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New Duke Energy plan uses home batteries to put energy back on the grid

About 9% of Duke Energy customers installed a residential battery before the utility offered incentives to customers to install new solar systems with a battery.
Vivint Solar
About 9% of Duke Energy customers installed a residential battery before the utility offered incentives to customers to install new solar systems with a battery.

Duke Energy customers can now save money on their electrical bills while putting stored energy from their home batteries on the grid. The new battery-control program grants Duke permission to draw energy from home batteries during periods of high demand.

“This program guarantees that we get the energy from that battery at the specific times the grid really needs it,” said Brian Lusher, a products and services manager at Duke Energy.

In return, battery owners get money back on their monthly utility bills. The amount of money that customers get back will depend on their battery.

“What we decided to do is pay the customer based on the value we know that specific battery model will provide to the system,” Lusher said.

Duke Energy forecasted that North Carolina will experience an unprecedented increase in energy demand during the next decade, driven by a growing population and economy. Meanwhile, the state aims to achieve carbon neutrality by 2050, eliminating climate-warming fossil fuel emissions. One strategy for meeting future energy demand is to boost home energy efficiency and manage when homes draw power from the grid.

Lusher says this new initiative is a way to do that by encouraging customers to use batteries — and allowing Duke to tap that energy at times of high demand when fracked-gas generators kick in.

For example, afternoon heat during the summer persists even as the sun goes down and solar generation declines. Customers tend to turn on their air conditioners when they return home from work, putting strain on the grid during a time when less renewable energy is available.

To offset this, a home battery might charge during the day and discharge electricity during the late afternoon when the sun is lower, spreading out energy demand.

Current batteries might store enough to offset a house, rendering it virtually invisible on the grid. As batteries improve, Lusher anticipates that power from residential batteries will stretch a little farther, while staying local.

“If you are the one customer on your street that has a battery, that energy’s not leaving your street,” Lusher said.

About 9% of Duke Energy customers with solar installed a residential battery. Not every battery connects to a solar system — some homeowners purchase batteries in lieu of a gas-powered generator to power their homes in a pinch. For homes enrolled in the battery-control program, Duke will not deplete batteries below 20% charge.

Duke Energy predicts that enrollment in battery control programs will make approximately 5 megawatts available to grid operators by the end of the first full calendar year — enough to power about 1,200 homes. This might not seem like a lot when you compare it to one of Duke’s proposed gas combustion turbines which typically provide 450 megawatts of power, but the benefits extend beyond those energy savings.

Battery control lowers energy lost due to transmission, reduces residential energy demand during periods of high demand, and increases the proportion of the state’s energy mix that comes from renewables. In short, battery control reduces the amount of time that a fracked-gas generator has to run.

While Duke Energy forecasts about 700 people enrolling in the first year, that is not a limit.

“There is no upper cap on providing these programs at this point, because we want to get customers on these programs,” Lusher said.

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Zachary Turner is a climate reporter and author of the WFAE Climate News newsletter. He freelanced for radio and digital print, reporting on environmental issues in North Carolina.