The objective of this study is to assess the commercial viability to develop cost-competitive carbon fiber composites specifically suited for the unique loading experienced by wind turbine blades. The wind industry is a cost-driven market, while carbon fiber materials have been developed for the performance-driven aerospace industry. Carbon fiber has known benefits for reducing wind turbine blade mass due to the significantly improved stiffness, strength, and fatigue resistance per unit mass compared to fiberglass; however, the high relative cost has prohibited broad adoption within the wind industry. Novel carbon fiber materials derived from the textile industry are studied as a potentially more optimal material for the wind industry and are characterized using a validated material cost model and through mechanical testing. The novel heavy tow textile carbon fiber is compared with commercial carbon fiber and fiberglass materials in representative land-based and offshore reference wind turbine models. Some of the advantages of carbon fiber spar caps are observed in reduced blade mass and improved fatigue life. The heavy tow textile carbon fiber is found to have improved cost performance over the baseline carbon fiber and performed similarly to the commercial carbon fiber in wind turbine blade design, but at a significantly reduced cost. This novel carbon fiber was observed to even outperform fiberglass when comparing material cost estimates for spar caps optimized to satisfy the design constraints. This study reveals a route to enable broader carbon fiber usage by the wind industry to enable larger rotors that capture more energy at a lower cost.
The objective of the Optimized Carbon Fiber project is to assess the commercial viability to develop cost-competitive wind-specific carbon fiber composites to enable larger rotors for increased energy capture. Although glass fiber reinforcement is the primary structural material in wind blade manufacturing, utilization of carbon fiber has been identified as a key enabler for achieving larger rotors because of its higher specific stiffness (stiffness per unit mass), specific strength (strength per unit mass), and fatigue resistance in comparison to glass. This report contains the testing process and results from the mechanical characterization portion of the project. Low-cost textile carbon fiber materials are tested along with a baseline, commercial carbon fiber system common to the wind industry. Material comparisons are made across coupons of similar manufacturing and quality to assess the properties of the novel carbon fibers.
Sandia National Laboratories (SNL) is developing a low-cost, environmentally safe, and weather-proof sensor system that can be deployed offshore for extended periods of time for wind resource monitoring. The system has clear economic benefits over meteorological (met) tower approaches and is easily relocated to multiple locations across a project site. The end development goal is a buoy or barge-based, balloon-borne atmospheric measurement platform that operates autonomously in all but the most severe weather conditions, provides data of comparable accuracy to a met tower, and provides more accurate wind data at higher altitudes than floating lidar at half the cost.
Atmospheric measurements are collected from anemometer modules (cup-version pictured) that are attached to a tether line between a balloon and barge at user-specified intervals. Each module samples wind speed, wind direction, pressure, temperature, relative humidity, and GPS-derived latitude, longitude, and altitude in situ at 1 Hz or faster and transmits the data wirelessly to a base station on a barge. Fiber-optic based distributed temperature sensing (DTS) also provides an almost continuous atmospheric temperature profile with a vertical spatial resolution of 0.25 m.
The levelized cost of energy for an offshore wind plant consisting of floating vertical-axis wind turbines is studied in this report. A 5 MW Darrieus vertical-axis wind turbine rotor is used as the study turbine as this architecture was determined to have the greatest ability to reduce the system cost. The rotor structural design was used with blade manufacturing cost model studies to estimate its cost. A two-bladed, carbon fiber rotor was selected in this analysis since the lower topside mass resulted in a reduction of the platform costs which exceeded the increased rotor cost. A direct-drive, medium efficiency drivetrain was designed which represents 25% of the costs and 45% of the mass of the combined rotor/drivetrain system. A direct-drive, permanent magnet generator drivetrain was selected due to the improved reliability of this type of system, while the cost was not significantly higher than for geared drivetrains. A platform was designed by first identifying the optimal architecture for the vertical-axis wind turbine at a water depth of 150 m. A survey was performed of floating platform types, and six characteristic designs were analyzed which span the range of stability mechanisms available to floating systems. A multi-cellular tension-leg platform was identified as the lowest cost platform which additionally provided some interesting performance benefits. The small motions of the tension-leg platform benefit the system energy capture while limiting inertial loads placed on the rotor’s tower and blades. A final design was produced for the multi-cellular tension-leg platform considering operational fatigue, storm wind and wave conditions, and tow-out design cases. The driving design load was stability during tow-out while ballasting the platform. System levelized cost of energy was calculated, including operational expenses and balance of system costs estimated for the wind plant. Opportunities for reduction in the component costs are predicted and used to make projections of the system levelized cost of energy for future developments. The opportunities and challenges for floating vertical-axis wind turbines are identified by the system design and levelized cost of energy analysis.
This report houses the deliverables provided by Stress Engineering Services on the floating platform design identification studies and the detailed final design iterations. The results were obtained under contract to and in partnership with Sandia to iterate between the platform design and the aero-hydro-elastic load simulations of the coupled vertical-axis wind turbine system. Through the analysis summarized in this report, a tension-leg platform with multiple columns was identified as the optimal platform when considering cost and performance. The detailed design and cost estimate of this platform architecture was produced in the final phase of study which is also described within this report.
Wind turbine yaw offset reduces power and alters the loading on a stand-alone wind turbine. The manner in which loads are affected by yaw offset has been analyzed and characterized based on atmospheric conditions in this paper using experimental data from the SWiFT facility to better understand the correlation between yaw offset and turbine performance.
This paper describes the process of transforming measured blade loads, with force estimation, to wind turbine quantities of interest. Uncertainty quantification on the blade load measurement and force estimation is derived and used to estimate uncertainty on aerodynamic torque and rotor thrust for sample cases. A methodology is defined for calculating mean values and quantifying the uncertainty in these important quantities of interest for wind turbines when your available data includes only blade root moment measurements. This paper is not intended to provide precise values for these uncertainties at the current stage, however, sample measurement uncertainties are defined and used along with representative mean values to identify the sensitivity of uncertainty in torque and thrust to the constituent variables and associated uncertainties. The largest contributors of the uncertainty when using blade strain gage measurements to estimate rotor loads is identified for the sample cases revealing the components that have the largest effect on the resulting quantity of interest’s uncertainty, and those which have negligible effect on the uncertainty.
To reduce the levelized cost of wind energy, wind plant controllers are being developed to improve overall performance by increasing energy capture. Previous work has shown that increased energy capture is possible by steering the wake around downstream turbines; however, the impact this steering action has on the loading of the turbines continues to need further investigation with operational data to determine overall benefit. In this work, rotor loading data from a wind turbine operating a wake steering wind plant controller at the DOE/Sandia National Laboratories Scaled Wind Farm Technology (SWiFT) Facility is evaluated. Rotor loading was estimated from fiber optic strain sensors acquired with a state-of-the-art Micron Optics Hyperion interrogator mounted within the rotor and synchronized to the open-source SWiFT controller. A variety of ground and operational calibrations were performed to produce accurate measurements of rotor blade root strains. Time- and rotational-domain signal processing methods were used to estimate bending moment at the root of the rotor blade. Results indicate a correlation of wake steering angle with: one-perrevolution thrust moment amplitude, two-per-revolution torque phase, and three-perrevolution torque amplitude and phase. Future work is needed to fully explain the correlations observed in this work and study additional multi-variable relationships that may also exist.