Electrical and Energy

Meeting the first target of 40GW by 2010 requires the manufacture and installation of around 10,000 wind turbines; and there are several logistical challenges that must be overcome to achieve this aim. Offshore wind power is at an early stage of development, and there remains a necessity to streamline all aspects of the supply chain from component manufacture, to turbine design, to installation processes.

Offshore wind power as an industry is set to undergo intense growth over the next 10-20 years. The EWEA (European Wind Energy Association) has established targets of 40GW of offshore wind power production by the year 2020, and 150GW by 2030. This move towards a European grid represents a 28% annual increase in market growth; it will enable the trade of electricity between states, and cement Europe's status as technological leaders in the wind power industry.

The designs of offshore turbines were generally borrowed or adapted from their onshore counterparts; so production of offshore wind turbines had been reliant to an extent on the market growth of the onshore industry. As recently as 2008 this led to supply shortages during periods of high onshore demand. Offshore wind power, however, must be viewed as an entirely different concept to onshore wind power. With the potential for larger turbines, and no limitations on aesthetics or noise levels, manufacturers are developing specifically designed offshore turbines which could increase to up to 10MW in capacity.

Siemens, for example is currently supplying its SWT-3.6-120 turbines for use in the London Array project. The 3.6MW turbine has a 120m rotor, and the three-bladed cantilevered construction will start to produce electricity at wind speeds of 7mph. Supply and installation, however, consists of shipping the turbines from Denmark to the UK, transferring them from barges to installation vessels, before installing the turbine, the hub, and finally the blades.

To establish mass production and cost efficiency of supply and installation, there are several initiatives in development, and various logistical problems to navigate. Design is moving towards the creation of more 'intelligent' turbines, with advanced control monitoring and preventative maintenance. While the development of 'simple' turbines with fewer moving parts designed to be changed easily, will also significantly reduce costs both in terms of construction and operation and maintenance.

1 Spinner 2 Spinner bracket 3 Blade 4 Pitch bearing 5 Rotor hub 6 Main bearing 7 Main shaft 8 Gearbox 9 Service crane 10 Brake disc 11 Coupling 12 Generator 13 Yaw gear 14 Tower 15 Yaw ring 16 Oil filter 17 Generator fan 18 Canopy

Exploded view of Siemens SWT-3.6-20 nacelle, Source: siemens.com

The concept of a twin blade, downwind turbine is at design stage and could appear on the market in the coming years. Twin blades are much louder than three-bladed turbines so have not been considered appropriate for onshore development. There are no concerns over noise levels offshore, and installation could be a much quicker process as nacelles can be stacked with the rotor pre-mounted, rather than installing one of the blades at sea.

A variable speed, direct drive turbine is another possibility in the near future. Gearboxes are one of the most difficult parts to replace on a turbine, and multi-pole gearless turbines operate at a lower drive train speed which would decrease the amount of stress placed on other components. Gearless turbines are generally much heavier than those with conventional gearboxes, so designs must be produced with lighter components to reduce the weight at the top of the tower before this can become a reality.

Wind turbines are currently manufactured in such a way that any part or component cannot be replaced easily. Due to the difficulty in accessing wind farms far out at sea, and the problems of on-site repairs, it is important that purpose built offshore turbines are designed with operation and maintenance in mind. At the moment O&M is very much site specific, and as the industry learns more from existing wind farms, so the process can be standardized to create a sub-industry purely surrounding O&M. It is reasonable to expect to see swing-off systems being introduced, which will allow a spare nacelle to be fitted whilst one is undergoing a service. Preventative, automated systems that can carry out oil and filter changes without the need for humans are also on the horizon. Other initiatives such as multi-coated blades and modular drive trains will help to reduce the amount of maintenance required, and therefore reduce the amount of downtime for each turbine.

The substructure of a turbine is one of the largest single cost factors of the overall project, and reducing the cost of construction, transportation and installation of these foundations will have a big impact on supply chain optimization. Again, much of the technology has been adapted from onshore foundations with monopoles being the most common substructure in use on offshore wind farms today. The design of specific offshore foundations, with reduced manufacturing costs is essential to ease this link in the supply chain.

Crucially, wind speed and therefore potential power production, increase greatly in deeper water. Several different concepts are being tested to enable the installation of 10MW or larger turbines on wind farms at depths of 60 meters or more.

One such design is the Sway concept produced by the Norwegian company of the same name. The floating tower can be installed in depths of up to 400 meters, taking advantage of higher wind speeds. The tower is filled with ballast, and the center of gravity is much lower than the towers center of buoyancy thus giving it stability. It is a unique concept as the blades face downwind, and the entire turbine can rotate to suit the direction of the wind; this optimizes the amount of power generated from the wind, while at the same time reducing the stress on components. Sway claim that reduced manufacturing costs, a long life span, and the ability to support large turbines make this a viable and economic option.

The manufacture and assembly of turbines at quayside is a big driver in cost reduction. Large sites will be needed to produce as much as possible close to the harbor and reduce transportation costs. Equally, the design of turbines and foundations as a single entity is being considered, rather than viewing them as separate processes.

Sourcing the necessary materials to produce wind turbines could also prove to be an issue when it comes to the supply chain. Norwegian foundation manufacturer, Seatower has designed a gravity base foundation which can be deployed at 50 meters in depth, and can be floated to site pre-commissioned, without the use of cranes for installation.

To enable onshore construction and the development of the offshore wind energy industry, suitable ports and harbors must be purpose built, or current harbors must be renovated. According to a presentation by Chris Ehlers, MBA, MD renewable divisions, Siemens PLC, the following requirements would be needed to facilitate pre-assembly onshore:

• Storage areas of approximately 60,000 to 250,000 square meters.

• A dedicated, private road between storage areas and quayside.

• A quay length of between 150 and 250 meters.

• A quay load-bearing capacity of 3-6 tonnes per square meter.

• A seabed of sufficient bearing capacity.

• A minimum draft of 6 meters.

• Warehouse facilities of between 1000 and 1,500 square meters.

• Access for small vessels such as barges.

• Access for heavy and oversized trucks.

• License and approvals for helicopter transfers.

• Availability for the whole project installation.

The port of Bremerhaven in Germany is an example of the redevelopment of an area with the specific needs of the wind energy industry in mind. When its previous industries of shipping, shipbuilding and commercial fishery suffered an economic downturn in the 1990’s, the local authorities looked to the wind power industry as an alternative. As an industrial area it now houses two offshore wind turbine manufacturers in REpower and Multibrid, Blade manufacturer PowerBlades, which makes blades for Repowers 5MW and 6MW turbines, and Weserwind Offshore Construction, which designs and manufactures heavy steel offshore foundation structures.

The coming together of design, manufacture, storage, pre-assembly and installation from one purpose designed site will have a significant impact on the cost factors that currently hinder supply chain management. An integrated approach to the wind energy industry allows a site such as Bremerhaven to test and carry out research and development in near offshore conditions, it allows for manufacture on-site, and reduces transportation time and cost. It allows manufacturing companies to work closely together, and offers the potential for foundations and turbines to be taken directly to site from production plant by installation vessels working from the same harbor.

Several technologies and industries must co-operate to facilitate the cost reduction of the supply chain of the offshore wind energy industry as a whole. While many sectors of the industry are still in their infancy, there is an emphasis on design to drive down cost; as well as a focus on learning from the experiences of current wind farms to further smooth the processes of supply chain management. The pursuit of renewable energy from offshore wind is unabated, however, and the next ten to twenty years will see a dramatic improvement in the economic viability of offshore wind power.