May marks the third month in a row Oahu’s rooftop solar industry has seen growth in permits issued, following two years of declines.

The number of rooftop photovoltaic permits issued in May by the City and County of Honolulu was up 30 percent from the same month last year. The city issued 654 permits, up from 500 in May 2014, according data from Marco Mangelsdorf, who tracks rooftop solar permits and is president of Hilo-based ProVision Solar.

Mangelsdorf said the growth is a result of Hawaiian Electric Co. processing a backlog of customers waiting for approval and a fear that new solar customers will miss out on an incentive program that credits solar owners for the excess energy their solar systems produce. HECO proposed to change the incentive program, or net energy metering, in January, and is waiting on the Public Utilities Commission to approve the change.

The increase is “most likely largely due to the clearing of the HECO queue and PV contractors success at getting homeowners to believe that if they don’t act now, they will lose out on getting their systems net energy metered,”  Mangelsdorf said.

HECO has said 12 percent of its customers on Oahu have rooftop solar, far more than any mainland utility. The Oahu utility promised last year to clear a backlog of 2,749 systems that were waiting for HECO approval in October.

The solar industry took a hit when HECO announced in 2013 that all rooftop solar systems needed HECO approval before being connected to the grid. Applications started piling up after HECO was slow to approve systems in areas that already had a large number of rooftop systems. HECO said the delay was due to concerns about safety and the stability of the grid if more solar was added in those areas.