January 2014

Features - profile
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The world's largest Offshore Wind Farm is taking shape at Greater Gabbard

Scottish and Southern Energy is currently developing the Greater Gabbard offshore wind farm in a joint venture with RWE npower renewables.

 

More than 110 foundation monopiles, 90 transition pieces and ten turbines have now been installed offshore, as have both transformer platforms.

Commissioning of the onshore substation is well-advanced. Installation of the first export cable is complete and installation of the inter-array cables is well under way. The first turbines are expected to be commissioned in late summer and early autumn, and the first export of electricity will then take place. The entire wind farm remains scheduled to be completed in 2012.

Greater Gabbard is the world's largest offshore wind farm in construction. It involves the installation of 140 Siemens 3.6MW wind turbines located around two sand banks known as Inner Gabbard and The Galloper in the North Sea, off the Suffolk Coast. The maximum tip height of the wind turbines will be 170m above Mean Sea Level, comprising a nominal 105m hub height (relative to Mean Sea Level) and 130m rotor diameter.

The wind turbines will be arranged in a regular pattern on either side of the Inner Gabbard and The Galloper, with a minimum turbine separation distance of 650m. The layout for Greater Gabbard uses the following principles: The co-ordinates of the two turbine array areas, interconnecting cable corridor, and export cable route are fixed. Within these areas, there are specified areas of either "no build" or "restricted build"

Within the boundaries the minimum separation distances between the turbines do not fall below 650m for energy yield reasons. The air gap from the turbine blade to water level (MHWS) is greater than 22m.

The wind turbines will be inter-connected within each turbine array by buried subsea cables. These subsea cables will be connected into up to four offshore transformer platforms, which transform the turbine interconnection voltage to 132kV for transmission ashore by up to four export cables. Five permanent meteorological monitoring masts (nominally 105m tall) are also proposed, in addition to the existing 80m mast, for operational monitoring. The export cables will cross operational subsea telecommunications cables and an outline technical solution for the crossings has been agreed with the telecommunications cable operators.

The construction of the wind farm is anticipated to last for up to three years, with work taking place all year round. The inter-tidal works comprise the installation of export cables underneath the beach between Sizewell and Sizewell Hall, installed by horizontal directional drilling. The connection point to the electricity transmission system is at a new sub-station sited on private land. Buried electrical cable (up to four circuits) will be installed within agricultural land between the cable landfall and the sub-station location.

The connection will be effected by the "turning-in" of the southerly 400kV Bramford to Sizewell circuit into the sub-station. The sub-station will be jointly operated by GGOWL and National Grid Company. The specific onshore sub-station location at Sizewell has been selected as the best option as the site is relatively close to the Sizewell complex, and adjacent to the existing overhead line, therefore landscape impact is reduced when compared to options located away from the pylons. There is also likely to be no impact on public amenity and landowner consent has been obtained.

The land available has the ability to implement suitable mitigation and the site has good highways access. In addition, the sub-station will be set into the field and the cut material used for earthworks to screen the sub-station and to eliminate the need for offsite disposal of spoil.

greater Gabbard - wind farm

The UK Government has stated a target of generating 10% of electricity demand from renewable sources by 2010. This target has been extended by the Government to 15% by 2015 with an aspiration of 20% by 2020. In addition the UK has a commitment of reducing carbon dioxide gas emissions by 20% relative to 1990 levels by 2010 and 60% by 2050.

The UK has a binding legal commitment under the Kyoto Protocol to reduce its output of greenhouse gases by 12.5% of 1990 levels averaged over the period 2008 to 2012. The generation of electricity from renewable energy sources (such as the wind) produces no emissions, and by offsetting the combustion of fossil fuels helps to reduce emissions of environmentally harmful gases.

The primary objective of the Greater Gabbard project is the generation of energy from a renewable source. The electricity generated by the Greater Gabbard Offshore Wind Farm will contribute to Government targets, and will offset the annual release of approximately 1,000,000 tonnes of carbon dioxide, the main greenhouse gas.

The key national policy document relating to offshore wind farm projects is the Energy White Paper (2003). This is very supportive of the development of offshore wind and states, among numerous other positive statements: "Developing our carbon aims will require the rapid expansion of offshore wind not only within territorial waters but beyond".

The Greater Gabbard Offshore Wind Farm project will provide almost 5% of the UK's renewable energy target for 2010 and is the first project to apply for consent outside UK territorial waters. In addition it will enhance the security of energy supply for the UK, which is another key theme of the White Paper. Accordingly, the project can justifiably claim to be in the national interest.

The primary contractor for the project is Fluor. Fluor is constructing the balance of plant, including the installation of the wind turbines for the project. Fluor is consistently rated as one of the world's safest contractors. The wind turbines are being manufactured by Siemens.