I know that solar panels have to be cleaned pretty regularly to function with high efficiency. My guess would be that the cost and labor to clean the panels would be pretty high.
Quoting from National Geographic:
Winds at speeds of about 100 kilometers per hour (60 miles per hour) sweep through some deserts. With little vegetation to block it, the wind can carry sand and dust across entire continents and even oceans. Windstorms in the Sahara hurl so much material into the air that African dustsometimes crosses the Atlantic Ocean. Sunsets on the Atlantic coast of the U.S. state of Florida, for example, can be tinted yellow.