One big battery: Thousands of homes joined in a ‘virtual power plant’

Rocky Mountain Power program gives rebates to customers who let the utility use their home-battery systems when needed.

This story is part of The Salt Lake Tribune’s ongoing commitment to identify solutions to Utah’s biggest challenges through the work of the Innovation Lab.

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The Utah Supreme Court last month ruled against rooftop solar customers who wanted more money for the power they sell back to Rocky Mountain Power, but those willing to invest in batteries can still get a break from the power company.

The court last month denied Vote Solar in its suit challenging the compensation rate for “net meterers.” Under state law, utilities are required to buy excess power from rooftop-solar customers when they generate more than they consume. But the rate utilities pay for that power is far below what their customers pay for power.

While the solar companies and panel owners argue they should be paid more, the state’s Public Service Commission, which set the rate, successfully argued that raising the rate would force non-solar customers to subsidize the solar ones. Rocky Mountain also argued to keep the lower rate.

Rocky Mountain is singing a different tune to those who buy home battery systems. Under the WattSmart battery program started in 2021, the utility is offering thousands of dollars to Utah and Idaho customers who install home batteries.

But there’s a catch: Rocky Mountain gets to use the batteries. Participating customers have to give the power company permission to pull power from the batteries in times of need. With more than 3,000 customers participating, the utility can use the collective battery storage as a small power plant. Rocky Mountain even counts WattSmart battery customers as a power source in its 20-year Integrated Resource Plan.

“I did it for one simple reason: I like to be independent. In today’s world, when the power goes out, you have to have a backup,” said John Walsh, a retired Navy captain who lives in Draper.

To qualify for the credit, customers have to choose batteries from RMP’s preferred list, and they have to buy enough solar panels to charge the batteries. If they qualify, Rocky Mountain will pay them $400 per kilowatt of battery capacity. For a 6-kilowatt battery system — enough for a medium-sized home — that is $2,400. New solar and battery installations can easily cost more than $30,000, but there is also a federal tax credit that covers up to 30% of the cost of solar panels. Rocky Mountain also gives WattSmart battery customers a $15 per kilowatt annual credit.

Plus, those customers see their electricity bills drop. “I went to $162 a month down to 9.99 cents,” Walsh said.

Bill Comeau, vice president of customer experience and innovation for Rocky Mountain, said the battery program is a first step toward a modernized electrical system that copes with the daily fluctuations of renewable sources like solar and wind. “The need for the grid of the future is to be able to store that solar energy doing the day and use it during peak periods.”

Comeau said the utility is drawing on those 3,000 batteries every day for “daily load cycling,” which addresses the “duck curve” where peak consumption of power comes in the evening after solar production has dropped off.

RMP also can draw on the batteries when the renewables fluctuate because the sun is behind clouds or the wind dies.

And it happens automatically. “It’s seamless for customers,” Comeau said.

Walsh said he’s never noticed when the power company may be using his battery power, but he said he had plenty of electricity during outages last winter. “There were two blizzards that locked everyone in for two or three days. I had no problem because of my backup batteries.”

(Trent Nelson | The Salt Lake Tribune) An app shows the distribution of solar energy at John Walsh's Draper home on Friday, July 14, 2023.

(Trent Nelson | The Salt Lake Tribune) A Sonnen battery, powered by solar panels, at John Walsh's Draper home on Friday, July 14, 2023. Walsh said he added the battery because "in today’s world, when the power goes out, you have to have a backup.”

Walsh’s system includes an app that tells him in real time whether he is powering his house with his solar panels and battery or by drawing from the grid. Having that instant feedback has changed his habits, including doing what he can to shift consumption to when the sun is shining. “Yes. It motivates me. Do I really want to turn that light on? It makes you think about consumption.”

For Rocky Mountain, the difference between net metering and the battery program is about timing. Rooftop solar panels produce extra power when large, utility-sized solar farms also peak. In the western United States, that peak produces so much power that utilities can buy power for close to nothing and don’t really need rooftop solar’s contribution. But that changes when the sun goes down and the price of power goes up. At that point, utilities can draw on customer batteries for “peak shaving,” meaning it can avoid running coal plants or buying expensive power during the peak demand time.

Those in the battery program can still participate in net metering. They’ll only be selling power back to RMP when their batteries are fully charged but their solar panels are still producing.

And Comeau said the program is now open to customers who already have solar panels and want to add batteries.

The program recently won a “technology pioneer” award from the Peak Load Management Alliance for “a first-of-its-kind solution for customers who use batteries to turn intermittent solar into a manageable smart grid asset.”

Similar programs have emerged in Vermont and Arizona, but Comeau said Rocky Mountain is the first utility to make it an option for all residential customers.

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