Depends. Uf you have solar panels, the electricity is more or less free after you buy and deploy them. So if you have some drone fleet and solar panels + batteries, the only real cost you have is basically maintenance. The way many businesses work, variable cost is what matters. So you'd lease the drones, the solar panels & batteries (or just get a cheap energy supplier) and focus on handling and transporting packages. Drones are interesting for that because you can save time by flying point to point, and cost by not having to employ drivers/pilots.

Porque no los dos? As the truck drives down the street, the drones deploy out of the top...