Battery-Powered Home Backup Systems

“A storm can mess with a power line, knocking out power for hours, but our Internet, furnace, and refrigerator stay on,” says Phil Robertston of Woodstock, VT. Two years ago, Robertson signed up for a pilot program to install a Tesla home battery system called the Powerwall that’s based on the same lithium-ion technology the company uses in its electric cars. In blackouts, the battery provides backup power. The current cost, including installation work, is $15 a month for 10 years. The battery is the size of a small bookcase and can recharge either from a house’s own solar panels or from the grid.

Green Mountain Power, the largest power utility in Vermont, is discounting home battery systems for its customers because it also reserves the ability to remotely access the homeowner’s battery, drawing power back into the grid on hot summer days, when overall demand for power is high, and storing power in the home batteries of its customers overnight, when demand is low. “This technology benefits everyone,” says Green Mountain Power’s Kristin Carlson. “Even the customers who don’t add batteries benefit from lower electricity costs, because we have lower peak demand.” Green Mountain estimates its “virtual power plant” of 2,000 Powerwall units will be able to serve the equivalent of 7,500 homes during peak demand.

Shown: , $5,500
The second generation of the car company’s home battery packs a stackable 13.5 kWh of emergency backup to keep critical systems like furnace, well, oxygen machine, refrigerator, and Internet going for days. Homes with solar panels can use the Powerwall to store surplus power so it’s available when the sun isn’t shining. Price does not include typical installation fees of $800 to $2,000.

This is a market still in its infancy. Only about 900 home battery storage installations were connected to the U.S. electrical grid in 2016, according to industry analyst Brett Simon of GTM Research. But GTM projects home battery storage in the U.S. will grow roughly 200-fold in the next five years, with costs coming down as electric cars spur major improvements in battery manufacturing.

In Massachusetts, there’s no program yet for the power companies to supply themselves from customer batteries, but “it’s still a beautiful, self-sufficient thing to make solar on your roof, store it locally, and use it,” says Rob Meyers of South Mountain Company, who uses Sonnen Eco 10 batteries in high-end solar designs for homes in Martha’s Vineyard, where power outages are not uncommon. “We’re appealing at this point to people who fall in love with the cool new technology.”

Shown: , starts at $7,000
Flex is a “solar generator” alternative to traditional standby generators. Custom price quotes include permitting, installation, batteries, and solar panels, and may be eligible in full for solar tax credits. Flex is dedicated to backup (5 kWh or 10 kWh), and does not feed excess solar power back to the grid.

At the lower end, “our typical customer is someone who would have gone to Home Depot or Lowe’s for a generator to prepare for a power outage,” says SolarMax’s Guthrie Raimondo. SolarMax offers a solar backup-only system called Flex, conceived as an alternative to gas-powered backup generators. “Flex’s up-front costs are higher, but you get a full ten-year warranty and there’s less maintenance. And in a long-term outage, you may have trouble refueling a generator. Flex refuels itself as soon as the sun comes back out.” Prices start at $7,000 fully permitted and installed for a 5 kilowatt-hour (kWh) system to provide emergency power to minimal house systems such as a pump, boiler, and Internet modem.

Batteries still have a chance to pay for themselves on a nonemergency basis, even when utilities aren’t directly subsidizing them. In California, utility companies are starting to charge for electricity based on time of day and overall demand, and Orison, a San Diego startup, is promising to deliver a $1,999 freestanding wireless living room speaker next summer that simply plugs into the wall and doubles as a 2.2 kWh storage battery. Orison batteries provide emergency backup, but they are to earn their keep by reducing your electric bill, automatically time-shifting your purchases of energy from the utility company so you power the home from the battery when it would otherwise be expensive, and recharge from the grid when rates are low. Orison founder Eric Clifton even envisions his batteries in city apartments, where there’s little room for one’s own solar panels.

“If we install enough of these,” he says, “summer brownout warnings could be a thing of the past.”

Shown: , $1,999
Home battery systems are usually stashed away in the garage by a licensed electrician. This unit, however, is designed for the living room, and setup is as simple as plugging in to a standard wall outlet. The Tower has 2.2 kWh of backup (expandable to 13.2 kWh), and aims to pay for itself by storing cheaper, off-peak power. Now projected for summer 2018 delivery.