Water and electric power plants don't mix well naturally, unless you add some wind.

Water tends to corrode and short out circuits. So what's happening in the the renewable energy industry, where developers are putting jumbo-jet sized wind turbines into stormy seas, is at the very least an engineering miracle. 

What might be even more miraculous to skeptics like those populating Donald Trump's administration is that these multi-billion-dollar mega projects make increasing economic sense, even compared to new coal and nuclear power.

"If you have a sufficiently large site with the right wind speeds, then I do believe you can build offshore wind at least at the same price as new build coal in many places around the world including the US," said Henrik Poulsen, chief executive officer of Dong Energy A/S, the Danish utility that has pioneered the technology and has become the world's biggest installer of windmills at sea.

Across Europe, the price of building an offshore wind farm has fallen 46 percent in the last five years – 22 percent last year alone. Erecting turbines in the seabed now costs an average USD 126 for each megawatt-hour of capacity, according to Bloomberg New Energy Finance. That's below the USD 155 a megawatt-hour price for new nuclear developments in Europe and closing in on the USD 88 price tag on new coal plants, the London-based researcher estimates.

As nuclear power costs spiral, prompting a USD 6.3 billion writedown at reactor maker Toshiba Corp. and delays at Electricite de France SA's plant in Flamanville, the investment needed to build offshore wind capacity is plummeting. 

In Denmark, where the government shoulders much of the development risk, Vattenfall AB last year agreed to supply power from turbines in the North Sea at 60 euros (USD 64) a megawatt-hour in 2020. Dutch and German auctions due this year provide "ample opportunity" to beat that record low price, says Gunnar Groebler, the utility's head of wind.

The industry even is taking hold in the US, which for years shunned the technology as too costly for a place that historically enjoys lower power prices than Europe. 

A federal auction in December for rights to develop wind farms off the coast of Long Island resulted in a bidding war. Rhode Island has commissioned one plant, and developers are also considering work in Maryland, New Jersey and North Carolina. 

Although Trump said offshore wind was "monstrous" when it came into conflict with his golf course in Scotland, the US government's official goal for now is to install 86 gigawatts of turbines at sea by 2050. That's six times the 14 gigawatts of capacity now in place worldwide, according to the Global Wind Energy Council.

The strength of the wind off the coast makes the sea a natural place to anchor turbines. In European waters, breezes average 22 miles per hour about 360 feet (110 meters) off the surface, a good baseline for the scale of many installations, according to The Crown Estate, which leases out areas of UK seabed belonging to the Queen to wind farms. That's almost triple the average wind speed onshore.

While more steady gusts mean each turbine will yield more electricity, fixing the machines to the seabed requires deep concrete footings cast in often turbulent seas. 

The North Sea, the crucible of the modern offshore wind industry, suffers punishing storms and strong tides that batter turbines much of the year. Securing structures as tall as the Washington Monument in the ocean requires deep footings, specialized ships and cranes capable of lifting equipment that can weigh tons. Salt water eats away at machinery and fittings. Cables must be rugged enough for the worst weather. And if equipment breaks, it can take weeks before the seas are calm enough for a work vessel.

Oil majors that have spent decades building skills to work in those conditions are turning their attention to offshore wind as petroleum production subsides in the North Sea. Royal Dutch Shell Plc and Statoil ASA are among companies that won contracts to build offshore wind projects last year.

All told, a record USD 29.9 billion was invested in offshore wind in 2016, up 40 percent from the year before, according to Bloomberg New Energy Finance. It expects investment to grow to USD 115 billion by 2020. What's driving installations is an expected 26 percent drop in the costs, making offshore wind increasingly competitive with land-based turbines and solar and nuclear power – even without subsidy.

In years past, grid managers were reluctant to rely on fickle winds for power that flows only about 45 percent of the year. That's changing too. Battery costs have fallen 40 percent since 2014, making them a realistic way to help balance fluctuating flows of renewable energy to the grid.

Offshore wind projects coming online today are already delivering power at almost half the price of those finished in 2012 thanks to larger turbines and greater competition. That's emboldening developers to promise supplying power for even less, suggesting the industry will break more records this year starting the a contest in Germany in April, said Deepa Venkateswaran, analyst at Sanford C. Bernstein Ltd.

The UK remains one of the hottest markets owing to the need to replace aging power plants. Bids may reach as little as 80 euros a megawatt-hour in the next auction due to start in April, she said. That's comparable to about 68 pounds a megawatt-hour for the global onshore wind average, and well below the government's 2020 goal to bring costs below 100 pounds (USD 125.55) a megawatt-hour.

It's also much cheaper than EDF's new nuclear power program at Hinkley Point in Somerset, which last year won a 35-year contract to provide power at a cost of 92.50 pounds a megawatt hour once it begins generating. It's currently due to come online in 2026, even though EDF originally planned it to be cooking Christmas turkeys for British households in 2017.

"In this auction it is possible that the price achieved could be below 90 pounds," said Keith Anderson, chief corporate officer of Scottish Power Ltd., a unit of Spain's Iberdrola SA.

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European offshore wind breaks record