Extreme Weather Impacts on Offshore Wind Turbines: Lessons Learned

Vol. 27 No. 2

Ms. Diamond is Counsel at Lowenstein Sandler PC, in the firm’s New York City office.

Due to more intense weather conditions than originally anticipated, hundreds of offshore wind turbines in Europe are undergoing extensive repair. Many of these repairs are attributable to the turbines’ designs, which were not engineered to withstand the force and duration of certain metocean (meteorological and oceanographic) conditions and extreme weather to which they unexpectedly have been exposed. Miscalculations relating to violent, extended storms of greater intensity and stronger winds than predicted have caused more extensive damage than envisioned as a result of these storms’ impacts on wave height, wave force, and an active shifting seabed in the form of scour and migrating sandwaves. As a result, costly repairs to rectify turbine foundation issues and undersea transmission cable exposure are underway. Also, these weather events and the navigational risk mitigation measures implemented to address them have caused vessels navigating around wind farms to encounter breach of contract risks.

As the United States endeavors to launch its offshore wind industry, consideration should be accorded to these and other extreme weather-related potential risks to future domestic offshore turbines in the short and long terms. To protect against these risks, it is important to understand wind, wave, and tidal conditions, as well as shifts in air and sea temperature projected to occur over and beyond the next two decades—during an offshore turbine’s approximately twenty-year operational life cycle. Addressing these risks at an early stage will help inform policy and enable stakeholders to take adequate precautions to mitigate these risks where possible. This article will examine (1) issues impacting offshore wind turbines in the North Sea; (2) how these issues and other extreme weather conditions, including hurricanes, could impact turbines placed in the Gulf of Mexico or in Wind Energy Areas along the East Coast in the future; and (3) what, if any, risk mitigation measures can be taken from a policy and legal perspective to address these risks going forward.

The North Sea experience illustrates how weather conditions factor heavily into timing for offshore wind farm construction and general operations and maintenance procedures. Seas need to be as calm as possible for turbine foundation installations. Mean wind speeds vary seasonally. Generally, the spring and summer months are the only months during which the North Sea is relatively calm, turbines may be installed, and vessels can perform ordinary course turbine operations and maintenance procedures. However, during fierce storms, severe sea states arise, thereby increasing the health and safety risk that workers will slip on or fall off turbine platforms or the slick decks of installation or maintenance vessels, causing worker injuries or fatalities. Weather-related worker accidents and injuries must be minimized. Also, severe sea state waves may hold adverse consequences for turbines themselves. Whereas wind force impacts turbine blades, wave force impacts turbines’ lower to bottom areas, such as their platforms, foundations, and cables transmitting the wind energy generated to the transformer station. From a property risk perspective, wave heights surpassing 15 meters can significantly damage an offshore wind turbine’s platform. Although weather conditions are closely monitored so wind farm construction planners can prepare timing of operations and arrange back-up plans, incorrect estimates for extreme weather’s arrival time, intensity, and duration can result in unanticipated breaks during turbine installation and maintenance.

Currently, it is unclear how North Sea offshore turbines will withstand repeated exposure to extreme winds. Onshore turbines in the UK, for instance, generally are not designed to withstand sudden onslaughts of extreme winds. In December 2011, 150 mph winds hit Scotland and northern England, causing one onshore turbine to burst into flames. Extreme winds cause large vibrations and loads, creating significant fatigue on turbine blades even when they are not spinning and have automatically shut off when wind speeds (or other factors) reach certain maximum threshold levels, which will vary depending on the location of the turbine. This fatigue has resulted in smaller onshore turbines experiencing blade throws—having their blades torn off and hurled toward surrounding objects. In an offshore turbine context, where turbine blades are generally longer and heavier than onshore turbine blades, a falling blade can seriously damage or sink a vessel and injure or kill crew members. While RenewableUK, the trade and professional body for the UK’s wind and marine renewable industry, characterized extreme onshore winds as “freak weather,” with changes in global weather patterns, it is difficult to predict whether similar extreme wind anomalies will occur more frequently in the future, either onshore or offshore. Extreme winds, therefore, carry with them increased risk of turbine damage and the accompanying cost of turbine repair and replacement.

