Keeping roof-mounted solar panels clean can be awkward and dangerous. Dust and other muck falling on to barn roofs can reduce the amount of solar energy actually getting through to the PV panels underneath by anything from 2% to 10% a year.

But French farmers with PV panels on their barn roofs have found high-tech ways of doing the job, according to French magazine La France Agricole. The latest option on offer involves sending up a radio-controlled drone – usually an eight-rotor unit with a high-definition camera suspended underneath – to check on the state of the panels and relay the images down to the operator on the ground.

The camera also has infra-red capability to identify panels that are not working at full capacity. It can stay in the air for about eight minutes before the lithium batteries run out of power.

Once the drone survey has been done, the farmer can then send up a Gekko robot cleaner from Swiss company Serbot. This electrically powered unit uses a set of soft brushes to clean the PV panels, while a pipe from the ground supplies demineralised water to avoid scale build-up.

Cleaning a 1,500sq m array of PV panels takes four to five hours.

The process isn’t cheap and is obviously aimed at those with big PV arrays. The drone-equipped infrared survey costs €2,000-4,000.

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