Clearway Energy Group’s Mililani Solar is O’ahu’s first utility-scale solar + storage plant

Clearway Energy Group
Photo courtesy of Wärtsilä

Hawai’i-based solar developer Clearway Energy Group completed construction and reached commercial operations at its Mililani Solar I plant — Clearway’s fourth solar plant on O’ahu and the island’s first utility-scale solar and battery storage power plant.

The 39-MW Mililani Solar power plant is paired with a 156 MWh battery storage system and includes over 123,000 PV panels mounted on solar trackers measuring 6.5-feet tall and slightly more than three feet wide. Located on 131 acres in Mililani Agricultural Park, the project will provide grid services at a critical time with the decommissioning of the state’s last coal plant in September.

“Renewable energy is critical to Hawai‘i to be more affordable and resilient,” said Governor David Ige. “We are a step closer to that goal today because of the Clearway team, which understood the urgency and stepped up to deliver their project ahead of schedule.”

The $140 million project broke ground in April 2021 and installation of the panels and battery storage was completed ahead of schedule. Mililani Solar and Clearway’s second solar and storage plant under construction in Waiawa are together expected to contribute $9 million in taxes to the City and County of Honolulu. More than 240 local union jobs were created during construction of both plants and a permanent workforce will support ongoing operations and maintenance.

“Wärtsilä is proud to be leading the clean energy economy in Hawaii and addressing climate change in partnership with Clearway Energy Group and Hawaiian Electric. Power system optimization technology and flexibility solutions such as energy storage play a key role in balancing the state’s renewable energy power systems and ensuring power reliability for island residents,” said Håkan Agnevall, president and CEO, Wärtsilä.

Clearway has developed and operated renewable power plants in Hawai‘i for the past four years. In 2019, the company completed the construction and commissioning of three utility-scale solar facilities: a 45.9 MW site in Waipi‘o, a 14.7 MW in Mililani, and a 49 MW site in Kawailoa on O‘ahu’s North Shore.

“Projects like this one help our customers by providing electricity to the grid at one-third the cost of oil and help Hawaiʻi by moving us on the path to a decarbonized energy system,” said Shelee Kimura, president and CEO of Hawaiian Electric. “Working with experienced energy developers like Clearway, we will be bringing eight additional projects online over the next two years on Oʻahu, providing even greater benefits to our communities.”

Construction of Clearway’s second solar and battery storage plant in Waiawa, being built on Kamehameha Schools land, is expected to be complete later this year.

Altogether, Clearway’s five solar power plants totaling 185 MW will serve Hawaiian Electric’s grid and generate enough clean electricity to power more than 45,500 O‘ahu homes each year.

Project construction was led by Moss and the batteries were supplied by Wärtsilä.

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