Make of it what you will, but a study last year by Lux Research predicted that grid scale energy storage will be a $2.8 billion market by 2020. Enormous, if anything like accurate. So, how to master wind that blows when it feels like it; or the sudden cloud cover that causes solar output to plummet 90%? - load shifts that can mean power systems having to rely on gas plant back-up.
Academics and their commercial partners want not only to create something that works, but a storage battery that will be cheap, durable, and non-toxic. As Renewable Energy Focus (REF) reported earlier this year, one such project, Ambri, spawned by Massachusetts Institute of Technology (MIT), has already caught Bill Gates’s eye.
But it’s not the only one: Gates is also backing a Pittsburgh-based project exploring the possibilities of using salt water as an electrolyte. A cheaper raw material is hard to imagine.
It’s the culmination of work by former NASA scientist Professor Jay Whitacre. Whitacre had been playing around a couple of years with the possibilities of salt water, before forming a company, Aquion, which works closely with universities in Pittsburgh, in particular Carnegie Mellon.
“Jay’s primary interest was finding technology for storage batteries that would keep costs down,” Aquion vice president Matt Maroon told REF. “That philosophy is driving the entire company.”
The concept is quite straightforward. The battery couples a carbon anode (negative terminal) with a sodium-based cathode (positive terminal); and the water-based electrolyte separating them shifts ions (atoms with a positive electrical charge) between the two during charge and discharge. This technology is far cheaper than using expensive flammable electrolytes traditionally used in traditional lithium-ion batteries.
It’s attracted some serious investment. “We’re not trying to reinvent the wheel – the equipment we use is pretty standard,” says Maroon. “We’ve have been very fortunate in our fund-raising – we’ve raised more than $100million.” That money, from Gates and venture capitalists, not only helps fund manufacturing but also further research and development. Production began last year but these are still early days.
“Our primary application is off-grid solar – we’re starting small and then will grow into installing large scale and commercial outlets,” said Maroon. “As the market matures we’ll pursue a grid energy strategy. One key element is that we can stack the batteries up in parallel – scale up or down.”
Aquion now employs 150. Its biggest project to date is a 1MW installation in Hawaii – a popular testing ground - where electricity, derived mainly from imported gas, is notoriously expensive. “It was for a very large private home that can’t get a grid connection and has relied on propane generators,” Maroon said. The result: a propane bill cut by 97% through using solar energy that’s charged up the battery during daytime.
The company has forged a relationship with manufacturers such as Siemens whereby Aquion batteries can integrate with their power electronics. Aquion’s website includes a hard sell of the battery’s sound economics; ‘safe’ chemistry; the durability; that it can operate across fluctuating temperatures.
So what about those sound economics? Maroon says that Aquion’s unit cost is currently ‘well below’ $500 per KW hour. “We’ll easily reach $300 in the next 18 months and believe, with this chemistry, we can approach the $200 threshold.”
A story with some similarities is unfolding across the country in California. Just as Aquion has its roots in Carnegie Mellon and Jay Whitacre’s research, so another recent start-up, Alveo Energy, has sprung from work that began at Stanford University. Its quest is the same: to create a commercially viable, cheaper, and less toxic storage battery. And it involves using water.
The man behind this is research scientist Colin Wessells, and it’s been his life’s work for the last six or seven years. At the outset his aim was to develop and commercialize a battery using water, Prussian blue dye, iron and copper. “We were interested in a water-based electrolyte because there’s no flammability,” he told REF.
As Wessells and co-founder Professor Robert Huggin ploughed on, they urgently needed funds to keep going. “In 2012, I began raising money, working alone, without a salary or support,” Wessells said. But then, a breakthrough - their work caught the eye of the US Department of Energy. The result: a $4 million grant from its Advanced Research Projects Agency–Energy (ARPA-E).
“That was crucial,” says Wessells. “Soon after we got that a venture capital company in the San Francisco Valley said ‘there’s someone with better knowledge than us backing this’ – and put in $1.5 million. That grant had given us technological credibility. At the time, we had a decent understanding of positive electrodes, but water-based negative electrodes were still on the drawing board - negative- based electrode material was degrading within about an hour.”
