Pumped Storage Hydro

Kaua’i Island Utility and AES to co-develop solar-powered pumped storage project
Kaua’i Island Utility and AES to co-develop solar-powered pumped storage project

Hydro Review

Kaua‘i Island Utility Cooperative (KIUC) signed agreements with The AES Corporation to develop, construct and operate the West Kaua‘i Energy Project (WKEP), a solar pumped storage hydro project.

WKEP is an integrated renewable energy and irrigation project with several key components: renewable energy production via hydropower and solar photovoltaic generation coupled with pumped hydropower and battery energy storage to shift most of the project’s output to the nighttime peak. This project will offset the use of 8.5 million gallons of fossil fuels annually and supply irrigation water to support agriculture on state-owned lands, according to a press release.

The project will also rehabilitate the existing Pu‘u ‘ÅŒpae, Pu‘u Lua, and Mānā Reservoirs and the related ditch system infrastructure. In addition, historic diversion structures in KokeÊ»e will be modified to restore and increase flow to the Waimea River in compliance with the instream flow standard established by the Waimea Watershed Agreement and adopted by the Commission on Water Resources in April 2017.

“This project’s integration of pump storage hydropower with large-scale solar power is unique in the energy industry. Working with AES helps keep this important project moving forward while minimizing risk to our cooperative. Upon completion, the facility will operate at a cost that will benefit KIUC’s members for decades,” said KIUC’s President and Chief Executive Officer David Bissell.

“WKEP will deliver many benefits to KIUC’s members and the community-at-large. To name just a few, the project will move KauaÊ»i beyond 80% renewable generation, stabilize and lower electricity rates over time for our members, open up dormant agricultural lands for production, assure adequate streamflow and increase public access and recreational opportunities associated with the Pu‘u Lua Reservoir.”

The solar array will contribute up to 35 MW to the grid and will store up to 240 MWh for dispatch during evening peak. The hydro resources are expected to produce 24 MW on average daily, which includes 12 hours of storage.

The project is expected to meet roughly 25% of Kaua‘i’s electricity needs and will support the grid with long-duration storage capability. The pumped hydropower will provide 12 hours of storage daily, compared to the conventional four- or five-hour storage from existing solar-battery facilities. This long-duration storage capacity will allow the island to run on 100% renewable energy for prolonged periods without sunlight and will provide additional grid stability by balancing intermittent solar with firm hydropower.

A power purchase agreement (PPA) was executed and filed with the Hawai‘i Public Utilities Commission on Dec. 31, 2020. Environmental studies have been ongoing. A draft environmental assessment is expected to be filed with the Department of Land and Natural Resources in the first quarter of 2021.

KIUC has completed two solar-plus-storage renewable projects in partnership with AES: a 20- MW facility in Lāwa‘i and a 14-MW facility at the Pacific Missile Range Facility.

“AES has been a long-time provider of low-cost electricity for Hawai‘i and we are honored to continue our successful partnership with KIUC to support Kaua‘i and the state in transitioning to 100% renewable energy,” said Woody Rubin, AES clean energy chief development officer. “We look forward to continuing to work with the Kaua‘i community and stakeholders to develop this project responsibly, and to realize the agricultural, economic, and environmental benefits the project offers.”

KIUC is a member-owned cooperative serving 34,000 customers on the island of KauaÊ»i. KIUC’s Board of Directors has set a strategic goal of reaching 70% renewable generation by 2030. Currently, KIUC derives more than 60% of its power from renewable sources.