Call it a match made in paradise.

Hawaii’s Kaua‘i Island Utility Cooperative (KIUC) has signed a deal for a system that marries solar energy with hydropower, an innovative project that could herald future advances in energy storage.

KIUC is working with AES Corp. on the groundbreaking West Kaua‘i Energy Project, which will use a large solar array to power pumps lifting water to an uphill reservoir during the day. The reservoir will feed hydro generation during the evening peak.

The combination shifts solar generation into hours when the sun is no longer shining but demand is high. Solar power during the day will be more than enough to run the pumps and will also feed into KIUC’s grid during morning and afternoon shoulder periods.

Brad Rockwell, KIUC’s chief of operations, says the project should generate about 24 MW of hydro overall and 35 MW of solar when completed in 2024.

“It will provide about 25% of our annual energy needs,” he says.

As renewable generation continues to grow, storage is playing a larger role on the grid, mostly in the form of batteries.

“Lithium-ion is going to continue to be dominant,” says Jan Ahlen, NRECA’s director of energy solutions. “But there’s a lot of different technologies, and I think that’s a good thing. The storage industry is still developing.”

Rockwell says KUIC’s efforts make financial sense on Kaua‘i Island, where every gallon of fossil fuel has to be shipped in across the ocean. But circumstances are unique to each electric co-op.

Nevertheless, he sees a lesson for the industry.

“There are a lot of people who say you can’t run a grid on renewables or solar, but that’s not the case,” he says. “We’ve proven it can be done.”