Companies are lining up to offer battery-storage options to Hawaii customers that own solar panel systems — a move regulators and clean-energy advocates are hailing as a way to help the state reach its 100 percent renewable energy goal.

The need for such energy-storing technology was sewn into different regulatory orders and utility proposals when the state Public Utilities Commission announced it would limit the number of new residential and commercial projects allowed to export solar energy to the grid, but continue to allow solar panel systems that stored excess energy in batteries. Clean-energy organizations and solar energy companies said batteries used with time-of-use rates could provide an incentive for homeowners to continue adopting rooftop solar panels, but the cost of such batteries is still out of reach for most.

“Battery storage is going to become important, especially as we move forward,” PUC Chairman Randy Iwase said. “Especially given the fact that the grid today is reaching near saturation.”

In October the PUC ended the net energy metering (NEM) program that credits solar panel owners for the excess energy their photovoltaic systems send to the grid. The PUC is replacing NEM with a program that gives new solar panel owners a slower return on their investments. New solar panel owners who choose to send their excess energy to the grid will be credited 15.07 cents per kilowatt-hour. This new program has a limit of approximately 4,000 homes.

After that limit is reached, customers still will be able to add solar panels to their houses but will not be able to send power to the grid.

The current program that credits solar owners for the excess energy they send to the grid will enable them to recoup their investment in six to eight years. A solar panel system connected to a battery has an eight- to 12-year payback period. A customer using a battery is eligible for a 30 percent federal tax credit if it is used with PV panels. There is no state tax credit for batteries.

“It’s not quite ready for prime time, essentially,” said Colin Yost, principal at RevoluSun.

The list of energy companies working to provide energy storage solutions includes San Jose, Calif.-based JuiceBox Energy; San Francisco-based Sunverge Energy; Pittsburgh-based Aquion Energy; Honolulu-based Blue Planet Energy; San Mateo, Calif.-based Tesla; and Honolulu-based E-Gear LLC.

JuiceBox Energy announced Monday it had installed its first energy storage system on Maui, adding to the growing field of vendors offering energy solutions for Hawaii residents with photovoltaic panels.

Similar to competitors, the company said the 8.6-kilowatt-hour, lithium-ion battery pack could help shift excess solar production from daylight hours to nighttime hours, provide backup power if there are problems with Hawaiian Electric Co.’s grid, and meet the requirements for the state’s nonexport solar program.

San Francisco-based Sunverge Energy announced earlier this month it is offering an energy storage system that links to home- owners’ solar panel systems.

Ken Munson, co-founder and CEO of Sunverge Energy, said the system can be configured to meet the standards of the PUC’s new program, which allows customers to get solar but not send any excess energy to the grid.

“What matters most to Hawaii is it satisfies the requirements around time of use and self-consumption,” Munson said.

Sunverge’s system, unlike most other battery systems, has software that can help homeowners work with time-of-use rates. A 7.8-kilowatt-hour storage system with a 4-kilowatt solar PV system will offset a customer’s power bill by 41 percent, according to Sunverge.

The retail price for the Sunverge Solar Integration System is about $23,000, or $16,100 after a 30 percent federal tax credit, according to RevoluSun.

A system of approximately 8 kilowatt-hours, combined with a 4-kilowatt, 12-panel system, can power the essential load for a typical household for a full day in the event of a power failure.

Sony Blue Ion is a battery offered by Honolulu-based Blue Planet Energy — owned by Henk Rogers, the entrepreneur who made the computer game “Tetris” famous. The average Blue Ion costs $22,000, or $15,000 after the tax credit, according to RevoluSun.

For comparable size, Aquion’s saltwater electrolyte battery is about $13,000, or about $9,000 with the federal tax credit. The battery, the size of a washing machine, provides backup but not the capability to interact with the grid.

Tesla Powerwall is a rechargeable lithium-ion battery designed to store energy at a residential level for load shifting, backup power and self-consumption of solar power . Powerwall is a backup battery. The product does not include power controls or energy management software. Powerwall will be available to Hawaii in 2016.

“If the grid goes down, the battery works very much like an electric generator. It will come on and support critical load in your home,” said Jon Yoshimura, regulatory counsel and director of policy and electricity markets for SolarCity, one of the solar companies offering the battery.

E-Gear LLC offers an energy management system linked to a lithium-ion battery from LG Electronics Co. It can help homeowners control their property’s energy use by turning on water heaters at the best time, turning off appliances when the rate is high and providing stored energy when it is expensive to pull from the grid. Like Sunverge, residents can sell power out of a battery when it costs a lot, refill it with solar electricity or buy electricity when it is cheap.

“We designed and developed an energy management control that measures home loads and any energy generation,” said Chris DeBone, principal at Hawaii Energy Connection and Kumukit.

DeBone said Kumukit will offer E-Gear to Hawaii residents in the first quarter of next year. DeBone did not share the price of E-Gear when asked.

The Energizr, a renewable-energy storage technology from Sacramento, Calif.-based JLM Energy Inc., is also available in Hawaii. A system offers 8.8 kilowatt-hours of battery storage and can keep a PV system with up to 30 panels functional during a grid outage and power a critical load for about 24 hours.

The battery system offered by Hisolarbattery.com on Oahu and Maui Solar Project on Maui can serve as a backup during a power failure and can reduce the energy a PV home needs to purchase from the grid overnight or on cloudy days. The cost of the energy storage module, not including tax credits, is approximately $22,500.

Batteries need time-of-use rates to make sense financially, said Dave Gorman, RevoluSun’s director of sales for the Smart Home division.

“We need this time-of-use rate structure so people can get the value they should be getting for installing these batteries,” Gorman said. “The battery allows you, with the time-of-use rate schedule, to cancel out your electric bill. Right now with no official time-of-use rate schedule, the economics are not very good. I think most people who are getting them are getting them for altruistic reasons. It’s not like this great financial benefit.”

Clean-energy advocates and solar companies recently filed comments with the PUC saying HECO’s recently proposed time-of-use program needs to provide more incentive for solar panel owners with battery storage systems. The groups said the credit for exported power from solar panel systems should match the rate customers pay in time-of-use rates to encourage solar panel customers to buy the necessary equipment, such as energy storage systems, to send back excess energy when the grid needs it most.

Iwase, the PUC chairman, said the affordability of batteries will come down, similar to rooftop solar.

“It is true 15 years ago PVs were far more expensive than they are today,” Iwase said. “To say that battery storage is not feasible or not to get excited about it because of the cost, I suggest to look at what people were saying 15 years ago with PVs before the NEM program got started.”