Cleaning solar panels with Dreft: good idea or ticking time bomb?
Dreft may seem convenient, but it reduces performance and voids your manufacturer’s warranty. Find out about the risks and the safe alternative for streak-free panels.
By Hendrik Vandervoort3 min read
Many DIYers automatically reach for Dreft or other detergents when they want to clean their solar panels. Makes sense - you wash glasses and plates with them every day, so why not rooftop glass too? In this guide, we explain why Cleaning solar panels with Dreft can damage the performance of your plant, how exactly chemistry affects the fragile coating and why professional cleaning with pure water by Solarco is both smarter and more economical.
1. Why people reach for dish soap
- Availability - A bottle of Dreft is already in the kitchen cupboard.
- Price perception - A few drops cost almost nothing.
- Foam = clean - Lots of foam gives the impression of powerful cleansing.
- Unknown - Few manufacturers actively warn against household products.
Yet these arguments are misleading. Let's unravel the chemistry behind foam bubbles.
2. The chemical pitfalls of cleaning solar panels with Dreft
2.1 Surfactants
Detergent contains surfactants which emulsify fats. Perfect for food scraps, but on a solar panel they settle as microfilm once the water dries up. That film has three negative effects:
- Light reflection - Average +2 % reflection loss measured at film of 0.05 µm.
- Dirt magnet - The greasy layer attracts dust and pollen faster.
- Coating stress - Surfactants reduce surface tension; nano-coatings can come off.
2.2 Salts and dyes
Detergents contain sodium chloride as a thickener and dyes for brand recognition. When drying, salts crystallise into mini-scratch. Yellow-green pigment residues are hygroscopic and retain moisture: breeding ground for algae.
"We took micrographs of panels that had been cleaned twice with Dreft - the salt crystals looked like sandpaper," says Hendrik, CEO of Solarco.
2.3 pH level
Dreft sits around pH 8-9, so slightly alkaline. Anti-reflection coatings are designed for neutral water. Prolonged exposure to base accelerates silica etching processes, making gloss permanently dull.
Table 1 summarises the main Dreft components and what they do on PV glass.
| Component | Purpose in kitchens | Impact on solar panels |
|---|---|---|
| Anionic surfactant | Fat breaker | Forms light-absorbing film |
| Sodium chloride | Consistency | Crystal scratches glass |
| SLES | Foam enhancer | Attack silicone seal |
| Colouring agent CI 42051 | Branding | Pigmentation spots, algae growth |
| Perfume | Smell | Film attracts flies & dust |
3. Case study: 10 % yield loss due to Dreft
In 2023, Solarco documented a residential system in Aalst (24 panels, 7.9 kWp) where the owner was cleaning solar panels with dreft and sponge every spring. After three years:
- Hotspot detection: IR camera showed 12 °C temperature difference.
- PR drop: from 0.83 to 0.75 (≈ 10 % less yield).
- Coating scans: loss of 15 % anti-reflection efficiency.
- Cost: €840 in missed revenue, excluding repairs.
Solarco removed residue with a mild acid bath and pure water, after which the PR recovered to 0.80. Full recovery was impossible as some micro-scratches were permanent.
4. Pure water: the safe counterpart
4.1 What makes pure water unique?
- TDS < 30 ppm - No salts ➜ no crystal formation.
- pH 6.8-7.2 - Almost neutral ➜ coating-friendly.
- High surface tension - Binding to dirt without chemistry.
- Spot-free - Dries without streaks or film.
"Pure water behaves like a magnet: negatively charged water molecules envelop positively charged dust particles," explained chief operator Sander out. "That's why you don't need soap."
4.2 Comparison of pure water vs Dreft mix vs rainwater
| Feature | Pure water | Dreft + tap water | Rainwater |
| Minerals | < 30 ppm | 250 ppm | 50-80 ppm |
| pH | 6,8-7,2 | 8,5-9,0 | 5,5-6,0 |
| Residue formation | No | Soap film + salt | Dust/acid film |
| Reflection loss | 0 % | 2-5 % | 1-3 % |
| Warranty risk | No | High | Moderate |
5. Professional cleaning: more than a suds
5.1 Robotic and telescopic technology
Solarco uses telescopic brushes with split bristles and low pressure or fully autonomous cleaning robots for large roofs. Water consumption and pressure are precisely tuned to avoid scratching.
5.2 Safe working methods
- VCA-certified mechanics.
