Testing Zinc Air Battery Storage in the New York City Grid

Unlike conventional batteries, zinc-air cells from Eos Energy Storage draw oxygen from outside the casing, giving them a higher capacity-to-volume ratio, substantially lowering costs to where they're competitive with gas-fired power for specialized grid services like frequency regulation. That's how Steve Hellman, the president of Eos Energy Storage, sees the market today. "Eos's mission is to provide customers with energy storage that solves real problems - at a lower cost than incumbents," he told CleanTechnica. And EOS isn't alone. The rising numbers of grid battery demonstrations (with many different chemistries) bear this powerful trend out.

Eos is participating in a high-profile test in New York City, where it will soon install one of its zinc-air batteries with 36 kilowatt-hours of storage capacity at a local Con Edison facility. The project will be Eos's first opportunity to provide backup power on the grid, and it should prove their battery's ability to reduce the costs of building new power generation, even as surging population growth tests the utility's limits. This is part of ConEd's plan to keep up with gentrification in Queens and Brooklyn by investing $100 million to $150 million to reduce electricity consumption while building local supply. If successful, this will enable the utility to push back construction of a $1.1 billion substation until 2024, saving customers $400 million to $500 million. Soon, ConEd will also provide customers with incentives to buy more efficient lighting, batteries, and rooftop solar panels, all to reduce reliance on the traditional power grid.


Improving zinc battery chemistry

Although battery developers have been long attracted to zinc-air technology because it offers safe, inexpensive, high-energy density, in the past a couple of drawbacks - low efficiencies and short life cycles - limited them to small, non-rechargeable uses such as hearing aids. To solve those problems, Eos has completely rebuilt its zinc air battery, changing basics like the electrolyte and cell design.

While zinc-air batteries typically use potassium hydroxide, a solution that absorbs carbon dioxide from the air and causes potassium carbonate build-up that slowly clogs the cell's air pores, Eos's batteries use a pH-neutral electrolyte that doesn't absorb carbon dioxide. Problem solved. It also means it won't catch fire like lithium-ion batteries. The battery also has a new horizontal architecture that relies on gravity instead of a membrane to separate the electrolyte from the air. This prevents buildup on the zinc electrode from rupturing the membrane and causing cell failure. To maximize charge/discharge efficiency, the company tweaked the zinc-oxygen reaction with a mixture of chemicals that it hasn't disclosed. These additional reactions reduce the difference between charge and discharge voltages, improving efficiency from 60 percent to almost 75 percent. Eos says that these improvements mean that the rechargeable batteries can achieve 10,000 cycles, about a 30-year life, at the low price of $160/kWh for the DC system. "To accomplish this, we not only have to produce an inexpensive battery; we have to produce a battery inexpensively," said Hellman. Costs have been kept down by using a manufacturing system that doesn't require unique or exotic machines. "Inexpensive, highly commoditized, and readily scalable manufacturing processes (such as metal cutting and stamping, injection molded plastics, and stackable assembly) have been ingrained in the design and development of our technology since day one," Hellman added. "Whereas battery manufacturing typically requires significant capital and scale to bring down cost, we can build a pilot manufacturing line for far less and achieve cost targets that make our battery technology competitive with gas peaking plants."

Going global

The Con Edison demonstration sets the stage for the company's special Genesis Program, which involves projects with some of Europe's biggest utilities and North America's most innovative one. They include NRG, American Electric Power, National Grid, GDF Suez, Enel and others, which represent over 300 gigawatts of power generation, 1.6 million miles of transmission and distribution, and 76 million customers in over 70 countries.

NRG, which joined a $15 million Series B funding round for Eos last year, is interested in the battery for several uses: from large-scale load shifting, to profitable grid balancing and frequency regulation for Mid-Atlantic grid operator PJM. In Europe, with National Grid and Enel, Eos will optimize transmission lines connecting wind farms to the grid, which should defer the costs of building new ones. GDF Suez will use the batteries for micro-grids in expensive places like Mediterranean islands, where, along with a mix of solar and minimal fossil-fuel-fired generation, they will reduce or replace expensive diesel generators.

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Images: EOS