Cleaning solar panels and crop spraying do actually sound quite good used for drones.
Although I'm guessing crop spraying will need something a fair bit bigger than the designs to carry cameras.
Hardware tech and companies from across the world came together at the EU-backed Startup Olé conference in Salamanca, western Spain, last week. Roughly 150 startups had stands and 50 participating in different pitches during the well-attended two-day event in the historic university town. Similar events in the UK would be …
You might like to look at how big modern fields are.
Personally I'd expect the crop sprayer to be capable of independent flight.
What you have in mind reminded me of a design in an old book I saw ("Spies in the Sky" JWR Taylor) from Germany in the late 70's called the "Peewit." Looked like a short wide cylinder with a 2 blade rotor on top. The thing seems to be continually fueled by pumping fuel up the hose to it.
Because it's most likely a scaled up version of that which will be used for flying close to buildings. You could use a modified predator as a crop duster but that would only make sense if you were doing it on an epic scale.