There are two technologies that are highly fashionable nowadays: Drones and Energy efficiency (production, conservation, accumulation and clean energy).
Actual drones, mainly those of multirotor type, use electric motors that need a huge amount of energy to keep the drone up in the air. We could say in very colloquial words that they use “Brute force” to “grasp” the air. Up to now we have been using LiPo batteries for this purpose as they had the best energy density for its weight (about 200Wh/kg) compared to other batteries. But the reality is that drones with this sort of batteries are not able to fly more than one hour in the best cases, being 20 minutes the average flight time with payloads of 1 to 2kg. But is it enough?
I remember some years ago, mobile phones had an autonomy of at least one week. Now if you get your phone working all day you are almost lucky. But this seems to be ok for us, by now. In the case of drone applications, there are a lot of applications that do not need more than half an hour flight sessions, but other actual and potential application would really benefit, if longer flight times could be reached, like Search & Rescue, Shipping/ Delivery, Precision Agriculture, Law-Enforcement and border patrol, Geographic Mapping, Search and Rescue/ Healthcare.
Fortunately, some light is seen at the horizon for flight times increase. There are several improvements in the Energy Efficiency fields that will help drones have access to better energy density sources.
A few months ago I visited Quaternium, a Spanish company that announced the development of a multirotor drone prototype, able to fly four hours using a hybrid (petrol-electric) technology. This month (June 2016) they have announced their product HYBRiX.20, a multirotor drone able to fly 4 hours (2hr. with 5 kg. payload).
|HYBRiX.20 drone from Quaternium|
They use a petrol engine that produce electrical energy for the drone motors, using a battery as an energy buffer. The theory is simple, but the complex part is to get the correct equilibrium between several factors: Energy conversion efficiency, weight and distribution, vibrations and noise control, long term mechanical reliability (robustness) and battery optimization between other. But what is more important, they were able to jump from a prototype to a sellable product to the real market.
|From left to right: Jose Luis Cortes (founder & CTO Quaternium), Alejandro Alonso, and Alicia Fuentes (CEO)|
There are other companies, like Top Flight, a North American company, producing hybrid (petrol-electric) multirotor drones able to fly 2.5 hours with one gallon (3.8 litres) of gasoline. The solution is said to have an energy density of 1,500 Wh/kg, more than 7 times over LiPo batteries.
|Hybrid drone from Top Flight|
But hybrid (petrol-electric) is not the unique technology available for improving flight times, although it is possibly the most efficient at this time.
Graphene can make batteries that are light, durable and suitable for high capacity energy storage, as well as shorten charging times. The Spanish company Graphenano recently introduced, together with its Chinese partner Chint, graphene polymer batteries. The company expect to have commercial batteries at the end of 2016. The batteries are said to have a density of 1,000 Wh/kg. Independent analyses by TÜV and Dekra show that the batteries are safe and are not prone to explosions like lithium batteries.
Hydrogen fuel cell
A hydrogen fuel cell technology uses compressed hydrogen and oxygen from the air to generate electricity. The hydrogen and oxygen combine to form water, but the electrons from the hydrogen could be used as power supply for a drone, with a battery buffer. The only exhaust from the fuel cell is water vapor and refueling with compressed hydrogen takes a few minutes compared to recharging a battery, so it is also a clean source of energy.
There are several companies working on the application of this technology for prototype drones.
In USA the company Intelligent Energy is working on a multirotor drone prototype that can fly for 2 hours.
|Hydrogen fuel cell drone from Intelligent Energy|
In Singapore a consortium of Singaporean institutions and private sector companies including HES Energy Systems, ST Aerospace, DSO National Laboratories, and the Future Systems and Technology Directorate of Singapore’s Ministry of Defense, have worked jointly to achieve a record 6 hour endurance, 300km flight on the Skyblade 360 fixed wing UAV built in Singapore by ST Aerospace. The Skyblade 360 fuel cell system developed by HES and DSO is extremely lightweight in comparison to lithium batteries that typically power this sort of aircraft, and it is also extremely compact: its 1L fuel cartridge holds 1000Wh of usable energy.
It is nice to see we are getting alternatives to the "old" LiPo batteries for the drones market. This will open the space for a lot of possible real applications in a short time. The future is very promising.
Written by: Alejandro Alonso-Puig. HISPAROB Robotics Platform Vicepresident, Infinium Robotics CTO and Quark Robotics Partner.