Benefits of Offshore Wind Turbines

At this moment in time, with electricity demand around the world continuing to increase, one way we might reduce our reliance on non-renewable energies is to start using renewables, such as wind energy.

Wind energy is set to have an increasingly significant part in the future energy system

of Ireland. Government policies are committed to providing 10% of energy from

renewables by 2020 and to cutting 65% of greenhouse gas emissions by 2050.

Although there are clearly numerous similarities between the designs of onshore and off shore wind turbines, there are differences that result from the particular operating environment. The marine environment offers both advantages and disadvantages. Installation in water is extremely more difficult than on land and becomes increasingly harder with deeper water. Salt water is very highly corrosive. These negative factors are offset by more powerful and less turbulent winds and fewer restrictions on the area available.

Given their distance from the public, there are also fewer restrictions on noise elements, height and blade height allowing for faster blade speeds. Originally, offshore installations took advantage of the most appropriate sites, close to land in shallow water, and utilised onshore turbine designs. Even early large-scale offshore farms such as Horns Rev 1 which used turbines had originally been designed for onshore wind farms. However, the further use of offshore wind energy will require sites much further from shore and in much deeper water. Experience of offshore operations has already refined the turbine design, but major developments are underway including more radical designs. The Energy Technologies Institute, for example, has investigated a number of new possibilities including tension leg floating platforms, vertical axis turbines, large blades and optimised deep-water horizontal axis designs. The main aim of these projects, as with most offshore wind research, is to improve reliability and reduce costs.

Safety at sea is also of vital importance. The waters around the Ireland are extremely busy and offshore wind farms could possibly interfere with shipping lanes. The design of offshore farms seeks to optimise output which can conflict with the requirements for marine safety, particularly relating to the boundary of the farm and routing of ships. The design of turbines continues to progress, particularly in the drive train and control systems. More radical design innovations are being considered for offshore wind as it progresses into deeper waters further from land.

The lifetime of mechanical equipment is always a concern to owners and developers and wind turbines are no exception. The owners of wind farms will have invested a huge amount of capital to the building and installation of the turbines on which they will only obtain a return if the turbine is available to generate electricity. Keeping the turbine operational hostile locations is therefore critical to the economics of the development. This is particularly true for offshore developments where access and egress is limited by weather conditions. Turbines are typically designed for 20 years’ life and now many early turbines have completed such lifespans. Typically, modern onshore turbines are available to generate electricity 97-98% of the time. Availability of offshore wind is lower but improving, particularly as access for maintenance has increased from around 30% of the time five years ago to around 70% today.

1.7 The level and sophistication of operations and maintenance (O&M) has grown significantly in the last 5-8 years. In the first few years due to warranty, the O&M is usually carried out by the original equipment manufacturer. Later on, large owners may have their own O&M division, but there are also other specialist companies that fulfil this role. The wind energy business is coming of age in the context of O&M and for example, the condition monitoring is still at a fairly early stage. Offshore, the task is, of course, much more difficult but at the same time it’s critically vital. In the early days of offshore operations, access and egress was a major problem but now access and egress arrangements have been developed and availability is steadily rising. Increasing the level of early-stage engineering and testing of components prior to installation will also improve the performance of the turbines and the industry is steadily improving.

Comprehensive Supervisory Control and Data Acquisition (SCADA) systems are used in all commercial wind farms. They collect data from single turbines and from substations. Often there are meteorological towers that are also used to extract wind data for the site. In the last 10 years, a great deal of effort has been put into the development of analysis systems to investigate the behaviour of the operational farms and a high level of understanding has developed, allowing optimisation of both wind farm design and operation. There are sophisticated tools for examining both the behaviour of operational farms and also the estimation of the performance of the farms pre-construction. The latter has benefited greatly from recent developments in meteorology remote sensing, satellite data and computational tools as well as the application of computational fluid dynamics to promote understanding of the local flow over the site.

This subject does however remain an essential field for research and development and the science is moving fast. Early stage engineering, monitoring and maintenance are vital to keep turbines available to generate energy and improve performance.