LIHU'E, Kaua'i — The Kaua'i power company has authorized four companies to develop independent power plants that would use renewable fuel to make electricity in quantities approaching half the island's current demand.

"We could get as high as about 45 percent from biomass, waste-to-energy and wind," said Anne Barnes, spokeswoman for the Kaua'i Island Utility Cooperative.

That, if achieved, would be a level of locally produced power unprecedented since the height of the sugar industry, when plantations produced excess electricity by burning cane residue called bagasse and sold it to utilities.

Today, Barnes said, Kaua'i's renewable energy amounts to between 7 percent and 8 percent of total power production. Hawaiian Electric spokesman Chuck Freedman said the figure for the rest of the state is the same: about 7.5 percent.

Both KIUC and the Hawaiian Electric companies, which produce power on O'ahu, Maui, Moloka'i and Hawai'i, are moving aggressively into buying renewable energy. Freedman said the Kaheawa Wind Power facility on Maui, at 30 megawatts the biggest wind farm in the state, should start generating electricity this summer. Other wind farms are in various stages of development on O'ahu, Maui and Hawai'i, Freedman said.

Barnes said KIUC has signed an agreement with UPC Kaua'i Wind Power LLC to develop a wind plant on Kaua'i of between 10.5 and 15 megawatts. The company is a joint venture of the Boston-based wind farm developer UPC and Makani Nui Associates, which is developing Maui's Kaheawa wind field. No site has been announced for the Kaua'i wind project.

Another Kaua'i project is a small-scale version of Honolulu's HPOWER plant. The 5.3-megawatt waste-to-energy plant would be built by Barlow Products. KIUC said the Colorado-based Barlow is a leader in small-scale waste-to-energy technology. Its system would not require the pre-sorting of county municipal trash. It would be designed specifically for the size of Kaua'i's trash flow. Although KIUC has invited Barlow to build the facility, the company has not reached agreements with the county for allocation of the island's trash.

A third plant is a proposed 7.5-megawatt biomass-to-energy facility that would burn wood chips from trees grown on the island. Green Energy Hawai'i is in partnership with Hawaiian Mahogany, which grows trees on 3,600 acres on the island. Most of the trees are a cabinetry-quality variety of eucalyptus and albizia. The power plant could burn chips from entire trees, or from wood waste from sawmill operations.

Bill Cowern, spokesman for Green Energy Hawaii and Hawaiian Mahogany, said the plant could be operational in as little as 12 to 15 months. Barnes said KIUC estimates it should be working in 18 months at most.

And the fourth facility is a proposed 4.5-megawatt biomass plant that the Maine outfit Cleaves & Co. plans to move from California. The plant, built in the 1970s, was operational until 2005. The company initially plans to import walnut shells as a fuel source, but hopes to find a locally generated biofuel crop.

Barnes said KIUC sought proposals and approved the four named operators. However, in each case, the utility's only commitment to date is an agreement to buy power from the companies if they build their plants, and if a price for the power can be agreed upon. While they may be in negotiation, no purchase-power agreements have been completed, she said.

Freedman said the Hawaiian Electric companies are actively soliciting proposals to produce electricity from renewable sources.

"We're looking to make those renewable numbers go way up. We have solicited interest from companies all over the world. The technologies are just improving," he said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.