Is the Ultracapacitor a Replacement for Batteries?

Many engineers want to know if ultracapacitors will ultimately replace all batteries. The answer is, no. A typical follow-up question is, “Will the ultracapacitor replace some batteries?” and here the answer is, “yes.” While this may not seem like a revelation, the significance is in the manner ultracapacitors will replace some batteries.

We have discussed the difference between power and energy in past blogs and noted that most, if not all, applications have a power component and an energy component. Of course, the ultracapacitor fills the need for power perfectly, while the battery addresses the energy component. So, this would suggest that a system containing both batteries and ultracapacitors will be larger and more expensive due to the incorporation of two technologies to fill the system needs for power and energy.

But the truth is just the opposite. Today’s batteries used in highly demanding electric energy applications are significantly oversized to manage the power component. In terms of the capacity of the battery in amp-hours or the total energy in watt-hours, batteries carry around a lot of excess volume and weight in active material (and the subsequent overhead) just to preserve the life of the battery and provide enough raw power to meet the demand of high-power cycling situations.

On the other hand, a battery designed for energy, where power is handled by another source, is significantly less expensive to make. The savings come through trading expensive materials for less expensive materials. An energy-optimized battery design has more active material and less inactive material, making it more efficient all around. And universally, inactive material is more expensive than the active material replacing it, so the cost decreases. In total, the energy-optimized battery could be more than 50 percent smaller, lighter and less expensive than its counterpart. Adding capacitors to meet the power needs will cost far less than the savings. The result is a smaller, lighter, more efficient and less expensive system with better reliability and longer lifetime.

So when battery proponents tell you that batteries can do it all, they are looking out for their own self-interest. Smaller, lighter and lower cost mean decreased revenue for battery makers, who are lobbying hard to preserve their stakes. There is no motivation for battery makers to get smaller unless driven by competitive pressure. But the true optimized answer to the energy storage architecture question is splitting power and energy and using each technology for its respective strength.

So, yes, capacitors will replace some batteries. In some applications, they will replace them outright, especially those where the energy demand is low and power demand is high. In others, they will replace some of the cells in a larger battery pack, bringing efficiency and reliability along for the ride. A win-win…unless, of course, you are a battery maker.

5 comments on “Is the Ultracapacitor a Replacement for Batteries?

  1. nhwank
    May 31, 2015

    Great summary, Mike, and encouragement for engineers to think system-level, rather than components level, and stimulate the dialog between purchasing and engineers. I would like to add though, that what appears to be a smaller optimized system, relies on increased complexity, a combination of bidirectional rectifier-inverters to accommodate the charge/discharge characteristics. It does drive-up the cost – and  complexity of the system. It may be a valuable cost-benefit-risk analysis to review real economics of a 480-V 3-phase production system, as many are outdoors rated, such as Bloom, or hybrid solar microgrids. Such system would require six Maxwell's BMOD0006 E160 B02 super cap modules, stringed like Christmas tree lights to reach close to the 1,000-V PV solar input spec, each stack contributing around 120Wh, or good for a 30-second fail-over interval at 14.4kW. On top of the cost ofr additional power electronics, there is cost to achieve true outdoor rating, as IP54 is good against splashing water, but not good enough to withstand a storm. How does the analysis look under these scenarios, what's the cost for $/W and $/kWh?

  2. Scott Elder
    June 3, 2015

    Great thesis Mike.  I'm always impressed by the work at Cap-XX, but everytime I think that a super-cap is required, I inevitably end up solving the problem with a cheaper battery.

  3. eafpres
    June 3, 2015

    Hi Mike–to me it is inherently true that a given system of XYZ specs has an optimum battery-capacitor solution.  In some cases this nets out to just a battery, and in some cases a pure cap could be optimal.  

    The comments from nhwank sparked a question.  Thinking about automotive and commercial, agricultural, etc. equipment that rely on batteries for starting and powering electrics when the engine is off, a major problem is discharging lead acid batteries during cold weather deeply enough that permanent sulfaction occurs.  I wonder if adding the additional circuitry nhwank mentions could include some smarts to prevent this?

  4. priya17
    June 4, 2015

    nice information

  5. anusha11
    June 5, 2015

    nice post thnak you

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