Germany/vawt development

1. A VAWT named Zephyr will be part of the Apollo-NG mission from open-resource.org.
2. PLEASE USE DOKUWIKI SYNTAX FOR FORMATTING #

Merged from the pad at Apollo-NG. Authors: Alex Shure, Chrono

Zephyr Project

Zephyr = Greek God of the West-Wind Concept of a complete DIY Wind-Harvesting system with sustainability, modularity, efficiency, resilience and safety in mind. This is just a loose draft of common agreements on design principles and common interfaces to keep modularity and development diversity at a high level. Benefits of many small turbines instead of a few big ones:

 * More Redundancy: Failure of a big turbine has more impact than a single small turbine of a group
 * Scalability: Park can grow with available resources and increasement in consumption
 * More realistic: It's easier to fabricate smaller turbines without specialized machines or cranes to put them up

Prototyping

Part of the modular system: a downscaled VAWT, with tiny dimensions. -> TIVA, TIny Vertical Axis wind turbine. lx: I would like to deploy 1-3 of these turbines at a nearby off-grid mountainbike downhill track, for which I am developing a MCU equipped timekeeping system. I hope to gain the interest for renewable energy / wind turbines of any passenger who rides or cheers there at a race.

Calculations

Power: (formula from the wiki entry) <m>h_1=0.32 m</m> d_1=0.32 m A_1=0.1024 m^2 h_2=0.48 m d_2=0.32 m A_2=0.1536 m^2 |m/s|km/h|P_{wind_0.1024m^2}[W]|P_{wind_0.1536m^2}[W] |1.8|6.5|0.35|0.5| |4.5|16.00|5.5|8.2| |6.25|22.50|15|22.6| |8.0|29|32|48| |m/s|P_{wind_0.1024m^2} [W]|P_{\rho=0.2}|P_{\rho=0.3} |1.8|0.35|0.07|0.1 |4.5|5.5|1.1|1.65 |6.25|15|3|4.5 |8.0|32|6.4|9.6 |m/s|P_{wind_0.1536m^2} [W]|P_{\rho=0.2}|P_{\rho=0.3} |1.8|0.5||0.1|0.15 |4.5|8.2||1.65|2.5 |6.25|22.6||4.5|6.8 |8.0|48||9.6|14.4 Assuming a bad (20%) or decent (30%) turbine design \rho_{turbine}=0.26 A rather bad permanent magnet alternator with \rho_{alternator}=0.75; A normal synchronous rectifier with superb-by-design perfomance of \rho_{rect}=0.98; A buck-boost inverter with a good performance of \rho_{rect}=0.85; => \rho_{overall}=0.25*0.75*0.98*0.85=0.16 Conclusion: A 0.32 x 0.32 drag-only VAWT generates about P_{mech} = 0.1...10 W and in average German wind conditions (3 - 4 m/s??) about 0.5 - 1 W. If we have a good alternator (which will be easier at this size because of the high rpm) and a synchronous rectifier (rectifier not necessary if buck/boost power supply doesn't need DC, are there suitable packages for this mode?), most of the power will be available as an input for a buck/boost converter, which can operate reasonably well at these small power ratings. Chrono developed a PDU (power distribution unit) which contains low power buck-boost inverters maybe a small scale version can be powered directly by this wind turbine, generating only 5 V and 3.3 V, omitting the 12 V. lx: I would go for a 0.32 x 0.48 m^2 VAWT and I guess the overall efficiency will be about 0.08 - 0.1. Assuming a worst-case average electrical power of 1 W after rectifying and regulating, one can still charge a cheap 4-pack of NiCd/NiMH (4 x 1.3 V = 5.2 V) which provides power for the system and for high power demands, e.g. activating the LED pattern at night. Charging all of the cells with 1 W from 0 % to 100 % takes (4 * 4 Wh) / 1 W = 16 h. At a wind speed of 8 m/s = 28,8 km/h and P_{el} = 48 W * 0.16 = 7.68 W, the batteries will be fully charged in just (4 * 4 Wh) / 7.68 W = 2 h 5 min. One AA cell contains 1.3 V x 2500 mAh = 3.25 Wh of stored energy. We don't fully discharge the batteries, thus only 3 Wh will be used. However, taking charging and internal resistance losses and a safety margin into account, we need about 4 Wh of energy to store and retrieve about 3 Wh of energy. 4 AA cells equal 4 x 3 Wh = 12 Wh of energy. Without simultaneous recharging, this is enough to provide: - five hours of one hp-LED shining at full brightness in white color or - ten days of one hp-LED flashing at full brightness with one color at a duty cycle of 10%, e.g. on for one second and off for nine seconds. - one MSP430G2231IPN14 16bit micro controller working for ages, at as low as 2V, it may consume 1 mW = 1/1000 W. Typical no-load best-case values from the MSP430 datasheet:

