The number of photovoltaic building permits issued for Oahu fell 40 percent in September compared with the same month last year.

The City and County of Honolulu issued 379 PV permits last month, down from 631 in September 2015, according to Marco Mangelsdorf, who tracks rooftop solar permits and is president of Hilo-based ProVision Solar.

Year to date, the number of solar permits issued was down 29 percent from the same period last year. There were 3,789 PV permits issued from January to the end of September, compared with 5,312 issued during those eight months last year.

Permits have been generally in decline since the state ended a popular solar energy incentive program a year ago. The solar industry has been struggling as a result.

In October 2015 the state Public Utilities Commission terminated a program that gave solar customers credit equal to the retail rate for the excess energy their systems sent to the grid. The program — net energy metering — helped many of its participants reduce their electric bill to roughly $17 a month.

When NEM ended the PUC replaced it with two options, called grid-supply and self-supply. And now only one of those two incentive programs, self-supply, is available.

All counties served by Hawaiian Electric Co. have met the state’s limit placed on grid-supply. The program lets customers export excess energy to the grid and credits them 15 cents a kilowatt-hour for the extra energy their systems send. That rate is roughly 8 cents less than the retail rate that had been offered through NEM.

Self-supply prohibits solar owners from sending excess energy into HECO’s grid. Most systems need batteries to meet self-supply requirements.

The self-supply program has seen a lackluster adoption rate, Mangelsdorf said.

“The adoption rate of customer self-supply, typically requiring battery storage, has been decidedly underwhelming with less than 60 in the pipelines for all three Hawaiian Electric utilities as of Sept. 27,” Mangelsdorf said.

Last week PUC officials said they would be starting a process in which they might reconsider the rules for grid-supply and self-supply.

“The commission recently formally opened the gate for the development and implementation of so-called phase two,” Mangelsdorf said. “The concern among PV contractors and their customers is that by the time phase two is determined and goes into effect, there may not be much of a local solar electric industry remaining.”

Some 442 solar employees have lost their jobs since the end of NEM, equaling a 42 percent reduction in the solar workforce over the last year.