"The success story is that we did not have any substantial damage," said John McLane, president of GCube Insurance Services, a global provider of renewables insurance. "It looks as if the turbines' design specifications did hold up."
Sandy was a category 2 hurricane as it tore through the Caribbean and ripped into Cuba on 25 October, with winds of nearly 50 metres per second (m/s). Two small wind projects in Cuba's hard-hit Holguin province were not seriously damaged and were soon providing electricity again to the grid, the government reported.
By the time Hurricane Sandy hit New Jersey on the east coast of the US, the storm had slowed to a post-tropical cyclone but with hurricane-strength winds. Manufacturer Northern Power Systems (NPS) had 74 turbines in Sandy's path, most in the US and a few in a small renewables hybrid project in the Bahamas.
Most of NPS's turbines were only offline for a few hours unless the local grid was down, said James Jennings, director of global marketing and product management. Minor damage was caused to one NPS turbine on Long Island in New York state when the storm surge reached the base, causing mild erosion of the foundation. Another NPS turbine, in Connecticut saw sea-water rise about 0.3 metres up the tower. The operator was advised to hose down the tower and reapply rust inhibitor, said Jennings.
NPS has advertised its North Wind 100 turbine as "hurricane resistant" since two of the turbines, at the Bahamas hybrid project, survived Hurricane Irene in 2011. Irene was a category 3 hurricane with sustained winds of almost 48m/s. A little more than 18 hours after Irene hit, the machines were operating again normally, the company said.
Manufacturer GE had more than 700MW of its 1.5MW turbines in several projects in the path of Sandy, from New Jersey and Pennsylvania to West Virginia and New York. Most were shut down for three to eight hours as Sandy pummelled the US, said GE spokeswoman Lindsay Theile.
At a project in New Jersey, wind speeds reached a ten-minute average of 30.3m/s Theile said, while two sites in Pennsylvania saw sustained winds of just over 20m/s, and continued to operate fully throughout the storm. "We have no reports of damage or ramifications from the storm," she said.
Utility firm Iberdrola had very little damage at its four projects in Pennsylvania and New York that encountered the hurricane, said spokeswoman Jan Johnson. The company's national operating centre in Oregon powered down the turbines before Sandy hit, to reduce wear and tear from automatic shutting off and turning back on while winds fluctuated. "They were back on in some locations within 12 hours," she said.
Three large projects with Vestas turbines - two in Michigan, and Brookfield Renewable Energy's Granite project in New Hampshire - were undamaged after the winds, the Danish company said.
Anders Vedel, Vestas' chief turbine research and development officer, contrasted the projects' resilience with the trouble encountered by nuclear plants. He said: "It's a huge positive for wind energy."
"It proves the reliability of the turbines and their ability to quickly resume normal operation much faster than the affected nuclear power plants," he said, pointing to news reports that Hurricane Sandy forced three US nuclear reactors to shut down and three to reduce power. One of them, in upstate New York, was offline for days.
Indeed in mid-November, operator Exelon's Oyster Creek nuclear plant in New Jersey was being inspected by the Nuclear Regulatory Commission (NRC) after damage caused by floodwaters, although the fuel was not affected, said David Lochbaum, a nuclear engineer and ex-NRC instructor now with the Union of Concerned Scientists. The plant, which was already offline for maintenance, was put on high alert during the hurricane.
Wind turbines are designed to withstand 100-year storms, but these are getting more frequent with climate change, said GCube's McLane. For example, there is concern about offshore wind projects in the Gulf of Mexico or an area like Corpus Christi Bay, where average wind speeds are low but hurricanes can be "off the charts", said Walt Musial, offshore wind manager for federal energy research body the National Renewable Energy Laboratory.
The International Electrotechnical Commission standards committee has been discussing how to define a special hurricane class of wind turbine for more than a year, Musial noted.