Not only that but who cleans ‘em?
I don't know about having solar in Kosovo (where the article is about). But here in Alabama I've never cleaned mine and I've had some of them for 2 years. Part of that is the ones I've had for 2 years are positioned at a steep pitch (thus, sediment doesn't sit on them long before even a mild rain makes rushing water clean them). And part of it is also about our winters giving us a few freezes every year where I wake up with a thin layer of ice on them. That diminishes their production for a few hours on those few mornings, but the ice melting and sliding off of them cleans them better than I can with a squeegee.
Admittedly, the panels I installed in August last year are installed at a moderate angle and, therefore, might require me rinsing them off a few times when pollen collects on them as we're experiencing our spring. So far I haven't had to do that, but I'm sure it's coming.