Vanadium Redox Flow Batteries: The Future of Grid Energy Storage

The vanadium redoxflow battery is big and long lived and it wont catch fire BY Z GARY YANG IS THIS THE ULTIMATE GRID BATTERY 36 NOV 2017 NORTH AMERICAN SPECTRUMIEEEORG GO BIG This factory produces vanadium redoxflow batteries destined for the worlds largest battery site a 200megawatt 800megawatt hour storage station in Chinas Liaoning province redoxflow batteries a specialized type whose time has finally come The VRFB was invented decades ago but has emerged only recently as one of the leading contenders for largescale energy storage How large VRFBs are being touted for gridscale uses in which they would store up to hundreds of megawatthours of energy In these applications they may be charged by large baseload power plants which generate electricity cheaply but are too sluggish to accommodate sharp increases in demand during peak hours Or they may be charged by renewable sources like wind farms whose generation doesnt always align well with demand Like most batteries VRFBs can deliver power nearly instantaneously so they can stand in for the traditional means of meeting peak demand fossilfueled peaker plants that in comparison with batteries are costly to maintain and operate and not as fast Lithiumion batteries too have been proposed for gridscale uses But here they are no match for VRFBs which have longer lifetimes can be scaled up more easily and can operate day in day out with no significant performance loss for 20 years or more Soon this technology will be the cornerstone of the largest battery installation in the world a 200MW 800megawatthour storage station being built in Dalian The first 100 MW will be installed by the end of this year with the remainder coming on line in 2018 The station will help balance supply and demand on the Liaoning province power grid which serves about 40 mil lion people filling the same function as a peaker power plant but without using scarce water Furthermore if the batteries are charged by the windgenerated power thats abundant in northern China no fossil fuels will be burned Should demand spike or the supply dip suddenly the battery station will be able to dispatch all or just part of its 200 MW within milliseconds The result will be a stable grid that can integrate more renew able energy At times wind generation in Liaoning province tops 7 GW or about 15 percent of total generation But much of that power isnt used because other sources already meet grid demand Earlier this year the amount of wind power in Liao ning that was curtailed or wasted reached 15 percent in the neighboring province of Jilin it was 30 percent The Dalian site will store that wasted energy for later use adding up to a few hundred gigawatthours per month The Dalian site is just one of several big VRFB installations being built in China so its reign as the worlds biggest battery may be short Meanwhile other countries are adopting VRFBs According to the US Department of Energys global energy stor age database since 2014 more than 30 VRFB projects in 11 coun tries have been deployed or begun construction these range in power from a few tens of kilowatts up to Dalians 200 MW While these projects reflect the surging interest in all forms of energy storage whats driving the renewed push toward VRFBs are important technological distinctions THE FACTORY SPRAWLS OVER AN AREA LARGER THAN 20 SOCCER FIELDS Inside its brightly lit and filled with humming machin ery a mammoth futuristic manufactory Robot arms grab components from bins and place each part with precision while conveyor belts move the assembled pieces smoothly down production lines Finished products enter testing stations for quality checks before being packed for shipping It has been called a gigafactory and it does indeed produce vast quantities of advanced batteries But this gigafactory is in China not Nevada It doesnt make batteries for cars and its not part of the Elon Musk empire Opened in early 2017 in the northern Chinese port city of Dalian this plant is owned by Rongke Power and is turning out battery systems for some of the worlds largest energy storage installations Its on target to produce 300 megawatts worth of batter ies by the end of this year eventually ramping up to 3 gigawatts per year The scale of this other gigafactory may be impres sive but the core technology it makes is even more compelling The Dalian factory produces vanadium 38 NOV 2017 NORTH AMERICAN SPECTRUMIEEEORG PREVIOUS PAGES RONGKE POWER TODAYS STATEOFTHEART vanadium redox flow batteries started out as a modest research project at the Pacific Northwest National Labora tory PNNL a US Department of Energy lab in Washington state The PNNL team which I led came together in 2007 at a time when world oil prices were steadily climbing The economies of China and India were experiencing doubledigit growth and environmentalists were concerned about the accelerating rate at which they and other coun tries were consuming fossil fuels In the United States awareness was starting to build about the potential of renewable but intermit tent energy sources like wind and solar Against that backdrop we decided to search for a better way to