Four days of evidentiary hearings began Tuesday involving a controversial energy plant on the Big Island, about 10 miles north of Hilo.

The plant, called Hu Honua Bioenergy, has been trying to open for many years, but its permitting has been bogged down in complex regulatory and legal fights over the cost of electricity produced and the amount of greenhouse gases it would release into the environment, among other issues.

Greenhouse gases, produced from burning fossil fuels, trees, solid waste and other materials, trap heat and contribute to climate change.

Located on a cliff overlooking the Pacific Ocean on Hawaii island’s scenic Hamakua Coast, Hu Honua proposes to burn eucalyptus, as well as albizia and strawberry guava trees to create energy. The $474 million, 21.5-megawatt plant is 99% complete. It was refurbished from an older plant that used to burn leftover leaves and stalks from sugar cane, and later coal.

The Public Utilities Commission this week is considering long-term environmental and public health impacts from Hu Honua’s proposed operation.

Some of the issues under consideration: what’s the potential for increased air pollution from greenhouse gas emissions over the project’s life cycle? And are the terms of a power purchase agreement between Hu Honua and Hawaiian Electric in the public’s best interest?

The company that built the biomass plant, Honua Ola Bioenergy, describes it as a modern renewable energy facility that will provide a homegrown energy source at a price not tied to the volatile fossil fuel power market.

On Dec. 28, the state’s Consumer Advocate filed a 53-page document saying it was unable to recommend approval of the proposed project because of remaining questions and concerns over whether the benefits of the plant outweigh the costs.

Besides the Consumer Advocate, Tawhiri Power, a wind farm near South Point on the Big Island, and Life of the Land, an environmental organization based in Honolulu, have raised objections to the project. All three question, among other issues, whether the cost of power generated by Hu Honua would be cost effective for rate payers. The projected cost of 22 cents per kilowatt hour over the 30-year life of project is more expensive than that of other solar-battery storage projects on the island, according to testimony submitted to the Public Utilities Commission.

Hu Honua says its power costs are what they are because the plant would provide reliable renewable energy 24 hours a day, seven days a week. In comparison, solar projects that cannot provide continuous reliable energy without being supplemented by fossil fuel plants make the total cost of their energy more than that of Hu Honua, the company says on its website.

During Tuesday’s evidentiary hearing, executives with Hawaiian Electric faced hours of questioning from commissioners and an attorney representing Hu Honua. The questions delved deeply into the intricacies of the utility’s application for commission approval of a power purchase agreement with Hu Honua and a waiver from competitive bidding. Those have been the subject of extensive litigation and regulatory proceedings over a decade. The questioning will resume on Wednesday.

The public can view this week’s proceedings on the Public Utilities Commission’s YouTube channel. They are scheduled for Wednesday through Friday from 9 a.m. to 4:30 p.m. each day.