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Can Battery Storage And Solar Work Together? Arizona's Largest Utility To Find Out

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Last week, Phoenix-based APS, Arizona’s largest utility, began testing a 1.5-megawatt-hour energy storage system. The shipping container-sized unit, developed by lithium-ion battery maker Electrovaya Inc., can dispatch power equivalent to 1,200 hybrid Prius sedans or 300,000 cell phone batteries. Here is a video with a description of how the unit works.

The energy storage system, located in Flagstaff, will see double duty over the two-year pilot. At its first stop, an electrical distribution substation, the unit will store electricity when demand and prices are low and dispatch it at peak, usually late afternoon and early evening, when demand surges. In about a year, the unit will be trucked a few miles away, to a neighborhood solar zone, to interact with a 500-kilowatt photovoltaic (PV) farm and cluster of rooftop solar arrays (more on this below).

Battery storage and solar, working together

Once installed at the Doney Park Renewable Energy site, home to the 500-kW PV farm, APS will use the energy storage system to supply power when solar output dips, as when a cloud passes overhead, and to help meet higher demand at peak after dark.

“One of the busiest times on our system is between 5 and 9 p.m. That’s when many customers get home from work, turn on the lights, the TV and the air conditioner. However, by that time, solar systems have largely stopped producing for the day,” APS Energy Storage Project Manager Joe Wilhelm said in a statement. “With storage, we can gather solar energy during the day and dispatch it in the evening.”

“Connecting the energy storage system to a small solar plant like the one in Doney Park was certainly attractive,” APS spokesman Dan Wool wrote in an e-mail. “But overall, Flagstaff offers a very stable system environment to test technologies such as energy storage. Flagstaff is not subject to the extreme desert temperatures and high customer demand we see in say, Phoenix.”

Flagstaff: clean energy incubator

The energy storage pilot burnishes Flagstaff’s reputation as an emerging clean energy incubator. The city is home to Southwest Windpower, one of the leading manufacturers of small wind turbines. My alma mater, Northern Arizona University (go Lumberjacks!), has built some of the most impressive green buildings erected anywhere, including the LEED Platinum Applied Research and Development Building.

Flagstaff is also home to an earlier APS solar project that complements the new energy storage pilot. In April 2010, the utility launched a Community Power Project in Flagstaff’s Doney Park neighborhood – the future destination of the Electrovaya unit. Funded by a $3.3 million grant from the U.S. Department of Energy, the 45-month study is analyzing the effects of adding a high concentration of solar to the grid in a single neighborhood.

APS owns, maintains, and receives the electricity generated by 125 photovoltaic systems it installed on homes and an elementary school in the area. Customers who agreed to host PV arrays are charged a fixed rate (PDF) for the electricity produced by the systems over 20 years. APS is also deploying smart grid technology to help facilitate the interaction between the energy storage system, the 500-kW PV farm, and the rooftop solar arrays.

The energy storage pilot is funded by APS. APS' Dan Wool told me he could not provide the project cost because of a non-disclosure agreement with Electrovaya.