I would suggest that blowing off sand with a strong airstream would scratch the solar panels, further reducing their efficiency. Or maybe there's other problems; in any case, I find it somehow ignorant to assume that nobody in the Pakistani government has ever heard of or considered a blower (or a broom).
I assume they have heard of blowers and probably knew sand would be a problem with this install. My take away is that project was a bad faith effort to serve as a strawman against renewables for oil. This is an engineering problem not a technological problem of solar panels. Having skipped over it implies questionable motivations.
Would those be a gasoline powered blowers ? ( ͜ʖ)
Perhaps a step down transformer that directly feeds a dyson blade style blower at one of the edges of each panel. More up front equipment and infrastructure cost but no employee wages. However I'm sure this is full of holes due to cost multiplied by number of solar panels and the number of transformers needed. It is also only able to clean only during the day assuming no battery or pumped hydro storage.