   0.1 µA RAM retention  

   0.4 µA Standby mode (VLO)  

   0.7 µA real-time clock mode  

   220 µA / MIPS active  

Excellent values! An 8-bit Arduino looks pretty old school against these numbers. ;-)

1. lx: I have 6 MSP430 in a DIP form factor in my lab and 3 spare ti MSP430 Launchpad proto boards with onboard hardware emulator and debugger. Chrono, do you want one?
   1. hmm, I was thinking, I have the tools to develop avr but nothing to develop msp, if you have one dev-kit to spare and linux tools are freely available I'd like

to consder going for msp as well, although I'd really recommend staying on avr for bigger projects since many people can do arduino now, so they won't have to much trouble with pure avr. Another arch always reduces the amount of people who can deal with it yet :(

1. 1. 1. I have a spare dev kit in my lab. there's a msp-linux community ... I don't have the tools for AVR, except an Arduino. So no debugging, HV-programming or hardware emulation. The full dev kit for an MSP430 is dirt cheap at $4.30, including two MSP430s in DIPs, a hardware emulator, spy-by-wire, debugging etc.

I agree with the Arudino-publicity argument, and I would always try to incorporate an Arduino, as it is the most simple and comprehensing development tool there is for beginners. However, the ti.MSP430s are relatively new. A downside is their not-so-easy dev environment. Eclipse or IAR or propietary, free software from ti can be used. I have not yet experimented with it, but I have Arduino experience. It would be new for the both of us. pro MSP430, con Arduino: - the price! can be bought with a programmer for $4.30 vs Arduino $25 or a third-party Arduino for maybe $18. This is a serious difference. - even the single MCUs are cheaper, also, the AtMegas for an Arduino bootloader are hard to get. - less external parts for operation at high speeds, Arduino/atmega168 and 328 need an external oscillator to operate at full speed (16 Mhz) - runs stable over a wide range of input voltage down to 1.8V - an excellent sleep mode with RAM retention at only 0.1µA and great power efficiency. 220µA in full operation mode is an excellent figure for off-grid low energy applications. Almost no load to the turbine. Can also be powered by a "Joule Thief" and a single old AA battery, or just two old AA cells in series (3V). That should last for ages, at a constant current of 0.25 mA and an old battery of 1000 mAh, the unit will still run for 180 days, and the MSP430 can be operated with a supply voltage as low as 1.8V. con MSP430: - less memory, but this depends on the package, (there are top-end msp430 processors which cost less than $1 vs an ever-expensive-avr) - less libraries available, smaller community At a small production run of 10 TIVAs and the demand for USB ISP, Arduino vs MSP430 would equal 10*$25 = $250.00 vs 10*$4.30 = 43.00 (!) A nice solution: => Write clean C-code and let it be compatible with MSP430 and AVR compilers. Some Arduino projects were easily ported to the MSP430. In realtime without battery backup, the hp-LED may be pulsed at full power and 10% duty cycle at quite low wind speeds and 100% at >6.25 m/s. <50cm long parts can be cut out at almost every small CNC machine. 48cm wings can be made out of: - styrofoam, Styrodur etc with a hot wire CNC cutter - the famous 2-by-4s with a planer - like an R/C plane wing with wooden rips and a foiled surface - sheet metal, aluminium sheeting bent over cores [rips] - wooden sheet material - plastic pipes fixed main shaft: Do = 8 mm, 608ZZ radial single race bearings rotating turbine assembly, rotor shaft where the bearings seat: Di = 22 mm At this size, a single I-beam design should be suitable, not a dual-bridge-H-rotor assembly. A V rotor looks promising, too. Resource demand is further reduced with this type of rotor. two bladed or three bladed? apparently, two bladed designs have severe problems with low wind conditions and self-starting issues? => three bladed. ack, three seemed most promising in most scenarios. V-rotor advantages:

