The state Public Utilities Commission said Tuesday it wants Hawaiian Electric Co. to come up with a plan in 90 days to expand rooftop solar in the islands through better use of battery systems.

Randy Iwase, chairman of the Public Utilities Commission, said the PUC is trying to fast-track interconnection approval for rooftop PV connected to storage systems.

Energy storage will be a solution to a major problem the utility has with high numbers of PV systems connected to the grid, Iwase said.

"What they (batteries) can do is reduce the back-feed to the grid at a time when there is not much use of electricity that is causing the problem," Iwase said.

Along with batteries, smart meters and smart inverters are other options that will help Hawaii modernize its grid, Iwase said.

"These things we have got to start looking at," Iwase said.

The PUC issued an order Tuesday saying HECO and several solar companies must supply proposals for new technical standards for inverters and energy storage systems within 90 days with the overall goal to add more rooftop solar.

"They must be considered, not just discussed. How do we use battery storage to increase the number of homes that can utilize PVs?" Iwase said. "That is part of the solution."

Rooftop solar owners need to be considered as a valuable partner for the utility of the future, Iwase said.

"There are 51,000 power producers on Oahu — they are the ones that own the PVs," Iwase said. "Are we going to have a monolithic energy company that produces that power and distributes that power, or, given the changes that occur, is that business model obsolete?" Iwase said.

In addition to looking for ways to add energy storage, the PUC mandated the utility provide weekly updates of its progress clearing the backlog of rooftop solar applications waiting for approval since Oct. 31.

HECO said 90 percent of those rooftop photovoltaic systems will be approved by the end of April.

Along with the orders regarding customer-based rooftop solar, the PUC issued a separate order that limits the amount of money the utility automatically receives every year for its new renewable energy projects. All expenses above the limit have to be approved by the PUC before development.

In recent years, HECO has been automatically reimbursed the full amount of expenses for renewable-energy projects as part of the so-called "decoupling" policy.

"What this decoupling cap will do will decrease each bill by $1.67 each month on Oahu," Iwase said.