While it is obvious that bouts of increased extreme winds, wave heights, and wave force can result in increased financial risk associated with damaged turbines, what is less obvious are the other related risks these occurrences bring to vessels navigating around wind farms. During a severe sea state, brutal storms and their high mean wind speeds are correlated with significant wave heights. These factors can increase navigational risks. High waves can be dangerous to smaller vessels, causing them to become disoriented, lose stability, or capsize due to cargo shift. Vessel damage can contribute to vessel control loss, loss of emergency power, damaged or lost cargo, loss of shipping gear, increased collision risk with other vessels or turbines, and loss of investment (financial loss). Drift is also a serious issue that has plagued vessels navigating around North Sea wind farms. This is because violent storms can cause vessels traveling in a shipping lane or at the edge of the “safety zone” boundary area outside a wind farm’s perimeter to become disabled due to engine failure. Rough currents, turbulent waves, and extreme winds can thrust such disabled craft into other objects, including offshore turbines. To reduce drift risk during such weather conditions, vessels are often rerouted. The new course a vessel takes, though, may increase breach of contract risk associated with that vessel’s failure to deliver its goods on time. These breaches can result in payment of liquidated or other damages to the recipient party to whom the goods are owed. Such vessels’ owners would likely also incur additional charges, including carrying, fuel, and docking charges, if a vessel is forced to dock at an unanticipated location further away from its originally charted course.

Extreme weather conditions have also caused about four-fifths of all North Sea offshore turbines to sustain failing grouted connections. Most of these turbines possess a monopile foundation. In a monopile turbine, the turbine’s blades are connected to one pole, or monopile, which fits into another slightly larger-in-diameter, tubelike outer vertical transmission piece just above the water’s surface. This double-tube structure continues through the water into the ocean floor, where it is anchored. Cement grout is inserted to fill the gap between the turbine’s inner monopile pipe and its outer vertical transmission piece, all of which constitute the turbine’s foundation. While grout sets to a strength generally similar to that of stone, it also needs to withstand the turbine’s weight, as well as the lateral force of the wind. As context for the size and weight of a monopile turbine, in the Scira Sheringham Shoal offshore wind farm (Sheringham Shoal) located in the Greater Wash off England’s North Norfolk coast, each of the ninety monopiles are an average of approximately fifty meters long, five meters in diameter, and 450 tons and have been pile driven between twenty-three and thirty-seven meters into the seabed. Violent storms and their accompanying extreme winds and waves have caused North Sea monopile turbines to experience bending movement between the monopile and the transition piece (an extension of the turbine’s tower), causing some of these turbines to tip and no longer stand vertically.

Moreover, dissolved or cracked grouting has caused these turbines to shift on their foundations. See Monopile Worries Mount: Grouted Joint Doubts Linger, Wind Energy Update (Apr. 10, 2012). Hundreds of millions of dollars in repairs are associated with rectifying this grouting issue. Measures are being taken to address this matter, although their effectiveness remains to be seen. One such measure includes DNV KEMA’s modifying its industry guidelines to lower the acceptable load threshold that can be placed on grouted connections. See DNV KEMA, Offshore Standard DNV-OS-J101: Design of Offshore Wind Turbine Structures, Sec. 9 (Sept. 2011). A second measure, adapted from the oil and gas sector and used at Sheringham Shoal, uses steel and rubber spring bearings to reduce stress on the grouted connections. A third measure is a design modification based on recent industry research: using conical grouted connections. Conical grouted connections, made from well-defined steel cones, replace cylindrical grouted connections between the concentric monopile and vertical transmission piece. The grout in the cone-angled section adds pressure to reduce sliding motion between such two pieces. Id. at 140. Conical connections are now the new industry standard for offshore wind farms. Design defects associated with this new technology may not become apparent until after several seasons of harsh weather. Notably, the London Array wind farm, which will be the largest wind farm ever built, plans to employ this new technology. The lack of a historical track record and the uncertain effectiveness of these technological design advances may be a risk that wind farm investors and developers may be willing, or may need, to take.

