The deep waters off the coast of California could become home to the country’s largest offshore wind energy project and a test case for a technology that is still in its infancy.

The 765-megawatt project, proposed by Seattle-based Trident Winds, would sit about 25 miles off California’s central coast, near the town of Cambria. If built, it will be larger than the 630-megawatt London Array off the coast of Kent, – the world’s largest working offshore wind farm that began operating in 2013.

The Trident project, which could power more than 200,000 homes, reflects an interest by the US to embrace offshore wind energy as part of a broader strategy to develop low-carbon electricity sources. The country has no offshore wind farms, though a number of projects are in the research phase to determine their profitability. The very first project to come online in the US is under construction off the coast of Rhode Island: the 30-megawatt Block Island wind farm that is expected to begin operating later this year.

Offshore wind development already has taken off in Europe and other parts of the world. The UK, for example, has installed more than 5 gigawatts of offshore wind power plants, meeting 10% of its total energy demand.

“It’s just another very valuable resource that not only will be benefiting energy generation, but will create a new industry in the state of California,” says Alla Weinstein, CEO of Trident Winds.

Trident is proposing an unprecedented project in a state that has frowned on coastal energy development ever since a 1969 blowout at an offshore oil drilling platform near Santa Barbara, which released more than 3m gallons of crude oil into the waters. The resulting images of soiled beaches and oily seabirds were splashed around the world and helped launch the modern environmental movement.

Recent attempts to build machines to harness the power of ocean currents off the state’s coast also drowned in failure as they ran into technical and financial problems and protests from local communities.

California has some of the world’s toughest coastal development regulations. The state’s first large seawater desalination project, for example, took more than six years to win government approval and survived 14 lawsuits before construction started.

“On the one hand, we want to support, in some fashion, renewable energy,” says Sara Aminzadeh, executive director of the environmental group California Coastkeeper Alliance. “On the other hand, we wouldn’t want to support anything that has serious impacts on marine issues. There is so much that is unknown about constructing something like that essentially in the middle of the ocean. So it could be a tough issue for us.”

Trident submitted an application to the US Bureau of Ocean Energy Management in January to lease about 50 square miles of ocean for 30 years. The project will also need approval from several state agencies.

“Not a lot of people have heard about offshore wind potential in California,” said Doug Boren, Pacific region supervisor in the Office of Strategic Resources at the Bureau of Ocean Energy Management, the federal agency with jurisdiction over the project. “So we are moving fast and furious for getting California up to speed on things.”

Nearly all of the offshore wind projects in the world installed wind turbines on platforms attached to ocean floor by concrete or steel pillars built into the seabed, in waters no more than 200 feet deep. The promise of stronger and more consistent winds farther offshore, however, requires a different technology for deep water.

Within 50 nautical miles of the US coasts, more than 60% of the best wind energy sources – measured in wind speed, duration and timing – are in water that is too deep to build foundations drilled into the seabed, according to the US Department of Energy.

The Trident project calls for mounting 100 turbines on floating foundations in water that’s roughly half a mile deep. Floating foundations, which are kept in place with anchors and cables, have so far been used only in small pilot projects in places such as Portugal, Norway and Scotland. The anchors themselves may be giant concrete blocks or huge steel structures with hooks that grab the sea floor, not unlike a ship’s anchor.

The Norwegian firm Statoil claims to be the first with a commercial-scale floating wind project, which it expects to begin operating later this year off the coast of Scotland.

Floating foundation design poses multiple technical challenges. The structure has to be able to withstand the harsh environment of the choppy ocean and high winds while supporting the weight of the turbines, which can be damaged by the pitching and bouncing motions at sea.

Floating foundations tend to be more expensive because their anchoring systems actually require more steel than a fixed platform. Bringing power to shore also requires longer power cables, which add to the cost.

Some costs could be lower for floating turbines, however. Installation can be cheaper and easier since the turbines and their floating platforms are constructed onshore, then simply towed to sea and anchored. Fixed turbine projects, on the other hand, must rent time aboard expensive, specialized industrial ships – first to install the foundations, then to assemble the turbines on top of them.

Currently, floating wind energy is much more expensive than fixed offshore wind energy, says Tom Harries, an analyst at Bloomberg New Energy Finance. That’s likely to remain so for some time because fixed offshore installations are dropping dramatically in cost while floating projects are still emerging from tests, he adds.

By 2020, floating wind projects will likely cost an estimated $9m per megawatt, compared with $4m per megawatt for fixed-foundation projects, according to Bloomberg New Energy Finance.

“Conventional offshore wind is on this race to the bottom in price, which is kind of bad news for floating wind,” Harries says.

Raising funds to finance projects with a novel technology will therefore be a significant hurdle for Trident. The company could line up investors more easily if it could secure a power purchase agreement from a California utility. The agreement typically commits the utility to buy the electricity from the project for 20 to 25 years, making it a guaranteed source of income for investors. Trident has yet to find a buyer for its energy.

The few floating wind projects in the US are struggling to sell contracts for their electricity. A 30-megawatt project in Oregon called WindFloat Pacific, for example, received a $4m Department of Energy grant to assist with planning and design, only to find it couldn’t lure a buyer for its expensive electricity.

Weinstein, who declines to disclose any cost estimate for the project, says she is undeterred by all these challenges and has been called “brave” for choosing California to pioneer a new field of renewable energy. She intends to start construction as early as 2021 and bring the project online in 2025.

She believes the timing for developing the project is right. Last October, California’s governor Jerry Brown signed a new law requiring half of the state’s electricity to come from renewable resources by 2030. This means the state, which has been a friendly place to develop solar and land-based wind farms, must double its current level of renewable generation in just 15 years.

To win government approval, Trident will have to prepare a lengthy report to investigate the potential environmental impact of its project.

California’s coast is a major migration route for several whale species, and the underwater structures of the floating wind turbines could pose an entanglement risk.

“All the marine mammals, they have pretty good sonar detection,” Weinstein says. “So because we’re talking about fairly thick lines, they can detect those obstacles in the water and swim around them. There have been no known incidents of marine mammals tangled up in mooring lines of offshore oil drilling platforms.”

She also says the turbines will not produce any noise or vibration that might be bothersome to marine life. But whale scientist John Calambokidis questions her claim. He notes the proposed project site is near the Santa Lucia Bank, an area “very heavily used” by blue, fin, sperm and humpback whales. Federal law has designated each of them as endangered species.

“Unfortunately, what we’ve seen historically and most dramatically in the last few years is that even simple lines can form an entanglement risk,” says Calambokidis, co-founder and research biologist at Cascadia Research in Olympia, Washington.

“I think you have a vulnerability that comes from not recognizing it as a threat,” he says. “We frequently see humpback whales interacting and playing with kelp, which is almost like a rope structure. It will be draped over their backs, looped in their tails. They will roll around in it.”

Another concern, as with all wind energy projects, is the potential for birds to be killed by the whirring blades. A British study found that many birds actively avoid offshore wind turbines, but its authors cautioned that many unknowns remain.

“It’s the first of its kind, so it will be important to think about whether we need additional (regulatory) procedures to consider its effect on our oceans,” says Aminzadeh, of Coastkeeper Alliance.

“In general, we want to think about whether this is the right place for this project. A lot of times, the factors that lead a private company like Trident to a location such as this are not [to do with] whether it’s the best place from an environmental perspective.”