Kaua'i Island Utility Cooperative (KIUC) recently signed agreements with The AES Corporation for the development, construction, and operation of the cooperative's solar pumped storage hydro project, also known as the West Kaua'i Energy Project (WKEP). A power purchase agreement (PPA) was also executed and filed with the Hawai'i Public Utilities Commission on December 31, 2020.

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 into the nighttime peak. This project will offset the use of 8.5 million gallons of fossil fuels annually and supply irrigation water delivery to support diversified agriculture on state-owned lands. The project will also rehabilitate the existing Pu'u 'Opae, Pu'u Lua, and Mana Reservoirs and the related ditch system infrastructure. In addition, historic diversion structures in Koke'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.

When operational, the solar array will contribute up to 35 megawatts directly to the grid and will store up to 240 megawatt hours for dispatch during evening peak. The hydro resources are expected to produce 24 megawatts on average daily, which includes 12 hours of storage to be used overnight.

KIUC has completed two solar-plus-storage renewable projects in partnership with AES: a 20- megawatt facility in Lawa'i and a 14 MW facility at the Pacific Missile Range Facility. AES has more than 200 MW of solar, solar + storage, and wind resources in operation or under development across Hawai'i.

"WKEP will deliver many benefits to KIUC's members and the community-at-large," Bissell said. "To name just a few, the project will move Kaua?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." He added that rehabilitation of the reservoirs will also assist first responders in addressing wildfires.

The project is expected to meet roughly 25% of Kaua'i's electricity needs, and will also support the grid with long-duration storage capability. The pumped hydropower will provide twelve hours of storage daily, compared to the conventional four- or five-hour storage from existing solarbattery 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.

Environmental studies for WKEP have been ongoing. A draft environmental assessment (EA) is expected to be filed with the Department of Land and Natural Resources in the first quarter of 2021.


WKEP Project Diagram. Source: AES

Photo: Pu'u Opae is one of the three reservoirs to be rehabilitated as part of the project. Source: AES