Additionally, seafloor conditions such as scour and sand dune migration are often underappreciated risks, as are extreme weather impacts on such conditions. Seafloor dynamics, including wave conditions, tides, currents, water flow velocity, marine growth, terrain, and ice formation, can create chronic scour, or the depletion of seabed sediment. Scour can cause erosion around offshore turbine bases located in sandy soils, making such turbines’ foundation anchoring less sturdy and reducing the turbines’ stability. A five megawatt (MW) offshore turbine costs about £6 million (about $9.5 million), with its foundation costing approximately £3 million, (about $4.7 million) depending on water depth. See BVG Associates, The Crown Estate: A Guide to an Offshore Wind Farm (2011). Because foundation costs constitute a substantial part of a turbine’s overall cost, scour is a major concern for monopile offshore wind turbines’ foundation design.

Moreover, many North Sea offshore turbines are located in seabeds of mobile sediments. Research shows that these turbines’ foundations are more susceptible to scour impacts than originally predicted. Extreme weather causing seafloor sediment to be more mobile than anticipated could result in higher scour incidents than previously thought, potentially causing cable exposure. An offshore turbine’s transmission cable generally runs down the turbine’s shaft and is anchored near its base. If the seafloor erodes at the turbine’s base, this cable can become exposed and will need to be reburied.

Traditional scour protection measures have not always been successful. For example, a 2005 study indicated that the scour protection for certain turbines in the Horns Rev I wind farm, located in the North Sea off Denmark’s west coast, had sunk unexpectedly as much as 1.5 meters adjacent to the turbines’ foundations, causing cable exposure. See Long Lasting Scour Protection for Offshore Wind Farms (Mar. 2, 2012). To prevent further cable damage and further turbine sinking, the developer was responsible for filling the scour holes with stones and placing additional stones in between these turbines’ foundations and the seafloor. A developer’s financial ability to shoulder costs related to addressing more frequently occurring, underrated risks such as scour needs to be considered.

Similar to scour, sand wave migration can cause cable exposure. Sand waves typically occur in shallow seas, with tides largely impacting their migration. Sand wave migration rate can have adverse consequences for turbine cable installations. This is because if a cable was originally buried under a sand crest on the ocean floor, it can become exposed if the crest migrates and leaves a trough in its place. Because sediments can be highly mobile, and because sea floor topography—particularly ridges—can accelerate water flow, cable burial assessments need to be conducted to plan both how deep cables need to be buried and how high sediment transport areas can be avoided.

Cable exposure is an expensive and difficult problem to fix. Few installation vessels available globally can lay subsea cables or conduct cable repairs. High demand and global competition for these vessels make such vessels available at a cost premium. Also, installers may downplay weather risks and underestimate the time it will take them to complete cable installation. This could be problematic, as the cable-laying permit the installer obtains could be of insufficient duration. The installer may be unable to complete its job within the permitted timeframe, and the job could go unfinished. These delays may increase the project developer’s time and costs for completing cable installation and repairs.

Additional Risks That Climate Change, Nor’easters, and Hurricanes Pose to Offshore Turbines in U.S. Waters

