The neighbor islands are betting on the power of falling water to support expanding renewable energy as Kauai, Hawaii island and Maui look to an energy storage solution called pumped storage hydro.

Kauai Island Utility Cooperative, a member owned utility on Kauai, is developing a pumped storage hydro project, which would use solar power produced during the day to push water uphill to a pond. At night the water would flow downhill through a pipe to turn a turbine and generate electricity.

Jim Kelly, communications manager for KIUC, said he expects the project will be operating by 2019 with a cost of roughly $60 million to build.

As weather and time of day affect Kauai’s grid with 40 percent of the energy mix coming from solar projects, the pumped storage hydro would help the island level out the fluctuating production of solar power, Kelly said.

"Whenever you have the most plentiful cheap power, you pump it uphill," Kelly said. "At night when we actually need it and the sun isn’t shining, you let it go and it comes down the pipe, turns the turbine and makes electricity."

Paniolo Power Co., a subsidiary of Parker Ranch Inc. on Hawaii island and Innovative Power Project LLC on Maui are also working to build pumped storage hydro systems for their islands.

The storage technology enables the use of more renewable energy, said Jose Dizon, general manager for Pani­olo Power.

"Pumped storage hydro is the right resource for the neighbor islands," Dizon said. "We’re in a period of technology disruption, and this is a time to try to new things."

Pumped storage hydro will help burn less fuel by taking the place of the fossil fuel generators, Kelly said.

"We have to keep a certain amount of our traditional generators on spinning reserve. You have to keep them going in the background, or else all of sudden you have a cloud that comes over or it starts raining and solar is just off. It happens in split seconds," Kelly said. "You have plants running on idle ready to go when you need them in seconds’ notice. They are on and burning fuel, but it’s expensive."

The water in Kauai’s project would travel through a buried 4-foot-wide pipeline that would span 5 miles and drop 3,265 feet from the upper reservoir at Puu Lua to either the New Haele­ele Reservoir or the Poli­hale Reservoir.

The finished project would supply 25 megawatts to the grid, Kelly said.

"Without something like this, we are going to have a situation where on a sunny day where it’s not hot, people aren’t using their air conditioner … (we) are going to have all this energy we are not going to use," Kelly said.

Paniolo Power said it has identified 49 places on Parker Ranch property that could support the pumped storage hydro as it works on adding options to the power supply plans Hawaiian Electric Co. submitted to the Public Utilities Commission in August.

"We’re trying to come up with an alternative plan for the PUC to consider," Dizon said, "provide the utility and commission with information. There are alternatives to their plans that are probably much more compelling."

Dizon said 40 companies have responded to Pani­olo Power’s request for qualifications.

Dan Suehiro, vice president of Innovative Power Project, said the Maui company plans on building two new reservoirs with a capacity of 150 million gallons each to support a pumped storage hydro system that would use treated wastewater.

Suehiro said the need for the project is triggered as Maui Electric Co. plans to retire its four oil-fired Kahu­lui generating units by 2019.

"It is an excellent to opportunity to compete with a pumped storage hydro project," he said.