The Kauai Island Utility Cooperative and Alexander & Baldwin Inc. announced plans Monday to build a 6-megawatt photovoltaic project on the island’s south shore that would be the state’s largest solar power plant, supplying enough energy for 1,800 homes.

Alexander & Baldwin would develop and build the project and sell the electricity to KIUC at a fixed price under a 20-year power purchase agreement, the companies said.

Pending state and county regulatory approvals, construction is expected to begin in late 2011 and be completed by the end of 2012. It would be built on a 20-acre parcel owned by A&B next to KIUC’s Port Allen Station power plant.

The project would be the third large-scale PV project tied to the KIUC grid. The utility in February began buying power from a 1.21-megawatt project in Kapaa, and a 3-megawatt facility in Poipu is on track for completion in the next few months.

David Bissell, KIUC president and chief executive officer, said with the addition of the Port Allen project, Kauai “will likely have the highest percentage of solar PV on its system anywhere in the country.”

Combined with existing hydroelectric power and several other previously announced biomass and other alternative energy projects, KIUC will be able to meet more than 20 percent of the island’s energy needs with renewable sources, said Teofilo “Phil” Tacbian, KIUC board chairman.

The PV facility also marks the first time A&B is developing a stand-alone energy project. The company’s previous ventures in energy development were primarily to support its agricultural operations, with excess energy being sold to utilities.

A&B operates hydroelectric plants on Kauai and Maui that were built to serve its sugar operations. The company also operates a biomass-fueled power plant on Maui in a plant that generates electricity by burning sugar cane residue, also known as bagasse.

“Our company’s century-long commitment to generating renewable energy for Kauai’s residents and businesses dates to the very origin of McBryde Sugar Co. through the operation of our hydroelectric facilities at Kalaheo and Wainiha, which currently generate about 5 megawatts of electricity for KIUC,” said Christopher Benjamin, A&B’s chief financial officer, who oversees the company’s agribusinesses unit and energy-related activities.

The Port Allen facility, like the one being built in Poipu, will include a battery storage system that will kick in and help smooth out short-term fluctuations in energy output during cloudy periods.