store renewable energy as a means of promoting its adoption while also improving grid reliability Our group included the labs top experts on power materials and chemistry as well as an intellectualproperty lawyer Peter Christiansen who has a background in power engi neering Peter helped focus our efforts on tech nologies that would have the greatest societal impact In 2009 our group began receiving sig nificant support from the DOEs Energy Storage Program which boosted our annual RD budget to US 10 million At the outset it wasnt at all obvious that flow bat teries were the way to go Indeed we started off by reviewing all of the various battery technologies including lithium ion sodium sulfur advanced lead acid redox flow and a few other novel concepts Then as now attention was being lavished mainly on highpower lithiumion batteries According to Greentech Media over 90 percent of energy storage systems deployed in the United States in 2015 and 2016 were Liion batteries and thats likely to be true this year as well The tech THE POSITIVE and negative sides of a vanadium redoxflow battery are separated by a membrane that selectively allows protons to go through During charging an applied voltage causes vanadium ions to each lose an electron on the positive side The freed electrons flow through the outside circuit to the negative side where they are stored During discharging the stored electrons are released flowing back through the outside circuit to the positive side THIS BATTERY FLOWS e e e e V4 V4 O2 O2 O2 O2 H H H H Cl Cl Cl V5 Cl Cl Cl H H H H H H H H H H H H H H H H H H O2 O2 O2 V3 V3 V2 O2 O2 O2 IONSELECTIVE MEMBRANE NEGATIVE CELL V2V3 PUMP POWER SOURCELOAD POSITIVE CELL V4V5 ELECTROLYTE TANK ELECTRODE T SPECTRUMIEEEORG NORTH AMERICAN NOV 2017 39 ILLUSTRATION BY James Provost battery maker NGK Insulators recalled its products and temporar ily halted production Redoxflow batteries RFBs by contrast offer features not found in other batteries In theory they can be easily scaled up to megawatthours sustain their performance over much longer life times and be much safer if built around nonflammable materials In contrast to Liion and other solidstate batteries which store elec tricity or charge in electrodes made from active solid materials an RFB works more like a reversible fuel cell To discharge the battery takes the chemical energy stored in liquid electrolytes and converts it into electrical current reversing the process to charge Each flow battery cell has a negative side and a positive side Depend ing on whether the battery is charging or discharging each side will either produce or take in electrons that are flowing through an out side circuit The two sides are separated by a membrane that selec tively allows protons to pass through During charging a voltage applied across the positive and negative sides causes vanadium ions in the electrolytewhich is flowing through the batterys stack of thin platelike cellsto each lose an electron on the positive side The freed electrons pass through the outside circuit to reach the negative side storing electrical energy During discharging the accumulated elec trons on the negative side flow back through the outside circuit and are taken up on the positive side releasing the stored electrical energy The first redoxflow batteries were developed in the early 1970s by Lawrence Thaller and his group at NASA as a possible energy source for deepspace missions They used an iron solution on the positive side and a chromium solution on the negative side But the use of different elements led to crosscontamination as iron and chromium ions tended to diffuse across the membrane separating the two solutions In the mid1980s Maria SkyllasKazacos and her group at the Uni versity of New South Wales in Sydney demonstrated an improved RFB that used the same elementvanadiumon both sides of the bat tery so there was no risk of contamination Vanadium is an abundant silverygray metal cousin to niobium and tantalum that is primarily nology has steadily advanced as a result of several decades of intense work on batteries for electric vehicles and also mobile devices such as laptops tablets and smartphones Teslas Powerwall for example is intended for residential and business energy storage but it uses essentially the same Liion cells as those in the companys electric cars For the gridscale applications we were target ing however lithiumion has major shortcom ings To make battery packs capable of storing megawatthours requires many thousands or even millions of Liion cells each of which needs to be managed individually as well as collectively with the other cells Even then Liion batteries can supply power over only relatively short durations typically 2 hours or less To create a longerduration battery manufac turers would have to make the electrodes thicker and pack them with more active materials which would raise the price Or utilities could simply install more Liion battery packs adding to the cost The performance of a Liion battery also degrades over time giving the battery a typical lifetime of 10 years or so That may be fine for a family car but is less desirable for use on the power grid And Liion batteries