Fraunhofer scientists have recently made an important breakthrough with their development of an improved Redox Flow Battery. Over the area of a half square meter, a bit over 4.5 square feet, the new redox stack battery holds 25-kilo watts.
The Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT in Oberhausen, Germany is intensely motivated. The German Federal Government has set itself the objective of generating the total electricity the country needs from sun, wind, and biomass, by 2050. Nuclear power is already being shutdown and power costs to consumers is on a steep climb up.
More and more electricity is being generated from intermittent sources of power, such as solar and wind energy. Storage devices to deliver powerful electric energy flows are necessary to level out the irregularities in the intermittent power supplies.
Batteries are an option with Redox flow batteries offering an effective way to balance out fluctuations in the supply of renewable energy and thus guarantee its constant availability. Redox batteries store electrical energy in chemical compounds, the liquid electrolytes. The electrolytes are charged and discharged in small reaction chambers. Several of these cells are lined up in stacks.
A Redox battery stores energy in electrolyte solutions contained in tanks. The electrolyte circulates from these tanks through a cell, which generates electricity from the fluid in a chemical process. The most common type of Redox battery is the vanadium redox flow battery. The vanadium is charged and discharged in small reaction chambers. Several of these cells are lined up in stacks, which increases the battery’s power. Redox flow batteries offer several advantages; they are cost-effective, robust, durable, and can be individually customized.
But the current batteries on the market, are about 1/16th square meter and can only generate 2.3 kilowatts (kW) of power..
The Fraunhofer scientists have succeeded in significantly increasing the size of the stack increasing its capacity. The new design is for stacks up to a half square meter in size. The eight times larger cell compared to the previous systems results in power up to 25 kW with almost 11 times more power.
The prototype has an efficiency of up to 80 percent, and can take a load of up to 500 amps of current. The Fraunhofer scientists will introduce the new battery at the Energy Alliance’s Fraunhofer booth at Hannover Messe, Hall 13, booth C10.
The technology story begins with the scientists testing new membrane materials and researching battery management and battery design. Flow simulations helped them to optimize the cell structure. A complete redesign of the battery followed which enabled the Fraunhofer team to make their breakthrough.
“The biggest challenge we faced for producing batteries with this level of performance was the development of a completely new stack structure and the scale-up,” explains Dr. Jens Burfeind, Group Manager for Electrochemical Storage Systems at Fraunhofer UMSICHT.
The UMSICHT experts are working together with colleagues from the Fraunhofer Institutes for Chemical Technology and for Solar Energy Systems to conduct intensive research into redox flow batteries as part of a project funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety. The research work is carried out at the institute in Oberhausen, home to one of Europe’s largest test laboratories for redox flow batteries.
“Successfully redesigning the battery stacks was an important step in developing redox flow batteries that could, for example, supply 2000 households with electricity,” says Dr. Christian Dötsch Division Director Energy at Fraunhofer UMSICHT.
Feeding 2000 average German households would require a capacity of around two megawatts, so the next fixed objective at Fraunhofer is to develop a stack that is two square meters in size and has a capacity of 100 kW.
Put in a very simplified context example 2000 German households need 2 million watts or 1 thousand watts each. Fraunhofer’s 2 square meter battery stack could support 100 homes or 2% of a such a battery each. However, not every home is going to be the same, other countries are going to average less and others, America for example, much more.
Fraunhofer hasn’t released estimated costs, but they are using the word breakthrough, and the progress looks to justify that term.
Redox isn’t new or especially exotic technology. Life expectancy and charge/discharge cycle counts aren’t discussed. But there is little about the redox technology that is vastly expensive, difficult to recycle or terribly complex. The problem will be efficiency, as the batteries will need AC power converted to DC to charge and feeding power back out another conversion of DC to AC. Conversion is not free.
A typical nuclear plant or large coal facility makes a billion watts, essentially continuously. Compared to Fraunhofer’s next battery objective at 100,000 watts there would need to 10,000 batteries, plus making up the difference from the battery capacity and the actual usable capacity. Add the wind turbines, solar panels, wiring, conversion costs, grid rebuilds, and personnel needed to keep it all going and the costs can just boggle the mind. Getting to a billion watts continuously is a huge project.
That’s not to say a battery stack storage unit buffering each wind turbine at its base isn’t a great idea. The innovation looks great; the question is can the application ideas make it be even greater.