Lies. I'm using solar panels since 2022, still producing same peak energy and not cleaned them once. Some companies/electricians will try to sell you a cleaning and maintenance service for ~80-100EUR/year here but it's basically throwing money.

I live in a fairly arid place (Bay Area) where it rains in winter but gets quite dry and dusty in the summer. I've had rooftop solar since 2016 and have noticed that generation decreases by as much as 8-10% when the panels are covered in summer dust.