Fixed Foundation Innovation - the way forward for Deeper Water
1, Peter Broughton2, Garron Lees1
1ODE, Wimbledon, London, UK, 2MEES, Wimbledon, London, UK
To date, most solutions for deeper water are focused on floating technology rather than on the water depth. The Articulated Wind Column (AWC) is focused on the challenge of getting large turbines in to deeper water economically. While floating technologies will be needed for the ultra deep, most of the worlds deeper offshore sites are under 200m meaning that cheaper and simpler fixed solutions are the way forward.
The Articulated Wind Column is a crossover technology with 40 years of use in oil and gas re-engineered for mid to deep water environments (50m to 200m). Designed to accept turbines of 8MW and above, field demonstration sites are now being sought with a 6MW - 8MW deployment in the range of 90 -100m water depth.
The AWC design is concerned with cost effectiveness, ease and flexibility of construction, ease of installation and removal, and the ability to support very large turbines in the future. Constructed from steel or concreate, according to local capabilities, the AWC has an articulated joint at the foundation’s base that enables the AWC to be a robust, stable and durable solution for larger turbines in deep water.
The paper looks at the process of adapting the technology from its oil and gas roots, through an examination of the use of articulated compliant sub-structures, engineering trials and tank testing. It goes on to the evaluation and selection of the potential demonstration sites and considers the advantages gained when the need for piles, and anchors is removed.
A desktop review of the application of articulated columns in the oil and gas industry was undertaken and cross referenced against design undertaken by the company in the 1970’s. Engineering and design work was undertaken to optimize the design for use with wind turbines and aerodynamic and hydrodynamic model testing of the AWC was undertaken. This engineering work looked at both technical performance in terms of being able to support large turbines and the ease of construction based on materials used. A market review was undertaken to evaluated the possible market for fixed deep water offshore wind and this identified a number of sites that where further investigated for use in a demonstrator project.
The engineering and model testing demonstrated that the AWC was an economic and technically feasible solution for deep water, large turbine applications when modeled with an 8MW turbine in 90m of water. The modelling demonstrated a tilt of more than 6 degrees occurred in only 0.002% of the time, well within parameters set by the turbine supplier. As a consequence of looking for a demonstration site, it was found that the AWC increases the UK offshore wind market size. The AWC opens much of the North, West and South West to offshore wind, this is of particular relevance to Scotland where only c. 1.9GW of offshore power is accessible by conventional technology, but deep water technology would open up over 60GW of potential.
The focus on developing economic deep water offshore wind should'n just be limited to floating solutions. Development of fixed structures for mid and deep water applications are likely to result in a lower cost of energy in deep water faster. The AWC’s simplicity of design, construction, installation and lack of seabed preparation provides many advantages. The design flexibility to use the most competitive materials locally expands the supply chain and as is the case of AWC can result in production line batch production. Developing deeper water requires that fixed solutions are also part of the mix, not just floating solutions that are optimized on for the ultra-deep markets. Government needs to support and encourage demonstration projects that promote cheaper deeper wind, rather than just floating.
The challenge is economically accessing higher wind speeds in deeper water for lager turbines. Both fixed and floating solutions need to be part of the mix and engineers, developers, investors and Government need to be open to and supportive of development of fixed foundations rather than focused just on floating. This paper should allow the audience to consider if we as an industry have been open enough to adapting and extending the range of fixed solutions in to deeper water