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Massive windmills floating miles off the coast of Oahu may power tens of thousands of homes and businesses within the next decade if projects go forward as planned.

Federal officials on Wednesday issued a call for information and nominations to scope the wind industry’s interest in commercial wind leases in two areas covering some 240 square miles off of Kaena Point in the northwest and 517 square miles off Honolulu to the south.

There are already three unsolicited lease requests from two potential developers, and . Each project, which would cost upwards of $2 billion, proposes an offshore floating wind energy facility with a capacity of roughly 400 megawatts.

Abigail Ross Hopper, director of the U.S. Interior Department’s , which issued the call, estimated the process would take seven to 10 years.

“This is an initial proposal,” she said. “Our job is to solicit information from communities.”

Hopper was serving on a panel discussing near-shore ocean technology at the three-day in Waikiki.

The bureau will publish a notice of intent to prepare an environmental assessment in the call areas Friday in the Federal Register, Hopper said, which opens a 45-day public comment period.

Early concerns include seabirds flying into the 600-foot-tall windmills, impacts on freight traffic and fishing vessels, and effects on Department of Defense activities. But project developers say these issues can be addressed.

Also serving on the panel was Ted Peck, former state energy administrator who now heads Holu Energy, which is working with Progression.

The project proposes 40 to 50 turbines, about 1 to 2 miles apart, with the closest about 14 miles southwest of Honolulu. Peck said the windmills might be mistaken from shore, if they’re visible at all, as sailboats but not freighters.

“This wind farm which we’re proposing would provide about a quarter of Oahu’s energy needs,” he said. “That is huge in terms of energy impact for one project. So this is a big muscle movement and really a big opportunity for us as a state.”

Hawaii Gov. David Ige signed a bill last year mandating that the state acquire 100 percent of its electricity needs from renewable sources by 2045, a goal that Hopper called “aggressive and progressive.”

Any major offshore wind project would need approvals and permits from county, state and federal agencies, plus a power-purchase agreement with Hawaiian Electric Co.

HECO’s latest 30-year energy plan, submitted to the state Public Utilities Commission in April, said it of offshore wind energy.

But company officials have cautioned that off-island resources, such as wind turbines, need to be studied further to better understand their respective risks and relative costs.

Offshore wind energy is gaining momentum nationally.

The Bureau of Ocean Energy Management’s offshore program has identified wind energy areas in federal waters off seven Atlantic states and awarded 11 commercial wind energy leases off that coast, the agency said in a statement.

Nine of those leases were issued as a result of competitive sales that generated about $16 million in winning bids for more than 1 million acres, the , and earlier this month the bureau announced it will propose an offshore wind lease sale for an area near New York.

“Today’s announcement marks another milestone in the President’s plan to support clean, renewable energy from the Nation’s vast wind and solar resources,” U.S. Secretary of the Interior Sally Jewell said in the statement.

“Hawaii has important offshore wind energy potential, and we will continue our work with stakeholders across the spectrum to create a path forward for sustainable offshore energy development in the right places with the lowest conflicts across the Aloha State,” she said.

In addition to offshore wind energy, companies are moving forward with projects to utilize wave energy — another issue panelists discussed at the energy conference Wednesday.

Duke Hartman, vice president of business development for , explained that the governor wants renewable sources of energy that offer constant power and can be ramped up or down quickly to handle intermittent sources like solar.

He said his firm is working on ocean thermal energy conversion, or OTEC, that could meet this request for base load and dispatchable power. The technology is still in relatively early stages, but he sees it as a solution to get to 100 percent renewable energy.

The OTEC process generates electricity by using the cold seawater from deep in the ocean and warmer water at the surface. The heat from the warm seawater boils a liquid refrigerant that has a low boiling point, creating a high pressure vapor that spins a turbine-generator before being condensed back to a liquid by the cold seawater, and then being pumped back around in a continuous cycle, Hartman said.

Hartman said the “Holy Grail” for the process is going big and offshore. For now, there’s an effort to get 5- to 10-megawatt pilot plants going to demonstrate to investors that the technology works. Then he sees potential for 100-megawatt plants — roughly 12 of which could power all of Oahu.