How to clean solar panels in NZ (and how often you need to)

Do solar panels need cleaning in NZ?

Less than people expect. MySolarQuotes says panels tilted at 10° or more self-clean in the rain, removing the majority of dirt and debris, so most pitched NZ roofs stay reasonably clean. Rain won't shift everything, though: salt spray, bird droppings, lichen and leaf litter build up, and those are what a wash is for.

Flat or low-pitch installs are the exception. Water sits on them and leaves a dirty line along the bottom edge of each panel, so they need attention more often.

How often should I clean my solar panels?

Once a year is the usual recommendation (MySolarQuotes), and less if they look clean and your output is where it should be. Check more often if you live near the sea, under trees, near a busy road or gravel driveway, or anywhere birds gather, because salt, sap, dust and droppings stick where rain can't move them.

• Coastal homes: salty grime builds up regularly, so look at them a few times a year.
• Under trees: leaves and sap collect along the frames and bottom edges.
• Rural and dusty sites: dust from roads, paddocks and harvest settles and bakes on in summer.
• Birds: droppings block light on individual cells and don't wash off in rain.

How do I clean solar panels safely?

Use plain water and a soft brush or non-abrasive sponge, ideally from the ground with a long-handled brush and a hose. Abrasive cleaners can scratch the glass. Never walk on the panels, and don't go on the roof without proper safety equipment: if you're not comfortable at height, a professional cleaner is the safer choice.

1. Pick a cool, overcast morning or evening. Cold water on hot glass is best avoided, and panels in full sun are hot to touch.
2. Hose the panels from the ground to loosen dust and droppings.
3. Work over them with a soft brush or sponge on an extension pole, using plain water.
4. Rinse off. Leave stubborn lichen or baked-on droppings to soak rather than scrubbing hard.
5. Check your monitoring app over the next sunny day to see the difference.

MySolarQuotes notes the system can stay on while you clean, but that DC electricity is still running through the panels even when it's off. Don't touch damaged panels, cracked glass or loose cables; call your installer.

Avoid pressure washers, scourers, solvents and household detergents that leave a film. If your panel manufacturer's manual says anything different, follow the manual: some warranties name approved cleaning methods.

What else does solar maintenance involve?

Very little. Watch your monitoring app, keep panels clear of shade from growing trees, and look at the inverter's display for error lights. EECA says your installer should talk you through maintenance and cleaning when the system goes in and leave you the manuals, so those are the first place to look for your system's specific needs.

• Compare this month's output with the same month last year in your app. A steady drop with clean panels is worth a call.
• Trim trees that start shading the array. Shade on one panel can pull down a whole string on a string inverter.
• Check the inverter for warning lights, and keep its vents clear.
• Have the system checked after storm damage or if anything looks loose.

How long do solar panels last in NZ?

Harrisons Solar says most panels last at full capacity for over 25 years, and that after 25 to 30 years output commonly sits 10% to 20% below the original rating. EECA's minimum warranties to look for are 10 years on the panels as a product, 5 years on a string inverter, 10 on microinverters, and 5 on workmanship.

The inverter is the part most likely to need replacing during the life of the panels, which is why its warranty length is worth comparing between quotes. See how to read a solar quote for the rest of the checklist.