The most common drones, the ones you might see down the park, are currently powered by lithium batteries. It is common for one of those drones to have no greater flight time than 30 min. This is due to the energy density of the batteries. Lithium batteries are good, and have got a lot better over the last 6 years. The price is also relatively cheap. However, the quest for more and more endurance is forever present. This has lead to groups of people looking for more energy dense alternatives.
The following graph shows the price and energy density of lithium batteries over time.
The graph shows how far technology has come but unfortunately both lines are flattening out. With the introduction of the Giga factory by Tesla the price is expected to come down by 30-50% however there does not seem to be much increase in energy density in the near future. The average increase in energy density of the past few years is about 3%
There are two main alternatives to lithium batteries.
Petrol and Hydrogen.
Some companies are looking in to petrol powered drones. There is a long history of petrol powered drones. Marilyn Monroe (Original name Norma Jane) built target drones in a factory during WWII. She was discovered when she posed for a photo with one of their fixed wing drones.
Picture Credit MotherBoard
You can see clearly in the photo that these drones are powered by internal combustion engines. Batteries at that time would have been dominated by lead acid, which did not hold much energy and are very heavy. Petrol is good as it is energy dense, it is easy to refuel and the parts are common and ubiquitous. This allows for long endurance and increased lifting capacity. However there are many down sides. There are many moving parts, they are heavy, require a lot of maintenance. Also, they are noisy and polluting. This hasn't stopped a few groups of people from trying.
Picture Credit Quaternium
The Hybrix by Quaternium is a petrol hybrid. It has a petrol engine that charges an on board battery that then supplies the rotors. It is claimed to have 4 hrs endurance (with no payload) and a lifting capacity of ~5kg. These stats are pretty good when it comes to drones used for logistics. However it weighs 20kg and it is very noisy. It sounds like a lawn mower.
Other groups are working on similar drones that have similar stats. However, there are not as many for sale as you would think. Most groups are only at experimental stage or just projects in their garage.
Hydrogen powered drones are very new. They do not have the same history as the internal combustion engine but they are showing a lot of promise. Hydrogen is similar in energy density to petrol however the engine has very few moving parts which means less maintenance and it is not so loud. It also means that the drone can be lighter. Hydrogen can be manufactured using renewable sources and the drones that I have seen have similar endurance and lifting capacity as the petrol multi-rotors that I have mentioned above. The main problem I can see so far is that the hydrogen need to be stored in cylinders under pressure. This also means that changing out a cylinder would be just as fast as refueling a petrol tank.
The drone pictured below is one from Singapore called the Hycopter by H3Dynamics.
Picture Credit New Atlas
The clear tubes are the storage tanks. H3 claim that they have a 4 hr endurance and a ~5kg lifting capacity.
In My opinion, hydrogen will be how delivery drones of the future will be powered. Combined with VTOL we will be able to get even more endurance. Expect to see a hydrogen powered drone delivering to you in the future.
Happy ordering :)
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