You've had your solar panels for a year or so. The app ticks along. Power's being generated. And at some point, you've probably wondered: do these things actually need anything done to them, or do they just keep working?
It's a reasonable question. The installer handed over the system and left. Nobody gave you a maintenance schedule. When you search online, you get "solar panels are basically self-maintaining" sitting right next to "get them professionally cleaned every six months." The gap between those two positions is where a lot of NZ homeowners get stuck.
This is what a professional solar panel service actually involves, what you receive at the end of it, and how to work out whether your specific installation needs regular professional care.
A thorough service should follow these steps.
Before anything gets touched, the technician does a visual inspection of the entire array. They're looking for cracked glass, wiring issues, frame damage, corrosion, bird nests, or debris that could affect drainage. This baseline matters. You need to know what you're starting with.
The cleaning uses soft-bristle brushes or microfibre cloths with purified or deionised water. Purified water matters as tap water leaves mineral residue on the glass, which blocks light and undoes half the benefit of cleaning. The technician applies gentle pressure only. High-pressure washing damages seals and the glass surface.
The process removes dirt, dust, bird droppings, lichen, pollen, and organic growth. On NZ installations, lichen deserves specific attention. Auckland's humidity creates conditions where lichen bonds chemically to the glass. Rain won't remove it. Specialist cleaning solutions are required.
While cleaning is underway, the technician also inspects frames and mounting hardware for corrosion, loose fittings, warping, or damage. Gutters and drainage areas around the panel array get cleared of debris.
After cleaning, the system gets a performance check to confirm it's generating correctly.
A professional service should end with a written condition report. This includes before and after photos, a record of what was found, documentation of what was done, and any issues flagged for follow-up. Ask for this as a matter of course. It's your maintenance record for the system, and it's what lets you track the panel's condition across multiple service visits rather than starting from scratch each time.
Professional cleaning generally doesn't include repairs or electrical work. If the inspection turns up a faulty inverter, damaged wiring, or a structural problem with the mounting, a good technician will document it and refer you to a qualified electrician or your original installer. Be cautious of any cleaning service that also offers to fix what they find; that's where the conflict of interest starts.
One to two hours on site, depending on array size and contamination level. A small residential array in reasonable condition takes less time than a larger system with significant lichen or heavy bird activity.
You can clean your own panels if you do it correctly. Soft brush, gentle water flow, no harsh chemicals. It's similar to washing a car properly.
The practical limits are real though. Tap water leaves mineral spots. Safe rooftop access requires the right equipment. And most people who clean their own panels won't also inspect frames, check mounting hardware, or verify that performance actually improved after cleaning. Those inspection steps are where the real value sits in a professional service.
Rain cleans panels on steep roofs reasonably well, assuming consistent rainfall and light contamination. That's the baseline where DIY and occasional professional cleaning may be sufficient.
Several environmental factors change this calculation. If your installation matches one or more of the following, professional cleaning on an annual or biennial schedule will likely recover more output than the service costs.
Anything under 10 degrees doesn't self-clean. Rain runs off too slowly to carry debris away. Light rain leaves dust as dried mud rather than washing it. Accumulation on flat-roof systems is inevitable, not a possibility.
Bird droppings reduce output by 10 to 15 percent immediately. They're acidic and bond to the glass, so rain doesn't shift them. Dust reduces output gradually. Droppings reduce it fast.
Seasonal pollen, sap, and leaf debris land on your panels. Research from the US National Renewable Energy Laboratory found tree pollen reduces panel efficiency by over 15 percent, and rain doesn't reliably remove it. This fact is important in NZ as generally our houses have a lot of trees and hedges in close proximity. Even if you don't have a lot of vegetation on your property, remember that the surrounding properties probably do. Pollen doesn’t respect property boundaries. Spring and autumn are worst.
