Solar panel cleaning in Wellington: when it's worth it, when it's not
Solar panels lose 5–25% output when dirty. Wellington gets salt, bird droppings and pollen. When cleaning pays back, when it doesn't, what method works.
Solar panels lose 5–25% of their output when dirty. Whether cleaning pays back depends on how dirty they are, your system size, and your power buyback rate.
The right method is low-pressure rinse with deionised or rainwater, NEVER detergents, NEVER high-pressure. Cleaning frequency: annually for most Wellington homes, twice-yearly for coastal or under-tree properties.
- 5–25%output loss when dirty
- 12 motypical Wellington cleaning interval
- 6 mocoastal or tree-covered properties
- $0extra detergent, water only
Solar panel installation in Wellington has roughly doubled over the past five years, and most homeowners get the same advice from the installer at handover: “just rinse them with a hose every now and then, you’ll be fine.” For most flat-roof installations in clean inland suburbs, that’s true. For everyone else, it isn’t.
This guide is the honest one. When cleaning your panels actually pays back, when it’s a waste of money, and what method to use if you decide it’s time.
How dirty panels lose output
The physics is simple. Solar panels generate electricity by absorbing photons. Anything sitting on top of the glass, dust, pollen, bird droppings, salt residue, lichen, leaf litter, blocks photons from reaching the photovoltaic cells underneath.
The loss range across the industry is 5% to 25% of rated output, depending on:
- How dirty the panels are. A light dust film: 5–8% loss. Heavy bird droppings or a layer of pollen + salt: 15–25%.
- Where on the panel the dirt sits. A single bird dropping in the middle of a panel can disable a full string of cells if the panel uses series wiring (most do). This is disproportionate to the area covered.
- How much rain you get. Heavy rain rinses some grime off naturally. Wellington’s frequent showers do help, but only with water-soluble dust. Salt and bird droppings stay put.
For a typical 6kW Wellington residential system generating roughly 6,500 kWh per year, a 15% loss is around 1,000 kWh of lost generation annually. At today’s buyback + offset rates, that’s between $200 and $350 per year of lost value.
When cleaning pays back, when it doesn’t
Pays back fast
Coastal-Wellington homes (Lyall Bay, Island Bay, Seatoun, Eastbourne), salt residue builds quickly.
Under deciduous trees, leaf debris and bird droppings.
System > 5kW, output loss adds up to real money.
Visible dirt or streaking, you can SEE the grime on the panels.
Probably not worth it
Sheltered inland suburb (Karori, Khandallah, parts of the Hutt) where panels look clean from the ground.
Steep-pitch panels >25° where Wellington rain self-cleans most contaminants.
System < 3kW, output loss is real but the absolute dollars are small.
Just installed (< 12 months), early-life cleaning usually unnecessary unless visibly grimy.
The honest rule of thumb: if you can see the panels are dirty from the ground, they’re costing you money. If they look clean, leave them alone for another year.
Wellington’s specific contamination profile
Wellington panels deal with three primary contaminants the installer’s manual doesn’t always mention:
Salt spray. Coastal southerlies carry sea-salt particles miles inland. Properties within 1 km of the south coast (Owhiro Bay, Island Bay, Lyall Bay, Seatoun) get measurable salt deposition on glass and frames within months. Salt isn’t just a soiling problem, it’s slowly corrosive to the aluminium panel frame and the wiring connectors. Annual salt-clearing is genuinely useful, not just cosmetic.
Bird droppings. Wellington’s gull and tūī populations are healthy and inclined to perch on roof ridgelines. A single bird dropping on a panel can shadow a whole cell string, disproportionately reducing output. Bird droppings also etch the glass surface over time if left long enough.
Pollen and pohutukawa-flower debris. December–January, Wellington’s flowering season, deposits a sticky pollen-flower-stamen mix on every flat surface in the region. Doesn’t wash off with rain. Needs an actual rinse.
