| Written by Michal Wozniakowski-Zehenter
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The location depends on several factors, with the most important (and obvious) one being wind. It needs to be strong and consistent enough to generate electricity efficiently, but not too strong to cause damage to turbines or their supporting structures. The depth of the sea is another important factor. Shallow waters make it easier to install and maintain while reducing the cost of construction for the fixed turbines, which are usually positioned in water not deeper than 60 meters and floating platforms which can be built on deeper waters. The average distance of offshore wind farms from the shore varies depending on the specific location and circumstances of the wind farm. In general, they are typically located within 20-30 kilometres (12-18 miles) of the coast, but they can be as close as a few or as far as 100 kilometres (62 miles) away depending on the regulations and costs of bringing the energy to the onshore power grid.
As mentioned before, wind strength is key – energy is being produced from 3-4 meters per second, with the maximum power output approximately around 12-14 meters per second, up to the cut-out speed of 25-30 meters per second, where the wind turbine will automatically shut down to prevent the damage. It is no different to maintenance, which is safe to perform during no to moderate wind conditions, so usually – maintenance of a turbine means that it’s shut down for a time being. Since each of the turbines can operate for 25 to 30 years before major components such as the blades or gearboxes need to be replaced, having in mind the harsh environment they are located in, with salt water, low temperatures, and exposure to lightning, maintenance is needed to be done regularly in monthly or bi-annual intervals. With an average of 20 to 50 structures in one wind farm (big wind parks can include more than 100 turbines), it is a constant process throughout the available time during the year. Visual inspections to check for any damages to the tower, blades and other components, lubrication of the gearbox and bearings, electrical cables and transformers checks with the cleaning of the turbine is daily work for thousands of maintenance crews around the world.
Accessing offshore wind turbines can be challenging, and specialized vessels and equipment are required to transport personnel and equipment to the turbines. Transportation may include crew transfer vessels (CTVs), service operation vessels (SOVs) and helicopters and they are part of wind farm safety.
CTVs are designed to transport personnel from the land to offshore wind farms and vice versa. These vessels are typically small, fast, and highly manoeuvrable, allowing them to operate in challenging conditions. They are essential for maintaining the workforce, and ensuring that technicians and other personnel can access the turbines safely and efficiently.
SOVs, on the other hand, are larger vessels designed to provide accommodation and support for the crew. They typically have a range of features, such as workshops, storage facilities, and helipads, that enable them to provide a wide range of services to maintain offshore wind farms.
Helicopters are also well-suited for this task as they can travel quickly and efficiently over long distances and can land on small or unprepared landing areas such as the turbine’s platform on the top of it.
There are many potential hazards to wind farm safety which need to be considered before approaching the turbine. To mitigate them, first and foremost, still, on the vessel everyone needs to wear proper Personal Protective Equipment (PPE). Hard hats to secure from falling objects, eyes protection against wind, debris and flying objects, noise reduction earmuffs or earplugs, high visibility clothing with protective gloves and safety harness to prevent falls and be attached to one of the many secure anchor points are the essentials for working in such a harsh environment. When this is done, it’s time to reach the turbine. There are, in general, two ways to enter the construction. One is from the bottom and one is from the top.
Once the helicopter is approaching the landing zone platform on the top of the wind turbine, workers are preparing to be hoisted. The doors are being open and all the crew, one by one, are dropped on the platform from a height of approximately 3-8 meters. Coordination between the pilot and the workers is done via the radio system. After offloading all necessary equipment and clearing the zone, the helicopter takes off to the shore until the pickup time occurs.
The biggest hazards in this situation are the height of the construction (usually it’s 50 to 80 meters above sea level) where personnel is located with the potential of slipping, falling over the barrier, being hit by wind gusts and flying parts of equipment. That’s why everything needs to be secured and stored properly, workers need to anchor to the safety points within the platform. Helicopters are also used to transport the crew to SOVs for easier disembarkment with bigger cargo transportation. They are later transferred to the turbine by different vessels.
