by Julian Spector
July 21, 2017

Enough with all that lithium-ion talk. 

Sure, it makes up 97 percent of all the stationary storage capacity installed in the U.S. so far this year. But if energy journalists only focused on clear market leaders, we'd be spending a lot less time covering solar power, which, despite strong growth, constitutes only a sliver of the U.S. electricity supply.

Scale matters, but so does momentum, and I keep running into developers of lithium-ion alternatives with limited deployment who are taking concrete steps to scale up and compete where the incumbent is weak. This week's installment of Storage+ is all about them.

The entrepreneurs in this space have their work cut out for them, having chosen to abdicate the massive production scale that comes with lithium-ion manufacturing. They have to scale little-known chemistries while racing lithium-ion cost declines and banking on markets evolving toward longer-duration service.

Here are a few of the companies chugging along in that direction. 

How will 20-year PPAs change the market for storage technologies?

Zinc-iron flow-battery maker ViZn ran the numbers and said it could beat the record-breaking 4.5-cent per kilowatt-hour Tucson Electric Power PPA by substituting its technology for proposed lithium-ion.

Long-duration battery makers often wax poetic about how cheap they can deploy several years into the future, but this particular claim raised some useful points about how to think about the emerging utility-scale solar-plus-storage market.

As these 20-year PPAs become more common -- and they will -- the storage industry will feel more pressure to provide 20-year solutions to match solar modules. Current lithium-ion systems will need to swap out batteries to maintain capacity throughout that system lifetime.

This might be the big play flow battery makers have been waiting for. The off-grid/weak-grid market has been an early source of revenue, but usually in the form of small, isolated projects in far-flung places that take a lot of work to reach. The margins are much slimmer on mature grids.

To capitalize on this, flow batteries need to win the confidence of the utilities taking on these long-term deals. Then they have to prove that the low maintenance costs of flow technology really do beat out the lifetime costs of lithium-ion, which benefits from a cheaper upfront cost.

There's also an issue of backward compatibility, which hasn't really entered the discourse yet, since most lithium-ion systems are still quite new. If you're swapping in cells or modules on a decade-old system, who knows how far the new stuff will have advanced, and what will be required to calibrate it to run cohesively with the older remnants?

In the view of ViZn's Vice President of Marketing Mike Grunow, lithium-ion will continue to work well for single-purpose power application deployments, but flow will take over the long-term multiple-purpose applications for power and energy applications.

"Lithium-ion is going to turn out to be like First Solar: a good panel for a specific application that happens to be full of toxic stuff and has an awkward supply chain and needs an end of life recycling program," he said, referring to the carcinogenic cadmium that goes into First Solar cells and necessitates an end-of-life recycling program, but is not harmful in the finished product. Cost-effective recycling for lithium-ion remains a big question mark for the industry.

To test this theory, we just need to find a utility willing to bet on flow for solar-plus-storage. Any takers?

Generously season with iron and salt

Iron-redox flow battery maker ESS has taken some steps toward broader deployment.

The Portland, Oregon-based company recently delivered two 30-kilowatt systems to the Army Corps of Engineers, which will test them in a forward operating base environment. They will be charged by a 60-kilowatt diesel generator running at peak efficiency, after which the generator can turn off and allow the batteries run the site. The batteries can ship dry and be filled with potable water onsite to get up and running.

ESS also is sending its full-sized 50-kilowatt/400-kilowatt-hour shipping-container-enclosed systems to the UC-San Diego microgrid and to a renewable power plant in Lubbock, Texas, where DNV-GL will test its performance.

The key ingredients of iron, salt and water are cheap and abundant, but building the stacks by hand is expensive. To cut production costs, ESS is moving to a new factory where the stack production will be automated. It will take about six months to get the new system up to speed, but in 2018 production capacity should reach 300 megawatt-hours, VP of Business Development Bill Sproull told me at Intersolar.

This storage system has a unique approach to thermal management -- it likes heat. The chemistry operates at 50 degrees Celsius (122 degrees Fahrenheit ) which means warm ambient temperatures aren't a concern. If anything, the challenge is insulating against freezing temperatures outside that might cool down the reaction too far. 

The near-term strategy is to use the demonstration projects to raise awareness about the technology, and to work with EPCs and project developers to get units in the field around the world. But, Sproull said, the company is getting revenue from its demo projects. "We have not had to donate systems to anyone," he said. 

SimpliPhi has the production capacity to ramp up operations

I caught up with lithium-ferrous-phosphate battery maker SimpliPhi at Intersolar, and I was told the company has now installed 15 megawatt-hours, most of which is residential and paired with solar.

This company got its start making rugged batteries to assist Hollywood productions shooting in hot, remote environments. They found the technology that succeeded in those conditions also works well for military applications, but the company has since branched into a more widespread effort to replace lead-acid wherever possible.

Now the company is looking to sell more into the U.K. and Australia, and is considering entering the data center market. One trick up its sleeve: SimpliPhi has a factory in Ojai, California with 20 megawatt-hours of production capacity. That's enough to make in a year more than the company has sold in the past 15.

That flow battery/underground cavern storage mashup we've all been waiting for

Flow battery economics get better as they scale up in energy capacity, and we haven't seen anyone poke the upper limits just yet. Really gargantuan flow batteries would pose a land-use challenge, though, which is why this new project out of Germany is so intriguing.

German gas storage firm EWE Gasspeicher wants to fill two salt caverns, each around 100,000 cubic meters in volume, with brine in order to create a redox flow battery that has capacity of up to 120 megawatts and 700 megawatt-hours. Salt caverns have long been used to contain natural gas and compressed-air energy storage, but this is the first I've heard of putting a flow system down there.

That clears away any concerns of marring a city skyline with a tower full of electrolytes. To make it work, though, the particular chemistry has to be safe enough to pump into the ground.

Gasspeicher plans on using an experimental chemistry called brine4power that involves "recyclable polymers dissolved in salt water," rather than vanadium dissolved in sulfuric acid, for instance.

First the company will build aboveground pilots at 20 kilowatts/40 kilowatt-hours and 500 kilowatts/2.5 megawatt-hours. If those tests go well, which is by no means guaranteed, it hopes to complete the cavern system by 2023. 

A system as big as 700 megawatt-hours, which can hold its charge over a long period of time, starts to move into seasonal storage territory. But as a reminder of just how hard it will be to shift renewable generation from high to low production months, that whole battery could only power Berlin for an hour. Seasonal lulls are going to last a lot longer than that.

Hello, hydro

Speaking of pumping large volumes of fluids for storage, we've got a rare new entrant in the pumped hydro category.

The San Diego Water Authority has opened up an RFP for a 500-megawatt, 5- to 8-hour duration pumped hydro storage system. The project would involve building a new reservoir uphill from the existing San Vicente Reservoir.

This would build on the Water Authority's existing assets by generating revenue streams from storing cheap renewable generation and delivering it during lucrative peak times. It leverages some obvious synergies: expertise in dealing with water and a location already designed for holding large amounts of water.

The concept approaches water like investing one's savings: If it's going to be sitting there doing nothing for a while, why not make some money with it?