Björn Kramer, Expert Offshore Lifting Equipment
Alexander Heitmann, Head of the Offshore Wind Energy Department
TÜV SÜD Industrie Service GmbH
Men and materials must be lifted about 90m to access wind turbine nacelles during installations, maintenance, and servicing. Offshore turbines are equipped with modern service lifts and lifting equipment to transfer loads from base to nacelle. However, working conditions at sea involve particular risks which are particularly critical for components and occupational safety. For example, extremely heavy loads must often be transported safely from the service boat to the nacelle. Workers must be able to safely lift and transport heavy equipment from a boat rocking in high waves, when loads are swinging from a crane, and when the entire tower is oscillating in the wind.
Swinging in the wind
Under these conditions, impact and crush hazards are an ever-present risk. Given this, any measures that optimize the transport process and promote occupational safety can simultaneously reduce the time taken for maintenance and repair work. Because of the favorable wind conditions offshore and the high yields from these multi-megawatt turbines, long periods of downtime involve far higher financial losses than for onshore turbines.
In addition, maintenance and repair costs are relatively high. According to the German Wind Energy Association, service and maintenance account for around one-quarter of the total operating costs of offshore wind turbines, compared to a low single-digit percentage for their onshore equivalents. Optimized and efficient transport processes at the turbine can help reduce these costs by significantly speeding up maintenance and repair processes.
A further aspect is that service boats can be used more efficiently and teams can arrive on-site faster. This is an important consideration because offshore wind farms cannot always be accessed safely. In adverse weather conditions, the time frames for completing repairs are often short. In the study dena-Netzstudie II, the German Energy Agency (dena) quotes a figure of 65% in reference to accessibility by boat for a coastal site in Denmark. This figure may be considerably lower for sites further out to sea.
Time is money is energy yield
There is room to improve safety levels. The installed lifting equipment, service lifts, and ladders are all in line with state-of-the-art technology and present no dangers. However, experience in practice has shown that at the planning stage, insufficient attention is often paid to the differences in conditions at offshore turbines compared to the onshore sector. For example, offshore lift systems involve greater potential hazards than their onshore equivalents. Their long trailing cables do not hang vertically, but follow the oscillations of the tower. If these cables become caught on components, the safe operation of the lift may be endangered.
Because offshore wind technology is a relatively new industry, safety-relevant considerations such as these have only emerged as operation of the first turbines has progressed. It has become clear that the aim must be to establish a continuous, smooth transport chain from boat to nacelle right from the planning phase.
Experience into planning
Although manufacturers, suppliers, operators, and official authorities have incorporated many of these aspects into current planning, all stakeholders are still performing pioneering work. Existing standards must undergo regular review of their suitability for offshore operations, and further development. The mature technology that already has a proven record in the onshore wind energy sector must be adapted and improved for conditions at sea.
Standards applied by the shipbuilding, oil and gas industries are stricter. However, because these standards were designed for far harsher conditions and involve significant levels of additional costs, simply adopting them unchanged would not be a practical solution. Nevertheless, they may form a useful basis from which to develop dedicated standards for offshore wind turbines that address their specific ambient and operating conditions. WPE&D
Filed Under: News, Offshore wind, Safety