What they did is explained here, the process is quite involved:
> Each of the 400,000 installed panels required one litre of water to clean. A 15 days cleaning cycle required 124 million litres of water (enough to sustain 9000 people) while rain in the Cholistan desert is rare and far between. Providing such huge amount of water in desert terrain, became a challenging and daunting task for management team. Besides, the manual cleaning methods allowed setting of dust before it was re-cleaned.
Every day they're using 20.7 litres of water to keep a single panel clean. It's an interesting problem, but I'm certain there's a better way if one were willing to develop better automation.
> Each of the 400,000 installed panels required one litre of water to clean. A 15 days cleaning cycle required 124 million litres of water (enough to sustain 9000 people) while rain in the Cholistan desert is rare and far between. Providing such huge amount of water in desert terrain, became a challenging and daunting task for management team. Besides, the manual cleaning methods allowed setting of dust before it was re-cleaned.
https://www.wikiwand.com/en/Quaid-e-Azam_Solar_Park