A few years ago, interest in offshore wind energy was so strong that developers proposed spending tens of billions of dollars to plunk hundreds of turbines the size of skyscrapers in the Atlantic Ocean from Maine to Virginia.

But several of those projects have recently hit the skids after executives miscalculated the impact that the pandemic and rising interest rates would have on supply chains. The industry has found it much more difficult to manufacture, transport and erect wind turbines than it had expected. Just two dozen or so turbines have been installed in U.S. waters, compared with more than 6,000 in Europe, which has been building offshore wind farms for decades.

As a result, the cost of offshore wind energy will be higher than anticipated and its climate and economic benefits will, in some cases, arrive years later than expected.

Some wind farms may be delayed. Others may never be built.

To date, Eastern states have awarded contracts to build roughly two dozen offshore wind farms with 21 gigawatts of electric capacity, or enough to meet the needs of more than six million homes. But developers have canceled or asked to renegotiate rates for nearly half that capacity. Analysts are downgrading expectations: About 15 gigawatts of offshore wind will be installed by 2030, according to BloombergNEF, a research arm of Michael Bloomberg’s financial data and information company. That’s about one-third lower than what it had expected as recently as June. Europe has already installed about 32 gigawatts of offshore wind capacity.

Orsted, a Danish company that has built around two dozen offshore wind farms, mostly in Europe, has canceled two giant arrays planned for waters off New Jersey and is reconsidering two more intended to serve New York and Maryland. The company said it would be writing off as much as $5.6 billion. BP, which paid $1.1 billion for a 50 percent stake in the Norwegian energy company Equinor’s U.S. offshore wind portfolio in 2020, recently wrote off $540 million of its investment.

States like New York and Massachusetts are scrambling to save projects — and appear to be acknowledging that they will need to pay higher prices for the electricity generated by offshore turbines than they had expected.

“The U.S. offshore wind market is still in its infancy, and some states might have been trying to run before they could walk,” said Atin Jain, a senior associate at BloombergNEF. “Now they’re getting more realistic about the challenges facing developers, and that’s going to help in the long run.”

The East Coast has long been considered a prime location for offshore wind. Much like those in the North Sea, its waters are relatively shallow, ideal for turbines. Northeastern states have also set ambitious renewable energy goals to tackle climate change, but it is often expensive and difficult to transport wind or solar power to dense coastal cities and suburbs.

The lack of other viable options for cleaning up electric grids in the Northeast explains why few states, and President Biden, have given up on their lofty goals for offshore wind.

In an interview, Ali Zaidi, Mr. Biden’s national climate adviser, pointed to the large offshore projects underway in Massachusetts, New York and Virginia, noting that the industry had grown rapidly from a standing start three years ago. The administration plans to complete federal reviews for at least 16 offshore wind farms by 2025, each capable of powering hundreds of thousands of homes.

“There are projects that are facing turbulence, and that’s not trivial,” Mr. Zaidi said. “But it’s not enough to take us off course from advancing significant progress.”

Energy executives say the industry is learning from its mistakes and making investments that should pay off in the coming years. Dominion Energy, a large utility based in Virginia, is moving ahead with a massive wind farm and is spending $625 million on the first U.S.-built ship capable of hauling the more than 300-foot-long blades and other components for wind turbines out to sea.

“We needed to have confidence in our schedule,” said Robert Blue, Dominion’s chief executive. “One way to have confidence is to have a vessel,” he added.

‘The World Looked Totally Different’

Orsted, the world’s leading offshore wind developer, gained traction in the United States by buying a Rhode Island company called Deepwater Wind for $510 million in 2018. Deepwater had the only operating U.S. offshore wind farm and owned a portfolio of proposed projects.

It was a heady time. Developers were eager to crack a new market and they rushed to sign contracts to provide electricity from offshore arrays under development at rates that assumed little or no inflation. They did not expect a lot of turmoil.

That turned out to be a bad bet. Under former President Donald J. Trump, a longstanding critic of wind turbines, the federal government held up permits. Then the pandemic wrecked supply chains, making parts more expensive. Later, the Federal Reserve sharply raised interest rates to tame inflation, driving up borrowing costs.

