Forecasters say 90-degree weather is just around the corner, ushering in heavy use of air conditioners on O'ahu and testing the electric company's ability to keep the power flowing.

Three times between November 2005 and June 2006, Hawaiian Electric Co. issued urgent calls for conservation when electricity output barely kept up with demand.

HECO yesterday said it expects the system will be able to handle power needs this summer.

"We have sufficient resources to meet demand," said Darren Pai, a HECO spokesman. "But we encourage people to practice conservation — it helps them save money on their electricity bill; it helps us manage the system better; and it helps all of us work toward protecting the environment."

To give itself a little more slack, the utility has begun offering some O'ahu homeowners a $5 monthly credit if they let the company install devices on residential air conditioners that allow HECO to remotely shut down the units temporarily during system emergencies.

When all 19 electrical generating units on O'ahu are running, there's power to spare.

O'ahu's power system can generate 1,700 megawatts, and demand has peaked twice at about 1,300 megawatts, Pai said. The amount of electricity that can be produced on O'ahu hasn't changed much since 1992.

HECO records show that the daytime demand for power hit an all-time high of 1,300 megawatts on a day in August last year. The record for evening peak demand, also 1,300 megawatts, occurred in October 2004.

But so far, demand has not outstripped supply, and the 400-megawatt cushion appears to be holding steady.

"The demand for power on Wednesday (of this week) was the same as it was last year," Pai said.

RESERVE MARGIN

At times when power generation units are taken off-line for maintenance or have to be operated at less than full capacity on an emergency basis, as happened at HECO's Kahe plant earlier this year when sea grass clogged cooling units, "the reserve margin starts to get thin," Pai said.

On June 2 last year, 37,000 HECO customers had their power cut, some for as long as four hours, when three generators failed at the same time.

In most cases, when it appears that power generation may be insufficient to meet demand, HECO issues emergency calls for conservation, which allows the utility to avoid blackouts.

Recent history shows customers on two occasions since November 2005 heeded the HECO warnings about power usage and cut back, averting blackouts.

As a longer-term solution, HECO hopes to build a new, $137 million power-generating plant at Campbell Industrial Park in Kapolei. The plant would help create more peak-hour reserve capacity, Pai said. The company hopes to have the new power plant built and operating by 2009 on a site next to the city's H-Power garbage-to-energy plant.

Pai said only homes in 'Ewa are being offered the $5 air-conditioning credit program during the initial phase, because of the large number of newer homes with central air conditioning in the area. But the company hopes to expand the volunteer program across the island.

To qualify, homeowners must have a central A/C unit at least 2 1/2-ton capacity. Homes with split air-conditioning systems and window units do not qualify. HECO will install the devices for free, usually in less than an hour.

BRIEF SHUTDOWNS

Homeowners will receive the $5 credit whether an emergency shutdown is activated or not.

The air conditioners may be shut down for one to two hours during emergencies or peak demand. In general, that would happen at midday during the summer months or in early evenings during the fall months.

As of Wednesday, HECO had installed about six units and hoped to install about 100 by the end of the year and 600 in 2008.

Tim Craig, a lead forecaster for the National Weather Service Honolulu office, said the mercury at Honolulu International Airport could hit the 90-degree mark soon.

Actually, we're overdue.

90-DEGREE MARK

"It wouldn't surprise me a bit to see us hit 90 degrees any day now," Craig said. "It's gonna come — we're heading into the summer months. The 90-plus temperatures are more common on the lee side of the island with all of the asphalt and concrete storing and radiating the additional heat."

While the 90-degree mark will be achieved soon, the summer in general is expected to be mild. A long-term forecast by the National Weather Service predicts a tendency for somewhat below-normal temperatures in Hawai'i for the period of May through June.

That's due to an apparent transition from El Nino conditions, which result in warmer-than-normal ocean surface temperatures, to La Nina conditions, which bring about lower ocean temperatures, according to the Weather Service.

Reach David Waite at dwaite@honoluluadvertiser.com.