Recipient Organization
SONSIGHT INC.
17609 CLINTON DRIVE
ACCOKEEK,MD 20607
Performing Department
(N/A)
Non Technical Summary
Well over 50 % of US land area constitutes low windspeed sites, yet wind turbines are either not effective or only marginally effective in such low winds. To extract significantly more energy from such DOE Class 1 or Class 2 winds requires substantially increasing turbine blade rotor diameter. However, due to limitations on turbine blade tip speed, this cannot be done without significantly decreasing blade rotor rpm, which in turn, due to limitations on generator output at low rpm, is typically costly to do. The lower the generator rpm at rated power, the more costly and massive it is (mass impacts installation costs). As a result, with current technology, it would not be economically feasible to make or buy turbines that generate a significant portion of their rated power within prevalent DOE Class 1 or Class 2 winds. Since most people live within such windspeed sites this is a severe drawback. Sonsight Inc. has been investigating innovative low rpm wind turbine
generator designs. The current proposal is for demonstrating the feasibility of adapting and utilizing a low rpm generator to develop a novel low windspeed horizontal axis wind turbine that generates over 250 % more power in low DOE Class 1 and Class 2 winds than that generated by other ~5 kW wind turbines. Moreover, doing this at less cost, and with less mass and aerodynamic noise are also to be demonstrated. The research also includes analyses of the potential resulting economic and environmental impact.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
The Phase 1 work will utilize a combination of testing, modeling and analysis to show that the proposed turbine is technically and economically feasible, and to more fully quantify its environmental and economic impact. The Phase 1 work includes looking at the following questions: (a) Will contemplated magnetic circuit modifications in the generator provide expected improvements? (b) With respect to overall turbine performance, what are the significant blade rotor design tradeoffs? (c) How do changes in the various furling mechanism parameters affect the furling wind-speed? (d) How can form best compliment function in the basic turbine layout? (e) What are the updated cost and mass projections? (f) What are the quantifiable economic and environmental benefits of the overall project? (g) Which of the several available test sites is best suited for the Phase 2 field testing? The specific technical objectives are: 1. Update, test and enhance generator. The turbine design
is strongly driven by the generator characteristics. This step is required input to that design. 2. Design, and characterize turbine blade-rotor. This step required to develop the blade rotor. 3. Obtain turbine output and furling model. Used with objective 4, this provides a detailed model of turbine performance for demonstrating overall technical feasibility, and also serves as a development tool that aids in obtaining the turbine design. 4. Develop prototype turbine design and obtain field test site. 5. Update cost and mass estimates and analyze implementation impact.
Project Methods
Using a combination of modeling and testing, appropriate modifications of an experimental low-rpm generator will be investigated for subsequent turbine mounting. Generator performance characterization will be done on our motoring dynamometer test stand. To determine power conversion capacity and efficiency, voltage and current are simultaneously measured and processed with the torque and speed. Cogging torque is determined from the cyclic variations in the torque meter output when measuring the open circuit generator. There are four families of NREL airfoils of particular interest to us. A blade design within the constraint of these airfoil families will be optimized for overall power coefficient CP and benign stall behavior over our range of tip speed ratios (TSR). Besides the blade profiles, the chord, twist and angles of attack must be determined. To this end, for each airfoil family, the empirical curves for the aerodynamic properties of the airfoil will be
utilized within the blade element momentum method to determine the angle of attack and the lift coefficient for different blade sections between the root and the tip. These parameters will then be used to determine the blade-rotors CP over a range of TSR. Integral to this analysis is determining the blade chord and twist, which together with the blade profile fully specify the blade design. Another consideration is the number of blades comprising the blade-rotor. Over a range of TSR, CP will be considered as well as ease of fabrication and post stall lift and drag characteristics in a down-selection process to determine the most suitable blade-rotor design. The NREL developed FAST code will be utilized with the generators bench test data and the blade rotors characterization data to determine turbine output and loads as a function of wind-speed, and determine the furling wind-speed and furling generated loads. The generator and blade-rotor designs will be combined with the furling
data to obtain an overall experimental turbine design. Analyses will also be performed to better understand environmental and economic impact on a local as well as a national level. Wind speed distributions will be combined with calculated turbine output values to obtain yearly energy production estimates as a function of wind speed class. These with updated cost and usage estimates determine payback period for representative rural regions, which will be used to help estimate regional environmental and economic impact. And utilizing small wind turbine usage projections, the overall national impact of the research can be further analyzed.