For higher than 30 minutes you really want to look into planes instead of quadcopters. Running 4/6/8 heavy duty motors forces battery life to be an issue.
A plane has significantly less than that which lets them go for longer.
Good point Skywalker X8 or 1900 are good for longer range FPV planes, I've seen some setups with 80-100km range (UHF Setups) which is pretty impressive.
People have looked at it, but I think the general consensus is that there's not enough surface area on the airframe to generate enough electricity to make a significant impact.
Depending on the exact motor+prop setup, peak draw of between 200-400W is pretty common for fixed wings in the 1.5-2M wingspan range, and cruise is often around half of that.
I get 30 minutes on a HobbyKing Bixler 1.1 with a 5aH battery. I'm using an EzUHF for control with an EzOSD and 1.3Ghz for the video downlink. In a noisy place, like the suburbs of San Antonio, TX I could get 4 miles of range reliably before the video started breaking up. I'm in AK now and have flown to 12 miles with rock-solid video.
A plane has significantly less than that which lets them go for longer.