This article is from the In-Depth Report The Clean Energy Wars

Is the Secret to Cheap Energy Storage Hiding in Harlem? [Slide Show]

The material in disposable batteries may hold the secret to making an inexpensive storage system that can feed the electrical grid

© David Biello

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Ensconced in a former warehouse in Manhattan's Harlem neighborhood, an energy start-up has equipment not typically associated with battery manufacture—restaurant-grade mixers, pasta-makers and even rolling pins. This kitchen equipment makes ingredients that the company hopes will turn the familiar alkaline battery into a cheap way to store the electricity from massive wind farms.

Like many other battery start-ups, Urban Electric Power has survived so far on city and state business development grants for its Harlem location as well as research funding from the Advanced Research Projects Agency for Energy (ARPA–E). But what also distinguishes Urban Electric from their peers (aside from the restaurant gear) became obvious during a recent tour of the new facility with Secretary of Energy Ernest Moniz—namely, the lack of glove boxes that fill other experimental battery shops. "That's because the materials we work with are so safe," says Valerio De Angelis, interim CEO of start-up battery maker Urban Electric Power.

Such boxes, with long, thick gloves sticking out waiting for scientific hands to fill them, protect researchers from the caustic, volatile or otherwise dangerous chemicals they work with in the quest for a cheap and stable battery. But at Urban Electric, the young researchers work with relatively stable, well-known and old chemistry: zinc paired with manganese dioxide. Could the same chemistry employed in disposable batteries clear the path for even larger scale deployment of renewable resources such as wind and solar power?

View a slide show of the makings of these alkaline batteries.

The money from ARPA–E came in pursuit of exactly that old energy holy grail: grid-scale storage of electricity. Such storage could be the key to enabling more renewable sources of electricity generation—providing power when the sun is not shining or the wind not blowing—or simply making the best use of existing resources, such as sucking up power that would otherwise be dumped from always-on nuclear reactors. "Storage gives you massive flexibility," Moniz notes, adding that it can help improve reliability and resilience as well by providing backup power. "The issue has been the cost."

So ARPA–E set a goal for members of its Grid-Scale Rampable Intermittent Dispatchable Storage, or GRIDS program, like Urban Electric Power: a big battery for less than $100 per kilowatt-hour of storage. "The only thing we could think of to do that is a massive rechargeable Duracell," says chemical engineer Sanjoy Banerjee, founder of Urban Electric and director of The Energy Institute at City College of New York. Disposable batteries have employed zinc and manganese for decades, and given that all the components have been in use for that span in so-called alkaline batteries, the cost of everything from the electrodes to the separators is very cheap, much cheaper than lithium ion or any other kind of battery. "It's probably the lowest cost battery that can be put together."

Of course, a disposable battery lasts for just one charge. Recharging such batteries has been difficult in the past because the zinc develops flaws that prevent the battery from working.

The key to preventing that degradation turns out to be flow. In the case of Urban Electric, that means little propellers attached by magnets to the bottom of the plastic container holding a series of zinc–manganese dioxide pouch cells. The fans circulate a fluid that keeps the flaws from forming, and the ions flowing in and out of the electrodes. That fluid also turns out to be cheap: water. The convection from a little bit of water flowing around the pouch cells prevents the formation of tiny fibers on the zinc electrode, known as dendrites, that kill off a typical alkaline battery. "We use very little flow," Banerjee says. "It's really just stirring."

The team is also working to improve the manganese electrode, using a graphite binder to help improve its electrical conductivity. They mix manganese, graphite and isopropanol, then squeeze the black doughlike material out with pasta-makers and roll it by hand into strips. "It's exactly like making pasta," says David Kohn, a UEP staffer.

On the other side of the lab the team works to ensure that only zinc is deposited on the negative electrode and then is completely stripped off between cycles. The process is the same, although the dough used here is more of a slate gray. The thickness of the pasta sheet determines the amount of energy that can be stored. A current collector in the form of foils or chicken wire or a honeycomblike sheet is added to the back and the whole thing is left out to dry, "usually overnight," says Melissa Menard, a senior scientist at Urban Electric. It's a bespoke battery production line at present, which is why the handmade batteries currently cost roughly $200 per kilowatt-hour to make.

But Urban Electric Power estimates its battery can store grid-scale electricity at a cost of roughly $91 per kilowatt-hour, once this bespoke process is industrialized (and the goal is to do that by 2017). "A lot of these start-up companies eventually hit a roadblock, but some of them don't," Moniz notes. "If they can get below $100 a kilowatt in a manufacturable system, that would be a significant place to be."

Alternative energy
It's not all just for storage at the size of megawatts. In fact, the first demonstration—at City College of New York just 10 blocks away—will use nearly 900 of the batteries to help Consolidated Edison, the local utility, with its highest electricity demands of the year as well as maintaining the quality of the power, such as keeping the electrical frequency at 60 hertz. The 448 batteries already installed cope with 300 amps in and out and are closely watched by many other organizations as well, including various agencies of New York State and the federal government. Con Ed is observing particularly closely to see if such cheap battery arrays might reduce the need for new substations in limited (and pricey) New York City real estate. "Distributed storage is a way to maintain peak power," says Urban Electric's De Angelis, and make sure the lights—and air-conditioning—do not fail on a hot summer day.

"You can put it in the basement," adds Banerjee. "It's very safe."

If cheap enough, the batteries could also find use as a replacement for polluting diesel generators throughout the developing world. As it stands, even with hundreds of the little propellers running in these batteries, "the lights in the room take up more power," notes Kevin Galloway, principal engineer at Urban Electric.

One challenge is integration: How do the batteries work with the other machines that make up the electricity supply, such as inverters that transform current from alternating (AC) to direct (DC)? What control systems are needed to ensure that a battery functions properly and safely? But the biggest single challenge is similar to other potentially disruptive technologies: getting permission from the utilities to hook up to the U.S. electric grid, which is effectively the world’s largest machine.

According to company data, the batteries have maintained performance over more than 3,000 cycles of two hours’ charging followed by two hours’ discharging so far—and newly arrived (and still in the process of being set up) testing racks should reveal more. The goal is to create batteries that last for 10,000 cycles or more and the system seems to be capable of handling charge/discharge pulses lasting as little as 12 minutes. The batteries also don't seem to prefer a particular amount of charging to operate. The batteries work the same between 20 percent charged and 78 percent charged, according to Alexander Couzis, Urban Electric's vice president of technology and production.

The batteries will be competing against other technologies, such as other battery chemistries, compressed air, molten salts, flywheels and the like. And the U.S. already has nearly 25 gigawatts of energy storage, nearly all of it in the form of water pumped up a hill so that when it flows back down it can pass through turbines and re-create electricity. Cheap batteries would free energy storage from that geographical trap. Already, California has enacted a law requiring state utilities to buy 1,325 megawatts of such storage to cope with its growing renewable energy supply and the U.S. Department of Energy has set up a Joint Center for Energy Storage Research at Argonne National Laboratory

In the case of Urban Electric Power it remains to be seen if their batteries are manufacturable and scalable—and therefore can play a role in places like California or New York City. And despite the slightly altered old adage in this field: "liars, damned liars and battery suppliers," Urban Electric aims to make good on its promise. "We're not well trained as liars," De Angelis says. "We're just a mix of engineers and entrepreneurs."

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