SolLab technical team - Installers with UDT and SEP certificates - More than 1,000 installations in Pomerania since 2011. - Observations from service reviews 2024-2025
Dirty panels are money thrown down the drain - literally. With an RCEm of £0.132/kWh and a grid price of £1.20/kWh, every kilowatt hour lost through dirt costs you almost as much as an evening bought from the grid. In this article, we explain how much you are really losing, how to wash your photovoltaic panels so as not to spoil your guarantee and why in Pomerania the issue is slightly more complicated than everywhere else.
How much are you really losing on dirty panels?
The answer depends on the degree of soiling. Light road dust reduces performance by 3-5%. Vegetation pollen in spring (especially birch and grass) - up to 10%. Bird droppings on one cell - a localised hot-spot that can reduce the whole string by 20-30%. Thick layer of industrial dust or salt spray after winter in Pomerania - up to 25%.
|
3–5% loss of efficiency with light dust - often invisible to the naked eye |
20–25% maximum loss in heavy soiling or hot-spot from bird droppings |
~£300 estimated annual installation loss of 8 kWp in the absence of washing (according to SolLab data) |
Source: NREL (National Renewable Energy Laboratory) research, SolLab's own observations from measurements before and after washing
One wash of an 8 kWp installation can recover 200-400 kWh per year. With autoconsumption (£1.20/kWh), this PLN 240-480. When selling to the grid (PLN 0.132/kWh) - only PLN 26-53. This is another argument in favour of consuming the energy produced on site, not feeding it back into the grid.
Rain is no substitute for washing. This is the most common myth among PV owners. Rain washes away loose dust, but it does not remove bird droppings, salt (in Pomerania), pollen or dried dust from construction sites and roads. After rain, hard water stains also remain on the glass of the panels - which, when dry, form a layer of mineral deposits that block light.
When to wash photovoltaic panels - and how many times a year?
Most panel manufacturers recommend washing 1-2 times a year. In practice, the optimum frequency depends on the location:
| Location/conditions | Recommended frequency | The most important date |
|---|---|---|
| House away from busy roads and trees | 1x per year | Spring (April-May) |
| House near road, farmland | 2x per year | Spring + autumn |
| Coastal zone (Tricity and surroundings) | 2-3x per year | Spring + summer + autumn |
| Installation with pigeons or large trees | 3-4x per year | After each breeding season |
| Installation after a hailstorm or sandstorm | Immediately | Immediately after the incident |
Pomeranian specificity - salt and birch pollen: In coastal areas (Tricity, Sopot, Gdynia Orłowo, Władysławowo), the air contains microscopic sea salt crystals which, when dry, form a sediment that is difficult to remove. In addition, May in Pomerania is the peak pollen season for birch trees - panels can become covered in a yellow layer of pollen within 2-3 days. Owners of installations in the Tri-City should plan their first cleaning not in June, but as early as mid-May.
How to clean photovoltaic panels - step by step
Step 1 - Choose the right moment
Wash only in the morning (before 9am) or evening (after 6pm). Never in full sunlight - hot panel glass in contact with cold water may crack (thermal shock). Optimum air temperature: 10-22°C. Do not wash in freezing weather or immediately before forecast rain.
Step 2 - Prepare the equipment
What you need: soft microfibre cloth or non-abrasive sponge, bucket of clean lukewarm water, optional telescopic mop for cleaning the panels (£40-80 in DIY stores).
What not to use: hard bristle brushes, abrasive cleaners, chlorine detergents, vinegar (destroys frame seals).
Step 3 - Soak and wait
First, gently dampen the whole panel with clean water - give a moment (2-3 minutes) to soften dried dirt, especially bird droppings. Never scrape off dry dirt - they scratch the anti-reflective glass with microscopic nicks.
Step 4 - Wash with movements along the panel, not in circles
Wash in a horizontal motion from top to bottom. Circular movements loosen dirt particles and can cause micro-scratches. Pay particular attention to the edges and corners - this is where deposits take the longest to build up.
Step 5 - Rinse generously and allow to dry
Rinse the panels with plenty of clean water. Especially important in Pomerania: rinse off salt deposits thoroughly, do not let them dry on the panel. Do not wipe dry - microfibre can leave microscratches. Allow to dry naturally.
