Batteries are preferably to be used under circumstances where there is no possibility for charging, and besides this, in fields where it is important to store energy given the smaller mass and volume. Military applications of batteries include radio appliances, lamps or most electricity powered devices and equipment.
Supercapacitors, also called as ultracapacitors, are electrochemical energy storage devices that combine the high energy-storage-capability of conventional batteries with the high power-delivery-capability of conventional capacitors. They have many advantages, such as high power density, high energy density, long cycle life, fast charge and discharge, instantaneous high current discharge, low cost, easy maintenance and no pollution to the environment.
It is well known that supercapacitors can send out their entire charge almost instantaneously and are capable of millions of charge/discharge cycles without degradation. What’s more they have extremely low internal resistance or ESR and offer cycle stability in a wide temperature range – from +65 °C to -40 °C (batteries can’t perform well below 0 °C). Supercaps are perfect when a large power demand is required in a short period of time.
These devices have earned their significance in numerous applications, viz., to power hybrid electric/electric vehicles and other power and electronic systems which require electrical energy for their operation. In military Supercapacitors are used in applications where the charge can more or less be maintained continuously, but at times we want to obtain enormous amounts of energy impulsively in a very short period of time. Today, in cutting edge (sometimes pilot) systems these areas of application already exist.
Laser Directed Energy weapons
Directed energy weapons have been researched for decades but are now making their way onto naval platforms. These systems will allow our naval combatants the ability to target multiple adversaries at significant ranges and to
deliver energy at the speed of light to relevant targets
Laser weapons have now in deployment phase in the militaries of the United States, Russia and China. These systems are presently being used to destroy with a laser beams drones and in future against enemy aircraft, ballistic missiles and anti-ship ballistic missiles. These systems requires kiliwatts to megawatts of power to operate. The energy needed is generated by a generator rotated by the engine of the aircraft or that of the ship on which the weapon is mounted. Naval ships, especially older platforms, were not built to deliver the power necessary to sustain use of a high-powered laser. Some form of energy storage will be needed if the ship’s power generation cannot support a new, pulsed load on the order of hundreds of kilowatts to megawatts.
In the case of a fast-moving distant target (i.e. an aircraft, not to mention a missile), it is not possible to hold the laser beam on the target, therefore, the energy that can destroy the target must be delivered in the form of single radiation that occurs in some milliseconds. Such type of ‘firing’ laser, which does not only disrupt the navigation of the target but it also destroys it, presupposes approximately 10-100kW impulse performance. Currently, only supercapacitors are capable of accumulating electric power for a few seconds and delivering it in a matter of milliseconds.
Electromagnetically accelerated projectiles, i.e. railgun
While the laser proves to be efficient against flying objects (most of the aircrafts and the missiles are not armoured, in addition, minor damage can entirely cripple a fast-moving object), railgun is efficient against bunkers and tanks.
In electromagnetic railgun the stored electrical energy in capacitor bank will be used to accelerate a projectile to hypersonic speeds. First, electricity generated by the ship is stored over several seconds in a pulsed power system. Next, an electric pulse is sent to the railgun, creating an electromagnetic force accelerating 14.5kg (23lb), high velocity tungsten slugs from a 155mm cannon to around 5,800 m/sec (19,000 ft/sec or about 13,000 miles per hour).
The kinetic energy of the 12.7 kg projectile hitting the target at multiple sound speed corresponds to the impact of several kilograms of TNT. On the basis of the published results, the ready-made railgun is capable of launching 10 HVP type projectiles per minute at an approximate 7.5 times the sound speed (7.5 Mach). This means nearly 40 MJ of muzzle energy for which – ignoring the losses – a capacitor capable of delivering minimum of 200MW electrical power is needed. Capacitor bank has been developed by BAE Systems to generate enough charge to provide the 64 Megajoules of power needed to shoot the U.S. Navy’s electromagnetic railgun.
