Solar panel cleaning by drone in Thailand: why, how, and how often
Rooftop solar is growing fast on Thai factories, warehouses, hotels and car parks. Dirty modules produce less, and most roofs are not safe to walk on. This guide explains what soiling costs, how a drone cleans an array without contact, and how to plan it.
Short answer: soiling from dust, pollen, soot and bird droppings reduces the output of photovoltaic modules, and the loss grows during the dry season when there is no rain to wash them. A tethered drone cleans the array from above with purified water at low pressure, with no brush, no detergent and nobody on the roof. Cleaning before the hot dry months, and again after the burning season in the north, is a reasonable starting calendar; the right frequency is set from the inverter data.
Why dirty modules matter
A photovoltaic module produces in proportion to the light that reaches its cells. A film of dust cuts that light; a bird dropping shades a cell and can create a hot spot that damages it. In Thailand, three things make it worse: the dry season leaves months without rain, agricultural burning in the north and north-east deposits soot, and traffic dust settles on arrays near roads and industrial estates. Low-pitch roofs and carports do not self-clean in the rain either; water pools at the lower edge and leaves a dirt line.
Why not just send someone with a hose
Walking on modules cracks cells and voids warranties. Tap water leaves mineral marks that reduce output themselves. Brushes scratch anti-reflective coatings. Detergents can damage seals and are prohibited by many manufacturers. And a factory roof is a fall hazard: most Thai roofs have no walkways or anchors.
How the drone does it
The tethered drone flies over the array, two to three metres above the modules, and sprays purified water at low pressure in passes aligned with the rows. Purified water dissolves the dirt and dries without minerals, so there is nothing to wipe. The pilot and ground crew stay on the ground. A warehouse roof of several thousand square metres is done in a day; nobody sets foot on the roof.
How often
It depends on the site. A reasonable starting point for a Thai industrial roof is a cleaning before the hot dry season, when soiling builds up, and a second one after the burning season for sites in the north. Arrays near a cement plant, a quarry or a busy road need more. The best indicator is the inverter data: when output on a clear day drops noticeably below the previous month at the same irradiance, it is time. See also how often to clean in a tropical climate.
What we have done
In France, CleanAlta cleans solar canopies and rooftop arrays with the same drone, as well as metal warehouse roofs. Photos and video on the roof and solar page.
Questions about solar cleaning
Does the drone touch the panels?
No. Only water touches the modules, at low pressure. No brush, no pad, no feet.
Can it damage the modules or the warranty?
Purified water at low pressure is the method most manufacturers recommend. We clean early in the morning when the modules are cool, to avoid thermal shock.
Does the plant have to be switched off?
Usually no. We agree the procedure with the plant operator beforehand.
Can you measure the gain?
Yes, with the inverter data before and after, at comparable irradiance. We ask for access to it on pilot sites.
Investors, property groups and corporates
We present the Thai launch plan and the figures in a direct meeting, under NDA. Building owners can also apply for a documented pilot job.