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LIHUE, Kauai — Kauai’s community-owned utility company is preparing a mix-and-match approach to generating electricity that will combine multiple techniques in a novel approach to creating renewable electricity.

If the Kauai Island Utility Cooperative’s project gets online as planned by sometime in 2021, it will be a huge Rube Goldberg-like contraption in the mountains above the island’s west side.

This is how it would work: Three existing reservoirs and a system of water distribution ditches dating to the plantation era would be revamped to become essentially a closed system. Water in the uppermost reservoir would be released in the mountains at about 3,300 feet above sea level. It would drop about 1,500 feet through a 22,000-foot pipe to the middle reservoir.

Along the way, some of the water would run through a conventional hydroelectric turbine, adding power to KIUC’s grid, and then continue downhill to an irrigation system on the plains near Kekaha, a thriving agricultural area. Water supplies to Kekaha agricultural users have not been adequate to meet anticipated future demand.

At night, the remaining water would drop through a second pipe — this one about 12,000 feet long — flowing through additional hydro turbines before finally coming to rest in the bottom reservoir. As it flows, it would generate power during periods of darkness, when solar generators can’t work.

The following morning, power from a newly constructed solar array would pump the water all the way back up to the top of the system, replenishing the top reservoir that is also already served by existing water sources flowing through century-old ditches and tunnels. The following night, the process would start all over again.

When all of the generating capacity is added up, the new system — known as “pumped storage” — would produce 25 megawatts of electricity, equal to the biggest fossil fuel-powered generator in KIUC’s system today. It would represent, according to David Bissell, KIUC’s CEO, 15 to 20 percent of Kauai’s entire electricity needs, enough to provide power to about 10,000 homes.

In the whole process, not a single gallon of oil would have been burned, since it relies on existing reservoirs and water sources adapted to new uses and gravity power to turn the turbines. It wouldn’t be a pilot project so much as a unique chance to take advantage of natural resources, including plentiful sunshine and water as well as mountainous terrain.

“This is pretty much it for Kauai in terms of pumped storage,” Bissell said. “You have to have the right combination of available water and the right topography.”

A bonus, Bissell said, is that improving the technology of the antique tunnel and ditch water system would restore stream flows that have withered in recent decades. The issue of streams and rivers going dry on Kauai has been a stubborn political mess.

Pumped storage has been in use for decades on the mainland and in Europe, but many of those systems rely on conventionally generated power to pump the water back up to the top of gravity-fed systems. Few — if any — of the existing installations has the critical sheer drop in height that Kauai’s would.

No other utility in Hawaii uses pumped storage or has announced plans to do so.

KIUC is already one of the nation’s leading power companies in capitalizing on solar generating technologies. It has both conventional solar systems and two others either operating or under construction that use gigantic battery banks to store power produced during the day to be dispatched to the grid after dark.

The results are dramatic. KIUC currently uses renewable energy sources for 43 percent of its power, Bissell said. It also has two new solar plants under way that should bring KIUC’s grid to 60 percent renewables by the end of this year.

Still another new solar-battery station is planned at the U.S. Navy’s Pacific Missile Range Facility at Barking Sands, according to Bissell. It would get Kauai to 70 percent renewables by sometime in 2019 —  long before the pumped storage project would be complete.

The rapid progress has brought out calls for KIUC to retire, or even remove, some of its existing conventional generators, all of which are powered either by diesel fuel or naphtha. There are three such plants on Kauai. With one exception, the machinery is old and hard to maintain. But as Bissell was describing the pumped storage system, he also acknowledged the unfortunate truth about the vicissitudes of weather.

Kauai has been having a far wetter rainy season than normal. Even with the best renewable technology, if there isn’t any sun, solar plants won’t work — batteries or no batteries. Kauai homeowners who have rooftop solar panels producing electricity and hot water have seen bills rise precipitously this year as the lack of sunshine has required old-fashioned electric water heater backup that draws power from KIUC’s grid.

Heating water can account for nearly a third of a household’s conventional electric bill.

So when Bissell talks to community groups, he’s often asked when the dinosaur generators will be dismantled and all of KIUC’s fossil fuel generating capacity eliminated. The short answer, he said: It can’t be. There will always be cloudy days.

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