Backyard Batteries: Residential Storage Finally Passes Pilot Phase

Shutterstock / Zlatko Guzmic
Published On
Apr 16, 2018

A new partnership between an Arizona production homebuilder and a German battery maker might accomplish what a seemingly endless number of pilot projects have not. It could prove residential solar-plus-storage installations make economic sense and can improve grid operations. Under a plan co-developed with the local utility, the home-sited batteries will essentially take the development off-grid during peak-demand periods, and homebuyers will see significantly reduced electricity bills.

Located in Prescott Valley, Ariz., about 90 miles north of Phoenix, Jasper is a master-planned community set to break ground this summer. Developed by Mandalay Homes, a nationally recognized leader in high-efficiency home building, and land developer Arizona Eco Development, the project is anticipated to include 2,900 homes when complete. Jasper also will mark the entry of a connected battery system called sonnenCommunity, from German battery manufacturer Sonnen, in the United States.

In Germany’s deregulated utility market, Sonnen has set up near-independent utilities at a community scale, in which neighbors buy and sell rooftop-generated electricity among themselves. Such an arrangement isn’t currently feasible in the U.S. market. However, the software and controls enabling sonnenCommunity batteries to act as a single virtual power plant (VPP), based on signals from the connected grid, can be applied to help homeowners use less grid-supplied electricity during peak-demand periods.

“The fleet will charge during the specified hours the utility wants us to charge,” said Blake Richetta, Sonnen’s senior vice president responsible for the company’s U.S. operations.

This will mean timing the batteries to tank up between 10 a.m. and 1 p.m., when the local utility Arizona Public Service (APS) is typically oversupplied with electricity generated by rooftop panels. Homeowners will draw down that stored energy during the peak 3 p.m.–8 p.m. period.

“We’re going to become virtually invisible to them through those hours,” he said.

Cost has been a stumbling block in rolling out solar-plus-storage at a large scale. The viability of this plan begins with Mandalay’s efficient home designs, which have been rated to use less than half the energy of the average new U.S. house. In Arizona, where energy use is primarily driven by electrically powered cooling systems, this is an important advantage. Lower electricity demand means fewer solar panels and smaller battery systems to match a home’s demand.

“The stronger the house is on its own, it makes all the other conversations so much easier to get to,” said Geoff Ferrell, Mandalay Homes’ chief technology officer.

Jasper’s homes will only require a 2-kilowatt (kW) rooftop array to match its demand, versus the 7-kW to 8-kW system in an average home. Batteries only need to be scaled to a capacity of 8–10 kilowatt-hours (kWh) instead of the 20-kWh system that could be needed to keep all systems up and running in a traditional design.

Ferrell described the math behind rolling the system out as a standard feature rather than as one-off upgrades.

“It’s much more viable because it’s so much smaller,” he said.

The partnership between homebuilder and battery manufacturer began after a presentation Ferrell heard Richetta give describing the sonnenCommunity. Sonnen was exploring options for bringing its community model to the United States, and Mandalay Homes wanted a battery partner to help bring its already-efficient homes closer to true net-zero energy status. Soon after, Mandalay Homes began a conversation with APS to see about structuring a rate for the community’s homeowners that would recognize the value their stored energy could bring to grid operations.

“The way solar was introduced, the utilities have been forced to accept this energy, and they’ve been villainized in a way,” Ferrell said.

In fact, Mandalay had resisted adding solar in previous projects because Ferrell and company CEO Dave Everson didn’t want to contribute to what they saw as a problematic oversupply of solar energy that suddenly left the system as daylight waned. However, by adding storage, solar peaks and valleys can be flattened. The combined capacity of Jasper’s batteries will total 29 megawatt-hours, potentially enough to eliminate the need for coal-fired peak generation.

This project, announced in October 2017, has generated significant interest from other home developers. As of mid-February, Richetta said, the company had agreements for more than 18,000 such installations in other planned developments across the country. He sees this growing interest in energy storage as an opportunity for electrical contractors to expand their businesses into new areas. For example, Sonnen’s storage-control systems are just a piece of a broader approach by the company that includes home automation features such as lighting and window shade controls.

“We are very interested in local partnerships, and obviously, this bridges the gap from just being a solar guy, to being a high-end lighting-control guy,” he said.

About the Author

Chuck Ross

Freelance Writer

Chuck Ross has covered building and energy technologies and electric-utility business issues for a range of industry publications and websites for more than 25 years. Contact him at

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