New Modeling Tool Analyzes Floating Platform Concepts
The United States has a large and accessible offshore wind resource. According to a report published by DOE's National Renewable Energy Laboratory (NREL) in 2010 (Large-Scale Offshore Wind Power in the United States), winds off the coasts of the United States have a gross potential generating capacity four times greater than the nation's current electrical capacity. However, most of that resource is located over water with depths greater than 60 meters. Even though the United States has the second most land-based wind capacity installed as a nation, it currently has no offshore wind installations. The majority of today's offshore wind farms are located in shallow water off European coasts. That means that these European turbines can be installed on bottom-mounted substructures at depths of 35 meters or less. Because these substructures aren't practical for deeper waters, floating wind turbine platforms will be needed to fully leverage all of the United States' vast offshore wind resources.
Designing deep water turbine concepts requires more complex models than land-based wind turbines because of the harsh marine environment in which they must operate. To meet this need, researchers at NREL's National Wind Technology Center developed a new, complex modeling and analysis tool.
The wind system modeling tools currently used for land-based applications simulate a wind turbine's dynamic response to wind conditions and calculate the loads the turbine can endure. They do not account for waves, sea current, hydrodynamics, and platform and mooring dynamics. The new NREL tool combines the computational methodologies used to analyze land-based wind turbines with hydrodynamic computer programs and methodologies developed for the offshore oil and gas industries.
The offshore enhanced simulation tool adds needed elements to account for dynamic responses. These elements include six degrees of freedom (DOF) to characterize the motion of a turbine support platform, comprising translational surge, sway, and heave DOF, as well as rotational roll, pitch, and yaw displacement DOF. NREL used its tool to analyze three primary floating platform concepts: Massachusetts Institute of Technology/NREL's tension-leg platform, the OC3-Hywind spar buoy, and the ITI Energy barge system. NREL also compares these systems to a land-based turbine. You can read about the results of this work in A Quantitative Comparison of the Responses of Three Floating Platforms.
Ultimately, NREL's new modeling tool will enable wind turbine designers to develop cost-effective offshore technologies, and will help resolve the fundamental design trade-offs between the floating system concepts.
NREL, located in Golden, Colorado, provides industry with the technical support it needs to develop advanced wind energy systems. NREL's research capabilities include design review and analysis; software development, modeling, and analysis; systems and controls analysis; turbine reliability and performance enhancement; certification and standards; utility integration assessment; wind resource assessment and mapping; technology market and economic assessment; workforce development; and outreach and education.