Within roughly a kilometre of the ocean, salt spray accumulates on the glass and blocks light. It also accelerates corrosion of frames and mounting hardware. If metal fixtures around your home; railings, outdoor fittings, air conditioning units, rust faster than you'd expect, your panels are in the same environment.
Fine particles from cement and building materials accumulate faster than natural dust and are harder for rain to shift. If there's been active building work within a few hundred metres in the past 12 months, it's worth checking your panels.
Lichen growth happens across a wide range of suburbs, not just coastal or heavily vegetated areas. If your panels haven't been cleaned since installation and you're in Auckland, lichen is worth checking for.
Your monitoring app or inverter display is the first place to look. If output is noticeably lower than the same period last year and the weather pattern hasn't changed significantly, contamination is a likely cause.
From the ground, using your phone camera with zoom, you can often see white streaking from bird droppings, a visible film, or greenish patches from lichen. Significant visible contamination at ground level usually means measurable output loss.
Check the pitch of your roof visually. If your panels sit nearly flat or on a low-slope roof, rain self-cleaning won't be effective.
Look at what's around the roof. Trees that drop leaves or pollen onto your car are dropping the same material onto your panels. Nearby construction in the past year is worth noting.
Industry research across NZ and Australia puts output loss from dirty panels at 15 to 25 percent under typical contamination conditions. For heavily soiled panels; significant lichen coverage, persistent bird activity, or extended periods without cleaning; that figure can be considerably higher.
The loss is gradual and invisible. Your system still produces power. The monitoring app still shows numbers. The drop only becomes visible when you compare against expected output or a previous clean baseline.
Start with the Home Energy Health Assessment. It takes around three minutes and gives you a clear picture of where your systems stand. If professional solar cleaning is warranted, you'll know. If it's not, you'll know that too.
For most NZ installations, once every one to two years is a reasonable starting point. How often your specific system needs cleaning depends on your environment. Flat roofs, coastal locations, properties with nearby trees, and areas with significant bird activity all accumulate contamination faster than steeply pitched roofs in low-risk locations. Your monitoring app is a reliable guide. If output drops noticeably compared to the same period last year, contamination is a likely cause.
Rain helps on steeply pitched roofs with consistent rainfall and light contamination. It doesn't reliably clean flat or low-angle installations, where water runs off too slowly to carry debris away. It also won't remove lichen, which bonds chemically to the glass and requires specialist cleaning solutions. Bird droppings and tree sap are similarly resistant to rain. If you're relying on rain to maintain your panels, check whether your roof pitch actually supports that. Many NZ installations don't.
DIY cleaning with a soft brush, gentle water flow, and no harsh chemicals is valid for light maintenance on accessible, low-risk installations. The main limitations are tap water leaving mineral residue, rooftop access requiring proper safety equipment, and the absence of any inspection component. A professional service includes cleaning with purified water, inspection of frames and mounting hardware, a performance check, and a written condition report with photos. For installations in higher-risk environments, the inspection component is where the real value sits.
Dirty panels reduce output rather than causing immediate damage in most cases. Bird droppings are an exception; they're acidic and can degrade the glass surface if left long-term. Lichen, if left to establish and spread, can also cause surface damage over time. The more common consequence of neglected panels is gradual, invisible output loss. The system still runs. It just generates less than it should.
A condition report from a professional solar service should include before and after photos, a record of the contamination found, documentation of the cleaning carried out, and details of any issues identified during the inspection; frame corrosion, loose mounting hardware, wiring concerns. Anything outside the scope of a cleaning service should be flagged clearly for referral elsewhere. If a service doesn't provide this in writing, ask why. It's a basic professional standard, not an optional extra.
That depends on your installation. For systems in low-risk environments; steeply pitched roofs with consistent rainfall and no nearby trees or significant bird activity; the case for annual professional cleaning is less clear. For installations on flat roofs, coastal properties, or areas with trees, construction, or high bird activity, the output recovered from a professional clean typically exceeds the cost of the service.