The first utility-scale solar farm on Oahu linked with batteries recently began commercial power production ahead of seven similar projects slated for completion over the next two years.

Clearway Energy Group started selling electricity from the 39-megawatt facility in Mililani to utility company Hawaiian Electric on July 31, and on Thursday held a ceremony with government officials, utility representatives and others to recognize the $140 million project’s completion.

Craig Cornelius, CEO of San Francisco-based Clearway, said in a statement that the delivery of Oahu’s first major solar and energy­-storage facility elevates Hawaii’s transition to reliable carbon-free power.

“We’re proud to help Hawaii achieve its clean energy goals and we are grateful to Hawaiian Electric, whose partnership has been critical in reaching this important milestone,” he said.

The battery system, housed in liquid-cooled cases stacked inside gray metal lockers adjacent to some of the more than 123,000 photovoltaic panels covering 131 acres of former pineapple plantation land within Mililani Agricultural Park, allows power from the project to be used between sunset and sunrise.

The batteries also allow more consistent delivery to the electrical grid during cloudy daytime periods depending on the variable needs of Hawaiian Electric.

Fully charged, the batteries at Clearway’s Mililani Solar I project are capable of supplying the grid with 39 megawatts of power, which is the production capacity of all the solar panels, for four hours, or 156 megawatt-­hours in total.

Shelee Kimura, president and CEO of Hawaiian Electric, said in a statement that Mililani Solar I and upcoming similar projects will benefit ratepayers by providing electricity to the grid at one-third the cost of oil while also moving Hawaii further toward a decarbonized energy system.

Mililani Solar I is selling power to the utility for 9 cents a kilowatt-hour under a 20-year agreement.

Rebecca Dayhuff Matsushima, the utility company’s vice president of resource procurement, added, “We’re excited that these renewable energy projects coming online include the added benefit of battery storage, which provides grid stability and more value for our customers.”

Clearway stands to become the biggest renewable energy supplier in the state once a sister project to Mili­lani Solar I, a 36-megawatt solar farm paired with a 144-megawatt-hour battery system in Waiawa, is completed. The Waiawa project is expected to begin operating by the end of this year or in early 2023.

The solar farms with battery storage represent part of the shift to achieve the state’s goal of having 100% power generation from renewable sources by 2045. Also as part of this shift, a 180-megawatt coal-fired power plant on Oahu owned and operated by AES Corp. is slated for retirement Sept. 1 after 30 years of operation.

All or nearly all of Oahu’s upcoming solar farm projects with batteries, including Clearway’s Waiawa project, have suffered delays in development due to issues including problems obtaining components from China amid coronavirus shutdowns, as well as permitting setbacks and design difficulties.

John Woody, a Clearway senior vice president, said the company took steps to accelerate construction of Mililani Solar I that included shipping equipment to Hawaii and ordering panels and batteries exceptionally early.

Even obtaining utility poles for the project proved to be a challenge because of supply issues. This difficulty was overcome, Woody said, when Hawaiian Electric allowed Clearway to have some of its own poles that Clearway later replenished.

“It was a true partnership with (Hawaiian Electric) to bring this project in on time,” he said. “We’re really committed to the state of Hawaii, and we’re strongly aligned with the state’s 100% renewable energy goal.”

Woody said Clearway is working on plans for more renewable energy projects in Hawaii, which would be subject to selection by Hawaiian Electric under a competitive proposal process that also requires approval from the state Public Utilities Commission.

Clearway’s strong position in the Hawaii market started with a large foothold it acquired in 2016 in a takeover of existing plans for three Oahu solar farms initiated by another developer.

These three projects — a 46-megawatt facility in Waipio, a 49-megawatt facility in Kawailoa on the North Shore and a 15- megawatt facility known as Mililani Solar II, which is located next to the most recent addition — began operating in 2019.

All three were initiated by First Wind, which previously developed a wind farm in Kawailoa. A subsequent developer, SunEdison, acquired the three projects but ran into financial trouble of its own that led to bankruptcy. Hawaiian Electric terminated power-purchase agreements held by SunEdison in 2016, which led to Clearway stepping in and negotiating lower-cost agreements to revive the three projects.

Collectively, Clearway’s four operating and one almost-complete solar farm projects have a production capacity of 185 megawatts of electricity, or enough to power about 45,500 homes each year on Oahu.