The Public Utilities Commission on Thursday approved a pilot program offering special time-of-use charging rates for up to 20 Hawaiian Electric Co. electric bus fleet customers.

The program starts March 31 and will run for five years, subject to annual reporting and potential adjustments. Bus fleet customers include tour buses, school buses and public transit vehicles.

The program will encourage charging during midday, when there is abundant solar energy on the grid, and overnight, when electricity demand is low, by offering rates up to 25 percent less than the standard rate during those times, according to Hawaiian Electric.