LEAD ARTICLE
ConcreteversusSteel
To date the Government and offshore wind industry has concentrated its energies on expensive steel piles and jackets. It appears they are reluctant to use a cheaper and superior system offered by concrete Gravity Base Structures (GBS).
In order to meet carbon reduction targets no-one, either in Government or Industry, appears to have considered the true through-life costs and long- term impact of steel structures.
We are, therefore now in a situation whereby any area shallow enough to construct in steel has been substantially developed using pile-supported wind turbine generators, ignoring the fact that wind farms could be constructed far more economically further offshore and away from view, fishing grounds and shipping lanes.
A MORE CONSIDERED APPROACH It therefore seems timely for a more considered approach to be adopted as future large offshore wind developments will be about scale, low unit cost and repeatability. The offshore wind supply chain will be required to deliver a large number of foundations in a very short timeframe, ensuring safe and cost-effective transportation, installation and maintenance.
GRAVITY BASE STRUCTURES (GBS) Concrete GBSs are cheaper and easy to install, have better fatigue characteristics, are easier and cheaper to maintain and can be removed relatively easily thus obviating legacy problems.
SELF-INSTALLING GBSS Self-installing GBS are easy to install and avoid the very heavy cost of complex installation vessels with their attendant high project risk. These facts are apparently not clearly understood by Government, who provide little real support for the development of this potentially all-British technology.
Understandably GBS is lobbied against by steel pile and tower system suppliers and the owners of the expensive and highly profitable ship operators. However, if the Wind Industry in general and the developers in particular were to fully appraise GBS, these systems would very quickly become the industry norm.
MASS PRODUCTION GBS could easily be made and commissioned with their Wind Turbine Generators (WTGs) fitted and ready for deployment using mass production line techniques at several centres around the UK. This system, incidentally, would create substantial employment within the supply chain and avoid importing steel structures from Europe.
“FLOAT AND SINK” TECHNOLOGY It is certainly very thought-provoking to envisage WTGs being towed from an inshore construction site on their self-floating foundation structures, fully- assembled, tested, 90% commissioned then installed using standard marine
tugs, operating at a fraction of the cost of complex and very expensive specialist installation vessels currently employed and being able to be deployed within hours. A true “Float and Sink” technology.
Sub-stations can also be assembled and commissioned in-dock and delivered in the same way. The only off-shore commissioning would be running and connecting the cables between installed units; such a scenario should be today’s reality.
“PLUG AND PLAY” SCENARIO Wind farms containing hundreds of GBS- based WTG and sub-station units could be easily developed and made operational within a minimum time-frame; offering a true “plug and play” scenario in 60 metres of water and beyond.
To give an idea of what could be achieved – imagine the allies trying to build Mulberry Harbour on D-Day using steel piles. The outcome would have been very different. Using GBS technology Mulberry went in overnight and was crucial to victory.
DEPLOYMENT
The concrete GBS systems are stable during tow even with large (10mW) WTG’s. Deploying them in the North & Irish Seas would require very little or no sea-bed preparation using specialised integral foundation pads; where scour protection is required, this too can be fitted to the GBS in-dock on pre-installed frames which are deployed once the GBS is sited.
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www.windenergynetwork.co.uk
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