Plans to spend tens of millions of dollars to build hydroelectric power plants in Nuuanu and Wahiawa are now moving through the state legislature.
The facilities would be Oahu's only hydroelectric plants, using new technology to ensure that the water that generates power does not go to eventually go to waste.
"It's pretty exciting. It's using the existing reservoir to capture water and run a turbine to generate power when we need it most, at night and at a time when the demand for power is really high," said State Rep. Chris Lee.
Last week, Lee's Energy and Environmental Protection Committee was one of two house committees that approved measures to provide funding to the Honolulu Board of Water Supply's pumped storage hydroelectric project, located at its Nuuanu reservoirs.
Separately, three other state Senate committees have approved funding for a study evaluating a possible purchase of the Wahiawa Dam from the Dole Food Company. The state would then upgrade it by building a hydroelectric power plant there.
The Nuuanu plan could cost up to $51 million. The Wahiawa system would cost much more.
Hydroelectric power generation has been used on Kauai and the Big Island for decades. On the Garden Isle, hydroelectric power provides about 9 percent of the island's demand.
Unlike these plantation-era power plants, though, the Wahiawa and Nuuanu proposals would use technology that recycles the water.
Water that's used to turn the turbines at the Wahiawa Dam would eventually flow back into Kaukonahua Stream. It would then be pumped back to the reservoir through a massive pipeline using solar power during the day, when it's cheapest; or wind power during the late night, when much of that wind energy is not being used.
"Solar and wind that you could not use would no longer be wasted," said Henry Curtis, executive director of the Life of the Land, an environmental group.
The Water Board's Nuuanu plan relies on low-cost, off-peak electrical power to pump water from one one reservoir to another, two miles away, in upper Nuuanu.
That reservoir is at an elevation nearly 600 feet higher than the first. During peak hours, water stored in the upper reservoir would be released to turn turbines that produce electricity.
According to the Water Board, a similar system was used in the late 1880's to light electric street lamps in Downtown Honolulu. The remains of that old pipeline can still be seen near Reservoir No. 1, along the Pali Highway.