Solar Panel Cleaning

Easy does it on the glass.

Solar panel cleaning across Horowhenua and the Kāpiti Coast, done slowly and carefully. Plain water and a soft brush on a long pole, worked from the ground where we can, and nobody standing on your panels. If yours don't need a clean yet, we'll tell you.

Get a free quote Do mine need it?
Do they even need it?

Honestly? The rain does a lot of the work.

Here's the straight answer. Round here, the rain does a lot of the cleaning for you, and EECA says a clean about every 12 months can be enough for most homes with good rainfall. Places by the beach, under trees or popular with the local birds may want one more often.

NIWA's 1981 to 2010 averages put Levin at about 1,160 mm of rain a year and Paraparaumu Airport at about 1,010 mm, with a millimetre or more falling on over 100 days a year at both. The angle helps too. Trina recommends tilting its panels at least 10 degrees so rain can wash the dust off, and Canadian Solar says panels tilted 15 degrees or more generally may not need cleaning, because rain has a self-cleaning effect. Current Generation, an NZ installer, says typical NZ roof angles are between 15 and 35 degrees.

Rain has its limits, though. A 2024 study led by researchers at the German Aerospace Center (DLR) points out that most earlier studies find rain often only partly cleans panels, and that light rain can even leave them dirtier. It also says bird droppings, pollen and similar stuff are tougher for rain to shift than ordinary dust. Then there are the dry spells, when the rain stays away. A dry spell here means 15 days or more with under a millimetre of rain a day, and NIWA says the Wellington region averages two a year, mostly in summer, lasting around 19 days.

So for most homes, solar panel cleaning isn't an every-three-months job. Have a look from the ground once a year, and sooner if you're near the beach, under trees, or the gulls have claimed your roof.

Sources: EECA, make the most of your solar system, NIWA climate normals 1981 to 2010 for Wellington and Manawatū-Whanganui, Trina Vertex user manual, Canadian Solar installation manual, Current Generation on NZ roof pitch and DLR, cleaning of PV modules through rain

EECA's rule of thumb

How often, roughly

  • Most homes with good rainfall: a clean every 12 months can be enough.
  • Coastal or dusty spots: a wash every 3 or 6 months may be needed.
  • Shady trees: trim back the ones that shade your panels.
  • How to wash: plain water or a tiny bit of detergent, and never hot water, pressure washers, abrasive brushes or steel wool.

EECA is the government's Energy Efficiency and Conservation Authority. This is general guidance, not a rule, and your panel maker's manual has the final say on how your panels get cleaned.

How we clean them

Gentle is the whole job.

Panel makers don't all agree on how their panels should be cleaned. So we start from the strictest common ground, and only go further if your panel's own manual says it's fine.

Plain or purified water

Nothing added. REC prefers de-ionised water, and Jinko warns that hard, mineral-heavy water can leave deposits on the glass. Confirm: your water setup, for example filtered tap water or purified (RO or de-ionised) water, and whether you test it on each job

Soft brush, long pole

A soft brush on a water-fed pole, worked from the ground wherever the panels can be reached. Nothing scratchy and nothing metal. Confirm: how far your pole reaches, and what happens when panels can't be reached from the ground

Cool panels only

Early morning, late afternoon or a grey day. REC says panels run about 20°C hotter than the air, and cold water on hot glass can cause cracks. Trina and LONGi both limit how far the water temperature can be from the panel's.

No pressure washer

No blaster, no steam and no scraping. Bird mess gets soaked soft and wiped, never chipped off. Canadian Solar says damage from scraping or rubbing off dry dirt voids its warranty.

No chemicals, by default

Water does the job. If something stubborn needs more, we only use what your panel maker's manual allows, and only once you've said yes.

Feet off the panels

Nobody stands, kneels or leans on a panel. REC, Jinko, Trina, LONGi and Canadian Solar all say the same thing.

Confirm: every point above matches how you'll actually work, before this page goes live

Sources: REC quick guide to cleaning, Jinko installation manual, Trina Vertex user manual, LONGi maintenance manual and Canadian Solar installation manual

After: same panels, same spot, after the clean
Before: panels with bird droppings, dust or salt film on the glass
Before
After

Placeholder: shoot the same panels from the same spot, before and after a clean, and they drop in here.

