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The United States’ most plentiful offshore wind resource is found in waters so deep that floating platforms are needed to support the turbines—posing major challenges for offshore wind to deliver electricity at a commercial scale and competitive cost. In order for floating wind to become a viable marketplace technology, optimized designs, configurations, and operational practices need to be identified to achieve cost parity with fixed-bottom platform designs.
A recent study by the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) unveils a new strategic vision for floating offshore wind. Researchers identify barriers that must be overcome to bring down the overall cost of energy produced, then outline a vision for an integrated systems approach with the potential to significantly improve the market feasibility of floating wind plants.
“While we’ve made great progress with innovations related to individual components and tools, only a comprehensive systems-based approach can allow floating wind technology to fully mature in commercial markets,” said NREL Offshore Wind Platform Lead and study co-author Walt Musial. “A multidisciplinary effort makes it possible to simultaneously focus on a wide range of factors and then optimize designs to achieve a minimum system cost.”
Choosing an Integrated vs. an Iterative Approach
Much of the 2,000 gigawatts of U.S. offshore wind domestic electricity-generating capacity is found near coastal population centers. More than 58% of this resource is located in water depths of 60 meters or greater, where the engineering challenges of fixed-bottom installations directly connected to the sea floor make them technically and/or economically infeasible. Floating platforms are needed to most effectively harness wind energy in these locations.
Floating wind turbine substructure prototypes were initially adapted directly from proven offshore oil and gas platforms concepts. While this first wave of designs proved that the floating technology can meet durability and energy production demands, baseline cost analysis indicates further optimization, innovation, and upscaling to commercial plant sizes will be required to make floating wind energy systems economically viable.
Detailed modeling by NREL researchers shows that needed cost reductions are unlikely to come from a single breakthrough invention, but will require the deliberate combination of design building blocks that span multiple disciplines—a complementary combination of innovations in technologies, design features, and installation and operational strategies.
To achieve this vision, the NREL approach uses a fully integrated systems-engineering and techno-economic design to capture the complex interactions among physics, manufacturing, installation, and operation of floating wind systems and identify optimal designs that dramatically reduce costs.
The current approach to offshore wind system design is iterative, with each company bringing to the table its own area of expertise and profit motive.
“One manufacturer designs the turbine and tower, another company designs the substructure, and sometimes a separate developer tackles array layout and logistics. The tremendous complexity of the physical environment for floating installations and interplay of design components make this divide-and-conquer approach quite costly and less effective in identifying workable solutions,” said NREL Senior Research Engineer and study lead author Garrett Barter.
Building on Experience and Filling Gaps
The NREL study examines the current state of floating offshore wind technology and highlights gaps in development and areas that could benefit from additional tools and innovation. Researchers looked at system components including turbines, platforms, moorings, and controls. They also reviewed plant-level factors, such as wake and array effects; manufacturing, installation, operation, and maintenance; grid integration; and environmental impact.
“While the promise of new systems engineering design tools capable of tackling the challenges of floating wind sounds tantalizing, to be successful and more than just an academic exercise, they must incorporate prior lessons learned,” said NREL Senior Research Engineer and study co-author Amy Robertson. “Experience from oil and gas and fixed-bottom projects can quickly steer a new tool towards solutions that are most likely to provide the greatest performance and cost reductions.”
The study itemizes important experience-based engineering and operational considerations and describes the advantages of factoring them into design decisions to narrow the options for cost-effective designs. For instance, structures that can be towed to deep water locations for deployment and to shore for maintenance offer both logistic and economic benefits to operators. Designs that use this know-how and can be standardized for use in a wide range of ocean environments and ports promise greater economies of scale for manufacturers and more widespread adoption by industry.
Developing New Tools
Researchers also perceive that existing engineering-focused tools do not adequately factor in cost and systems design considerations, while systems engineering tools lack sufficient fidelity of the physics to capture all critical design drivers. To bridge this gap, DOE’s Advanced Research Projects Agency-Energy (ARPA-E) recently initiated a new program, Aerodynamic Turbines Lighter and Afloat with Nautical Technologies and Integrated Servo-control (ATLANTIS), to revolutionize floating offshore wind turbine design and design tools. NREL and its ATLANTIS collaborators from the University of Illinois Urbana-Champaign and Colorado State University are pursuing the vision put forth in the paper by creating the open source Wind Energy with Integrated Servo-control (WEIS) toolset to optimize floating offshore wind turbines.
Targeting Cost-Effective Floating Wind by 2030
Once system optimization tools are developed, they can be used to quantify the cost-benefit trade-offs of individual technologies and different system or industrial strategies. Researchers envision the study eventually feeding into a research program that includes optimization of whole systems—including entire wind plants and their supporting logistics—as well as trade-off and sensitivity studies related to substructure, anchoring, turbine, rotor, generator, controls, and materials innovations.
NREL’s proposed integrated systems design approach aims to help industry deploy cost-effective floating turbine systems by 2030.