‘Flow battery’ technology could revolutionize energy economy
Dr. Michael Marshak and his wife are new Boulder residents. Marshak is an assistant professor of chemistry at CU Boulder. His wife works for a Boulder consulting firm.
Before moving here, Marshak was a major contributor to developing an inexpensive “flow battery” technology that could potentially revolutionize the energy economy of the United States and the world by converting clean, green but intermittent energy sources — wind and solar — into steady, firm “dispatchable” sources.
In a Boulder coffeehouse, Marshak engaged me with the story of how, after receiving his doctorate in chemistry from MIT, he hiked the entire Pacific Coast Trail, from Mexico to Canada. No wonder he likes the Boulder outdoor lifestyle!
On returning to Cambridge, Marshak was hired by Harvard professor Michael Aziz, who was seeking to develop a storage battery using low-cost organic molecules for electrolyte, rather than expensive, rare, often toxic metals.
Marshak researched in the Harvard Chemistry Library, looking for compounds that gained and lost electrons readily, and could survive in corrosive environments such as a battery. He found an answer in a 90-year-old paper, describing compounds called quinones. Quinones are found in nature; one version is in rhubarb.
Amazingly, Marshak’s first battery — a solution of quinones in sulfuric acid — worked! He later synthesized a special quinone molecule, which increased solubility and power density. He also changed the electrolyte from an acid to a base solution (less corrosive), and used ferrocynanide (which sounds toxic but isn’t, it is a food additive) as a substitute for the toxic bromine.
Electrolytes in a flow battery are stored in tanks. Pumps push the electrolytes through a fuel cell outside the tanks, generating power. The amount of power stored depends on the tank size; the battery can discharge over many hours. If the fuel cell needs repairs, the electrolyte can remain in the tanks.
Lead-acid and lithium-ion batteries must be replaced every 5-7 years. But the quinone-ferrocyanide electrolyte may last much longer, even decades; the battery does not appear to degrade as it goes through repeated charge-discharge cycles. The round-trip energy efficiency (power out versus power in) is stable at 84 percent; the current efficiency is 99+ percent, meaning almost no unwanted by-products are produced. And the battery works well at room temperatures, or hotter.
Flow batteries are inappropriate for vehicles, due to their size and weight.
However, for homes and businesses, the quinone battery has several advantages — it is non-flammable, relatively non-toxic (using the equivalent of rhubarb and a food additive for electrolyte), and most important, it is cheap.
Rough estimates of the cost of electrolyte alone are $50 per kilowatt-hour of storage. The costs of the balance of the system — tanks, tubing, pumps, fuel cell — would probably bring the cost to roughly $100 per kilowatt-hour. Compare this with the cost of the Tesla lithium-ion industrial storage batteries, at around $250 per kilowatt-hour.
As noted, wind and solar are intermittent. Clouds or nightfall reduce or stop solar panel production; winds may blow strongly, weakly, or not at all.
Reasonably priced battery storage is a solution. Production on sunny days and windy nights exceeding the immediate load, can be stored for future use without curtailment. Batteries reduce or prevent loss of productivity due to power failures. Batteries coupled with microgrids provide power for key activities during devastating weather events. Batteries mean reduced or eliminated “demand charges” for businesses using heavy equipment — such as this newspaper. Batteries mean reduced or eliminated “peak loads” that bedevil power companies on late summer afternoons, when most customers turn on air conditioning. Batteries mean, eventually, that Boulder citizens and businesses may be able to trade with one another for unusual power needs.