What the makers say

Your panel maker wrote the rules.

Tell us your brand

Panel makers publish their own cleaning instructions, and the ones we read tie the warranty to following them. Here's what five makers say. We check the manual for your exact panel before we pick up a brush.

REC

Garden hose, and no harder.

  • De-ionised water is best. Rainwater or tap water is the fallback, as long as there's no grit in it.
  • A soft sponge, microfibre cloth or soft brush, on a pole if you like.
  • No pressure washers, steam cleaners, blades or metal scourers. REC says they'll void the warranty.
  • No standing, walking or leaning on panels. REC also says it doesn't provide warranty for the application of any sprays or treatment.
Jinko

Water only, thanks.

  • Preferably cleaned once a year, and more often where it's dusty.
  • Early morning or late afternoon, when the panels are cooler. Its Australian manual says cool to the touch.
  • No chemicals. Jinko says they may affect the warranty.
  • Never clean a panel with broken glass or exposed wiring, and never stand on one.
Trina

Mind the temperature.

  • Soft cloth, sponge or soft brush. Household glass cleaner only for grease.
  • Keep the water close to the panel's own temperature. Trina sets a tight range for the difference.
  • Not in the heat of the day, in strong wind or in heavy rain. No steam cleaners, and no alkaline or strong acidic solvents.
  • No water on the back of the panels or the cables, and no stepping on them. Installed within 50 m of the sea? Trina says to consult them so the warranty stays valid.
LONGi

There's no off switch.

  • Town supply water is fine. Soft brushes, soft sponges and soft cloths.
  • Clean early, at dusk or on a dull day, and not when it's below 5°C. Don't cast shadows across the panels while you work, because shade can cause hot spots.
  • Don't splash the cables or wash the junction box directly.
  • Panels have no switch and stay live, even in dim light. Never clean one with broken glass or exposed cables.
Canadian Solar

Tilted panels may not need it.

  • Panels tilted 15 degrees or more generally may not need cleaning, because rain has a self-cleaning effect.
  • If they're dirty, water and something non-abrasive, in the cool part of the day.
  • Never scrape or rub off dry dirt. Damage from doing it voids the warranty.
  • No chemicals it hasn't approved, and no standing on panels. It says daylight voltage in an array is enough for a lethal shock.
So what's the rule?

They don't all agree.

  • Detergent is the big split. Jinko says none, REC allows a mild washing-up liquid rinsed straight off, Trina allows glass cleaner for grease, and Canadian Solar only what it's approved.
  • Pressure limits vary a lot too. We stick to the gentle end.
  • All five agree on soft, non-abrasive tools and nobody standing on panels. That's where we start, with plain water on top.
  • Manuals change by model, edition and country. The one for the panel on your roof is the one that counts.

Confirm: you check the maker's cleaning section before every job, and keep a one-page cheat sheet for each brand you meet

Sources: REC quick guide to cleaning, Jinko global installation manual (2024) and Australian edition (2023), Trina Vertex user manual (2025), LONGi operation and maintenance manual (2024) and Canadian Solar installation manual (US edition, 2026). These are the editions we could find, and the rules for your exact panel may differ.

The serious bit

Panels are live whenever it's light.

Solar panels make electricity whenever light hits them, grey days included. Switching the system off at the inverter doesn't change that.

Trina and Canadian Solar both say the voltage in an array in daylight is enough to kill, and LONGi says panels have no off switch at all. Trina adds that cracked or broken panels are a shock hazard, and a worse one when they're wet.

So we leave the electrics alone. Water never gets aimed at junction boxes, connectors, cabling or the back of a panel, and we don't touch, unplug or move any of it.

Some makers want the array disconnected from the rest of the system before cleaning, and say connectors must never be pulled apart under load. That's a job for you or your electrician, not us. Confirm: your isolator and electrics policy, for example the owner or their electrician switches off where the maker asks for it, and you never touch the switches, connectors or wiring yourself

Then there's the height. WorkSafe says fall risks have to be managed from any height, with no minimum height, which is a big part of why we work from the ground first. Confirm: whether you'll go up on roofs for solar at all, and the access gear and training you'd use if so

Sources: Trina Vertex user manual, Canadian Solar installation manual, LONGi maintenance manual, Jinko installation manual and WorkSafe, working at height

Stop signs

If we spot any of these, we stop and tell you.

