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## Anemometer - wind speed measuring
[[File:Porch-anemometer.jpg|border|thumb|Anemometer data logger prototype on porch]]
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
_A lot of these insights are from the [Wind Energy Coursera](https://www.coursera.org/learn/wind-energy/home/welcome) course._
### Wind turbine terminology
[[File:Nacelle-wind-turbine.JPG|border|thumb|Drivetrain of the nacelle]]
- 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
[[File:Forces-on-blade.JPG|border|thumb|Forces acting on blade]]
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.
[[File:ForcesOnVAWTairfoil.JPG|border|thumb|Vector diagram of the aerodynamic forces acting on a VAWT airfoil. Here U is the freestream velocity, ω is the angular velocity of the turbine, R is the turbine radius, Urel is the relative freestream velocity as seen by the turbine blade, and Ft(lift) and Ft(drag) are the tangential components of the lift and drag forces, i.e., Flift and Fdrag, respectively.]]
### Materials - stress and strain
[[File:Aerodynamic-load-wind-turbine.JPG|border|thumb|]]
[[File:Stress-strain.JPG|border|thumb|]]
### Wind energy extraction
[[File:Efficiency-betz-limit.JPG|border|thumb|Mechanical power of a wind turbine]]
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.
[[File:Betz-power-coefficients-different-types.JPG|border|thumb|Betz coefficients for different turbines]]
__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
[[File:Towers-wind-energy.JPG|border|thumb|Different options for tower construction]]
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</br>
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: <br/>
(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 integral time scale
- you have to detrend te time series to get rid of high-frequency fluctuation
## 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