Taking the planned firing speed into consideration, one charging cycle takes 5-6 seconds, and the required 40-50MW power demand puts an immense burden on the electrical system of the carrying platform. By comparison, if all electrical appliances of an average household are simultaneously switched on, only 4-6 kW is required meaning that the power demand of the railgun commensurate with that of a small town”
But the energy needed to do this is equal to about 18 kilowatt hours, which is equivalent to the amount of power an average American household uses in an entire day. And the power supply must be able to deliver large currents, sustained and controlled over a useful amount of time. The Navy has chosen high-performance batteries from K2 Energy to power its electromagnetic railgun capacitors. K2 Energy specializes in lithium iron phosphate battery technology and will provide the self-contained battery that acts as an intermediate energy store system to power the capacitor bank.
EMALS Catapults of aircraft carriers
The Electromagnetic Aircraft Launch System (EMALS) is a megawatt electric power system by General Atomics to replace the steam-driven catapults installed on US Navy aircraft carriers.
Experts from the few countries deploying aircraft carriers have been long waiting for the introduction of the electromagnetic catapult because the currently used steam catapult has many weaknesses. The steam powered catapult is very big in size, rather heavy, and a very complicated system. For seawater is an extremely aggressive corrosion agent, the necessary steam is developed from desalinated water, and desalination is a very energy-intensive process. The system is supplied with the steam from the turbines, thus there is no need for heating a separate boiler, but constant level of pressure must be maintained in the system to ensure preparedness, moreover, between two launches it takes quite a lot of time for the system to reach the proper level of steam pressure again. Power needed for the aircraft of various weights can only be roughly controlled, and the enormous pulling force puts a big strain on the structure of the aircrafts. In addition to this, the high-pressure hot steam runs the high risk of causing accidents, plus the system also has high maintenance needs.
Railguns also require a massive bank of capacitors to generate the charge, while EMALS uses and stores energy from the ship’s own power systems. And while the friction between the railgun projectile and the rails generates considerable heat which could make a ship firing a railgun easier to detect, EMALS produces less heat than its steam progenitor.
The latest super aircraft carrier of the United States, the USS Gerald Ford (CVN-78), currently undertaking its sea trials, is equipped with electromagnetic launch units or systems (EMALU or EMALS21) replacing the steam catapult. Despite the many initial problems, in principle, these are free of the shortcomings of the steam catapult. Here, the energy needed for the launch is stored kinetically in huge rotating rotors. It is obvious that research and development will be focused on the possible substitution of mechanical parts with high space and maintenance needs.
Vehicle drive train
More and more experts are dealing with hybrid and purely electricity driven vehicles. At the current level of technology, only batteries can store the energy needed in such vehicles, but supercapacitors can improve a few parameters of the system. As it has been pointed out earlier, at a higher load the loss of batteries significantly grows, thus, in theory a supercapacitor functioning as a buffer can have beneficial effects on the efficiency of the system.
As the energy density and power density of the batteries deteriorate at low temperatures, a buffer supercapacitor would provide the starting current needed for the cold-start of a conventional diesel engine. The so-called hybrid batteries produced for such purposes are currently available.
The American Oshkosh Corporation known for its military vehicles went even further. The newest, electricity powered version of the HEMTT25 military vehicle – first produced 35 years ago – has been available in its product range since 2011. HEMTT A3 is equipped with a 470LE Cummins diesel engine, which does not only drive the wheels but it also drives a 340kW generator which constantly charges a series of supercapacitors of 1.9 MJ nominal capacitance, and drives four AC engines of 480V (one per each axle) through an inverter.
Oshkosh claims that the ProPulse version consumes 20% less fuel than the diesel driven version with the same capacity, but this is not the most remarkable novelty of the system. With the help of the supercapacitor, the ProPulse is suitable for supplying military facilities, communication stations, military medical units, etc. with medium-level consumption needs, but it is also capable of launching a 120kW electric power-impulse making it an ideal platform for radars, land-based laser or railgun weapon systems.
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