What absolutely not to do - mistakes that cost a guarantee
- Pressure washer aimed directly at the panel - Pressure above 40 bar can penetrate the frame seals and destroy the laminate from the inside. Several manufacturers prohibit the use of pressure washers altogether. If you do use one - keep at least 30 cm from the surface and use a fan tip
- Cleaners with alcohol, acetone or ammonia - damage the anti-reflective coating and seals
- Scraping dried stains with a metal object - scratches on anti-reflective glass are permanent and reduce performance forever
- Washing during production - in the midday sun - thermal shock, risk of glass breakage
- Walking on panels - frames and links are not designed for point loads
Check your manufacturer's warranty card. JA Solar, Jinko Solar and most Chinese manufacturers require washing according to their guidelines as a condition for maintaining the performance guarantee. Failure to wash regularly can be grounds for refusal to accept a claim for a drop in output. Panel maintenance guidelines are also published by International Energy Agency.
Panel cleaning water - does it matter what kind you use?
Yes - and more than you think. Hard water (high in calcium and magnesium) leaves white deposits when it dries, which block light and are difficult to remove. In the Tri-City, the hardness of tap water is around 11-15 German degrees - that's medium-hard water.
- Best option: demineralised (deionised) water - leaves no residue. Available in water dispensers or as a professional cleaning service
- Good option: Tap water + final rinse with soft water or rainwater
- Avoid: waters from the Baltic Sea or from wells with a high iron content - they leave stains that are difficult to remove
Professional installation washing uses deionised water filtration systems - after such washing, the panels dry without any deposits. If you have an installation of more than 6 kWp and don't want to risk mistakes when washing on the roof, it's worth considering having one wash a year together with a technical inspection. Two in one - clean panels and peace of mind about the condition of the installation.
Summary - washing photovoltaic panels at a glance
- Dirty panels lose 3-25% performance - for an 8 kWp installation, between £200 and £400 per year
- Rain is no substitute for washing - only removes loose dust, not salt deposits, pollen or bird droppings
- In Pomerania, wash 2-3 times a year - first spring cleaning preferably in mid-May
- Wash in the morning or evening - never in direct sunlight, risk of thermal shock
- Do not use pressure washers directly, hard brushes or agents with acetone - risk of loss of guarantee
- Demineralised water is the best choice - leaves no residue
Panel cleaning + SolLab technical inspection - one order, two services
We wash the installations with demineralised water, without the risk of deposits. On occasion, we check the condition of MC4 connectors, inverter and DC wiring. We operate in Gdansk, Gdynia, Sopot and the whole of Pomerania.
Make an appointment for cleaning + maintenance → +48 608 435 001
FAQ - Cleaning of photovoltaic panels
How often to wash photovoltaic panels?
Minimum once a year - in spring after the pollen season. In the coastal area (Tricity and surroundings), we recommend 2-3 times a year due to salt deposits. If there are nesting birds under the installation - after each breeding season, i.e. every 3-4 months.
Does rain wash photovoltaic panels?
Partial. Rain removes loose dust, but does not wash away bird droppings, salt deposits or pollen. After rain, hard water stains are often left on the panels which, when dry, form a light-blocking deposit. Cleaning once a year is necessary even with regular rainfall.
What to clean photovoltaic panels with - which cleaning agents?
Clean water (preferably demineralised) and a soft microfibre cloth are best. If you use a cleaner, choose products dedicated to PV panels with a neutral pH. Avoid products with alcohol, acetone, ammonia and chlorine - they damage the anti-reflective coating and frame seals.
Can photovoltaic panels be cleaned with a pressure washer?
With great caution. Some manufacturers completely prohibit pressure washers under the terms of the warranty. If you use - maximum pressure of 40 bar, minimum distance of 30 cm, fan tip (not point). Never direct the jet directly at right angles to the edges of the panel.
When is the best time to wash photovoltaic panels?
In the morning before 9 a.m. or in the evening after 6 p.m. - never in full sunlight. Hot glass and cold water risk thermal shock and cracking. Best annual date: May, after the birch pollen season, before the panels warm up to summer temperatures.
How much does it cost to wash photovoltaic panels?
Self-cleaning costs only time and water (optional £40-80 for a telescopic mop). Professional washing of a 6-10 kWp domestic installation costs £200-400. This price usually includes washing with deionised water and a basic inspection of the condition of the panels. When commissioned together with a technical inspection, it is often cheaper than two separate services.
