Introduction
As observed in the previous post, various meteorological phenomena can significantly impact wind turbines. In this post, we will focus on understanding how storms affect wind turbines. To do so, it’s important to define what a storm is – a violent atmospheric disturbance characterized by low barometric pressure, cloud cover, precipitation, strong winds and possibly lightning and thunder. [1]
Storms can be very strong like the formation of hurricanes. The formation of a hurricane begins with a cluster of thunderstorms moving over the ocean’s surface. As these storms encounter warm surface water, they absorb heat energy, leading to increased moisture in the air. If conditions align correctly, the storm can develop into a hurricane. [2]
This is significant because offshore wind turbines are exposed to these intense oceanic storms and can suffer more damage than onshore ones.
How do storms affect wind turbines?
Storms encompass different phenomena such as high-speed wind, rainstorms, and lightnings. Each one of these can affect and damage wind turbines in various ways:
High-speed winds
High-speed winds pose a significant risk to wind turbines. Each turbine has a cut-out speed, which is the maximum wind speed it can handle without straining the rotor. When wind speeds exceed a turbine’s design limits, the turbine can shut down to prevent damage, halting energy production. During storms or hurricanes, wind speeds can surpass this cut-out speed, potentially causing damage to the turbines.
The damage of high wind speed, especially during hurricanes in offshore locations, can include loss off blades and buckling of the supporting system. The worst harm is the buckling of the towers because, while blades can be replaced, their loss can still cause structural damage. In 2003, a wind farm of seven wind turbines in Japan was destroyed by typhoon Maemi. This example illustrates the strength of such storms and the damage they can produce. [3]
Rain
Rain is one of the main characteristics of a storm and can cause short-circuits and damage to essential components. Raindrops cause erosion in the wind turbines, especially on the blades. Impact erosion by raindrops is considered one of the major causes of Leading-Edge Erosion (LEE), which reduces the efficiency and lifespan of the blades. [4]
Thunderstorms and lightning
Wind turbines, as tall structures, are susceptible to lightning strikes during thunderstorms. They can receive downward lighting, which is the most frequent type, or initiate upward lightning. Downward lightning can be particularly damaging due to its high frequency. [5]
The most exposed part to lightning damage are the rotor blades. Blades are equipped with an air termination system that consists in various discrete receptors. It is hoped that the lightning will attach to these receptors and not uncontrolled locations. If the lightning is attached to the discrete receptors, the most common harm is melting and vaporization of the receptors themselves. These receptors need to be changed during the lifetime of the blades. When the lightning is attached to uncontrolled parts like drain tubes or down conductors, different damages can occur including severe harm where replacement or reparation is needed. The most damage occur in the blade tip area. Also, if the lightning currents are present in the down conductor system, the connection components can be stressed, and the overvoltage produce harm in electronics controls systems, sensors, and communications. [6]
What is being done to prevent this damage?
Wind turbine operators implement a variety of strategies to minimize the impacts of storm-related damage.
Mitigating high-speed wind damage
Involving high wind speeds, when the speed surpasses the cut-off limit, the blades begin to feather or point into the wind to reduce their surface area and catch less wind reducing the velocity of it and keeping the production of energy. In some cases, the blades can even be locked down to ride out severe gusts.
For this process there is an anemometer that measures the wind speed to feather and unfeather the blades whatever the case is needed. This shut down process was on full display at Rhode Island Block Island Wind Farm (offshore) when the winter storm Stella in 2017 stroked and for a few hours the wind speed surpassed the cut-off limit. [7]
Protecting against rain erosion
To mitigate the detrimental effects of rain on turbine blades, advanced protection methods have been developed. These include specialized coatings, leading edge protection systems, and shells. [8]
Lightning Protection Measures
Even though some lightning damage is unavoidable, moderns’ maintenance methods and lightning protection techniques con significantly reduce it. Since the blades are the most damaged part, solutions focus primarily on them. Early detection and mitigation are essential to prevent harm.
One of the most effective techniques is to maintain the blades clean and inspect them regularly. Dust, for example, acts as a lightning magnet so maintaining the blades clean helps preventing the attraction of lightning. [9] Additionally, a lightning protection system can help secure the turbine from strikes.
Advanced materials and research initiatives
Also, some projects like Carbo4Power aim to develop advanced materials for offshore wind and tidal turbine rotor blades. These materials will be lightweight, strong and multifunctional. By using intelligent architectures and nano-engineered hybrid materials, the project aims to enhance the operational performance and durability of these blades. These technologies ensure precise shaping and assembly of materials, resulting in a reduction of approximately 20% in scrap material during the fabrication process.
What is AIRE doing?
In addition to physical protection strategies, enhancing our ability to predict wind turbine responses under real climate conditions, from storms to calima, is crucial. AIRE aims to tackle both aspects of these aspects. On one hand, we are designing new airfoils, and on the other, we aim to improve the accuracy of current predictive models by incorporating new key parameters for turbine siting, wind farm design, component design, and O&M strategy planning.
To achieve this, AIRE will conduct a variation analysis, which helps refine our model settings to more accurately capture high-altitude winds and precipitation patterns. This process will optimize the parameterization, the way complex weather conditions are represented in the model. The results will then be analysed to improve prediction accuracy for precipitation and dust, aiming to reduce uncertainties by 2% using real climate data.
To accurately assess how precipitation affects turbine blades and develop solutions, a fully resolved CFD-rotor simulation of a selected multi-megawatt wind turbine will be performed using OpenFOAM software. Precipitation will be simulated using particles with specific physical properties according to defined scenarios and measurements and the blade damage model, which estimates erosion evolution based on time series of weather data and wind turbine operational data will be further developed and validated.
IWES mesoscale simulations for turbulence upstream and downstream of the wind turbine. @Leo Höning
Two airfoils will be designed to work efficiently under conditions of dust or precipitation and mesoscale simulations and satellite data will be utilized to generate an erosion atlas for representative zones (offshore, high altitude, complex terrain and sand-laden air). This setup will serve as the foundational resource for the developed toolbox.
As demonstrated in several studies [10], preventing blade erosion by reducing tip speed during heavy precipitation events can save costs and prevent income loss due to blade degradation. This is why AIRE aims to mitigate the adverse effects of phenomena such as dust storms and heavy rain, protecting turbine longevity and ensuring reliable wind energy generation.
References:
[1] https://www.britannica.com/science/storm
[2] https://oceantoday.noaa.gov/fuelforthestorm/
[3] https://www.pnas.org/doi/epdf/10.1073/pnas.1111769109
[4] https://onlinelibrary.wiley.com/doi/epdf/10.1002/we.2617
[7] https://www.energy.gov/eere/articles/how-do-wind-turbines-survive-severe-storms
[8] https://www.sciencedirect.com/science/article/pii/S0960148123008728
[9] https://www.windsystemsmag.com/preventing-lightning-damage-to-turbines/
Author: Zoe Cardell
Editor: Lucia Salinas
November, 2024