But the extra venture capital allowed Wessells and his team to tackle the materials science. Now they think they’ve cracked the problem – after six months’ testing of prototypes, there’s ‘no evidence’ of degradation.
Alveo abandoned working with copper once Wessells found it could be replaced with ‘significantly less expensive’ metals – though he prefers not to say which ones. That’s understandable in a copycat world where the stakes could be high.
Where might it all lead? First, Wessells hopes, to batteries that will be a good source of back-up storage – ‘though they can’t be high voltage because that turns water into its constituent gases, hydrogen and oxygen.’
He believes that when Alveo products come to market, they could eventually replace lead acid batteries. “The up-front cost of ours won’t be much less than lead batteries, but they’ll have a much longer life,” he says. The constant cycle of charge and discharge is highly demanding: ‘the cause of lead batteries wearing out’. But, he claims, “we can do tens of thousands of discharges with ours.”
“We’re scaling up the prototype. That may be ready in two years to demonstrate to an installer, so it can be integrated as part of a big system. In terms of bringing it to market, it might be a further two years after that.”
Long term, Alveo’s market is big solar and wind systems. “But we’re not ready to go straight in … though there are battery manufacturer salivating at that opportunity,” says Wessells.
For scientists at Harvard, the quest to escape metals-based technology has produced something quite new: a flow battery exploiting the electrochemical properties of a family of molecules known as quinones. The breakthrough, announced early last year, received worldwide attention. Now the drive is on to bring it to market.
Flow batteries store energy in chemical fluids housed in external tanks rather than the battery container itself. The battery’s two main components - electrochemical conversion hardware through which fluids flow, and storage tanks which dictate the energy capacity - can be independently sized. Thus the amount of energy that can be stored is limited only by the size of the tanks.
The design means storage is cheaper than in traditional solid-electrode batteries, where power conversion hardware and energy capacity are packed together in one unit. These maintain peak discharge power for less than an hour before being drained - ill-suited for storing the electricity created intermittently by wind and sun.
Harvard’s project, like Alveo’s, has received ARPA-E funding; also money from the US National Science Foundation, and private donations. The Harvard team led by Dr. Roy Gordon, a professor of chemistry and materials science, studied more than 10,000 quinone molecules in the hunt to find which would work best.
“A wide variety of quinones are in all plants and animals, so we didn’t have to look far to see that evolution has adapted them for chemical storage of energy,” Gordon told REF. “We discovered that, by careful selection, we could adapt them for safe, efficient and cost-effective storage of electricity. Quinones are abundant in crude oil as well as in green plants – there’s plenty of petroleum available to make the materials (needed).”
The university is now working with its collaborator, Sustainable Innovations, based in East Hartford, Connecticut, to produce a marketable product. Earlier this year, Sustainable announced that its own scientists, working alongside Harvard’s, had replicated the results on a bigger scale. This cleared the way for a new round of designs – the aim to create a prototype three 3KW battery, possibly by mid-2016.
“It’s a big deal – we’re scaling up from a cell the size of a postage stamp,” says company chief executive Trent Molter. “Our demonstration cell was the size of a small laptop, a building block to the next step - a 3KW battery the size a home could use, depending on what part of the world you live in. And that will be a stepping stone towards scaling up to industrial size.”
Scaling-up sounds far simpler than actually it is. “The fluids have to travel a much longer distance, and you need to carry these with sufficient velocity to maintain the reaction kinetic,” said Molter. “You also need to be able to remove the (chemical) product, otherwise it will stick to the electrodes and make them ineffective.”
“We’ve had conversations with companies in the process of ‘greening’ with solar power, who are very disappointed in the choice of storage there is at the moment. But it could be three or four years before we get to the point of commercially producing industrial systems.”
The prototype 3KW storage system will, at first, ‘still have a man in the loop.’ The priority then will be getting fully automated; ‘to have it interfacing with renewables.’ The successful creation of that automatic system will be a landmark day for Molter and his team. But he knows it won’t be easy. “There’s a lot of work to do to deal with the vagaries of renewables,” he said. “It’s not the only one -interfacing with grid will be a big challenge, too.”
ABOUT THE AUTHOR
Andrew Mourant is a freelance journalist whose specialisms include renewable energy, education and the rail industry