This is the second in a three part series of blogs examining how natural disasters like hurricanes impact our energy generation.
Recently, we published a blog on the Intermittency of Fossil Fuels highlighting the connections between natural disasters (earthquakes, floods, drought) and their impact on traditional power plants and wind farms. Since then, Hurricane Irene raked the East Coast with deadly force and devastating floods and the intermittency question has come back in a new form: Can wind turbines survive a hurricane?
If you’re limited for time, I’ll get right to the point: Yes. Wind turbines can survive hurricanes. Both structural engineering and risk analyses are vital to ensuring wind farms are developed to survive reasonably expected problems.
Why are hurricanes a concern for wind farms?
In the Southeast, wind farms have been proposed in coastal and offshore areas. Wind Capital Group has proposed an onshore wind farm in Palm Beach County, Florida. The Sugarland Wind Farm would have a capacity of up to 150 MW in the heart of hurricane-prone Florida. In North Carolina, two major wind parks have been proposed onshore including the 300 megawatt (MW) project near Elizabeth City and another 300 MW (See “Irene Would Have Impacted Two North Carolina Proposed Wind Farms” below) project between Camden and Currituck Counties. These two multi-million dollar projects would have been directly in the path of Hurricane Irene – highlighting the importance of wind turbine survivability during hurricane force winds.
Offshore wind farms are being proposed in Texas, Georgia, South Carolina, North Carolina, Virginia, Maryland, Delaware, New Jersey, New York, Rhode Island and Massachusetts. Had any of the offshore wind projects from North Carolina up to Massachusetts been built, they too would have been impacted by Irene. Over the past decade, each of these states has been impacted by a hurricane, tropical storm or tropical depression. Therefore, it is not a question of if a hurricane will impact proposed wind farms, it is only a matter of when.
How do energy project developers deal with risk?
Although you may not realize it, there is an entire industry dedicated to evaluating risks associated with myriad variables: the insurance industry. Unlike investors in financial markets, “risk” is a nasty word to insurance companies to be avoided. Anyone that owns a sports car, or a home in a flood zone knows that the higher the risk of a “total” loss of an asset (such as a completely destroyed car that is a “totaled” car), the higher the insurance premiums are to protect those assets. Energy developers similarly have projects insured to protect against unforeseen disaster – the random earthquake, the freak tornado, the extreme weather. For nuclear developers, the private insurance industry will not insure a new nuclear reactor without a guarantee from the federal government that taxpayers will pick up the tab should a developer default on a loan. These “loan guarantees” are essential for the nuclear industry to secure insurance, even though this industry has a 50% default rate on previous loans. Higher risks (either from natural disasters or manmade ones) may impact whether or not a project developer can get project financing – loans or debt – at lower interest rates. Also, higher insurance premiums increase operation costs of energy projects, and thus, impact the electricity prices we eventually pay as consumers.
What is the risk of a hurricane destroying a wind farm?
A properly designed wind farm should be able to withstand hurricanes that are likely to pass within a wind farm’s lifetime – usually within the next 20 – 25 years. Hurricanes are but one natural disaster that must be considered for some projects – earthquakes, floods, tornadoes and even fires are also risks that must be considered when constructing wind farms. Significant or unusually strong hurricanes and storm impacts, like floods, are often called “the storm of the century” or “a 500-year storm.” These terms, while sometimes used casually, actually have real statistical meaning. For some examples, in any year, a “10-year flood” has a 10% chance of occurring, while a “100-year flood” has a 1% of occurring each year. As such, a 10 year flood is not expected to be as severe or damaging as a 100-year flood. A 500-year or 1,000-year weather event is extremely severe – but the risk of each of those happening any such year is 0.2% and 0.01% respectively. It should be noted that there is no guarantee that a 100-year flood will definitively occur in the next 100 years. In fact, an analysis for New Orleans shows the risk of a 100-year flood occurring is actually 26% within 30 years, and 63.4% within 100 years. Therefore, the risk that a wind farm in Massachusetts being hit with a Category 5 Hurricane is much lower than a similar wind farm somewhere along the Gulf Coast. Wind farms in Iowa at more risk from winter weather than say, a wind farm in Texas.
