Kathleen Davis, Associate Editor
Partnering with the British energy company Innogy (formerly National Power), the Tennessee Valley Authority (TVA) is poised to construct a $25 million commercial electricity storage plant in Mississippi.
Block diagram of the Regenesys energy storage system Click here to enlarge image
The TVA board has approved construction, which is slated to begin this year. The 12 MW energy storage plant is “designed to improve power quality and system reliability while having a minimal impact on the environment,” according to TVA.
Both companies are touting the plant’s unique technology, stating that it will be only the second of its type in the world and the first in the United States. That “unique” technology (officially entitled the Regenesys Energy Storage System) is based on regenerative fuel cell design.
How it works
According to Innogy, the Regenesys system works with a simple chemical reaction. To store electricity, the energy is converted into chemical potential by sloughing off the charge into two liquid electrolyte solutions. To flip the switch back, the electrolyte solutions are allowed to interact, creating a chemical reaction between the salt solutions.
Using this chemical reaction as a stepping stone, the Regenesys system centers on fuel cell modules. (See figure.) Setting themselves apart from secondary batteries, Innogy pushes the electrochemical cell foundation as the real differential in the equation. It breaks down to simple size issues: Most secondary batteries utilize electrodes in both the transfer and storage processes, making capacity and power rating related to the electrodes’ size and shape. Regenesys, however, has a cell with a compartment for each electrolyte; the two are separated by an ion-exchange membrane, allowing the reaction to occur while the electrolytes continue to flow into and out of the cell through separate manifolds.
Innogy states that economies of scale can be achieved by linking these cells together, with an electrode shared between two cells. Stringing them together like interwoven chain-link, the cathode of one cell becomes the anode of another-their bipolar module. And, according to Innogy, the Regenesys system can be operated from one extreme to the other-from full charge to discharge-without any damage to either the electrolytes or the electrodes. Regenesys can also be grid connected and capable of turning from gathering electricity to giving in less than a fraction of a second (Innogy lists the speed at 0.02 seconds).
Where it’s going
Regenesys has been tested at Innogy’s Aberthaw power station in South Wales since 1996. The first commercial plant to utilize Regenesys began construction in August of last year. The process will add a 15 MW/120 MWh utility scale storage plant to the existing 680 MW combined cycle gas turbine power station at Little Barford, Cambridgeshire, U.K. With a discharge cycle of six to 14 hours and design turnaround efficiency hovering between 60 and 65 percent, the predicted life span of the addition is 15 years.
“The Regenesys technology should offer grid system planners a flexible means of storing electricity in bulk,” said Ross Sayers, executive chairman of Innogy. “This would allow better use to be made of a cleaner generating plant by reducing the need to operate a less efficient peaking plant.”
“We have been developing Regenesys for a number of years, taking it from the laboratory to larger scale testing and evaluation,” he added. “The innovation could have global significance and the plant in Cambridgeshire is thought to be a world first.”
TVA seems to agree with that evaluation of potential significance. TVA chief operating officer Ike Zeringue stated that Regenesys “has the potential to change the shape of the industry.”
TVA’s Mississippi Regenesys plant should take approximately two years to construct at a total cost of $25 million. The TVA contract with Innogy (to design the plant and provide fuel cells) rests right around $10 million. Operation for the Mississippi plant is slated for 2003. Advantages, however, move beyond financial considerations according to TVA.
“The entire system requires about two acres of land and can be located near an existing substation,” said TVA director Skila Harris. “That helps reduce the need to build additional power lines and lessens the environmental impact of building a power plant.”
And Innogy seems just as excited about their collaboration with TVA. “We’ve been talking to TVA for some time about the technology’s potential, and we are delighted to have secured a commercial deal overseas,” Sayers said.
He added, “This is an exciting development for the whole electricity industry.”
More information about the Regenesys system can be found online at www.regenesys.com or by calling 011-44-1793-877777. Tim Meeks, communications manager with TVA, may be contacted at 256-386-2903.