• least amount of material for a given lift-type wing surface
• best wing volume vs static structural volume ratio
• only one wing-fixture-point
• no bridges, less moving parts
• less connections, less machining operations, less screws or welds
• dissassembly is easier
• uses a higher surface at a larger height, less turbulences at the ground
• (tbd) less prone to oscillations?
• snow can't set onto most of the rotor
• can be adapted to also use up-winds in urban environments, especially interesting at the top of buildings.

(switch to monospaced font in wiki for this ASCII-art.

__ __ <-test if winglets make a difference

\      /                                                            
 \----/    <- a rope to cope with centripetal forces at high rpm    
  \  /    <- wings in V-form                                        
   \/    <- plate with wing-fixtures and seats for the two bearings 
   ||    <- shaft/rotor coupling with two bearings                  
  _/\_    <- any type of stand or clamp, generator, electronics     
                                                                    

I was thinking that we can't have a reliable _absolute_ measuring device, so if all devices are built the same way then we can have a _relative_ measuring device... That is right, because there is not wing-tip-speed ratio at drag devices. no-load drag wings have a wing-tip-speed ratio of one, thus being as fast as the wind ;) we would have to have half-cups as wings to form an actual absolute wind speed measure device, like those things you can buy.. build a lovely grid and show, that wind turbines can be fun. it would be easy to deploy and portable, system voltage of 5V would provide charging power for mobile phones etc. USB power output would be cool, fed by a 5 V buck-boost converter and 4 AA cells. measurement is difficult anyways, because devices would have to be calibrated in a (diy) wind tunnel or something, to get reliable results...

• can serve as a measure+log device for wind speeds
• has on-board electronics: switching power supply, 3.3V or 5V system voltage for MCU and electronics+LEDs, goldcap ?, mcu recommendation: either a low power ti MSP 16bit on a launchpad or the ordinary Atmel Atmega 328(pu) with an Arduino bootloader (or derivative) -> both would be diy-friendly and cheap.

   logging shield with shunts and opamps, goldcap, hprgb shield with logic level mosfets, software pwm.

• can be deployed on a field, in an urban environment etc and may be connected (for example cheap NRF24L01 node-based-network)
• one high power RGB LED acts as a universal signal: can be an indicator for wind speed, keep-alive.. or a 3 x 8 bit digital pixel.

If deployed in an array on a field or in an urban environment: in low natural light conditions, at sundawn or in the night, the wind pattern can be determined by the flash+color pattern of the small wind turbines. MCU logging onto e.g. micro-sd card or via wireless link is an optional step. It would be a very cool art piece at night if all turbines would be connected to a master (which would be easy outdoors on a field) or connected in a grid. A pattern could be generated and all turbines could flash in sync. single flashes could be emitted with full power even if the wind conditions are bad, just the off-periods may be pretty low then. small VAWTs could be attached to the top of a tree, especially to free-standing ones. No pole required and higher wind speeds gained: win-win Alex has got 16 high power RGB LEDs attached to aluminium star heatsinks, each with three 350 mA rgb emitters, 3 Wcontinuos, 4,6 Wpeak. best light vs current value may be at 180-260 mA, still visible from long distances. For a rough estimation, if the VAWT is working and how the wind condition is: Stick a thick wool or thin polythene (bin liner) tell-tales onto the top of the blades. This gives an indication of the relative speed of the blades and it is quite simple to see if the turbine is just being blown around by the drag on the downwind rotor or 'actually' running. -A tell-tale in the centre of the rotor between the blades; so one can see the airflow through the rotor. As the rotor starts this will still blow out sideways, but when the rotor is running (without any load), it will hang limp indicating very little air flowing through the turbine. A gust or putting load on the turbine/generator will cause it to blow out sideways due to the wind which gets through.