Anticipated global temperature increases and elevated sea levels associated with climate change may impact offshore wind turbines scheduled to be located in U.S. waters. According to the World Meteorological Organization (WMO), 2001–2010 was the warmest decade in recorded history. See World Meteorological Organization, Press Release No. 943, at www.wmo.int/pages/mediacentre/press_releases/pr_943_en.html. The WMO has found that Arctic sea ice in recent years has declined due to higher global temperatures and in 2011 was 35 percent below the 1979–2000 average. Id. A decrease in sea ice translates into sea-level rise. This could significantly impact the offshore wind industry’s supply chain in the long term. A sea-level rise of only a few meters may cause ports and highways to become flooded or completely submerged. Significant infrastructure repair may be needed due to flooded or submerged ports, resulting in vessels being rerouted to other ports. This could be a logistical nightmare if only one port servicing offshore wind farms is built on the East Coast. For instance, the Department of Interior (DOI) has designated a number of Wind Energy Areas (WEAs) as target areas for offshore wind farm development on the Outer Continental Shelf (OCS), off the respective coasts of Virginia, Maryland, Delaware, New Jersey, Rhode Island, and Massachusetts as part of its November 2010 “Smart from the Start” initiative. See Salazar Launches “Smart from the Start” Initiative to Speed Offshore Wind Energy Development Off the Atlantic Coast, Press Release (Nov. 23, 2010). Barges carrying 5 MW–9 MW offshore turbines that need to be partially preassembled portside, and vessels engaged in these wind farms’ construction and maintenance would dock at this port. The following illustrates what could occur if only one major East Coast port is capable of servicing offshore wind farms. As part of New Jersey’s 2010 Offshore Wind Economic Development Act, the Port of New York and New Jersey is designated as a wind energy zone for qualified wind energy facilities, where wind manufacturers will receive special tax and other financial incentives to build their facilities. If the sea level rises a few meters, projections show that large areas around Newark Bay and Arthur Kill, including the Port of New York and New Jersey and any manufacturing facility located there, would be flooded or submerged, as would certain New Jersey and Manhattan roadways. Vessels servicing East Coast offshore wind farms would have to dock elsewhere, although such other facility may not exist on the East Coast. While port flood risk may be remote at this time, it has the downstream potential to have significant future consequences.

Also, nor’easters and hurricanes pose unique risks to offshore turbines. Historical data gathered from North Sea offshore turbines cannot address these risks, as nor’easters and hurricanes are not found in the North Sea. These two events may have serious implications in terms of turbine design, satisfaction of energy production requirements, and turbine repair or replacement costs for turbines located along the East Coast or in the Gulf of Mexico. Nor’easters, storms that travel along the East Coast, are cyclones that generally occur in winter and have hurricane-force winds accompanied by heavy snow and rain. These storms cause pounding surf and wave swells. Although wave height depends on wind direction, air temperature, and water temperature, it is difficult to predict how warmer waters and air from climate change will impact waves higher up the Atlantic Coast. While twenty-year records of wave data are available for certain areas along the Atlantic OCS, insufficient wave data has been collected to sufficiently understand storm impacts on waves and currents throughout this area.

Atlantic hurricanes are tropical cyclones that form in the Atlantic Ocean, Gulf of Mexico, and Caribbean Sea. Because they are fueled by warm, moist air, a rise in air and ocean temperatures further up the East Coast than has been the case historically could mean that hurricanes could last longer and travel farther up the East Coast in the future. Wind farms in WEAs, consequently, may be at increased hurricane risk. This is cause for concern. According to NASA’s website, hurricanes are the most violent storms on Earth. The National Oceanic and Atmospheric Administration’s (NOAA’s) National Hurricane Center uses the Saffir-Simpson Hurricane Wind Scale (SSHWS), which assigns hurricanes a Category 1–5 rating, based on each hurricane’s intensity. Hurricanes wield destructive power in the form of extreme winds and storm surges (an abnormal rise in sea level, over and above the predicted tides). A Category 2 hurricane, with wind speeds of 96–100 mph and storm surges of 6–8 feet above normal, can cause moderate damage at landfall, while a major hurricane of Category 3 level, with wind speeds of 111–130 mph and storm surges of 9–12 feet above normal, can cause extensive damage at landfall. Offshore wind turbine damage at sea, where hurricanes draw their fuel from the heat of the water and water evaporating from the water’s surface, may be more severe.

Because hurricane intensity and frequency may be correlated to climate change impacts, the risk probability of a “black swan hurricane” event—a low probability, hard to predict event with disproportionately high or catastrophic damage consequences—has real cost implications in terms of the damage it could cause to an offshore wind farm. A warmer atmosphere holds more moisture and is expected to generate more extreme weather, including more powerful hurricanes, potentially increasing the probability of a black swan hurricane.

