I have seen hydrogen fuel cells power drones for 3 to 5 hours but most fuel cells on the market that i have seen are really overpriced!
I have also heard of goodenoughs new glass electrolyte battery coming out in a few years its suppose to have incredible specs.
Hybrid electric gas / battery powered drones also get great flight times down side is they are really loud and cause a lot of vibrations
When this stuff becomes mainstream its going to change the drone industry!
Are there any other forms of powering a drone similar to these?
Really need something with 3 to 5 times the effeciency of li-pos!
Yes, I think "nobody" replied because there is no energy source which provides 3x the energy density of batteries which are suitable for small aircraft.
Beyond all the "promising" battery technologies (lithium air, sodium) which will not be on the market for a while, you're right that fuel cells are expensive (and weigh around 2kg minimum at the moment) and petrol(gas) hybrids are loud and have vibrations (and are still limited to heavier aircraft, because the engine and fuel tank weigh quite a lot).
Strictly it's not "efficiency" that you want, but energy density. You can gain a small improvement (~25%) in energy density by using Li-ion instead of LiPo, but this comes at the cost of lower power density (you can't draw a high current) so they're not very practical for multirotors. But a lot of UAV manufacturers are using Li-ion for fixed-wing UAVs.
But if you're looking for long endurance (fixed-wing) check out my new thread:
As an aside, one power source with very good energy and power density is a gas turbine. But again, they're expensive, and only practical for larger aircraft. But a turbine hybrid has the advantage of being able to operate at maximum efficiency for the whole flight since the RPM of the turbine can be fixed.
Thanks for the reply. Very informative. I've actually been looking into turbine engines. Seen this one https://jakadofsky.com/index1.php?lang=en&bereichID=11
Have you seen any others mind??