Cleaning Solar Panels With Little or No Water: A Guide for Drought-Hit India

Solar panels and water make an awkward pair in a drought. Dust settling on a panel cuts its output, and the usual cure is washing. The Council on Energy, Environment and Water (CEEW) has estimated that cleaning a solar plant in India uses roughly 7,000 to 20,000 litres of water per megawatt for each wash, and big plants are often washed weekly. A 2019 Bridge to India study found that more than half of India’s solar capacity sits in arid or water-stressed areas. With drought declared across large parts of several states in 2026, the question for farmers with solar pumps, homeowners and plant operators is the same: how do you keep panels producing while using as little water as possible?

The short answer: clean when the dust loss justifies it rather than on a fixed calendar, use the least water your module maker allows, and on large plants consider waterless robots, but only after checking that dry cleaning will not void your module warranty.

How much does dust really cost?

Indian field studies put the loss from dust (soiling loss) at roughly 0.2% to 0.5% of output per day in dry months:

• A Delhi study measured an average of about 0.25% per day, or about 7.6% a month, with higher rates in winter than in summer or the monsoon.
• A rooftop study in India’s composite climate found about 0.39% per day in spring, 0.34% in winter and 0.24% in the monsoon, when rain does some of the cleaning.
• A north-India rooftop study recorded up to about 0.47% per day, or about 10% over a month.
• A utility-scale plant studied over dry periods averaged about 0.18% per day, with some sections reaching 0.46%.

So panels left alone through a dry month can lose several per cent of their output, more near construction, cement works, unpaved roads or freshly ploughed fields. Rain resets much of the loss, which is why monsoon months need far less cleaning. These are study averages, not a forecast for your site. The reliable way to know is to measure: compare the generation (or the pump’s run-time and water output) on two equally sunny days just before and just after a cleaning. If cleaning barely changes the numbers, you are cleaning too often.

First, check what your module maker allows

This step decides everything else, because the wrong cleaning method can void a module warranty:

• Dry rubbing is not allowed by every maker. Canadian Solar’s manual says not to scrape or rub dry dirt away because it may cause micro-scratches, and states that damage from inappropriate cleaning voids the warranty. First Solar, by contrast, lists dry brushing as an accepted method. Two makers, opposite answers: read the manual for your exact modules.
• Water quality limits are specific. Indian makers Navitas and Insolation ask for soft water with total hardness below 60 mg/L, near-neutral pH (6.5 to 7.5) and TDS below 400 mg/L. Trina allows TDS up to 1,000 mg/L but hardness of only 0 to 40 mg/L, and First Solar prefers RO water. Hard borewell water leaves white mineral marks as it dries, and those marks block light.
• No abrasives, no harsh chemicals, no high pressure. Manuals consistently rule out abrasive powders and de-greasers, and cap spray pressure (several cite about 4 MPa).

If your installer cannot show you the cleaning section of your module manual, ask the manufacturer for it before choosing a method.

Low-water and waterless options, from simplest to most advanced

1. Clean less often, at the right time

The biggest saving is not cleaning when it is not needed. Skip cleaning after a good rain. Clean in the early morning or late evening, when panels are cool; several module manuals ask for cleaning in the cool part of the day. Panels tilted at 10° or more shed dust better when it does rain, which is one reason our panel tilt tool never recommends a flatter angle.

2. Low-water wet cleaning

A soft brush or sponge with a single bucket of the cleanest water you have, followed by a soft squeegee, uses far less water than a hose. Use RO or soft water where you can; if your water leaves white marks when it dries, it is too hard for panels. Professional crews on rooftops use pure-water pole systems such as the one in our Unger water-fed pole review.

3. Manual dry cleaning

A soft, clean brush or microfibre cloth used without water removes loose dust, but only if your module maker permits dry cleaning. It does not remove bird droppings, cement dust or caked mud, which need water. Never use a stiff brush, a broom or a cloth that has picked up grit.

4. Waterless cleaning robots (large plants)

Robots that run along rows of panels and sweep them dry are already used on large Indian plants, especially in Rajasthan. Ecoppia has announced deployments with SB Energy, Azure Power and Fortum, and Airtouch signed contracts to clean ReNew’s plants in Rajasthan. Indian makers include Skilancer and Taypro. Most performance and water-saving figures published for robots come from the vendors themselves, so treat them as claims to test. Our Skilancer SS-01 review sets out the checklist for any robot: a full datasheet, written confirmation from your module maker that the brushes will not affect the warranty, a measured before-and-after at a comparable site, and a plan for the soiling a dry brush cannot shift.

5. Anti-soiling coatings

Coatings that make glass shed dust can help, but field results fall short of lab results. A 2025 study of desert sites found coatings that were up to 80% effective in the lab delivered 20% to 50% in the field, and other research shows repeated brushing wears coatings down. Before paying for one, ask for at least two years of independent field data from a climate like yours, and check whether applying it affects your module warranty.

6. Electrostatic cleaning (not available yet)

MIT researchers demonstrated in 2022 a way to make dust jump off panels using an electric field, with no water or brushes. It is promising, but it is still research. We found no commercial product, so ignore anyone selling it today as proven.

For solar pump owners

Pump panels are usually ground-mounted and within reach, which makes them easy to clean safely, but farm dust and nearby ploughing soil them quickly. Clean at dawn with a soft cloth or brush and a bucket of the cleanest water you have, never with detergent powder, sand or a stiff brush. A dirty array shows up directly as less water: if the pump starts later in the morning or delivers noticeably less on a clear day, cleaning is due. Our PM-KUSUM status guide covers where the solar pump subsidy stands.

For homeowners

Most rooftops need cleaning every two to three weeks in dry, dusty seasons and much less in the monsoon. A soft mop with a little clean water at dawn is enough. Do not climb onto a sloping or wet roof, and never walk on panels. If your system has a monitoring app, use the generation figures to decide when cleaning is actually paying off.

For EPCs and O&M teams

• Measure before you buy. Use a soiling station or a pair of reference cells (one cleaned, one left alone), or compare irradiance-normalised output before and after cleaning; see our irradiance meter review. That turns the cleaning schedule into a cost decision instead of a calendar.
• Put the module maker’s cleaning terms in the contract. Any robot or coating supplier should state in writing that their method meets the module manufacturer’s cleaning guidance.
• Track water as a cost line. In drought districts, water may have to be trucked in, and its price and availability change the payback of a robot.
• Keep a wet-cleaning fallback. Bird droppings, cement and post-storm mud need water even on robot-cleaned plants.

Frequently asked questions

Can I clean solar panels without any water?

Sometimes. A soft dry brush or a dry-cleaning robot removes loose dust, but only use one if your module maker allows dry cleaning. Sticky dirt such as bird droppings still needs water.

Does dry cleaning scratch solar panels?

It can. Canadian Solar warns that rubbing dry dirt may cause micro-scratches, while First Solar accepts dry brushing. The brush, the type of dust and the glass coating all matter, so follow your own module’s manual.

What water should I use?

The softest you can get: RO or demineralised water is best. Indian makers ask for hardness below 60 mg/L and TDS below 400 mg/L. If water leaves white marks when it dries, do not use it on panels.

How often should panels be cleaned in a drought?

There is no fixed rule. Indian studies show losses of about 0.2% to 0.5% a day in dry months, so many sites need cleaning every two to three weeks, but measure your own system and clean when the gain is worth the water.

We last checked this guide on 3 November 2026. Module cleaning rules differ by manufacturer and model, so your module’s own manual always overrides general advice, including ours.