Hawaiian Electric Co.’s push to reduce its reliance on fossil fuel for power generation took a major step forward Friday with the deactivation of its oil-fired Honolulu Power Plant.

HECO was able to take the 115-megawatt power plant offline as the result of an increase in the amount of renewable energy it generates or purchases from third parties, according to utility officials.

"This is a sign of Hawaii’s progress in reducing its dependence on oil. Thanks to the tremendous growth in renewable energy and more efficient use of electricity by our customers, we’re able to deactivate older, oil-fired generating units," said Ron Cox, HECO’s vice president of power supply.

The Honolulu Power Plant, next to Aloha Tower in downtown Honolulu, was built in 1920 and upgraded in 1957.

It accounted for about 6 percent of the utility’s firm generating capacity on Oahu.

The plant’s 34 employees were given other jobs within the company.

HECO subsidiary Maui Electric Co. plans to deactivate two of four generating units at its oil-burning Kahului Power Plant this year. The remaining two are scheduled for deactivation by 2019. On Oahu, HECO said it will deactivate two oil-fired units at its Waiau Power Plant by 2016.

Generating units that are deactivated can be returned to service if needed during an emergency situation, according to HECO. By contrast, when a unit is retired, or decommissioned, it is permanently removed from service.

Hawaiian Electric said more than 18 percent of the electricity used by its customers comes from renewable resources, already surpassing the state’s 2015 goal of 15 percent.