Kuala Lumpur gets (generous assumption) about 100 lightning strikes per square kilometer per year [0].

If a single drone could service a lot of square km, then it could conceivably collect a lot of electricity. E.g. if it could service 20 square km: 20 * 100 * 8mWh = 16gWh per year. Not bad, but an upper bound, and it hinges a lot on that first parameter (service area).

[0] https://forum.lowyat.net/topic/5376210/all

I thought it was muuuuuch more than that! I've learned something otday!