To protect against black swan hurricane risk, improvements in offshore wind turbine design are needed. An increase in frequency of Category 2 or higher hurricanes could have severe implications. Offshore turbines need to be able to survive the combination of fierce winds, increased wave heights, and intense wave force accompanying Category 2 and potentially Category 3 or higher hurricanes without sustaining damage. At a minimum, offshore turbines for U.S. waters need to be designed so that their blades and gears can withstand the wear and tear that potential increased frequency of Category 1 hurricanes may cause. Carnegie Mellon University researchers found that turbines placed in U.S. waters may be vulnerable to hurricane-force extreme winds because offshore turbines currently on the market are only designed to withstand Category 1 hurricane wind speeds. See Carnegie Mellon Team Finds Hurricanes Pose Potential Risks to Offshore Wind Turbines, Press Release (Feb. 14, 2012). Despite such findings, industry executives and engineers maintain that a Class 1 turbine (designed with current technology) should be able to withstand a Category 3 hurricane. However, whether a particular turbine design can handle the load from these hurricanes and what level of incremental damage blades and gears will sustain after repeated exposure to such conditions at a particular location remains unknown.

Rating agency criteria for offshore turbine hurricane risk is currently unavailable. Investors, such as investment banks, need to be comfortable quantifying risk and damage probabilities involved in a potential investment as certainty makes projects financeable. To gauge long-term project performance and return on investment, such investors may look at rating agency criteria, methodologies, and factors a rating agency considers during its rating and surveillance process for certain asset classes, including renewable energy project types. This, however, is not an option with respect to offshore wind projects. While Nationally Recognized Statistical Rating Organizations (NRSROs), such as Fitch Ratings, have established ratings criteria for onshore wind farms, they do not have established ratings criteria for offshore wind farms; because no U.S. offshore wind farms exist, it is impossible for any NRSRO to gather historical U.S. offshore turbine data on which projections and ratings may be based. U.S. wind farms that will be located in the Atlantic Ocean and Gulf of Mexico inherently carry with them risks that do not apply to onshore turbines: risks associated with hurricanes in open waters, wave damage, and a shifting seabed. Lack of rating agency criteria and lack of history on which such criteria can be based may provide insufficient comfort to risk-adverse investors. Hurricane risk, therefore, may deter certain investors from financing a U.S. offshore wind project.

According to a March 2012 J.P. Morgan report, hurricane risks in the Gulf of Mexico are substantial and difficult to insure on a cost-effective basis. See J.P. Morgan, Eye on the Market (Mar. 22, 2012). This market report indicates that if an oil platform sustains serious hurricane damage, there may be insufficient value remaining in the oil well to substantiate its repair costs. Id. Similarly, there needs to be an economic justification for repairing or replacing an offshore wind turbine. If such a turbine sustains serious structural damage from a hurricane, depending on when the damage occurs during the turbine’s approximately twenty-year life, repair costs may exceed either the amount of future revenue that would be generated during the remainder of the mended turbine’s life or the amount of damages that would need to be paid to the applicable utility for failure to deliver the contractually agreed-upon amount of electricity. Replacing a severely damaged turbine also may not be cost effective, given the turbine’s age or the timing for decommissioning or replacing other turbines in the same array. Consider what may happen if numerous turbines in an offshore wind farm simultaneously experience severe damage. Moreover, nor’easters and hurricanes may have unknown, adverse implications with respect to subsea cable damage, which also could need to be repaired or replaced if a turbine falls or if seabed conditions change more quickly than anticipated. This makes offshore turbines highly leveraged investments, insofar as they are leveraged with respect to replacement costs.

Hurricanes that occur more frequently or are of greater magnitude than originally anticipated may be difficult weather risks to insure. Property insurance needs to be in place to cover turbines that experience catastrophic damages past their warranty period. Business interruption insurance needs to be in place to mitigate risks associated with failure to deliver the contracted-for amount of energy, as well as the time it takes to conduct turbine and/or cable repair or replacement for energy transmission purposes. Added to the difficulty of quantifying and setting insurance coverage for nor’easter and hurricane risk is that few insurers currently insure offshore wind projects globally.

Lessons Learned: What Steps Can Be Taken to Mitigate Extreme Weather Risks

If we as a country are committed to launching a domestic offshore wind industry, we must have long-term policies and programs in place to identify risk mitigation measures that can be implemented to address extreme weather-related offshore turbine risks. Grout, scour, and sand wave migration issues have caused North Sea offshore monopile turbines to experience foundation instability, structural issues, and cable exposure, due to inaccurate estimates for extreme weather conditions. As experience with these turbines illustrates, current wind turbine design technology may be at a crossroads, walking a narrow line between engineers creating a defective product and engineers creating a product that is currently a technological impossibility. Regardless, offshore turbine designs will need to undergo specialized improvements to withstand hurricane risks in U.S. waters.

