A company called UniEnergy Technologies (UET) has installed a new large flow battery on the grid in Snohomish County in Washington state. The 2MW, 8MWh battery system may seem like a small installation compared to recent projects in Southern California and Hawaii, but it's quite a step for the nascent flow battery industry. In fact, this installation is currently the largest capacity containerized flow battery system in the world. It's housed in 20 connected shipping containers and will be used by the Snohomish Public Utility District (otherwise known as SnoPUD), which has also invested in lithium-ion battery installations.

Flow batteries are less common than their lithium-ion brethren. But as grid-scale batteries go, they offer some interesting advantages to lithium-ion that could really pay off as some of the more obvious hurdles, like energy density and temperature sensitivity, are overcome. Flow batteries generally use two electrolyte chemical solutions stored in separate tanks, which are pumped into a common area where the solutions come in contact, often through a membrane, creating electrical charge. Flow batteries are cumbersome and much less energy-dense than lithium-ion batteries, but battery capacity is only limited by how much solution you can store. On a grid-scale level, that’s an advantage—grid-tied batteries don’t need to be portable or light, but they do need to store a great deal of energy.

UET’s vanadium redox (short for reduction-oxidation) flow battery is based on electrolyte chemistry developed with funding from the Department of Energy at the Pacific Northwest National Laboratory (PNNL). The company was founded by Gary Yang, a former research fellow at PNNL who worked on flow batteries at the lab. Yang licensed PNNL’s technology at UET's inception, hoping to build flow batteries based on vanadium electrolytes that, at least according to a PNNL press release, were capable of “delivering 80 percent increased power capacity [and] 90 percent increased efficiency, with about half the operating cost” of other vanadium redox flow batteries available at the time. The electrolyte chemistry also gave batteries “greater operational temperature range,” a sticking point for many flow batteries that existed in 2012.

UET then spent several years developing the technology, eventually running a demonstration project in 2015 that lasted for a year and a half. The demonstration project required 10 shipping containers and stored 3.2 MWh of energy.

With this new installation, PNNL says it will still be involved, “providing analytical and technical support” to help UET “[test] the performance of the battery systems and [evaluate] the economic impacts of the various services provided by them.”

If all goes well, more flow batteries could be integrated onto grids in the US and around the world. This week, the Energy Storage Association wrote a letter to Congress urging lawmakers to consider energy storage as a part of any future infrastructure bills that the Trump administration might propose. A preliminary infrastructure wish list from Trump's transition team that leaked in January included seven proposed upgrades to US electricity infrastructure, as well as one mention of funding for energy storage in California. However, the new administration has also threatened to cut the DOE's budget by 5.6 percent; the Office of Science, which funds national labs like PNNL, is facing a budget cut of nearly 20 percent.

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This particular flow battery was installed in late 2016. SnoPUD spent the next few months testing it out to make sure it integrated well with the grid before officially commissioning the battery in late March of this year. A grant from Washington state’s Clean Energy Fund in 2014 helped the utility purchase the flow battery. (Four other energy storage projects, including a smaller flow battery system from UET as well as lithium-ion battery installations, also received grants from Washington state in 2014).

During installation, the shipping containers that make up the battery system were strapped down to specially poured concrete pads and carefully connected to the shipping containers on either side. According to the Snohomish Public Utilities District, each shipping container “weighed 24,000 pounds at delivery, and will weigh 80,000 once filled with the vanadium electrolyte solution.” UET spokesperson Renee Gastineau explained that each shipping container is its own module, with two tanks and the corresponding electrical stacks apiece. All the containers are connected to a power control system that integrates them to the grid.

As far as the vanadium solution, Gastineau explained that the mineral isn't particularly exotic—it has been used for a long time in steel manufacturing, and as such, its price is subject to fluctuations that reflect what's going on in the steel market. "The cost of lithium batteries has been dropping significantly," Gastineau told Ars. "The cost of vanadium has, too. Over a lifecycle of 20 years, we’re on par with a lithium installation," she said, referring to the price of an installation like this.

Although this flow battery is currently among the largest installed on a grid in the world, that distinction may not last for long. UET's sister company is Chinese flow battery manufacturer Rongke Power (both companies share a major investor, and UET buys its electrical stacks from Rongke, according to Gastineau). Last year, the China National Energy Administration approved a massive 200MW/800MWh installation proposed by Rongke for the Liaodong Peninsula in northeast China, a strip of land that's home to Dalian, a city of nearly 7 million people. The Chinese government has recently pushed to improve energy resiliency on the typhoon-wracked peninsula by adding more renewable power and energy storage.

Rongke's flow battery will be connected directly to a wind farm, Gastineau added. The Chinese company is currently building the gigantic flow battery in two 100MW/ 400MWh installations, with the first installation under construction and the whole project set to be complete by the end of 2018. UET may eventually help Rongke scale the system up.

Until then, though, Snohomish PUD will be testing out its more modestly sized flow battery for the foreseeable future. According to the utility's spokesperson, Neil Neroutsos, the system is currently working well. "We have charged and discharged the battery effectively as well as other functions. We will be running a number of use cases with this system over several years."

Correction: Dalian is in northeastern China, not northwestern China.

Listing image by Snohomish PUD