Six months after it received a $70 million rate hike, Hawaiian Electric Co. has told the state Public Utilities Commission that it may seek a new increase.

HECO filed a notice with the state regulatory agency last week that it may file a new rate request 60 days from now to help pay for its planned $164 million power plant in Kapolei. It could take as long as a year to win regulatory approval for such a rate hike.

HECO didn't give the amount of the proposed rate increase, saying it's still evaluating whether it will file a new rate case.

HECO spokeswoman Lynne Unemori said state law requires such notices at least 60 days before it seeks to increase rates.

"It's still up in the air now," she said.

Hawai'i residents already pay the highest electricity rates in the nation. And those rates have risen steadily during the past year as fuel costs have soared.

The proposed rate increase would help pay for the new 110-megawatt power plant being built at Campbell Industrial Park. The plant, which will be completed next year and use renewable biofuels, will give a much-needed increase to HECO's generating capacity on O'ahu.

HECO's last rate increase came in October, when the PUC approved a 4.96 percent hike for the company's 293,000 customers on O'ahu. That increase generated $70 million in new revenue for HECO but meant an increase of $6.61 a month for the typical customer.

That rate hike helped pay for new capital projects that were completed in 2006 and 2007.

They include a new systems operations dispatch center and energy management system for monitoring and managing the company's electric grid on O'ahu, new substations, new boiler and generator equipment, and upgrades and replacements of underground power lines in Waikiki.