Why this matters more in Wellington than in Auckland or Christchurch: wind. Wellington's wind carries contaminants further inland than any other major NZ city, and deposits them more aggressively because of the angle most southerlies arrive at. Your inland-suburb panels are dirtier than you think.
How to actually clean solar panels, and what NOT to do
There’s a right way to do this, and a list of wrong ways that void manufacturer warranties.
What works
Low-pressure water rinse, deionised water preferred (rainwater is the next-best substitute). A garden hose on low pressure, working from the bottom edge up to the top, is enough for most light contamination. For stubborn residue, a soft microfibre wash mitt on an extension pole.
Time of day matters. Early morning or evening, when the panels are cool. Cleaning a hot panel with cool water risks thermal shock, micro-cracks in the glass over time.
Pure water only. No detergents, no glass cleaner, no vinegar. Anything left behind by the cleaning solution creates a residue that attracts more dirt and reduces output.
What doesn’t work (and voids warranties)
Never use a water blaster on solar panels. Most residential water blasters run 2,500+ PSI. Solar panel glass is tempered but the silicone sealing around the panel edge is not, high pressure forces water past the seal and into the cell layer. This is a common cause of warranty disputes, most major panel manufacturers exclude pressure-cleaning damage from their warranty cover. Check your own installer documentation for the exact wording.
Don’t use abrasive pads or scrubbers. Even one pass with a kitchen scourer creates micro-scratches that scatter light and permanently reduce output.
Don’t walk on the panels. They’re not load-rated for body weight. Each footstep can crack cells you can’t see from outside.
Don’t clean if you can’t access them safely. This is the single biggest reason DIY solar cleaning is rarely worth it for Wellington two-storey homes, the access is the dangerous part, not the cleaning.
Frequency: what’s realistic
The honest answer varies by exposure:
| Property type | Recommended frequency |
|---|---|
| Coastal Wellington (1km from coast) | Every 6 months |
| Inland Wellington, mature trees overhanging | Every 6 months |
| Inland Wellington, open exposure | Every 12 months |
| Newly installed, clean inland | First clean at 18 months |
| Steep pitch (>25°), no trees, inland | Every 18–24 months |
If you’re booking a house wash anyway, the timing is convenient: solar panels rinse cleanly during the post-wash water-only rinse, and it adds maybe 15–20 minutes to a residential house-wash job.
DIY vs hire: the honest framing
This isn’t a “you must hire a professional” pitch, for a single-storey Wellington home with safe roof access, ground-rinse-from-hose is a reasonable Saturday job. The cleaning itself isn’t difficult.
What makes solar cleaning a frequent professional booking is the access. Two-storey homes, steep-pitch roofs, slippery moss-affected tiles, and the fact that working on a roof solo is a Worksafe-flagged risk all push it toward a hired job.
If you’re going to DIY:
- Use a long-handled water-fed pole from the ground if possible, never go on the roof if you can avoid it
- Wait for an overcast morning (cool panels, low UV, less slip risk)
- Tell someone you’re up there
- Use a harness if you can’t avoid the roof
If you’re going to hire it out, the typical cost in Wellington runs $80–$150 for a residential 6kW system as part of an existing house wash, or $150–$280 as a standalone solar-only clean. Standalone is more expensive because of the setup time.
What James does
Solar panel cleaning is included in the house-wash service if you mention it when booking. Method is low-pressure deionised water on a soft wash mitt, cool-panel timing, ground-pole where reachable, harness-and-safety-line for roof access where required. Public liability covers any damage during the work, and James photographs before and after as standard.
For standalone solar-only jobs, the call-out is a flat fee plus per-panel cost, generally cheaper than booking a roof contractor for the same job because the gear and chemistry are already in the van.
Get a quote or check the solar panel cleaning service for the detail.
James, Clear Water Blasting Services.
Written by James · Clear Water Blasting Services
Owner-operated since 2001 from Johnsonville. James does every quote and every job himself across Wellington, the Hutt, Kapiti, Porirua and the Wairarapa.
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