Now companies were stuck with the prospect of building multibillion-dollar projects to supply power at prices that no longer made sense.

“The world looked totally different,” Mads Nipper, Orsted’s chief executive, said last month, speaking of 2018 and 2019, when the company won a contract to build the first of the two New Jersey projects, Ocean Wind 1, that it has since scrapped.

A final blow, Mr. Nipper said, came in the past few months when it became clear that a ship that the company had booked to install the foundations that anchor the huge turbines to the sea bottom in 2024 would not arrive on time. This snafu threatened potentially huge cost increases.

Instead, the company walked away, but it had already run up huge losses.

“I am very doubtful that they will ever recover to what we thought” was ahead two or three years ago, said Anders Schelde, the chief financial officer of AkademikerPension, a Danish pension fund.

Like other companies, Orsted is now focusing on its more promising U.S. deals while trying to renegotiate or shelve others.

“The developers are going to have to choose which of the projects are viable and which are not and proceed accordingly,” said Eamon Nolan, a partner at the law firm Vinson & Elkins who specializes in energy.

Orsted recently began producing electricity for Long Island from a modest farm called South Fork Wind, and the company moving ahead with developing Revolution Wind, a $4 billion project that will provide power to Rhode Island and Connecticut. But the company is still deciding how to proceed with a different project in New York called Sunrise Wind, which may no longer be economically viable under its previous contract.

Lawmakers are also trying to salvage projects. Massachusetts and Connecticut now allow contracts for new offshore wind projects to be adjusted for any inflation that occurs before construction starts.

States are also bracing for higher prices. At an auction held by New York in October, the three winning companies offered to sell power to utilities at rates that were roughly one-third higher than earlier awards.

Gov. Kathy Hochul of New York, a Democrat, also announced another expedited auction for offshore wind next year, a move that could allow developers of four troubled projects, including Sunrise Wind, to rebid at higher power prices.

“It’s not like people have said, ‘We are abandoning these auctions,’” said Deepa Venkateswaran, an analyst at Bernstein, a research firm. “But they are demanding much higher prices, demanding much higher protection.”

The industry also faces a chicken-or-egg problem: One reason that offshore wind projects are expensive is that the United States lacks a robust domestic supply chain. But manufacturers cannot justify building large factories if they don’t know whether there will be enough demand.

“When there are a lot of project cancellations, that weakens the case for domestic manufacturing,” said Josh Irwin, senior vice president of offshore sales at Vestas, a Danish company that is the world’s largest turbine manufacturer. “We’re still in wait-and-see mode.”

Dominion is trying to remove some of the uncertainty with its new ship, Charybdis, which is named for a mythical Greek sea monster. Though it is months behind schedule and will cost the utility about 25 percent more than expected, executives said the 472-foot-long vessel would ultimately save the company time and money.

That’s because a longstanding federal law, the Jones Act, requires that only domestically built, owned and staffed ships can operate in U.S. waters.

“It won’t solve all the problems but it is a start to show a pathway to U.S.-built vessels,” said Lars T. Pedersen, chief executive of Vineyard Offshore, which is developing projects off Massachusetts, New York and California.

The Charybdis will be able to carry four to eight wind turbine components at once, depending on the size of the pieces. The ship’s crane can lift 2,200 tons — roughly the weight of six Boeing 747 jets.

Dominion said the ship would allow it to set up one turbine a day once installations began on the company’s 176-turbine project. That would be a big improvement from a pilot project Dominion undertook in 2020, when the company spent a year installing two offshore turbines. Because of the Jones Act, the company used European ships that it operated from a port in Nova Scotia, more than 800 miles away, slowing the project.

That experience helped convince Dominion executives that they needed a Jones Act-compliant ship that it could run from U.S. ports.

The Charybdis, which is being built in Brownsville, Texas, is about 70 percent complete, and Dominion expects to have it available for Orsted’s Revolution Wind project, near the Connecticut coast. The ship would then move to Dominion’s project, which the company hopes to complete by the end of 2026.

“We’re not trying to set records,” said Mr. Blue, Dominion’s chief executive. “What we are trying to do is deliver reliable, affordable and increasingly clean energy.”