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The Competition for Energy Storage

by Robert Springer

Upper reservoir & dam of a Pumped Hydro Storage Scheme in Wales. The lower power station has four water turbines which generate 360 MW of electricity within
60 seconds of the need arising.

♦ The Gold Standard of Energy Storage
Pumped hydropower has been the gold standard of renewable energy storage for decades. Its combination of efficiency (70-85%) and ubiquity (perhaps as much as 99% bulk storage capacity worldwide) have made it the go-to technology for energy storage.

Several American companies think they've developed technologies that will compete with and even surpass the efficiency of pumped hydro.  All of the following companies are developing technologies that they hope will become a meaningful part of the smart grid — and become a viable alternative to pumped hydro.

♦ Cool Compressed Air Energy Storage
Compressed air energy storage (CAES) has been around for decades, mostly using abandoned mines or salt caverns for the storage and retrieval of compressed air to generate electricity.  Since not every city has a handy mine or salt cavern, companies looking to exploit the technology have focused on smaller and more convenient methods of storing and retrieving the energy stored in compressed air.

The wedding rhyme, "Something old, something new, something borrowed, something blue," could be a tagline for SustainX's approach to CAES.  Using proprietary technology (something new) and proven, decades old technologies from other industries (something old, something borrowed), the company's ICAES (isothermal CAES) technology is "able to conserve the heat of compression at fairly low temperatures and reintroduce it during expansion and operate completely fuel free unlike traditional compressed air systems," said Richard Brody, the company's vice president of business development.  "We can store it in pipeline pipe or other pressure vessels.  We don't need salt caverns.  It's the first site-able bulk energy storage solution."

Brody said that a SustainX's ICAES system should last "at least 20 years" with regular maintenance, making them more cost effective than batteries.  "All batteries and most electro-chemical systems are expensive to start with and have a fairly short deep discharge cycle life," he said.  "You need to replace it every five or six years which absolutely kills the value proposition.

SustainX has a pilot plant at its headquarters in Seabrook, New Hampshire, with field demonstrations planned for 2014.  Brody said that wind and solar energy storage should be good markets for SustainX with grid stabilization a possibility as well.

Rechargeable liquid batteries (Flow batteries) -
home energy storage with long-life & high safety; in modular units.

♦ Battery Wars

Battery storage startups are scrambling to find cost-effective ways to store renewable energy, with the field being particularly crowded and competitive.
Aquion Energy is sitting pretty, CEO Scott Pearson said.  Recent trials of Aquion's Aqueous Hybrid Ion battery proved that "our batteries do what we thought they'd do," he said.  And "our customers want larger batteries and more of them."

The chemistry powering Aquion's sodium-water battery was developed by Dr. Jay Whitacre at Carnegie Mellon University, The batteries are "very simple conceptually - they're carbon, sodium and salt water," Pearson said.  "They require no maintenance over time and they're safe.  You wouldn't like the taste but you could eat one.  You wouldn't die."

Like other energy storage companies, Pearson sees opportunities for Aquion in wind and solar farms and microgrids.  Utilities could also benefit from Aquion's batteries.  "We can help balance out an intermittent supply," he said.  "From the utility side it;s reacting to demand.  If you have a spike in demand we can help."

"We're at a very interesting time in this company," Pearson said.  "We have a proven battery and we are now in volume production in 2013.  It's not a science experiment anymore — it's a vibrant solution."

Flow batteries are another promising battery technology.  "They are rechargeable liquid batteries," says Primus Power CEO Tom Stepien, who helped start the Silicon Valley-based company in 2009.  "Potential is stored as chemical energy, usually in one or two tanks.  That energy is converted to electricity, as those chemicals are pumped through a reaction chamber a reversible chemical reaction takes place.  The plates are zinc typically.  When I first heard about flow batteries four years ago, I said, 'Really?  Do they work?'  The reality is it's just another way of storing electricity."

The advantages of a flow battery over lithium ion and sodium sulfur batteries include a substantially lower cost per unit energy, long lifespan and safety (they don't run hot like sodium sulfur and lithium ion batteries), Stepien said.

They're also modular — the units are built and delivered in a shipping container (see above), which means they're easy to transport and relocate.  "Some batteries are like a custom home that takes six months to get up and running," Stepien said. "We have more of a mobile home approach rather than a custom-home approach."

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