With water, a soft brush, and the right technique, most homeowners can clean their panels safely.
But in southern Spain the bigger challenge is knowing when to clean and which products permanently damage your panels. Get those details wrong and a routine clean can void your warranty.
Do solar panels really need cleaning?
Yes – and in southern Spain, more than most places in Europe.
In my experience at Marblanc Solar, dirty solar panels can lose 30% or more of their output. That is not a gradual decline you will barely notice. It’s a significant drop that shows up in your monitoring data.
The good news is that output recovers immediately after a proper clean. Leaving panels dirty for extended periods compounds the problem – hard water deposits and biological material bond to the glass over time and become progressively harder to shift.
How often should you clean your solar panels?
In southern Spain, twice a year is a minimum for most installations.
Properties near pine forests, or in areas regularly affected by calima weather patterns, often need three or four cleans a year. The best guide is your inverter monitoring app. A sudden output drop outside of a cloudy period is usually a sign that soiling is the issue – not a fault with the system.
Does rain clean solar panels?
Not reliably.
Rain removes loose surface dust, but in southern Spain it often makes things worse. After a calima event, rain mixes with the fine Saharan dust sitting on your panels and dries into a thin, cement-like layer. That does not rinse off.
The same happens with pine pollen in spring. Rain during a heavy pollen period does not wash it away – it smears the pollen across the glass in yellow-green streaks that cut light transmission across the whole panel surface.
What makes southern Spain different?
What is calima dust and what does it do to solar panels?
Calima is a weather phenomenon where Saharan dust is carried north across the Mediterranean and deposited across southern Spain.
It arrives fast. A clean set of panels can be coated in a visible layer of red-brown dust within a single afternoon. The event typically lasts 3–5 days. In extreme historical episodes, deposits have reached over 6.5 grams per square metre.
The dust is fine enough to settle into frame edges where rinsing alone does not reach it.
What about pine pollen?
Pine trees in southern Spain release pollen between the end of March and the beginning of May.
In areas with significant pine coverage, seasonal deposits can reach 300kg/ha – up to 30g per square metre. On its own, dry pine pollen rinses off with water. The problem comes when rain falls during the pollen season. The pollen bonds with moisture and forms yellow-green streaks across the panel surface that a standard rinse will not shift.
A manual clean is the only solution.
Soiling Type Quick-Reference
Common soiling types affecting solar panels in southern Spain – frequency, build-up speed, and cleaning urgency.
| Soiling type | When it occurs | How quickly it builds | Risk to output | Cleaning urgency |
|---|---|---|---|---|
| Calima dust | Year-round, peaks spring/autumn | Hours | High | Clean within days of event |
| Pine pollen | Late March – early May | Days to weeks | Medium–High | Clean after season, or sooner if rain coincides |
| Bird droppings | Year-round | Immediate | High – causes hot spots | Spot clean as soon as noticed |
| General dust | Year-round | Weeks | Low–Medium | Scheduled clean |
| Hard water deposits | After any clean with hard tap water | Builds over multiple cleans | Medium | Prevent with correct water treatment |
What equipment do you need to clean solar panels?
The basics are a soft-bristled brush or microfibre cloth, a telescopic extension pole, and a garden hose with a gentle spray nozzle.
The extension pole keeps you safely on the ground and gives you the reach to cover the full panel surface without climbing. Never use a pressure washer. the force blasts water past the panel frame seals and causes damage that is not always visible until output has already declined.
For water, distilled water is the safest choice for home use. It contains no minerals and leaves no deposits on the glass. At Marblanc Solar, we use a biodegradable water softening agent to treat tap water on every job — achieving the same result without transporting large volumes of distilled water to site.
What you need:
- Soft-bristled brush or microfibre cloth
- Telescopic extension pole
- Garden hose with a gentle spray nozzle
- Distilled water – or tap water treated with a biodegradable water softening agent
- Mild dish soap (only for stubborn soiling)
What to avoid:
- Pressure washers
- Household cleaning products (window cleaner, bleach, ammonia-based sprays)
- Water-repellent coatings such as RainX
- Abrasive cloths or brushes
How to clean solar panels: step by step
The process starts with the system off, the panels cool, and all loose debris brushed away dry before any water is introduced.
A gentle rinse from top to bottom removes the bulk of surface soiling. For stubborn residue – calima deposits, pollen streaks, bird droppings – a small amount of mild dish soap applied with a soft brush breaks it down without scratching the glass. A thorough final rinse removes all soap residue completely. No streaks. No product left on the surface.
Should you turn the system off first?
Yes – switch off via the main inverter or shutoff switch before introducing water.
The panels are weatherproof under normal conditions, but switching the system off removes any risk from an unexpected electrical fault. It takes less than a minute and is not worth skipping.
Hard water and mineral deposits: the hidden efficiency killer
Hard water leaves mineral deposits on the glass with every clean.
Most homeowners do not realise this is happening. The deposits scatter incoming light rather than letting it pass through to the solar cells. A panel cleaned with hard tap water over many months can perform worse than one that has simply been left alone – even if it looks clean to the eye.
Distilled water is the cleanest solution for home use. At Marblanc Solar, we treat our cleaning water with a biodegradable water softening agent on every job. If you are in an area with hard water this is an important detail.
Can you clean your own solar panels?
For a single-storey home with panels on a low-pitch roof and the right tools, yes.
For anything more complex, it becomes difficult quickly – and in some cases genuinely dangerous.
What about steep or multi-section roofs?
Steep roofs carry a real risk.
The tiles common across southern Spain can be slippery underfoot, and a fall from a roof causes serious injury. In our experience, most homeowners underestimate this until they are already on the roof. We have also worked on properties with multiple roof sections at different angles where some panels are simply unreachable from the ground – where safe access requires the right equipment and training.
A broken roof tile costs more to repair than a professional clean. The risk is not worth taking.
What happens if you use the wrong cleaning products?
The damage can be permanent.
Solar panels have specialised coatings on the glass – anti-reflective coatings that increase light transmission, and protective coatings that keep the surface weatherproof. You need to avoid:
- Window cleaners
- Bleach
- Ammonia-based sprays
- Most other household cleaning products
We have arrived at properties where a homeowner – or a window cleaner brought in to save money – has used the wrong products and stripped the anti-reflective coating from the panel surface. The glass looks clean. The output does not recover. The damage is not reversible.
Products like RainX or other water-repellent coatings cause the same problem. The panels already have manufacturer-applied coatings that do everything those products are designed to do. Applying something on top does not improve performance – it interferes with what is already there.
Use water. If needed, a small amount of mild dish soap. Nothing else.
Will it void your warranty?
Yes, it can.
Most panel manufacturers specify in their warranty documentation exactly how panels may be cleaned. Using unapproved products or methods – including pressure washing and household chemicals – is one of the most common grounds for a warranty claim to be rejected. If a window cleaner or non-specialist has cleaned your panels with the wrong products, contact your installer as quickly as possible.
Marblanc Solar Panel Cleaning Services
Southern Spain’s combination of calima dust, pine pollen and hard water makes panel maintenance more demanding than most of Europe. The wrong products, the wrong water, or an unsafe attempt on a steep roof costs more to fix than a professional clean.
As the lead for Marblanc Solar’s solar panel cleaning services, I always use a biodegradable water softening agent on every clean to eliminate mineral deposits – and brings the right equipment to reach panels safely on any roof configuration.
Book a solar panel clean with Marblanc Solar.
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