Oahu’s only large-scale wind farm was shut down indefinitely Wednesday after a stubborn fire destroyed the Kahuku facility’s battery system that transfers power from 12 giant turbines to the electrical grid.

The fire was still smoldering Wednesday night in the battery building that houses a 15-megawatt system, but wasn’t threatening surrounding structures.

Honolulu Fire Department Capt. Terry Seelig said firefighters planned to monitor the blaze in the evening, then leave it to the facility’s staff overnight.

The 9,000-square-foot building that housed the battery system, which smoothes out power fluctuations caused by changes in wind, was destroyed, he said. A cause and damage estimate were not available.

HFD workers first responded to a call from the First Wind facility about 4:45 a.m. Wednesday after a sensor in the complex picked up a buildup of heat, and video cameras showed flames growing in fuel cell banks.

Three engines, a hazardous materials crew and a tanker responded, but remained on standby because the First Wind staff planned to let the fire burn out as did a previous one in the battery building, Seelig said.

Various chemicals were released in the smoke, but the wind was pushing it toward the mountains and away from nearby homes, he said.

Jay Armstrong, a visitor from New Orleans who was taking a Genesis Aviation helicopter tour around noon with his 13-year-old daughter, Gabby, said he could see the flames and smell the smoke while about 1,500 feet in the air.

"It smelled like plastic," he said. "You could see it smoking pretty good. They had lots of vents on the roof and you could actually see flames coming out of some of the vents."

The battery system’s high voltage and chemicals hampered the efforts of firefighters, who were limited to using dry chemicals to smother the blaze and couldn’t immediately enter the building. They asked for help from Hawaiian Electric Co., which has a truck that can carry 1,000 pounds of fire-extinguishing dry chemicals.

Several hours after firefighters first arrived, they entered the building and found the fire burning by the door. They tried to douse the flames with chemicals from HECO’s truck, but backed off after using up the supply and spotting signs that the building was collapsing.

They then turned their attention to protecting surrounding buildings, Seelig said.

Kekoa Kaluhiwa, spokesman for First Wind in Hawaii, said the company idled its 12 turbines, which stand on 575 acres mauka of Kamehameha Highway.

Kaluhiwa said management hadn’t had an opportunity Wednesday afternoon to enter the battery building to assess the extent of damage.

"We have taken the project offline for the time being," he said. He said he doesn’t know if the turbines can transfer power to the electrical grid without the energy storage system.

The 30-megawatt facility, the island’s first large-scale wind energy operation, was developed by Boston-based First Wind. It has 2.5-megawatt wind turbines that can produce enough electricity for 7,700 homes. The three-blade turbines reach 460 feet at their peak and sit on steel towers 260 feet high.

The 15-megawatt battery energy storage system was designed by Xtreme Power Inc. of Kyle, Texas.

First Wind began selling electricity to HECO in March 2011.

Darren Pai, HECO spokesman, said the fire will not affect customers.

"We have sufficient generating capacity to meet our customers’ needs," he said.

The project’s output is a small part of HECO’s islandwide peak load of about 1,250 megawatts.

The fire Wednesday wasn’t the first at the wind facility.

In April last year — a month after operations began — firefighters put out a small fire in the battery room. According to an online report, the company that designed the battery system said the fire was caused by defective parts.