Concrete Contender for Most Cost-effective Foundations for Offshore Wind Turbines
17 Mar 2015
With the Government’s first agreements under the Contracts for Difference (CfD) Scheme awarded and the latest report from MEC Intelligence, yet again demonstrating superior cost and engineering performance - the forecast is set fair for concrete gravity bases
Based on an auction process, DECC has recently awarded contracts for two offshore wind developments and both have the potential to use concrete gravity bases.
Concrete gravity bases offer a reliable solution to developers because of the inherent strength that they possess, this is vital in depths of 25m to 60m and up to 200km from shore. Moreover, in terms of the immediate requirements from authorities and developers alike, the high damping properties of concrete minimises noise and vibration. The avoidance of piling noise during installation is a major benefit of concrete gravity bases as the impact on wildlife from piling noise is minimal.
With monopiles already ruled out for both CfD sites, East Anglia 1 and Neart na Gaoithe, due to the issues of underwater noise and the performance limitations in deeper water; both the projects’ requirements, at 30-41m and 40-60m water depth respectively, can be met by gravity bases.
Engineering performance is not the only project driver. Environmental and economic considerations are also a priority. Concrete bases are installed using gravity and consequently the impact on native sea-life is low, especially in comparison to other options. In Scotland, during the announcement of the Moray Firth project the Scottish Energy Minister Fergus Ewing expressed that the impact on wildlife as a result of the offshore wind farm development will be a key consideration. WWF Scotland, who support renewable energy as a means to reduce carbon emissions and the impacts of climate change, have also stated the importance of measures needed to minimise the turbines' impact on the marine environment.
As well as the carbon savings related to the energy production, concrete gravity bases also have lower embodied carbon than many steel alternatives.
When considering economic benefit of foundation solutions, the performance of concrete gravity bases is also superior. The recent study by MEC Intelligence compared the cost of a monopiles and jackets with gravity bases and suction buckets. The costs assumptions are based on actual values witnessed on projects and from inputs from industry experts.
The report concluded that the price fluctuations and vessel availability of steel solutions created an advantage for concrete gravity foundations.
With gravity bases constructed at a coastal fabrication yard, using concrete produced from locally-produced materials, by a local, skilled labour-force, the use of gravity foundations will also boost the local economy and UK GDP.
A typical manufacturing facility producing 50 bases per year will generate 500 to 600 jobs directly at the facility. The extraction and delivery of the concrete constituents will generate a further 100 UK jobs.
The Concrete Centre’s Interest Group for Offshore Wind member Seatower has recently delivered a demonstration project for the Fécamp partners EDF Energies, DONG Energy and wpd offshore.
The concrete gravity foundation is located 13km off the coast of Normandy, and in deeper waters. Petter Karal, CEO of Seatower said “Cranefree Gravity® foundations are generally more cost-efficient, quicker to install and less risky than current methods that use steel foundation designs. They also allow for local construction, which provides welcome economic activities to the coastal communities close to the wind farms.” He added “Our technology will ease and speed up the construction of offshore wind farms at a time when cutting costs and risks is necessary to help the sector progress to more challenging project sites.”
Cost reductions need to be achieved to meet the demands of the diminishing strike price and to provide UK consumers with a long-term supply of affordable, local, low carbon energy.
BVG Associates have stated that “The clearing prices announced for offshore wind … show that industry is reducing its levelised cost of energy (LCOE) faster than many people in the industry had expected”. “Our models show that the clearing prices of £119.89 and £114.39 per MWh, awarded to the East Anglia 1 and Neart na Gaoithe projects respectively, equate to a levelised cost of energy (LCOE) of just under £100/MWh for projects with final investment decision (FID) in 2016.”
With concrete gravity bases efficiencies are achievable as benefits can be gained from applying established and efficient working practices, innovation in technology and the confidence gained in the market will reduce perceived risks and hence the cost of finance.
Turbine manufacturers are already developing larger turbines with increased generation potential, but these are larger, heavier and will have an impact on tower and foundation requirements.
Concrete gravity bases provide the robustness and performance required to meet the engineering demands placed on foundation solutions and as widely reported, also represents a step change in technology that can deliver a cost saving against alternatives.
Concrete gravity bases will also meet the drivers for UK content, skills and competition required from the Supply Chain Plan.
However, these advantages are only unlocked by economies of scale. Economies of scale are delivered from a construction pipeline of projects and these rely on investment. As the Government framework from Electricity Market Reform, with contracts for difference (CfD) and supply chain plans roll out, we get ever nearer to the growth in low carbon energy that will benefit the construction industry and UK consumers.