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.