The Public Utilities Commission has instructed the Hawaiian Electric Cos. to offer residential customers a time-of-use rate program.

In an order issued Friday, the PUC said the time-of-use program should have three distinct periods of time and that the electric utilities should offer lower electricity rates during daytime and higher rates in evening hours. Traditionally, Hawaiian Electric Co., Maui Electric Co. and Hawaii Electric Light Co. offer one rate, which does not change based on time of day.

For the TOU program the “on-peak” period from 5 to 10 p.m. would have the highest rate, higher than the price a customer would pay at the current rate. The “mid-day” period from 9 a.m. to 5 p.m. would have the lowest rate, lower than the current rate, and the “off-peak” period from 10 p.m. to 9 a.m. would be higher than the current flat rate but not as high as “on-peak.”

HECO has to provide the exact numbers for the three designated time periods by Oct. 28.

The PUC said the time-of-use rates would encourage residents to shift their energy use from the “on-peak” evening period to the “mid-day” period so more renewable energy can be added to the grid.

The TOU rates would apply to Hawaii island, Lanai, Maui, Molokai and Oahu, and would be an option for residential customers. Participants’ bills will note what their bill would look like if they were not in the TOU program. Customers could opt out without a penalty.

“We’re excited about this new effort to help our customers and encourage them to manage their energy use,” said Darren Pai, HECO spokesman. “We are reviewing the order and will develop a time-of-use rate that meets the PUC’s specifications.”