The Public Utilities Commission and Hawaiian Electric Co. signed an agreement Friday reaffirming the commission’s power to decide on rooftop solar.

The agreement, signed by PUC Chair Randy Iwase and HECO CEO Alan Oshima, reaffirmed that HECO has a duty to approve solar systems.

“Stated simply, the policy is that the HECO Companies have an affirmative duty to interconnect a potential customer,” the agreement said.

HECO also accepted that it cannot make unilateral decisions on rooftop solar and all HECO denials of rooftop solar systems must first be reported to the PUC.

“What is in the ‘best interest’ of the HECO Companies’ customers is, in the final analysis, determined by the commission,” said the letter submitted on Friday.

The agreement was in response to letters HECO subsidiary, Hawaiian Electric Light, sent to some customers last week saying their rooftop solar systems would not be approved until the PUC ruled on HECO’s request to cut the amount it pays for excess solar power sent to the grid.

HECO and the PUC agreed Friday that technical difficulties are the only reason the utility can deny rooftop solar approval, and those technical reasons must be reported and approved by the commission before the utility sends a letter of denial to a customer.

“Future letters … relating to the denial or delay of interconnection of residential rooftop photovoltaic systems to the grid, shall first be submitted to the Public Utilities Commission … ten business days prior to the proposed issuance date with full documentation in support of their reasons for proposing to issue the letter.

Iwase said the PUC should have the final say in rooftop solar.

“Don’t send out the letter unilaterally,” Iwase said.

The PUC’s control over the utility is necessary to get Hawaii off of fossil fuels and adopt more renewable energy, said Iwase in an interview.

“We are not limited to rates,” Iwase said. “Not as I see it.”

In the letter, the PUC also denied HECO’s request that the PUC decide within 60 days on HECO’s proposal to cut solar payments.

“The undersigned agree that resolution of the NEM issues cannot be achieved within a 60 day period if all interested parties are to be provided with an adequate opportunity o address these issues,” the document said.