  • Cracked or shattered glass.
  • Loose, hanging or exposed wiring.
  • Burn marks, or wet or damaged connectors.
  • Panels too hot to touch. We wait, or come back another day.

Jinko and LONGi say never clean a panel with broken glass or exposed wiring, and Trina says to check for cracks, damage and loose connections first. A damaged panel stays dry, and you get a heads-up to call your installer or an electrician.

Confirm: your full decline-or-stop list, for example cracked glass, exposed or hanging wiring, wet or damaged connectors, brittle roofing or skylights, roofs too steep to work on, wet, frosty or windy days, hot panels, and jobs where the maker wants the array switched off and nobody's there to do it

Photo: a solar array with a tree or chimney shadow across part of it, from the ground

Sometimes a clean isn't the fix.

A clean helps when the glass is visibly grubby, there's bird mess or sap on it, or your output dipped after a long dry spell. If none of that's going on, dirt probably isn't your problem, and we'll say so.

We couldn't find any New Zealand measurement of how much power dirt actually costs a home system, so you won't see a percentage on this page. Got a monitoring app? EECA suggests using it to spot problems. Check a sunny day before the clean against a similar day after, and judge for yourself.

Shade

A tree, a chimney or the neighbour's new extension throwing shade on the panels. Water won't fix that. EECA's advice is to trim trees that shade them.

Faults

Cracked glass, damaged cables or an inverter playing up. We'll tell you what we saw and point you to your installer or an electrician. We won't guess.

Low on a clean day

If the glass looks clean and output is still down, that's a question for your installer, not a cleaner.

Source: EECA, make the most of your solar system

Getting the roof or house done too?

The roof treatment stays off the panels.

Roof treatments and house wash mixes are chemicals, and panel makers don't want chemicals on their glass, connectors or cabling. REC's guide says it doesn't provide warranty for the application of any sprays or treatment. LONGi says any vegetation inhibitor used near panels mustn't be corrosive or oxidising and should stay off the panels. Jinko lists herbicides and cleaning agents, and Canadian Solar lists pesticides and abrasive cleaners, among the chemicals to keep off connectors and junction boxes.

So on a combined job, the chemical work goes on first and is kept off the glass, the cabling and the connectors. The panels get their plain-water clean after that. Confirm: how you keep treatment off the panels, for example working around them, masking, or doing that roof face on another day

Got a steel roof? COLORSTEEL's maintenance guide lists the areas under solar panels among the unwashed, high-risk spots that need more extensive manual washing, and says regular washing is required to maintain its warranty. Worth a mention when you book a roof treatment. Confirm: whether you wash the sheltered roof around panels, and how you keep water off the cabling while you do

Sources: REC quick guide to cleaning, LONGi maintenance manual, Jinko installation manual, Canadian Solar installation manual and COLORSTEEL maintenance recommendations

How it works

Panel cleaning starts with homework.

The more we know about your system, the better we can match the clean to what your panel maker allows. Here's what helps.

Panel brand and modelInstall yearRoof typeSingle or two storeyNumber of panelsWhen they were last cleanedMonitoring app, if you have oneA photo from the ground

Pop it in the "Anything we should know?" box on the form. Model not handy? Your installer's paperwork usually has it.

01

Tell us about them You

Send the details above with your address. A photo of the panels from the ground tells us a lot about access.

02

We read the fine print

We look up your panel maker's cleaning instructions before we settle on a method. If we can't work out what's on your roof, we won't promise a method until we can. Confirm: what you do if the brand or manual can't be found

03

Clean, then a quick note

A gentle clean on a cool morning or a grey day. Then you hear what we saw, like shade, damage, or any panel we left alone and why. Confirm: whether you send a short job note and before and after photos

What it costs

Priced on your system.