To help investors, developers and insurance companies understand the risks associated with wind turbines in extreme weather events, engineering standards exist to explain wind turbine survivability. The International Electrotechnical Commission Standards (IEC) develops standards for wind turbines that are rated based on their abilities. One aspect of certification is the ability to withstand wind speeds considered for a “50 year extreme gust.” An IEC “Class 1″ turbine is designed and certified to withstand a 50 year extreme gust of 70 meters-per-second, or 156 miles per hour, meanwhile an IEC “Class 3″ turbine is certified to withstand an extreme gust of up to 52.5 meters-per-second, or 117 miles per hour. For reference, a Category 3 Hurricane has sustained wind speeds of 110 – 130 miles per hour and a Category 5 Hurricane (the highest category) has sustained wind speeds of greater than 155 miles per hour. The maps below highlight the risks of hurricanes striking the Gulf and Atlantic coasts – over the past 10 years, each state on the coast has seen some form of hurricane or tropical storm.
How do wind turbines handle extreme weather?
Wind turbines are designed specifically to harness the wind but they are also designed to withstand it. Modern wind turbines utilize several techniques to reduce the likelihood of harm. Active techniques require some sort of action by the turbine or operator to protect a turbine. These techniques are used to stop turbines and halt electric generation in extreme weather conditions and so technicians can perform regular maintenance. Passive techniques are built-in and require no additional activity to protect a turbine. The following list is a non-exhaustive list of active and passive techniques to reduce turbine damage:
- Turbine brakes – Most turbines are installed with turbine breaks that automatically engage if winds reach a certain speed – usually around 55 miles per hour. At the rated speed, the turbine brakes are applied and the rotor stops spinning.
- Blade feathering – Wind turbine blades can be tilted (feathered) remotely by an operator or automatically so instead of harnessing strong winds, wind is allowed to slip through the blades.
- Active yaw systems - Large turbines have active yaw systems that require a small motor that moves the nacelle (or gearbox, where the generator is housed) to point directly into the wind. By pointing directly into the wind, turbine aerodynamics allow wind to flow past the blades easily.
- Heavy monopoles – Monopoles can reach up to 100 meters in height and are meant to hold nacelles and blades that can weigh several tons. Thicker monopoles constructed with more steel and internal structures can support more weight and withstand stronger environmental forces like wind or waves for offshore structures.
- Strong foundations – For onshore wind turbines, most large scale turbines have a foundation pad constructed from concrete. These foundation pads are usually buried several feet deep to help anchor the turbine to the ground. Offshore turbines in Europe utilize heavy concrete gravity-based structures that are placed on the seabed or monopiles that are driven many feet into the seabed to keep turbines steady in high winds and waves.
These techniques have evolved with the wind industry for decades. Offshore wind farms are regularly popping up in European waters – waters that see very strong storms in the North Sea. As turbine size and wind farm size has increased, the financial risk associated with these projects also increase. A single turbine may cost several million dollars and a single offshore wind farm can cost more than one billion dollars. With the high capital costs, project developers, utilities, insurance agencies and customers want to ensure the projects have the best possible chances of withstanding extreme environmental conditions.
Despite the best efforts by any energy project developer, be it nuclear, coal, oil, natural gas or wind power, some power generators will be destroyed. At some point, the Earth will be struck by an asteroid, terrorists will attack energy infrastructure, major earthquakes will happen – but planning for all possible risks at all power stations is unrealistic and unfeasible. But why should hurricanes be expected to pose risks only to wind farms? Multi-billion-dollar oil rigs are subjected to hurricanes in the Gulf of Mexico almost annually – but that risk has not yet stopped the exploration and development of oil and natural gas. Oil rigs even sink, explode and get destroyed, but somehow those structures still are built and insured. Wind farms should be no different. This country has to chose between safer, renewable energy or more high risk energy choices.
Instead of giving ourselves false hopes that we can conquer nature, we should plan to the best of our ability, and expect that at times our structures can and will fail due to some unknown and unsubstantiated risk. Risks only exist if we allow them to – do we as a society prefer the risk of a coal ash spill, an oil rig explosion, radiation contamination, or the risk that a wind turbine might fall down during a hurricane?
Interested in knowing how our more traditional sources of energy and wind turbines weathered Irene? Be sure to read our past blog, Hurricane Irene’s Impact on Fossil Fuels and Nuclear Power, and check back tomorrow for our final blog in this series, Hurricane Irene’s Impact on Wind Turbines.
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