They can put solar panels that brush off sand and put wind turbines that use the wind from the Sahara.
They can even use mirrors and heat up a steam reactor in the desert. There would not be any damage and there is plenty of room to with no one around.
Covering the Sahara with solar panels would be quite expensive but if we covered only a portion of the Sahara, It might not be so bad cost wise. Plus we could gain good from using renewable energy and we would have to make sure we're not disrupting the ecosystem too.