In some ways, homeowners’ romantic notions of being energy independent fueled the recent growth in residential solar-plus-storage, says Wes Kennedy, instructor of HeatSpring’s Comprehensive Solar-Plus-Storage course.

The residential market was the fastest-moving market in solar-plus-storage, growing tenfold between 2017 and 2018, says Kennedy, who has been in the solar industry since 1996, employing battery-based solutions.   

“The idea of backup power or resilience has helped move the market,” he says. “It’s a romantic notion, tying into the American story about our pioneering spirit and ability to stand on two feet. That’s fueling the early adopter phase,” he says.

Aggregating Solar-Plus-Storage Benefits Utilities

But that’s not all that’s driving the market, says Kennedy. It’s becoming more and more financially and technologically feasible to aggregate smaller solar-plus-storage installations to provide resources to utilities.

“You have smaller resources, through communication and software, being bundled into a single resource,” he says.  “To the utility, 1,000 homes with solar-plus-storage look like a big dispatchable resource.”

While Kennedy has discussed the potential for this trend in his course in the past, it’s now starting to become reality, he says.

Keeping the Lights on with Tesla Powerwalls

One example is the 2,000 Tesla Powerwall storage units installed in Green Mountain Power territory. That pilot project is now full, according to the Green Mountain website. Under the program, homeowners’ solar, if available, charges the Powerwall, and so does power from the grid. Homeowners supply surplus solar generation to the grid and get credits. Under the program, homeowners pay Green Mountain Power $1,500 up front plus $15 a month for 10 years. Green Mountain Power controls the Powerwalls when the grid is offline.

In fact, the Powerwalls kept the lights on in  many of the homes recently when the utility had an outage, according to a Green Mountain Power press release.

What’s more, Green Mountain Power aggregated those systems and used them as resources during peak hours as an alternative to buying power, says Kennedy. That saved the utility more than $500,000 an hour, he says.

Sonnen Batteries Help During Peak Demand

In Arizona and Florida, Sonnen is also aggregating residential storage.  Last year, the company joined forces with Mandalay Homes, which built 2,900 homes in Prescott Valley, Ariz., and included a Sonnen battery in each home to help provide power during peak demand times. When that project is complete, the company will have 11.6 MW and about 23 MWh of energy storage, according to Utility Dive. The homes will be able to communicate with one another and create a network of clean storage systems, or a “virtual power plant” that can lower stress on the grid by supplying power during peak periods.

Another company, EnSync Energy Systems, aggregates solar-plus-storage, says Kennedy. The company recently announced that it signed a power purchase agreement with The Michaels Development Co. to build a solar-plus-storage project at an affordable housing development in Hawaii. The project includes technology allowing residents to exchange energy directly with one another.

“The high-level takeaway of these projects,” says Kennedy, “is that the market is growing very fast, and the residential sector is growing the most rapidly.”