Wind turbine system
Contents
Prototyping
Twisted Savonius V1
We attempted to prototype a twisted Savonius turbine to allow a more continuous application of force when the wind turbine spins. Ideally, both sails would be slightly offset to each other to allow airflow from one airfoil to the other. Such an offset can be seen in the following picture that inspired our design.
With our next prototype, we seek to combine a twisted Savonius turbine with a Gorlov turbine (Rajdeep Nath Dr. John Rajan; How to Design and Fabricate a Vertical Axis Wind Turbine: Design, Analysis, and Fabrication using Gorlov and Savonius Blades (p. 75)). We can 3D print the blades but might want to scale down the prototype to decrease printing time.
Current System
view and comment on system diagram
Equipment manuals
Aurora 3kW inverter - data sheet
Aurora wind interface box/rectifier - manual
TCMG-3kW Taechang N.E.T. Generator - online specs
3kW Discharger Breaker -
3kW Dynamic Braking Resistor - instruction manual
Anemometer
Wind direction meter
Anemometer - wind speed measuring
We are using a Vortex wind sensor. One revolution per second equals 2.5 mph. Since our anemometer has a relay (a mechanical switch), it creates a switch bounce. Therefore, we need a debounce circuit. Please refer to Electrical Control Unit for the repository and more information.
Research and background knowledge
Research papers, articles, media
Aerodynamics of vertical-axis wind turbines in full-scale and laboratory-scale experiments
Araya, D. B. (2016). Aerodynamics of vertical-axis wind turbines in full-scale and laboratory-scale experiments (Doctoral dissertation, California Institute of Technology).
Analysis of Different Blade Architectures on small VAWT Performance
Battisti, L., Brighenti, A., Benini, E., & Castelli, M. R. (2016, September). Analysis of different blade architectures on small VAWT performance. In Journal of Physics: Conference Series (Vol. 753, No. 6, p. 062009). IOP Publishing. https://iopscience.iop.org/article/10.1088/1742-6596/753/6/062009/pdf
General wind turbine knowledge
A lot of these insights are from the Wind Energy Coursera course.
Wind turbine terminology
- rotor - generates aerodynamic torque
- nacelle - converts torque into electrical power
- tower - hold nacelle and rotor blades
- foundation - hold the whole turbine in place
- VAWT - vertical axis wind turbine
- HAWT - horizontal axis wind turbine
Forces acting on VAWT and HAWT blades
If the vertical axis turbine has blades that use lift to create a net force that spins the turbine, the forces acting on the blade are equivalent to forces on horizontal axis turbines. The aerodynamic forces on the blades are described in the two image to the right.
Wind energy extraction
The mechanical power of a turbine can be calculated with the equation to the right. The Betz limit on the power of a fast-spinning wind turbine (59%) describes the maximum energy that a turbine can extract from the wind. Depending on the turbine design, the Betz power coefficient changes. Turbines that are based on lift (not drag) have generally speaking higher coefficients. Please refer to the different Betz based roughly categorized by turbine types to the left.
Rotating lift-based machines - horizontal axis wind turbine, a vertical axis wind turbine with blades (Gorlov or Darrieus)
Rotating drag-based machines - vertical axis turbines - similar to cup anemometer; Savonius (efficiency 10%-15%) could be nice for aesthetically pleasing turbine
Flying lift-based machines - pulls up sail that pulls on a cord that spins spindel
Machines using flow-induced vibrations
Towers types
The tower needs to withstand high torque. Metal ropes can be used to keep the top of the tower in place. Furthermore, the foundation needs to be solid and deep.
General tower types:
- tubular towers
- lattice towers
- tripod towers
Financing (for large-scale projects)
Our revenue is the production of net electricity in Wh (Annual Energy Production): Capacity of Farm x 8760h x capacity factor 0.25
1 - Simple payback time (SPT)
Simplistic Calculation
- estimate of annual production in Wh
- annual revenue - production x energy sale price
- annual operating costs
2 - Net present value (NPV)
(revenue - costs) - original investment
if less than 0, probably not profitable
excel has NPV function
3 - Levelised cost of Energy (LCoE)
goal is to find cost per MWh that can be used for comparison:
(Capital Investment + Operational Costs + Decommissioning Cost)/ MWh
Statistical Analysis of Wind Speeds and Turbulence
- Navier-Stokes equation (evolution equation) to calculate wind speeds in space
- statistical analysis, spectra, turbulence intensity is obtained by mean wind speed and standard deviation of wind speeds
- every wavelength (after Fourier transform) can be thought of as a length scale
- wind vector (u, v, w)
- integral length scale; from time series, we compute the auto-correlation function
- turbulence spectra
- averaging periods of 10 min are commonly used; 30 min period for turbulence studies; the larger integral time scale, the larger should be averaging period; sampling frequencies should be much smaller than the integral time scale
- you have to detrend the time series to get rid of high-frequency fluctuation