Ultracapacitors and Batteries: Mortal Enemies or Best of Friends?
February 16, 2010 by Michael Everett
Filed under Blogs, PowerOn Blog, Recommended Reading
I remember growing up and struggling through all the trials and tribulations of fixing a flat tire on a bicycle. It always seemed that when you had to get the wheel off to repair your tire tube all you had was a pair of poor-quality slip joint pliers from the bargain bin at the local hardware store. No sooner had you tried to remove the rusty nut from the spindle that the corners on the nut would round and the job would become a lot harder—if not impossible. And if you were lucky enough to get the nut off and remove the wheel, then the screwdriver that you were using to get the tire off the rim would further damage the very tube you were trying to repair. So the lesson I finally learned after my father said it over and over was: use the right tool for the right job.
So it is with energy storage.
Do battery makers compete with ultracapacitor makers for business? Do the two technologies fight over applications? The answer is that just like a screwdriver competes with a tire removal tool, they do. But as with tools, one specially designed for the purpose will always do a better job than one designed for another purpose and adapted to meet the existing need. And the definition of a “better job” is an optimization question when it comes to energy storage system design.
That is what is happening with ultracapacitors and batteries today. Batteries are being designed in where only ultracapacitors are needed. In contrast, ultracapacitors are being used where batteries just won’t do. Fortunately, there are some very progressive thinkers out there who recognize that energy delivery systems usually have more than one job to do and using the combination of the two is the best choice for the job. Delivery of energy and the delivery of power can be viewed as two different jobs, not just one. In this case, it is easy to take advantage of each technology for its strength.
I would point you to the 2009 published work detailing a collaborative effort between the National Renewable Energy Laboratory and General Motors in which a Saturn Vue Greenline “mild hybrid” vehicle was outfitted with batteries and then compared to the performance of the vehicle with ultracapacitors in place of batteries. The investigators were looking to find out what effect the capacitors had on overall performance and economy of the vehicle and to compare it with the battery-powered equivalent.
The conclusions are interesting to say the least. At the highest level, in this particular mild hybrid characterization, there is no degradation in performance using ultracapacitors in place of batteries. In fact, there is a positive benefit using ultracapacitors instead of batteries where it can be done. Considering the other capabilities of the capacitors that batteries lack such as very low temperature operations and long lifetime, this seems a case where the right tool for the right job in that vehicle was not regarded when the vehicle was designed.
I have to say my fathers’ voice echoes in my head every time I pick up the wrong tool knowing that in the garage the right one is but a few steps away. The short walk there has resulted in a lot of time saved and quality work performed instead of the alternative. Therefore, take the short mental “walk” before selecting the wrong energy storage device just because it is lying next to you.
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When will go down the prize of the supercapacitors? I think this is the only problem because they are not used, they are much more expensive than batteries.
Thank you for your question on the price of ultracapacitors. It is one that will be asked many times in the future as well. The cost of energy storage is a prime driver of market acceptance. As a developer and manufacturer of ultracapacitors targeting demanding and price sensitive markets such as automotive applications, Maxwell well understands that most applications are price-enabled.
One thing you need to watch out for is the comparison of a battery price with a capacitor price on the basis of relative energy storage capacity. Remember they are different devices; batteries are best suited for energy (high storage capacity), while ultracapacitors best suited for power (rapid charge/discharge rate). Price comparisonss are only valid when there is a “one-or-the-other” decision to make. In those cases, one must take into account the long service free life and the low total cost of ownership of ultracapacitors since they generally last the life of the application (one million+ charge/discharge cycles), while batteries generally have lifetimes measured in hundreds to thousands of cycles. But in those cases where ultracapacitors work with batteries or instead of batteries because the application is a power application that requires repeated bursts of high current, not sustained, steady energy flow, a battery may be a much more expensive choice because it must be oversized to handle that power requirement and may require frequent replacement.
So the price of an energy storage solution is a function not only of the price of the device itself, but the nature and requirements of the application. That said, Maxwell is focused on reducing the cost of ultracapacitors through technology, engineering and manufacturing efficiency. It is true as you state, that volume is a very strong influencer of price and as the volumes increase, cost will decrease and that will enable price reductions. The cost take-down will be a steady and continuous process and as successful implementation of the devices are realized the doors will open up for more and more applications because the economics will enable it.
I am trying to design a low cost energy storage solution for home users. The chpice is between batteries and capacitors. The requirement is to store about 1000 AH equivalent of storage 12 Volt battery. How much a capacitor storage may cost is $ value.
Abdul,
Thank you for your question. Unfortunately, the situation you are talking about is one where ultracapacitors would not be the right tool for the job. This is an energy application that requires more storage than ultracapacitors can provide cost-effectively. Ultracacpacitors are power devices that can charge and discharge in fractions of a second, but have relatively low storage capacity, compared with batteries. Good luck!
My dad boxed my ears once or twice over the right tool for the right job too, I’m glad he did, it has served me well. Ultracapacitors versus batteries isn’t an exact metaphor with pliers versus wrench, though point taken. Until now, industry has just given us a pair of lithium-ion vise-grips rather than a better fastening system, such as a quick release hub on a bicycle.
You have well indicated the basic discreet, time-dependent functionality of each technology, and suggested combinations of these technologies. I envision these technologies to marry and integrate at such a level that they both be contained in a single package – in fact, this may be necessary.
Pragmatic visionaries see sharp advances in nanotechnology shattering conventional cost take-down horizons.
Good luck in bottling up that demon Michael, and when you do, use the power and energy wisely.