One way to accomplish this goal is to implement federal legislation or institute federally funded, government entity-sponsored initiatives for ongoing research and development studies tailored to improving offshore wind turbine designs. The Department of Energy (DOE) has already taken several steps in this direction. First, in September 2011, it awarded $43 million to forty-one research projects across twenty states for purposes of jumpstarting the U.S. offshore wind industry. See DOE Awards $43 Million to Spur Offshore Wind Energy, EERE News (Sept. 14, 2011). These studies, however, lack permanence, as each is only scheduled to last several years on average. As a policy matter, long-term, ongoing studies in collaboration with colleges, universities, and private companies need to be established to evidence a firm federal commitment to the development and evolution of a U.S. offshore wind industry. Second, DOE Secretary Steven Chu announced on March 1, 2012, a six-year, $180 million program to fund four innovative offshore wind installations across the United States, as part of an initiative to diversify the nation’s energy portfolio and launch the nation’s offshore wind industry. See Energy Department Announces $180 Million for Ambitious Deploy U.S. Offshore Wind Projects, EERE News (Mar. 1, 2012). While there is a $20 million initial commitment in fiscal year 2012, this initiative is subject to congressional appropriations. Initiatives such as this must be definitively funded and last for a longer period of years, thereby evidencing a more permanent federal commitment to offshore wind development. Third, policy measures encouraging global collaboration for research and development purposes, and for data sharing, need to be adopted and supported, particularly in the area of technological innovations. Secretary Chu realized the importance of such collaboration, as indicated by his meeting with UK Energy Secretary Edward Davey in April 2012, during which they discussed accelerating the transition to clean energy technologies and entered into a new Memorandum of Understanding on “Collaboration in Energy Related Fields.” See Davey to Host International Clean Energy Talks (Apr. 23, 2012). As a result, the UK and United States will be collaborating on and jointly funding the development of floating wind turbines for deep waters. Id. Floating turbine technology means not having to repair turbine foundations on the seabed. High visibility government officials, in addition to the general public, must encourage and publicly support these multicountry collaborative efforts promoting technological developments. Moreover, the federal government’s investing in demonstration projects showcasing new offshore wind technologies, such as floating turbines, may be the needed first step for supporting the “test case” from which data on resilience to certain weather conditions may be extracted. Such demonstration projects’ success may encourage investors to gain confidence in financing offshore wind projects.

Increased interagency cooperation among federal agencies and publicity for such efforts are also needed for purposes of pooling and publicly sharing knowledge and scientific data. Cross-agency collaboration and data pooling among agencies such as NOAA, the Environmental Protection Agency (EPA), DOI, DOE, and the Bureau of Ocean Energy Management (BOEM) is necessary to reduce redundancy and expedite the siting, permitting, and approval processes for offshore wind farms and their turbines. It will also reveal more quickly whether the North Sea’s seabed, wave, and other metocean conditions are similar enough to those off the Atlantic Coast or in the Gulf of Mexico for purposes of predicting sediment transport, as well as scour and sand wave migration risk in U.S. waters for nonfloating turbines.

Finally, it is important that state and federal policymakers involved in the offshore wind farm developer selection process are adequately informed of the potential expenditures needed to cover potential risks, so that a developer’s financial strength and ability to cover both expected and unforeseen costs may be accorded due weight. Having a developer go bankrupt during the wind farm development process because of its inability to finance costs associated with unanticipated damages from weather conditions is undesirable and presents a situation against which precautions should be taken.

Adequately addressing extreme weather risks for offshore wind turbines is indeed challenging. To advance and successfully launch the infant U.S. offshore wind industry, innovations in offshore turbine design are necessary. With proper federal policies, initiatives, and monetary support to enhance collaborative scientific research and development efforts, advances in turbine design have a greater likelihood of occurring more rapidly and have the ability to help the U.S. wind industry get off to a positive start.


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