In Every Dream Home, a Storage System | MIT Technology Review

Home Energy Storage Enters a New Era

Advanced lithium-ion chemistries offer cooler operation, longer life spans.

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By Richard Martin on
September 17, 2015

WHY IT MATTERS 
Cheaper energy storage is needed to integrate renewable energy sources into the grid.

SimpliPhi’s installations, like this one for the Los Angeles Department of Water and Power,
can help reduce loads on the grid and integrate more power from renewable
sources.

Driven by the explosion of residential solar power, the market for home energy storage—which
attracted little interest until earlier this year, when Tesla announced its Powerwall battery—is
suddenly looking crowded.

This week at the Solar Power International show, in Anaheim, a company called SimpliPhi 

Power is unveiling a lightweight battery system for homes and small businesses that offers a longer life span than other lithium-ion batteries and doesn’t require expensive cooling and ventilation systems.

SimpliPhi’s bid comes a few weeks after another energy storage provider,Orison, released its design for a small plug-and-play battery system that, unlike the SimpliPhi and Powerwall options, does not require elaborate installation or permits for a home or small commercial setting.

Orison is not actually selling its products yet; it has launched a Kickstarter campaign to take pre-orders and expects to begin selling in early 2016. Its innovations center on the batteries’ controls and communication systems: simply plugged into a wall socket, the battery enables a bidirectional flow of electricity, charging itself when power is flowing and sending power into the home circuits
when it is not.

The growing popularity of residential solar panels is increasing interest in batteries that could store electricity from those installations. In the future, such storage systems could benefit homeowners, by giving them more control over how and when they obtain the power they need, while helping utilities by shifting demand to off-peak hours and smoothing out the load on the system.

SimpliPhi’s batteries use lithium iron phosphate, which dramatically reduces the risks of
overheating and fire.

For the moment, despite Tesla’s splashy entry into the market, such batteries still generally remain too expensive and cumbersome for most consumers. SolarCity, the largest solar provider in the United States, began offering a combined solar and storage system using Powerwall this summer, but it’s available only in newly built homes for now. And earlier this year rival SunEdison acquired Solar

Grid Storage, an integrator of solar arrays and energy storage—but it’s not yet clear exactly what that will mean for the market in home energy storage. 

The ultimate goal, for some users, will be to cut the cord completely: to install enough solar capacity and enough storage to get off the grid. But for most that won’t happen soon. “The market as we see is where people are still tied to the grid,but with distributed generation and storage, the grid becomes the backup,” says SimpliPhi CEO Catherine Von Burg.

Orison’s products will use a lithium manganese cobalt battery from a supplier that CEO Eric Clifton declines to name. SimpliPhi, on the other hand, is using a relatively new battery chemistry known as lithium iron phosphate. The absence of cobalt in the cathode makes lithium iron phosphate batteries less subject to material shortages (cobalt is scarce and expensive) and, more important, less prone to heating up—a problem with lithium-ion batteries, which have shown an alarming tendency to go into thermal runaway (uncontrolled heating that can destroy the battery) or even catch fire.

Lithium iron phosphate batteries are in use in a number of applications—BAE Systems, for instance, makes hybrid buses that use the technology—but have not been widely applied to distributed, stationary energy storage until now. Stuart Lennox,SimpliPhi’s CTO and founder, licensed the technology from battery pioneer John Goodenoughin the mid-2000s.

The downside of lithium iron phosphate batteries is that they offer much less volumetric capacity than other lithium-ion chemistries—about 50 percent less than lithium cobalt oxide, for example, according to energy storage scientist Stanley Whittingham, director of the Institute for Materials Research at Binghamton University. “If you’ve got a garage to put it in, it’s fine,” Whittingham says. “It’ll take over wherever volume is not an issue.”

The Orison systems will start at around $1,600 for two kilowatt-hours of power (the average American home uses about 30 kilowatt-hours of electricity a day). The Powerwall starts at $3,000 for seven kilowatt-hours. That’s enough to keep the lights on for several hours, but not to run your home on all day. SimpliPhi has not yet released prices for its home systems. For the moment, whether homeowners and small-business owners will pay thousands of dollars for energy storage remains an open question.