UniEnergy Technologies Goes from Molecules to Megawatts
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the vanadium, useful in energy storage because it can have four different levels of positive charge, or valence states, and changes among them easily. Vanadium ions remain in solution in the liquid electrolyte throughout the process—stored in two separate tanks—as opposed to the lead paste or lithium strut matrix at the heart of other common battery types. Winter says those battery technologies see their capacities fade over time in part because their solid active ingredients expand and contract with each cycle, causing cracking and fatigue.
The flow battery is “just a warm solution that gets circulated through this electrode stack, and that’s where the reactions occur,” Winter says. Current from the electricity grid charges the battery, adding electrons to push the valence states of the vanadium in the electrolyte farther apart, to +2 on one side of the stack and +5 on the other. This creates the electrical potential—stored as chemical energy—to be called upon when the battery discharges back to the grid. When the electrolyte passes again through the electrode stack, electrons go the other way. That creates a current flowing back onto the grid, returning the vanadium’s charge to +3 and +4, ready to be charged up again. As the vanadium passes through its four valence states, it changes to another of its four colors, which are represented in UET’s logo.
Unlike some other battery technologies, the vanadium flow battery can’t catch fire or fail because of a chemical reaction. It does pose health risks, of course, because of the corrosive acid in the electrolyte. But UET makes a point of emphasizing the safety and stability of this chemistry.
“You can charge it completely, you can leave it there, and come back a year later and you’ve got 98 percent of the capacity left in it—if you turn the pumps off. You physically separated your active species [in the two tanks]. So there’s first of all no mechanism for self-discharge,” Winter says.
That separation also provides a way to interrupt thermal runaway, an uncontrollable heat buildup that has plagued other batteries, by simply turning the system off.
UET can pack the tanks, plumbing, electrode stack, and control equipment into a standard 20-foot shipping container—making it easy to assemble, ship, and install the batteries. Speaking at a clean technology event on the Seattle waterfront last month, Winter looked out the window to the thousands of containers stacked at the port and described them as among “the least-appreciated high-tech things in the world.” (The 20-foot container is also the size preferred by the military, he adds.)
The company can fit a meaningful amount of energy storage into this relatively small package thanks to the advancements Li, Yang, and their colleagues made at PNNL, which doubled the energy density of the battery. The current design can store about 19.5 watt-hours of energy per liter of electrolyte, a mark UET believes it can continue improving on. (Imergy Power Systems, another vanadium flow battery maker profiled by Xconomy in December, says it can achieve 23 watt-hours per liter.)
On top of the containers, a small radiator—about the size of one for a truck—provides all the temperature regulation necessary, given the broad range of working temperatures.
“If I had to use a chiller or an air-conditioner [to maintain a narrow temperature range], it costs me 25 percent in system efficiency, because those things are incredibly inefficient,” Winter says. “They’re also unreliable and expensive.”
As it is, the battery is 65 to 70 percent efficient, with energy used to run the pumps and radiator, and lost through AC conversion during the round-trip from the electrical grid.
UET buys standard containers from China International Marine Containers with a few customizations, including ports near the top to allow multiple containers to be connected together “like a pack of Duracells,” Winter says, and a full, solid steel floor that serves as a secondary containment mechanism for the battery.
“That makes a dramatic difference to the cost of deployment,” Winter says.
Site preparation and engineering can make up a third of a typical large-scale battery’s total cost, he says. “We want to reduce that to something like 5 to 10 percent of the deployed cost.”
The batteries can be built on a simple eight-inch concrete slab with grounding points, grid interconnection, and communications hookups. Enough containers can be packed together to store up to 20 megawatts of electricity per acre. They can also be stacked two or three high, multiplying the capacity per acre.
As a standard unit of international trade, the container can be easily shipped to locations around the world.
UET believes this standardization, as well as the ability to manufacture and test the batteries inside its facilities rather than in the field, will help it compete on price and reliability. Its current pricing is about $875 per kilowatt hour of storage, or about $3,500 per kilowatt of peak power capacity, but the company expects those numbers to come down substantially through economies of scale and product improvements as it ramps up manufacturing.
The company has another potential pricing advantage, too: There are about 23,000 liters of vanadium electrolyte in each shipping container, filling tanks that take up about three-quarters of their volume and constitute three-quarters of their total weight. This is where UET’s relationship with Bolong New Materials—owned by UET’s Chinese investor—comes in.
“The big issue with vanadium has been massively volatile pricing,” says Bill Radvak, CEO of American Vanadium, a Vancouver, Canada-based mining company aiming to build a vanadium mine in Nevada to serve the energy storage market. “I’m not talking 20 to 30 percent, but 400, 500 percent increased pricing in a month or two. When vanadium electrolyte is 40 percent of the cost of your batteries, any kind of volatility like that obviously means you’re losing a lot of money with each battery cell.”
(UET says the electrolyte represents about a third of the price of its battery, assuming the two components are purchased together. It also offers the option of leasing the electrolyte.)
“That’s why certain research firms that look at energy storage at the macro level aren’t very big proponents of vanadium flow batteries,” Radvak adds. “Not because of technology, but because they just don’t believe there’s enough vanadium supply there to keep the costs down and keep the batteries competitive.”
American Vanadium has partnered with Gildemeister to market the German company’s vanadium redox flow battery in North America. “What we’ve done really is insulated our partnership from that global issue by having our own supply,” Radvak says.
So too has UET with Bolong New Materials, which Radvak describes as “a top-three global provider of vanadium specialty alloys and chemicals.”
Winter says Bolong is capable of producing enough vanadium electrolyte annually to build batteries with the capacity … Next Page »