Are supercapacitors going to spark the battery storage revolution?
According to a survey of 600 energy industry executives and experts, the technology will play a central role in improving the performance of batteries connected to the grid.
The survey was conducted by Lloyd's Register, a global technical consulting organization. Lloyd's is well respected. But some are calling its conclusions about supercapacitors into question.
"The storage technology that respondents believe will have the biggest impact is electrical technology such as supercapacitors, which will rapidly speed up charging times for large batteries," wrote the organization in its report.
While supercapacitors will indeed play a role in scaling storage, the idea that they can “rapidly speed up charging times for large batteries” is wrong, according to some analysts.
“The simple answer is 'no,' supercapacitors won't make chemical batteries charge faster," said Dr. Julia Attwood, an expert in emerging technologies at Bloomberg New Energy Finance.
Although supercapacitors are already being used to deliver very rapid charging to electric buses, “Some batteries can charge very quickly, but that's a property of the cell and pack design. It's not because of the supercapacitors," she said.
The confusion, said Attwood, may be due to a mixing of terminology.
“So, they might mean that energy storage systems made up of supercapacitors can charge very quickly, which is true. Occasionally I see energy storage technologies that aren't technically batteries referred to that way."
Jason Knights, head of media relations for Lloyd’s Register, said the views from respondents confirmed the value of supercapacitors in many applications, and as a way of complementing battery charging and use. But Knights also highlighted that there are developments under way in terms of how supercapacitors can offer a better solution than batteries which is evident in the findings of the report and gives an alternative view from Dr. Attwood.
He said the report signifies that supercapacitors will maximize battery cell life by maintaining slow and shallow charge/discharges. “The supercapacitors in essence do all the hard work.”
The report also identifies the fact that supercapacitors have begun to take on some roles traditionally assigned to batteries. But there is still some way to go although respondents in the Technology Radar survey see this technology as a root for further development and testing. New advances in materials technology, such as the use of graphene and other compounds, may also increase capacity in the near future, which could make the supercapacitor a real option to replace the battery if this is achieved. But capacity is the key in any question over whether supercapacitors replace batteries.
In the Lloyd's research, hundreds of professionals in the renewables, storage and nuclear sectors were asked which technologies will have the greatest impact on the energy sector.
Experts replied as follows for storage:
- Electrical technology advances (e.g., supercapacitors): 65%
- Software related advances (e.g., battery health monitoring): 60%
- Electrochemical storage innovations (e.g., lithium-ion battery advances): 59%
- Thermal storage innovations (e.g., phase change material): 57%
- Chemical technology innovations (e.g., hydrogen): 57%
- Mechanical storage innovations (e.g., flywheels): 42%
Despite the No. 1 spot for supercapacitors in the survey, both Attwood and Chris Robinson, a consultant at Lux Research, were skeptical that the technology will have an outsized impact on the future of storage.
However, the technology could have plenty to offer both stationary and mobile applications. “Supercapacitors have many complementary properties to batteries. They lend themselves well to high-power applications, can be charged and discharged very quickly, and can operate at low temperatures, all of which can be difficult for most batteries," said Attwood.
“By pairing the two, battery lifetimes and operating temperatures can be increased by using the supercapacitor to provide that first burst of power. A battery like lithium-ion can then take over for steady, longer-duration discharge, as these batteries have a much higher energy density than current supercapacitors," she said.
Judicious use of supercapacitors can take the strain off a lithium-ion battery designed primarily to deliver energy over a number of hours.
Supercapacitors manufacturer Maxwell Technologies is currently using the technology to provide voltage stabilization and stop-start systems, and claims to have units installed in a million vehicles.
And Oliver Ahlberg, co-founder and chief operating officer of Estonian supercapacitor manufacturer Skeleton Technologies, said his company’s supercapacitors could allow manufacturers to reduce the size of a traditional engine from 14 liters down to 8 liters.
Recovering braking power for use in acceleration is another area where supercapacitors can benefit vehicles, by absorbing and storing much of the kinetic energy from the braking system as electricity so that it can be used later. In the case of trains, considerable savings can be made, prompting different networks, including Beijing Metro and the Southeastern Pennsylvania Transit Authority to deploy them. SEPTA is even selling the recovered energy back to the grid.
Stationary storage can benefit from supercapacitors, too. Duke Energy is using Maxwell supercapacitors to support Aquion Energy’s large-scale batteries for a demonstration project in North Carolina.
The supercapacitor element of this Hybrid Energy Storage System (HESS) will be able to respond very rapidly to sudden changes in input from a nearby solar array caused by cloud cover. It will also reduce heat stress and degradation in the battery component, said the companies.
Supercapacitors could also provide a HESS with excellent frequency response capabilities, said Robinson of Lux Research.
One forecast estimated that the global market for supercapacitors will reach $5 billion by 2025. According to Robinson, the technology “will certainly find its niche.”
Note: this story has been change to reflect more commentary from Lloyd's Register.