More than 500 people have signed up for Hawaiian Electric Co.’s new time-of-use program.

HECO launched the pilot program Oct. 19 for residential customers who prefer to pay a varying rate depending on the time of day. Generally they pay less for their energy use during the day and more at night.

HECO said Monday the utilities tallied 508 customers who enrolled in the program as of Friday — 426 customers on Oahu, 61 customers in Maui County and 21 on Hawaii island.

Up to 5,000 customers at HECO’s three subsidiaries have the option to be a part of the program, which charges three different electrical rates throughout the day.

Oahu residents who enroll in the time-of-use program will pay 14.9 cents for every kilowatt-­hour from 9 a.m. to 5 p.m., 37.3 cents per kilowatt-hour from 5 to 10 p.m. and 23.7 cents per kilowatt-­hour from 10 p.m. to 9 a.m. The current flat rate on Oahu is 24.1 cents for every kilowatt-hour.

In September the state Public Utilities Commission ordered HECO to offer residential customers a time-of-use rate program looking to encourage residents to shift their energy use to the daytime when the most solar power is produced. The PUC said this would help add more renewable energy to the grid.

The program is voluntary and will run for two years. Customers have the option of leaving the program at any time without a penalty.

Local energy groups such as Blue Planet Foundation and Hawaii Energy — the state’s ratepayer-funded energy efficiency program — said they support the program because it gives customers options.

Some in the solar industry question the success of the program.

Robert Harris, director of policy at SunRun Inc., said he expects a small number will sign up for the program because the design doesn’t make sense for the majority of HECO customers.

“I’d be surprised if many people sign up for it. … If a customer has 75 percent or more of their load during the daytime, it might make sense for them,” he said. “But that’s not the typical customers, and, frankly, it’s not helping the grid to charge less for behavior they were already exhibiting.”

Those who use the majority of their energy during the day will benefit from the program.

HECO said customers who do laundry, cook, heat water or charge electric vehicles or energy storage systems in the day would benefit from the program. Customers who participate will receive information on their bills that compares their bill using the TOU program and the traditional residential rate.

Harris said he doesn’t expect many new solar owners or home energy storage system owners to sign up because the two-year limit doesn’t make it worth sizing a solar system around it.

“Why would someone spend money on a larger storage system or the like simply to take advantage of TOU? The payback is longer on the storage system,” Harris said. “Too risky.”