Firefighters are battling a fire at a wind farm in Kahuku that has shut the operation down and appears to have destroyed the facility’s battery building.

The fire started about 4:45 a.m. Wednesday and has been confined to one building, which houses a 15-megawatt battery system for the 30-megawatt wind project.

Honolulu Fire Capt. Terry Seelig said an alarm sensor showed a buildup of heat, and video cameras recorded a fire starting in the battery banks.

The batteries, which smooth out fluctuations in power output caused by changes in wind levels and connect the turbines to the electrical grid, were still burning about 4 p.m. and emitting various chemicals in smoke, which was blowing toward the mountains and not affecting homes, Seelig said.

Firefighters can’t use water because of the voltage in the system and have been using dry chemicals to try to smother the fire. But firefighters don’t have enough chemicals for the size of the fire and are being assisted by the Hawaiian Electric Co., which has a truck that can carry 1,000 pounds of fire-extinguishing dry chemicals.

Seelig said fire personnel are focusing on saving the surrounding buildings because the battery building appears to be collapsing.

“It’s basically going to be considered a total loss,” he said of the battery building.

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

“We have taken the project offline for the time being,” he said. He said the cause was unknown and no one was injured.

The complex is the island’s first large-scale wind farm, developed by Boston-based First Wind with a dozen 2.5-megawatt wind turbines that can produce enough electricity for 7,700 homes.  The three-blade turbines sit on steel towers 260 feet high, with turbine blades reaching 460 feet at their peak. 

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 is not affecting HECO customers.

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

The Kahuku project’s 30-megawatt output is a small part of HECO’s islandwide peak load of about 1,250 megawatts.

It’s not the first fire at the fledgling wind farm.

In April 2011, a month after operations began, firefighters put out a small fire in the battery room.