Drexel’s Energy Flow Capacitor: Is Grid-Level Electrical Storage Here Now?

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A Drexel University research team has developed energy storage technology that it believes can solve a vexing problem: how to cost-effectively store intermittent electrical energy from renewable sources at grid-level scale. The research team combined the concepts underlying flow, or redox, batteries used in electric vehicles (EVs) with those of supercapacitors in developing a liquid, electrochemical storage technology.

While large amounts of electrical energy can be stored using current battery technology, it’s slow to discharge and has a limited cycle-life as compared to electrochemical supercapacitors, which are limited in terms of the amount of energy they can store, a Drexel University news release explains.

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Electric Flux Capacitors: Grid-Scale Energy Storage?

Scaling up to grid-level size is a constraint with regard to using batteries and supercapacitors for grid storage of intermittent electricity flows from renewable energy sources such as wind and solar PV. Supercapacitors, which are similar to the lithium-ion batteries used in EVs, require large amounts of relatively costly materials to produce electricity. As such, they have only been used commercially at much smaller scales — consumer electronic devices, for example.

The Drexel University research team’s solution leveraged the comparative advantages of batteries and supercapacitors and applied new nanotechnology to develop an “electrochemical flow capacitor” (EFC) that it says can cost-effectively store grid-level quantities of electrical energy, and charge and discharge quickly, making it suitable to manage intermittent flows from renewable energy sources.

“Packing together thousands of conventional small devices to build a system for large-scale stationary energy storage is too expensive,” explained project lead Dr. Yury Gogotsi, director of the A.J. Drexel Nanotechnology Institute. “A liquid storage system, the capacity of which is limited only by the tank size, can be cost-effective and scalable.”

Consisting of electrochemical cells connected to two external electrolyte reservoirs, nano-scale carbon particles are used as energy carriers. A slurry of uncharged carbon particles suspended in electrolyte tanks are pumped through a flow cell, where they pick up and carry electrical charge. They then flow into storage reservoirs for use as needed.

“By using a slurry of carbon particles as the active material of supercapacitors, we are able to adopt the system architecture from redox flow batteries and address issues of cost and scalability,” Gogotsi commented.

The size of electrical-charge storage reservoirs determines the capacity of an energy storage system. In Drexel’s product, the system can be scaled up simply by increasing the size of the tanks, while the system’s power output can be increased by increasing the size of the electrochemical cells.

“Flow battery architecture is very attractive for grid-scale applications because it allows for scalable energy storage by decoupling the power and energy density,” added Dr. E.C. Kumbur, director of Drexel’s Electrochemical Energy Systems Laboratory.

“Slow response rate is a common problem for most energy storage systems. Incorporating the rapid charging and discharging ability of supercapacitors into this architecture is a major step toward effectively storing energy from fluctuating renewable sources and being able to quickly deliver the energy, as it is needed.”

In addition, the research team’s EFC energy storage system has a relatively long useful life as compared to the current generation of flow batteries, such that they can be used “in stationary applications for hundreds of thousands of charge-discharge cycles.”

“This technology can potentially address cost and lifespan issues that we face with the current electrochemical energy storage technologies,” Kumbur was quoted as saying.

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