While using transportation by water, CTVs are usually bringing personnel to the bottom of the construction. Sometimes with a small gangway, sometimes just stepping over, workers are coming to a small bridge or directly to the ladder, which they need to climb to access the interior of the wind turbine. This approach is also called boat-landing. There’s radio communication between the captain of the vessel and the operator of the gangway, to make sure that stability and the distance to the turbine allow leaving to perform maintenance duties. While going up, the harness must be anchored to safety points to prevent falling. If workers need equipment or spare parts, they are lifted to the lower platform by a crane from the vessel. After the unloading, CTV will wait in close proximity to the park for a pick-up of the personnel. In case of an emergency, each worker is equipped with Radio and, as a second source of communication, a satellite phone. SOVs use stable, secure gangway systems that adapt automatically to the sea movement and make the entire process the best possible of all three.
What kind of threats and hazards are in this scenario? Similar – slipping and falling off, being hit by flying objects, but also the height of the waves and instability while approaching the ladder or platform as well as injuries from being crushed between the boat and the entrance to the turbine.
When all the tasks are finished and the turbine is checked and ready to produce energy, it’s time for workers to go home. Procedures are reversed to what happened earlier in the day, with accessing the turbine. Of course, weather conditions might change so it’s very important to understand and be prepared for it – from stronger wind, and rain, to higher waves – the crew might need to be extra cautious with slippery floorings and railings, and bigger movements of the vessel (read more about RFID mustering and offshore safety concepts). But there is one more factor which can affect the safety of the workers. Human errors are caused by fatigue from working long hours in harsh environments, low temperatures, and wind conditions. Falling or slipping down might lead to severe accidents.
- What are the main reasons for accidents while working on offshore wind platforms?
Human error is one of the most common causes of accidents on offshore wind platforms. This can include mistakes in judgment, lack of training, fatigue, and inadequate communication. Adverse weather conditions like storms, high winds, heavy seas and lightning strikes can all contribute to increasing the risk. Any failure of the equipment including turbines, generators, and transmission systems or inadequate safety measures and lack of training can lead to accidents. Learn more about HSE standards in the North Sea ...
- What is the most common way to reach the offshore wind farm?
The most common way to reach an offshore wind park is by boat or helicopter. The specific mode of transportation will depend on the location of the wind park, the size of the turbines, and the available infrastructure. Boat transportation is often used for smaller wind parks located closer to shore, while helicopter transportation is more common for larger wind parks located further offshore. Additionally, personnel may use support vessels, crew transfer vessels, or specialized service vessels to reach the wind park.
- How long is the maintenance of the offshore wind turbine?
Generally, routine maintenance of offshore wind turbines is performed regularly, such as monthly or bi-annual inspections, and may take several hours or days to complete depending on the complexity of the task. During this time, technicians typically inspect and test the turbine's various components, including the blades, nacelle, gearbox, and electrical systems, to ensure they are functioning properly and to identify any issues that require repair or replacement. In addition, more significant repairs or upgrades may be required from time to time, such as replacing a blade or upgrading the control system. These tasks can take several days or weeks to complete, depending on the complexity of the repair and the availability of parts and equipment.
It's worth noting that maintaining offshore wind turbines can be more challenging and time-consuming than maintaining onshore turbines, due to the remote location and harsh weather conditions at sea. This can make it more difficult for the personnel to access the turbines and perform maintenance tasks, which can increase the time and cost of maintenance.
Approaching and leaving offshore wind turbines is daily work for many people. Weather conditions and types of transportation might vary based on the location, but safety is continuously considered while planning and performing tasks. Harsh conditions, big waves, and saltwater might contribute to the accidents by damaging the structure or making it slippery to move around. Also, fatigue and being tired might distract the crew to make mistakes. That’s why training and proper safety regulation and equipment help to mitigate those risks and execute operations successfully.
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