Guest Blog | June 4, 2012 | Energy Policy, Wind

This blog is part of a four-part series by Simon Mahan, Chris Carnevale and Jennifer Rennicks on hurricanes and energy. The blogs include Hurricanes and Climate Change, Hurricanes and Wind Farms, Hurricanes and Coastal Adaptation, and Hurricanes and Oil Rigs.

When I give presentations on the benefits of onshore and offshore wind energy, invariably I end up getting some sort of a variation on this question: “Wind farms are great, but what about hurricanes?” Unfortunately, the brevity of the question is disproportional to the lengthy discussion on technological, economical and philosophical issues required to answer it.

If you’d like a short answer, try this one: Wind turbines are designed to withstand extreme weather. The risks of a catastrophic weather event are fairly well known and can be planned for, to an extent. Wind turbines are generally expected to survive up to a Category 3 hurricane. But, when failure occurs, a wind turbine failure is better than a potentially catastrophic failure at a coal, natural gas or nuclear power plant.

For a lengthier answer, read on.

Wind Turbines are Designed to Protect Themselves

Generally, wind turbines are expected to withstand hurricanes, up to a Category 3 storm. Wind turbines cost millions of dollars apiece – so it’s in the best interest of a turbine manufacturer and wind farm developer to make sure those turbines are operating as much as possible. As such, turbines are designed to withstand the effects of extreme wind speeds, lightening, ice, rust, sand, hail and UV rays from the sun. For more information on how turbines protect themselves, check out our previous post on the subject. Also, check out this awesome video of a wind farm surviving a tornado.

Some areas of the country, like the Gulf Coast, experience hurricanes more frequently than others. Because of its long oil and gas history, the Gulf Coast has at least 50 years of experience working offshore in hurricane prone waters – and offshore wind turbine manufacturers and developers will deploy that existing experience when and where necessary. Thicker steel, stronger foundations and better structural design can help protect offshore structures from extreme wind and waves and prevent catastrophic turbine failure. When engineering fails, insurance can be used to protect the assets of a wind farm. Considering that offshore wind farms may be multi-billion dollar projects, it is more than likely that investors will require projects to obtain adequate insurance coverage to protect against large liabilities.

Hurricane Frequency and Intensity Determine Turbine Risks

As I mentioned earlier, generally, wind turbines are expected to withstand hurricanes, up to a Category 3 storm. If you live on the coast, ask yourself – when was the last time a major storm, a Category 4 or Category 5 storm made a direct hit on your state? Chances are, it’s been a while.

• Virginia – The state hasn’t been hit by a Category 4 or 5 storm in the past century.
• North Carolina – The state hasn’t been hit by a Category 4 or 5 storm in the past century. Hurricane Diana, which was briefly a Category 4 storm, hit the state as a Category 1 storm in 1984.
• South Carolina – The most recent major storm to directly hit South Carolina was Hurricane Hugo in 1989.
• Georgia – The last time any hurricane had a direct hit on Georgia was 1928 – and it was a Category 1 storm. “Gracie” came close in 1959, as did “Charley” in 2004, but neither directly struck the state.
• Florida –  Hurricane Charley struck the southwestern edge of the state nearly a decade ago as a Category 4 storm. Before that, Hurricane Andrew raked southern Florida from the east to the west in 1992. But the panhandle hasn’t been hit by a Category 4 or 5 storm in the past century.

Hurricanes do strike our region, but the chance that a major storm strikes a particular location with offshore wind turbines during their 20 year lifespan seems to be a manageable risk. But that doesn’t stop folks from suggesting otherwise.

An academic article written and published earlier this year evaluated the risk to offshore wind farms by hurricanes. While the paper came up with some dire predictions, they were only brought out by ignoring 160 years of history, turning off standard turbine safety mechanisms, and a generous dose of rounding numbers. The summation was this, “In the most vulnerable areas now being actively considered by developers, nearly half the turbines in a farm are likely to be destroyed in a 20-y period.” One of those “most vulnerable areas” was identified as Dare County, North Carolina. The researchers estimated that in a 20 year lifespan of a 50 turbine wind farm, the farm could lose a total of eight wind turbines off Dare County – or 16%. Not even close to half. Of those eight lost turbines, about five would be lost in Category 4 and Category 5 storms. The researchers noted that North Carolina hasn’t seen a Category 4 or Category 5 storm make a direct hit since at least 1850. Keep in mind, the researchers’ model turned off the yaw systems, which are specifically designed to prevent turbine damage from extreme wind. Definitely, this seems to be a worst-case scenario.

Regardless of the worst-case scenario, the researchers did run scenarios where active yawing was turned back on (the safety system). The risk that a single wind turbine would topple over 20 years dropped to 15%. The risk that half the turbines would buckle went down to “much less than 1%”. The researchers suggested using active yaw systems to “have a substantially reduced risk of being destroyed.”