The number of photovoltaic building permits issued for Oahu fell 26 percent in August compared with the same month last year.

The City and County of Honolulu issued 464 PV permits last month, a decline of 26 percent from 628 in August 2015, according to data from 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 27 percent from the same period last year. There were 3,410 PV permits issued from January to the end of August, compared with 4,681 issued during those eight months last year.

The decline has been largely attributed to the state ending a popular solar energy incentive program last fall.

In October the state Public Utilities Commission discontinued a program that credited homeowners an amount equal to the retail rate for the excess energy their PV systems sent to the grid. Many solar energy system owners lowered their electrical bill to approximately $17 a month through the program.

When ending the program, the PUC replaced it with two less attractive options. When issuing the decision, PUC Chairman Randy Iwase said he wanted to save space on the grid for other renewable energy options, such as community solar projects.

As of Sept. 30 there were 57,583 solar energy systems in the state. At the end of June, there were 65,751 solar energy systems in the state — 44,541 on Oahu, 10,617 on Maui and 10,593 on the Big Island — according to HECO’s website.

Only one of the two incentive programs now available to residents lets customers export excess energy into the grid. The grid-supply program credits new solar energy system owners 15 cents a kilowatt-hour for the extra energy their systems send into the grid, or roughly 8 cents less than the retail rate that had been offered previously.

The PUC also put limits on the total amount of energy it would accept from the grid-supply program. Oahu’s limit is 25 megawatts, Hawaii island’s limit is 5 megawatts and Maui County’s limit is 5 megawatts. Maui and the Big Island have reached the limit. Oahu is expected to hit its limit soon.