"according to reports they are developing drones that can fly 24 hours a day on solar power"
Titan Aerospace, bought by google recently (probably sub 100 million) has IP related to these solar drones. I don't think they have one flying yet, but if you google them, you will see that to make a 24hr solar powered aircraft, it needs to be fixed wing, very high altitude (above any clouds/winds/weather) and enormous.
The titan proposed planes are almost as big as a jumbo jet, are covered in PV cells, and probably only have a pretty small payload.
Single or Multi rotary wing aircraft use huge amounts of power to stay in the air. Much of the power is wasted to allow hovering. This is why jetpacks are pretty much short flight time toys.
For eg a 5 seater bell jetranger helicopter ,payload 400kg has a 750hp jet engine, pumping out pretty much 750hp all of the time in the air, using 100litres of jet A1 per hour, 300 litre tank. A 5 seater cessna 182 uses many times less power and fuel, not sure what this is but 5 to 10 times less, to lift a similar payload of about 500kg.
With current battery and solar and motor technology I believe it would be impossible to make a solar powered multirotor drone. If in the future that were possible, it would have to be so light, that it would be affected by wind even if very large, so flying above the weather, above 60,000 ft would be a requirement in all but the most still weather conditions. There just is not that much power in sunlight, even if you were to develop a 100% efficient PV cell that harnessed IR visible and UV combined.
So once again, I believe at least for the forseeable future, it is highly unlikely and probably phsically impossible, that we could have cheap weather proof self sufficient solar multirotor drones zooming about doing such jobs for days on end. You would need a person to launch and fly each drone, flight time about 10 mins currently using some pretty serious best energy density Lithium Cobalt batteries. How long would that take to fly the whole city, having to recharge or come back to swap batteries every 10 mins?