- Fall protection on sloping roofs.
- Non-life insurance included.
5.3 Inspection & reporting
Every turn includes a visual inspection and IR scan. Small defects are found early, preventing expensive burns.
6. Cost tag: DIY with Dreft vs Solarco service
| Scenario | Material costs | Risk of damage | Missed revenue | Time investment |
| Dreft method (1×/year) | € 2 soap + € 10 water | High | 5-10 % per year | 4 hours working by yourself |
| Solarco pure water cleaning | from € 125 (25 panels) | No | 0 % | 0 hours |
On average, a 5 kWp system earns €90 per 1 % return per year. At 5 % losses, Dreft therefore costs €450 per year. A professional turn therefore pays for itself after only three months.
7. Frequently asked questions
| Question | Answer (summarised) |
|---|---|
| 1. Can Dreft invalidate the warranty of my solar panels? | Yes. Manufacturers require pH-neutral cleaning (< 7.5) and can reject claims once soap residue (pH 8-9) has been shown to cause damage. |
| 2. How do I recognise soap film or salt residue on the glass? | Look at the panel in floodlight: do you see a rainbow haze or white rings? That is soap film or crystallised salt; a greasy fingerprint that does not disappear confirms residue. |
| 3. I don't have pure water. What is a safe alternative? | Use spot-free-rinse-water (car wash). Rinse generously and dry with a clean microfibre cloth; avoid plain tap water. |
| 4. Does rain remove enough dirt so that I don't need to clean again? | No. Rain contains minerals and city pollution; it washes away loose dust but leaves behind a thin film that absorbs light and attracts dirt. |
| 5. How much efficiency do I lose from one Dreft cleaning? | Laboratory tests show 2-3 % direct yield drop; repeated turns can cause up to 10 % permanent loss via micro-scratches and film build-up. |
| 6. What does professional cleaning cost if I have more than 40 panels? | Solarco charges €125 for the first 25 panels and ± €5 per panel above that. At >100 panels, the price drops to €1.50-€2.00 per panel, depending on accessibility. |
9. Conclusion & call-to-action
Cleaning solar panels with Dreft seems cheap, but is an expensive mistake in the long run. Soap film, crystal formation and alkaline damage can cost up to 10 % efficiency and permanently degrade the coating. Choose the safe route: have your panels treated with pure water by Solarco's certified experts.
Schedule your free inspection today via our solar panel cleaning-page and receive a no-obligation quotation. Share this article with neighbours and friends so that they too protect their investment!
Frequently asked questions
Can you clean solar panels with washing-up liquid?
No, washing-up liquid or soap is not recommended, because it leaves a thin film that attracts dirt and causes streaks every time it rains. That soap film absorbs light and so reduces output, while alkaline products can damage the coating over time. Clean with pure water and suitable brushes instead, without soap.
What equipment do you need to clean solar panels safely?
Safe cleaning calls for suitable non-abrasive brushes (with soft, flagged bristles that won't scratch) and pure water, without harsh cleaning agents or high pressure. A rubber squeegee used in one smooth downward stroke prevents streaks. For high or large roofs, professionals use telescopic poles or a cleaning robot, so nobody has to stand on the panels.
How does Solarco clean solar panels?
Solarco cleans with professional equipment: suitable non-abrasive brushes and purified water, without harsh cleaning agents or high pressure. For large installations and solar parks, we use battery-powered, manufacturer-certified cleaning robots. A visual check and, if required, a thermographic check are carried out before and after cleaning.
Can you use a pressure washer or Kärcher on solar panels?
No, never use a pressure washer. The high pressure can cause micro-cracks, damage the seals around the panel and force water into the junction boxes, leading to faults and lost yield. Always clean at low pressure, with pure water and a soft, non-abrasive brush.
What mistakes should you avoid when cleaning solar panels yourself?
Avoid pressure washers, hard or abrasive brushes, steel wool and household cleaning products, as they damage the coating and seals. Never clean the panels dry (this creates static and scratches) and never in full sun, because the water evaporates too quickly and leaves streaks. Don't use cold water on hot panels, to prevent thermal shock and micro-cracks.
Does rain clean solar panels?
No. Rain only washes away loose dust and often leaves minerals and stubborn dirt behind. Moss, lichen, bird droppings, pollen, Saharan sand and industrial fallout stay stuck to the panels, and it's precisely these layers that cost the most yield. Even a thin layer of dirt can mean 5 to 10% less output.