The number of panels is the starting point. Confirm: that solar is priced by panel count, as the bands below assume, and anything else that moves your price, for example storeys, access, heavy lichen or bird mess

Smaller system

Confirm: up to how many panels

$ to come

Medium system

Confirm: panel count range

$ to come

Larger system

Confirm: panel count range, and where it becomes a custom quote

$ to come

Added to another job

Panels done on the same visit as a house wash or roof treatment. Confirm: whether there's a combined price

$ to come

All prices include GST.

Two storeys, a steep roof or panels you can't see from the ground? Send a photo and we'll tell you straight whether it's one for us.

Solar questions, no spin.

Doesn't the rain keep solar panels clean?
Often, yes. Levin and Paraparaumu both get a millimetre or more of rain on over 100 days a year (NIWA), and Canadian Solar says panels tilted at 15 degrees or more generally may not need cleaning, because rain has a self-cleaning effect. EECA says a clean every 12 months can be enough for most homes with good rainfall. What rain is worse at shifting is bird droppings, pollen and other tougher stuff, and light showers can leave panels grubbier than before. That's usually what a clean is for.
How often should solar panels be cleaned?
There's no NZ-measured schedule, just guidance. EECA says every 12 months can be enough for most homes with good rainfall, and every 3 or 6 months for coastal or dusty spots. Jinko says preferably once a year, and REC says clean when you can see dirt on the glass. Our take: have a look at least once a year, sooner if you're by the beach, under trees or the birds love your roof, and clean when there's visible build-up or a dip in your monitoring app. Right on the water, within 50 m of the sea? Trina says to consult them so the warranty stays valid, so check your own maker's coastal rules too.
Will I get more power after a clean?
Maybe, but we won't promise a number. We couldn't find any New Zealand measurement of what dirt costs a home system, and anyone quoting you a big percentage should be able to show you where it came from. LONGi says dust and bird droppings reduce output, and that partial blockage can even cause hot spots, so a patch of bird mess is worth dealing with. The fair test is your monitoring app: compare a sunny day before the clean with a similar day after.
Will cleaning affect my panel warranty?
It can, if it's done wrong. Panel makers tie their warranties to following their instructions. REC, Trina and Canadian Solar all say the wrong cleaning can void it, and Trina says damage caused by failing to clean can too. So we can't promise anything about your warranty, that's between you and your panel maker. What we can do is read their cleaning instructions first and stick to them, which is why we ask for the brand and model. If your warranty matters to you, check with your installer as well.
Do my panels need to be switched off?
Switching off doesn't make them dead. Panels make voltage whenever light hits them, and LONGi says they have no off switch at all. Some makers, like Trina and Canadian Solar, want the array disconnected from the rest of the system before cleaning, so we go by your panel's manual. We don't touch switches, connectors or wiring ourselves. Confirm: who switches off when the maker asks for it, for example you or your electrician
Can't I just hose them down myself?
If you can reach them from the ground, sure. EECA's tips are a good start: plain water or a tiny bit of detergent, and no hot water, pressure washers, abrasive brushes or steel wool. Check your panel's manual too, since Jinko says no chemicals at all. Just don't climb up there and stand on them. EECA says you may need a contractor if the roof is steep or hard to get to, and that's where we come in.
When's the best time to clean them?
Early morning, late afternoon or an overcast day, while the panels are cool. REC and Jinko both warn that cool water on hot glass can crack it. We skip the midday sun, strong wind and heavy rain, which Trina rules out too, and LONGi says not below 5°C. Confirm: what happens if the weather turns on the day, for example you rebook at no charge
How much does solar panel cleaning cost?
It depends on your system, starting with how many panels you've got, and our pricing box above shows how it's set out. Confirm: your solar prices, so they go in the pricing box and on the prices page In the meantime, send us the brand and model, roof type, storeys and a photo from the ground, and we'll come back with a free quote for yours. The rest of our prices are on the prices page.
While we're there

The rest of the house, too.

All services

Roof Treatment

Moss and lichen treated at low pressure, and kept off your panels.

See Roof Treatment

Roof & Gutter Combo

A roof treatment and a gutter clean at one combined price.

See the combo

Gutter Clean

Leaves and gunk cleared, downpipes checked.

See Gutter Clean

House Wash

Low-pressure soft wash for the whole outside of the house.

See House Wash
Free quote

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