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Image: Skeleton TechnologiesThe short answer to the headline’s question is probably not. Perhaps this isn’t the answer you were expecting from the CEO of an ultracapacitor manufacturer. However, ultracapacitors and batteries are different technologies with different benefits for different applications. The idea a battle exists between the two is perhaps a bit of an energy-storage myth. What’s interesting, though, is the increasing number of applications where ultracapacitor technology unquestionably outperforms batteries, and the new solutions emerging as a result.

Understanding the difference between ultracapacitors and batteries
Ultracapacitor technology has been in development for several decades, but has progressed rapidly in recent years. This acceleration is the result of advances in nanomaterials (in our case graphene), the electrification of infrastructure and industry and increased concerns around fuel efficiency. The technology has already been adopted by a number of markets including motorsports, automotive, aerospace, heavy industry and transportation and renewables and grid.Unlike batteries, which rely on a chemical reaction, ultracapacitors

store energy in an electric field. This allows them to charge and discharge much faster than batteries. They can also survive up to a million charge and discharge cycles, whereas battery lifetime is restricted by degrading chemicals. Ultracapacitors have little or no internal resistance (down to 0,12 mΩ), allowing them to work at close to 100% efficiency. They are also significantly lighter than batteries, and generally don’t contain harmful chemicals or toxic metals.

Power density versus energy density
Crucially, the power density of ultracapacitors is up to 60 times greater than batteries. This high power density means it’s possible to recharge large banks of ultracapacitors in just three or four seconds. This means they are ideally suited for applications that require high bursts of power. These range from adjusting solar arrays on spacecraft, to powering kinetic energy recover systems (KERS); providing starting currents for trucks and other heavy transport, to dealing with short-term fluctuations caused by increased renewable generation in the power grid.

Where batteries win is energy density. (Remember power density affects how quickly a technology can release energy, while energy density affects how long it will run for). Ultracapacitors aren’t yet able to store the same amount of electrical energy as batteries, although breakthroughs have been made in recent months. Earlier this year, Skeleton Technologies released a product range with a capacitance of 4,500 Farads, marking the biggest increase in ultracapacitor energy density for 15 years.

Combining the two technologies provides the best of both worlds, and is the real key to unlocking the energy storage market.

A detailed look at ultracapacitors and batteries in electric vehicles
Ultracapacitors are good partners for lithium-ion batteries and other high-energy-density storage technologies. The two can be connected in parallel to create combined power supply units. Due to load leveling, ultracapacitors can significantly expand battery life and improve safety. In an electric car, for example, an ultracapacitor can provide the power needed for acceleration, while a battery provides range and recharges the ultracapacitor between surges.

If we continue with the example of electric cars, however, we see there are some applications where ultracapacitors are the obvious choice. In both electric and hybrid vehicles, for example, the limitation of battery technology results in inefficient harnessing of braking energy; costly battery replacements that reduce the financial savings from greater fuel efficiency; and over-dimensioning of the battery pack to handle high currents during acceleration. Batteries are much better suited to providing long-term low power, for example as a range extender.

Interestingly, Tesla Founder Elon Musk has been quoted as saying ultracapacitors are the future of the electric vehicle market and will replace batteries in the longer term.

Image: Skeleton TechnologiesWhen ultracapacitors are clearly the right choice
Ultracapacitor technology is ideally suited to two of the fastest-growing solutions in the automotive market: regenerative braking and start-stop systems. Start-stop applications enable an engine to shut down when it comes to a stop at a red light, or when sitting in traffic. Ultracapacitors then provide a short burst of energy that restarts the motor. It’s projected that as many as half of new cars will be fitted with these systems by 2022.

Regenerative braking is a key application where ultracapacitor technology clearly outperforms battery storage. Most people have heard of Kinetic Energy Recovery Systems (KERS) from Formula 1 racing. A KERS system captures the kinetic energy of a moving car during braking and then release it again during acceleration.

Ultracapacitors are ideal in this scenario because:

  • They deliver many times more power for weight than lithium-ion batteries.
  • They have efficiencies of up to 98%.
  • They are tolerant of high temperatures.
  • They charge almost instantly.
  • They are one of the cheapest technologies available for power discharges below 15 secs.

So why aren’t ultracapacitors more widely used?
The answer to this is question is simply because batteries are the incumbent technology. Power electronics are currently designed around battery technology, making the adoption of ultracapacitors more complex, as well as more costly. But times are changing. As ultracapacitors are used more widely every year, the technology around high-power devices evolves as well. Costs are coming down, engineers are gaining more and more experience with ultracapacitors and new applications are emerging.

Whether or not ultracapacitors will overtake batteries in the energy-storage market isn’t really important. What’s clear is there are many applications where ultracapacitors are the superior choice of technology. We are seeing increasing demand across industry, including the automotive, aerospace, industrial and renewables sectors.

The potential market for ultracapacitor technology is significant. And leading industry analysts predict the ultracapacitor market for electrical engineering will generate $3.5 billion in revenue in 2020.

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