Researchers look at materials to improve microgrids & renewable energy storage

August 23, 2017 Michelle Froese

Researchers are hard at work looking to come up with a battery technology that meets the economic and consumer needs of a rapidly growing demand for renewable energy storage of the micro-grid. Energy would come from the sun, wind, batteries, and other sources.

The findings include promising results from batteries using liquid, molten metal elements, salt-water, iron flow, zinc, lithium-air, and other chemistries to satisfy the needs of the electrical grid, according to information from Grist and the U.S. Department of Energy.

The high cost is a big problem, according to Eric Rohlfing, Deputy Director of Technology for ARPA-E, a division of the Department of Energy that identifies and funds leading-edge R&D. Since it was established by former President Obama in 2009, ARPA-E has funded $85 million toward developing new batteries that can meet that goal.

A 2012 study in Nature Magazine found that the average American would only be willing to pay about $13 more each month to ensure that the entire electrical grid could allow the U.S. electrical supply to run on renewable battery energy. That means utilities must be able to provide grid-level energy storage that would cost them less than $100 per kW-hour. According to Bloomberg New Energy Finance, battery prices continue to rapidly fall.

Presently, that rate is hundreds of $/kWh. According to many experts, it has to come down to under $100/kWh for batteries based on liquid, molten-metal, salt water, and other chemistries to be competitive in the market.

That hasn’t stopped researchers from trying to achieve that price goal. At laboratories at MIT, the Universities of Utah and Michigan, the U.S. Army Research Laboratory, and Harvard University, researchers are optimistic about their chances to hit that cost milestone.

Getting market-ready
Some success has been achieved getting renewable energy storage on the market. Aquion, a spinoff from Carnegie Mellon University, has its 35-MW/h salt-water storage battery deployed around the world in 250 installations. Its goal is to produce the least expensive and most reliable battery one can make.

“Our chemistry is very simple,” says Matt Maroon, Aquion’s VP of Product Management. “It’s also very easy to assemble. Our main piece of manufacturing assembly comes out of the food industry.”

Aquion claims that nothing in their battery is toxic, caustic, or flammable. All the materials in the Aquion batteries are abundant and easily obtained. One installation in Hawaii has been up and running for two years. Last year, the battery-plus-solar system powered several buildings for six months without ever falling back on a diesel generator.

Another spinoff company from MIT, Ambri, believes it literally has the next hot technology in energy storage: purified molten aluminum metal cells using a low-tech approach. Based in Marlborough, Massachusettes, it was co-founded about a decade ago by materials chemistry professor Donald Sadoway and Ph.D. student David Bradwell.

The improved materials run at a cool 900ºF, several hundred degrees lower than what has already been achieved by others. The Ambri process is doubled up and looped-back on itself. Some test cells have been running for nearly four years without showing any signs of wear and tear.

The company solved some pesky heat-seal issues allowing battery packs to reach a self-sustaining operating temperature that’s hot enough to charge and discharge without an extra energy input. Ambri plans to begin production within two years.

They used two tanks that hold the solutions containing molecules of charged atoms, called anolytes and catholytes, that store and release charge as the solution flows past the electrodes. To increase battery capacity, more material is added in the tanks and it flows through the same cell. By adding more cells, a faster rate of charge or discharge is achieved.

The scientists report that the most exciting anolyte is based on the organic molecule pryidium, which contains no metals and is intended to be dissolved in an organic solvent, further enhancing stability. Although other compounds exhibited longer half-lives, the pyridium anolyte provides the best combination of stability and redox potential, which is directly related to how much energy it can store.

Interesting work at Harvard University makes use of predictive modeling of chemical structures as well as flow techniques. Professor Michael Aziz and graduate student Andrew Wong devised a small experimental storage system that relies on organic molecules from a class of compounds known as quinones. These can be found in rhubarb, which stores and transfers energy.

Electrochemical electrolyte ingredients are dissolved in water and stored in beakers. When these solutions flow near each other, they create an electric charge. They call their system an organic mega-flow battery, which can become a renewable energy source. These carbon-based solutions get recycled in the batteries, keeping carbon out of the atmosphere.

The compounds tried included aloe vera, Vitamin K, nitrogen, and Vitamin B2. Typically about a 1-W output was obtained. They do admit that it would take tanks twice the size of a Goodyear blimp to produce about a million W.

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