The solar industry questioned the accuracy of Hawaiian Electric Co.’s rooftop solar numbers in a letter to the Public Utilities Commission.

The Alliance for Solar Choice, a solar advocacy group, said HECO’s April 2 report listing the number of customers waiting for rooftop solar approvals since at least October does not match industry numbers.

In the Monday letter, TASC said the total pending applications is much higher than the 206 applications HECO reported.

Four of the dozens of solar companies in Hawaii — Sunrun, SolarCity, RevoluSun and Alternate Energy — said they have more than 300 solar applications that have been waiting for approval since October.

"The actual number is likely even larger since the solar parties were unable to reach out to all of the island’s major installers," the letter states.

The utility’s report is accurate, said Darren Pai, HECO spokes­man.

"We can confirm that our numbers are based on projects that have been approved through notification letters sent to customers and solar installers. Customer applications are time-stamped as they are received," Pai said. "The applications are then reviewed for completeness. There were 2,749 completed applications on high-penetration circuits submitted before Oct. 22, the date that our commitment to clear the backlog was based on. Of those, 206 applications remain."

Colin Yost, principal at RevoluSun, said he was surprised when HECO announced it cleared most of the backlog because his company, with 90 applications waiting approval, would represent almost half of the remaining systems HECO said are pending.

"It’s not adding up, so let’s talk about it," he said. "We realized … that we have significantly more than what they are saying. Overall, they must have a lot more people out there."

Sunrun and its partners have 125 pending applications, Alternate Energy reported 50 pending approvals, and SolarCity reported 55.

HECO announced in January it could more than double the amount of solar it allowed on its grid. HECO announced it could safely go to 250 percent of capacity compared with the previous limit of 120 percent.

Roy Skaggs, project developer at Alternate Energy, said the announcement should have helped make room for the solar applicants before October.

"Anyone under 250 percent should be getting approval faster now. Instead, all we keep hearing about is how HECO approved over 2,500 applications from people that have been waiting months and in many cases over a year," Skaggs said. "There is no reason people should have to continue waiting if they’re under this 250 percent limit."

In the April 2 filing with the PUC, HECO said it approved 1,987 solar system applications on Oahu in March.

The utility promised last year it would clear its backlog of 2,749 rooftop solar systems waiting in October for approval, saying most would be approved by April and the rest by the end of 2015.

The utility said as of the end of March, it had approved 2,543 of the pending Oahu applications.

The backlog of applications started piling up last year after HECO was slow to approve systems in areas that already had a large number of rooftop solar 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.