Hawaiian Electric Co. ended its urgent call for customers to conserve power yesterday, saying that power reserves had returned to normal levels.

For three days this week, HECO asked customers to conserve electricity to avoid power failures from a system that was maxed out, with five of its 19 generating units out of service or operating at reduced capacity.

One of the utility's largest generators that was operating at a reduced capacity is now at full output, and the H-POWER facility, which burns trash to generate electricity, completed some repairs this week. H-POWER feeds 23 megawatts to HECO's O'ahu grid.

One generating unit is still operating at below capacity, and three others are down for scheduled maintenance, which takes several months to complete.

HECO spokesman Peter Rosegg said customers normally use about 1,200 megawatts during peak evening hours this time of year, which left only a 35-megawatt margin of generating capacity over demand. The company likes to have about 180 megawatts more power generating capacity than its normal demand, he said.

On Tuesday night, HECO remotely turned off the water heaters of about 5,000 residents participating in its EnergyScout program for a brief time, saving 3 megawatts during peak hours.

The company also put into service auxiliary diesel generators at its 'Ewa Nui and Iwilei substations Tuesday, providing an additional 9 megawatts.

"With the improved situation, we are no longer asking for special conservation, said HECO's Jose Dizon. "Conservation is still very important. Whether reserve margins are tight or not, paying special attention to using energy wisely should be part of our everyday way of life."

Reach James Gonser at jgonser@honoluluadvertiser.com.