Wind turbines, solar panels and a garbage-to-energy plant have joined the mix of resources powering Oahu’s homes and businesses in recent years. Now add eucalyptus trees from Hawaii island to that list.

AES Hawaii Inc., which operates the state’s only coal-fired power plant, began burning the home-grown fuel this week at its facility in Campbell Industrial Park as part of a test project. AES began the test Sunday and gradually increased the blend of eucalyptus chips to its bituminous coal supply until it hit its target yesterday of generating 5 mega­watts from the renewable source.

"It means an extra 5 mega­watts of a made-in-Hawaii fuel that can compete with imported oil on a cost per unit basis," said Jeff Walsh, president and general manager of AES Hawaii. "Eucalyptus is a viable and sustainable source of alternative energy that is fast growing and can be harvested and converted with minimal environmental impact," he said.

The coal-fired AES plant normally produces 180 megawatts of energy at its peak. The addition of the eucalyptus chips boosted that to 185 megawatts.

AES bought the eucalyptus trees for the test from a consortium led by Massachusetts-based GMO Renewable Resources. GMO Renewable has the rights to harvest timber grown on former sugar cane land owned by Kamehameha Schools on the Hamakua Coast.

The 5 megawatts generated from eucalyptus chips is enough to supply the energy needs of 5,000 Oahu homes a year. If all goes well the project could be expanded to 20 megawatts over time, producing enough energy for 20,000 homes, Walsh said.

At that level the biomass project would create about 10 to 15 permanent jobs and two or three part-time positions, he added.

AES will use the weeklong test to monitor emissions and evaluate the effects of the eucalyptus chips on energy output. AES, which sells power to Hawaiian Electric Co., is in the process of negotiating a power purchase agreement with HECO to make biomass a permanent part of its fuel at the Campbell plant. HECO will be able to count the energy generated from eucalyptus chips toward its goal of generating 40 percent of its power from renewable sources by 2030.

Any agreement between AES and HECO will have to be approved by the Public Utilities Commission. AES also must secure a long-term contract with GMO Resources or another timber supplier.

The Eucalyptus grandes trees used in the test were harvested from the 13,000-acre Sunbear Plantation, one of several Big Island timber plantations that sprung up in the last few decades to generate economic activity as sugar production in the area was phased out.

About 50,000 tons of eucalyptus chips a year is needed to maintain 5 megawatts of energy output, according to AES. The Sunbear plantation contains 2.5 million tons of eucalyptus trees, or enough to harvest about 250,000 tons a year on a sustainable basis, AES said.

Once the trees are harvested, the eucalyptus stumps resprout and produce a new tree that reaches maturity in 10 to 12 years. "They’re like trees on steroids," Walsh said.

At that rate, Sunbear would be able to easily produce enough timber to generate 20 megawatts of electricity on a continuing basis, AES said.

Arlington, Va.-based AES, the fifth-largest power company in the world, has successfully burned biomass at its plants in Europe.

The design of the plant at Campbell Industrial Park is such that it can burn a variety of fuels, including coal, wood chips and shredded tires, said Patrick Murphy, AES vice president.

The cost to produce energy with the eucalyptus chips will depend on a number of factors, but it will be competitive with the 15 cents per kilowatt hour that it costs HECO to generate electricity from oil, Murphy said. It won’t be as cheap as coal, which can generate a kilowatt hour for 2.9 cents, he said.

The eucalyptus trees used in the test project were shipped to Oahu whole and put through a chipper after they arrived.

Once the project achieves commercial viability the trees will be chipped at the plantation and shipped to Oahu in 8-ton bales, according to AES.