It's no secret that wind farms and solar plants have a reliability problem, and that a clear way to conquer that hurdle is to deploy batteries that store power and deliver it to the grid when needed.
But there are two obstacles limiting the success of that solution—the enormous cost and low durability of today's batteries.
Now, engineers at the City University of New York's Energy Institute in Manhattan say they found a fix: a nickel-zinc battery technology that is just as cheap as short-lived, lead-acid batteries and just as long-lasting as lithium-ion batteries, one of the costliest technologies on the market.
"There was a giant hole in the middle" between the top battery types, says Eric McFarland, a chemical engineering professor at the University of California, Santa Barbara and a consultant for the institute.
The four-year-old Energy Institute is in the midst of launching a company called Urban Electric Power that will commercialize its nickel-zinc battery technology. McFarland says the startup expects to create about 20 local jobs by the end of this year.
Perched in a clearing, the firm's Nickel-Zinc Flow Battery system will connect by cable to rows of wind turbines or fields of solar panels, storing up electricity generated on windy nights or extra-sunny days and sending power to the grid in peak periods.
The allure for developers is the return on investment, says McFarland. "If you have batteries, then you can strike a better deal [with utilities] because you're providing more reliable power around the clock."
Further, the upfront cost of the nickel-zinc system is expected to be less than other energy storage options.
The institute's kilowatt-hour nickel-zinc battery costs between $300 and $500, or as much as $100,000 for a 200-battery system that has a life of up to 15 years. Within a year, however, that kilowatt-hour price is expected to fall to $200 as the technology improves, the institute says. That would make it the same price as a lead-acid battery, which lasts only a year.
Lithium-ion technologies, by contrast, can cost up to $1,200 per kilowatt-hour.
Clean energy "is already expensive, and if you add expensive battery systems to that, then it's not economical," says Sanjoy Banerjee, the institute's director and a distinguished professor of chemical engineering at the City College of New York.
"To make it really work, it has to be very cheap."
The Basement Experiment
The Energy Institute's battery technology is currently in the prototype phase. In a musty basement at the City College of New York's century-old campus in Harlem, a cluster of 36 rectangular batteries are huddled on metal racks. Each is about the size of a small suitcase and can supply 1 kilowatt-hour of energy, enough to light up ten 100-watt light bulbs.
Black and red wires unfurl from the tops of the batteries and connect to what the institute calls the "advanced battery management system," a web-based program run on a single computer that serves as the battery command center. Through that program, engineers control when to recharge the batteries and when to release their power. The entire network is connected to the building's electrical system, which runs on fossil fuel, nuclear and hydroelectric energy.
From this basement room, the 36 kilowatt-hour system can supply about 5 percent of the building's energy needs during hours of peak electricity demand and recharge at night when the students have left.
The Energy Institute hopes to scale up the demonstration to 200 suitcase-sized batteries later this year, which would supply up to 30 percent of the building's energy use and save the college at least $6,000 in monthly energy bills.
The Challenge of Zinc Batteries
Banerjee says the research team chose zinc for its batteries because the metal is cheap, nontoxic and widely accessible.
It's only one of about a dozen startups using zinc for grid-scale battery storage, among the hundreds of companies and labs working in the space.
Why so few?
The reason is a stubborn problem called "dendrite formation," says Banerjee. He explains that zinc, which is used in disposable battery brands like Duracell, forms dendrites, or branch-like structures, every time a battery is charged and recharged. Those dendrites quickly build up and cause the batteries to short out.
Banjeree says he and his team of engineers found a way to tame the dendrites.
The core of each battery, a series of flat metal rods, sits in an aquarium filled with constantly circulating water-based liquid called the electrolyte. The flow helps to smooth out the zinc dendrites and to extend by 10 times the battery's life. With this setup, batteries can be "deep-cycled" 3,000 to 4,000 times, which means they can last for 10 to 15 years with daily use.
Since 2008, the Energy Institute has received more than $20 million in funding from the Department of Energy (DOE), the New York State Energy Research and Development Authority, Con Edison, Mitsubishi and the Nuclear Regulatory Commission. Among the awards is a $3 million grant from the DOE's Advanced Research Projects Agency-Energy, a government agency that bankrolls cutting-edge technologies.