and SMA warns that compressed air can damage the fans. That advice is for that SMA product only; I did not read other brands' pages (including Fronius and Huawei), and some brands' guidance differs.

Before you rely on this

This is guidance from one panel maker and one inverter maker. Intervals for your system, and who is allowed to open the inverter, depend on your model and your installer's terms. Skipping the manual's cleaning rules can also matter for the module warranty, so keep the manual.

Track it in Epimeleia

Add the panels and the inverter as separate items, attach both manuals, and set two reminders: a visual panel check at the start of each dry season, and a dust and fan check for the inverter every 6 to 12 months, as your manual states.