have known safety issues most notably the occasional explosion or spontaneous fire We also looked at sodiumsulfur batteries Once considered quite promising for utilityscale instal lations this type of battery operates at around 300 C to liquefy the sulfur and sodium which respectively form the positive and negative elec trodes But these batteries too have flammabil ity issues After a 2MW system at a plant in Joso City Japan caught fire in 2011 for example the THE OTHER GIGAFACTORY Rongke Powers battery factory in Dalian China is set to produce 3 gigawatts worth of vanadium redoxflow batteries annually by 2020 GRID FRIENDLY Vanadium redoxflow batteries last for 20 years or more retain their capacity even when fully discharged and charged and scale up easily to megawatt levels 40 NOV 2017 NORTH AMERICAN SPECTRUMIEEEORG LEFT RONGKE POWER RIGHT UNIENERGY TECHNOLOGIES And theres every reason to expect more utilities to opt for this energy storage technology China looks set to lead the way The countrys 13th Five Year Plan for PowerSector Development released last year aims to revitalize the electrical infra structure to allow the integration of over 300 GW of wind and solar power by 2020 It cites energy storage as a key technology in realizing this ambi tious goal and specifically recommends the scaling up of vanadium redoxflow batteries Meanwhile in California Hawaii Massachu setts New York and other states mandates and policies are colliding with simple economics to compel utilities to deploy energy storage at rates unimaginable even a decade ago As electricity customers come to expect every step of the electrical power chainfrom energy generation through transmission and distribu tion to the end userto be clean efficient reliable flexible and affordable the case for energy stor age grows ever stronger n POST YOUR COMMENTS at httpspectrumieeeorgvanadiumbattery1117 mined in China Russia South Africa and Brazil But the early VRFBs couldnt store much energyjust 12 to 15 watthours per liter of elec trolyte To serve any useful function the batteries would have to be huge A 1MW4MWh system would have occupied an area equal to one or two basketball courts Another problem was that the vanadium oxide tended to precipi tate out from the electrolytes resulting in a gradual loss in the bat terys capacity And as if those problems werent enough keeping the vanadium in solution meant that the batteries could operate only within a narrow temperature range between about 10 to 40 C The addition of thermalmanagement equipment and other control elec tronics further cut the batterys overall efficiency while increasing its size and complexity HESE SHORTCOMINGS NOTWITHSTANDING the PNNL team believed the technology had great potential So we resolved to develop new electro lyte chemistry membranes and prototypes With the VRFBs inventor SkyllasKazacos serving as an advisor we began by running simulations to investigate different electrolytes We tested the most promising ones in the lab and optimized their chemistry Finally in 2011 we succeeded in developing a new vanadium based electrolyte that relied on reactions with a chloride solution This seemingly simple change effectively doubled the energy density over that of existing VRFBs Because more vanadium ions remained stable in solution more of them were available during charging and discharging The resulting battery had a footprint that was onethird to onefifth as large as its predecessors and could function within a much wider ambient temperature range from 0 to 50 C without additional ther mal management Other modifications made the battery more reli able simpler to manage and more tolerant of electrolyte impurities PNNL licensed the breakthrough electrolyte chemistry to three US companies including UniEnergy Technologies UET a com pany that I cofounded in 2012 to commercialize the new VRFBs In the five years since then UET based in Mukiteo Wash has success fully scaled up the batteries and deployed several megawattlevel field demonstrations Our battery systems fit compactly in shipping containers making them easy to transport and deploy Weve also brought down the batteries cost A few years ago the cost of a 4hour VRFB system was about 800 per kilowatthour These days its about half that comparable to the cost of a station ary lithiumion system But thats not an applestoapples compari son As mentioned earlier like that of other solidstate batteries lithiumions capacity degrades over time and its life span is shorter Weve tested individual VRFBs through more than 14000 cycles fully charging and discharging each cycle and they still perform at 100 percent capacity This should translate into a life span of 20 years or more To date our company has installed several mega wattscale systems around the world with an additional 200 MWh either awarded or in contract BATTERIES INCLUDED Technicians top from the authors company UniEnergy Technologies in Mukilteo Wash work on a battery management system that monitors and controls the performance of a vanadium redoxflow battery At bottom a worker oversees the manufacture of VRFBs T SPECTRUMIEEEORG NORTH AMERICAN NOV 2017 41 TOP UNIENERGY TECHNOLOGIES BOTTOM RONGKE POWER