Fuel cells for UAVs?

Fuel cells for UAVs?

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All over the world there is an expectation for breakthrough in the field of fuel cells as a source of energy for various systems. Sources in Israel say that if such a breakthrough is achieved, many systems will be able to operate with higher efficiency for HLS missions. Fuel cells are The Next Hot Thing in the military domain, and nowadays mainly in the energy supplying field for various types of UAVs.

UAVs are energized at present by internal combustion motors, using regular or heavy (diesel) fuel. There are also UAVs powered by a rechargeable battery but their operating time in the air is very limited.

Here enter the fuels cells, which are good means of obtaining energy. But – they are still in their infancy, although there are considerable achievements, particularly in Israel, also an UAV superpower.

We are familiar with the various types of batteries. A battery is a chemical unit containing chemical energy that is converted to electrical current when connected to a load.  The battery is a closed device – containing all the chemicals internally – and with the capability of providing a predetermined amount of energy, till it becomes empty and practically ends its chemical role. Once the chemical reaction in the battery is over, the battery is in fact “finished” and it needs to be recharged by moving it back to its initial chemical state.

Compared to a battery, a fuel cell is an open device, with chemicals (in fact our fuel) entering into it, and as long as fuel gets in energy will be obtained from the device.  The main difference between the two device types is that battery is a device for energy storage while fuel cell is a device for energy conversion. The efficiency of a fuel cell is higher than that of a battery.

At present, there are several types of fuel cells on the market, differing by a variety of parameters, such as the type of chemicals entering the cell, its operating temperature, etc. However, the principle of operation of all the types is quite similar.

In a fuel cell of the hydrogen – oxygen type the fuel (hydrogen gas) flows through the anode, where it is separated into ions and electrons.  This separation is executed by a chemical reaction between the anode and the hydrogen taking place with the help of a catalyst.

Only positively charged hydrogen ions pass through the anode and the catalyst. The electrons having a negative charge cannot pass through the anode to the electrolyte, and they flow through an external load connected to the fuel cell, supplying the consumer device the energy needed for its operation.

The positively charged hydrogen ions passing through the anode, move through the electrolyte layer to the cathode, which receives, along with the cathode catalyst, oxygen flowing from the outside air. The oxygen reacts, with the aid of catalyst in the cathode, with the hydrogen ions coming through the electrolyte and the electrons coming through the external load. As a result of this reaction, water vapor is created. The main advantage of fuel calls is that in the fuel cell energy is obtained directly. Also, compared to internal combustion engines, the amount of heat produced in a fuel cell is low, and is not part of the process of producing electrical power.

In addition to the hydrogen – oxygen type of fuel cell, there are various other types of fuel cell. Their principle of operation is identical, but they are made of different materials serving as electrodes, catalyst and electrolyte, as well as the ions passing through the various electrodes.

It seems that at present the highest interest in fuel cells exists in the UAV industry. Ronen Nadir, CEO of BLUE BIRD developing and producing UAVs, says that the “Boomerang” type of UAV developed by the company is already operated by fuel cells. Nadir explains that the “rule of thumb” of fuel cells is that, unlike the two hours of UAV flight that can be obtained by 3 kg of a regular battery, with 3 kg of fuel cell(s) the UAV can fly 3 hours.   This is of course a rough computation, but it shows why Nadir’s company and other companies are trying to use fuel cells for powering UAVs.

In the recent years there were many publications about reluctance of military UAV operators from using fuel cells on UAVs, because of the perceived risk of using condensed hydrogen due to the danger of explosion of such a cell.

Ronen says that the above fears are no more than “an urban tale”. He says that the method of condensed hydrogen is the best one and that it does not present a danger at all. “We take a container weighing 2 kg, and put into it 120 grams of hydrogen”. He says that even if such a container explodes it does not look like a bomb but more like a cracked hotdog emerging from boiling water.  “The container into which we put the condensed hydrogen is made of metal and composite materials and is very resilient”.

BLUE BIRD produces fuel cells for its own use in the “Boomerang” UAV. The various components are purchased from external suppliers, but the company assembles the system based on its experience.

According to Nadir, the problem is with the size of the hydrogen container, preventing installation of fuel cell systems in small UAVs.

As said before, the “Boomerang” UAV is already operated using fuel cells, and it seems that in the future when the fuel cells are lighter they will serve also as energy source for smaller UAVs.

When a fuel cells system is installed in an UAV there is always a backup battery attached to it, enabling the UAV to take off at the stage when the fuel cell is only beginning its operation and supply of electrical energy.

Ronen Nadir expects that also after the fuel cell is smaller and more efficient it will be used only in mini-UAVs. The micro-UAVs will continue being operated by a battery, since its efficiency relative to weight is better.

Also other Israeli UAV producers are examining fuel cells and there is no doubt that they are The Next Thing in the field of unmanned vehicles.

In several locations in the world there are development centers of commercial fuel cells. “Horizon” of Singapore, for instance, has supplied already fuel cell systems to several producers of UAVs in Israel, and it goes on cooperating with some of them.

In parallel, Israeli companies are acquiring expertise in this field and it seems that they would prefer ultimately to produce the fuel cells by themselves, according to their particular needs.

Around the world attempts are made to utilize solar energy for powering of flying vehicles. There are some achievements, but they are not yet ripe for an operational system.  Of course, this sounds like the optimal system – a solar system receiving solar radiation and storing it for operating the propeller for many hours. However as long as this method based on sun rays will not be fully mature, fuel cells seem to be the best solution.

Arie Egozi i-HLS Editor-in-Chief
Arie Egozi
i-HLS Editor-in-Chief