Rotors

Compared to drag-only type rotors (Savonius), the lift-only type rotors (Darrieus) haven proven to be generally less suitable for low wind environments. However, the maximum speed of drag-only type rotors is always lower than a comparable lift-only type rotor, because a lift-only type rotor can rotate faster than the wind speed at the tips but with less torque. A drag-only type rotor can develop more torque, even at early stages in low wind conditions, but that would require a very specific and resource-intensive generator to acommodate for the very low rotational speed. A typical low end for a direct driven axial flux permanent magnet alternator with many poles is about 100 revolutions per minute. Everything under 100 rpm means huge additional resource investments into rare earth magnets and loads of copper (windings). Main focus will be on 3 types: - The C-Rotor and further development based on it, with less parts if possible. - A lift-only type rotor because of the wing form, which is formed by one profiled element. - A very simple H-Rotor made of half DN100-PE-tubes (standard sewer piping in Germany) as wings, preferably three or 3 x n wings

C-type vs simple H-type

con C-type, pro H-type:

• C-type requires two parts to form a wing -> more material
• wing tip has to be bent into an aerodynamic shape -> more complexity, especially at the mounting points
• upper wind speed limit is lower

pro C-type, con H-type:

• C-type requires lower wind speed, creates higher torque at lower wind speeds
• usable bandwidth of wind speed is higher

The standardization of the system and compatibility of components offers a perfect test environment for different rotor types to see how comparable surfaces will perform with different types in the same environment.

 * Define a common rotor to generator-shaft interface for easy rotor type interchangeability
 * No wind turbine assembly single rotor should be greater than 4 m² to avoid possible legal restrictions in Europe. A wind surface of 4 m² equals a 2 m diameter rotor with a height of 2 m.
 ^ I googled a bit and this restriction is not entirely true, however there won't be any concerns under 2x2. In certain "Bundesländern" there are even no regulations for wind turbines which have a pole heigth of < 10 m.
  Still it sounds like a sensible limit of size

VAWT Power Estimation

All calculations are made in the metric system. Corrections and additional apporaches are always welcome.

• • Power in the wind**

<m>P_{wind} = \frac{1}{2} \times \rho \times A_{wind} * v_{wind}^3</m>

|<m>P_{wind}</m>| is the power, which is available in the wind, as kinetic energy| |<m>\rho</m>|Density of air = about 1.2 Kg/m³ | |<m>A_{wind}</m>|Area of turbine = 4 m² | |<m>v_{wind}</m>|Wind speed in m/s |

• • Estimated Wind-Power conversion (mechanical)**

<m>P_{mech}=P_{wind} \times \rho_{turbine} </m> while <m> \rho_{simple drag turbine} = 20% \rho_{decent} = 30% \rho_{good} = 30% \rho_{superb vawt} = 40% </m> and <m> \rho_{superb hawt} = 50% </m>. A tuned VAWT may have a best-case efficiency of 40%, while a simple drag-based turbine with no optimization nor special aerodynamics may have an efficiency of about 20%.

C-Type Rotor =

 * Plans, Calculations & Prototype Images
 * Is a special type of H-rotor with a combined lift-and-drag-wing.

H-Type Rotor =

• may be the simplest design, very simple wing form possible.

Darrieus rotor = wings in helix-form, spiraled, lift-type simpler H-rotor: wings straight. Lift-type or Drag-type or lift-drag-type -> C-rotor

Mast Construction

 * Define a common mast/shaft/bearing system that is sturdy, resilient, easy 
   to handle and as simple & cheap as possible and reasonable to build

Base mount

<m>F_{pole} = \frac{1}{2} \times \rho \times C_d \times A_{wind} \times v_{wind}^2</m>

|<m>\rho</m>|Density of air = about 1.2 Kg/m³| |<m>C_d</m>|Coefficient of drag = 1.0 (cylinder Re > 100)| |<m>A_{wind}</m>|Area of turbine = 4 m²| |<m>v_{wind}</m>| Wind speed in m/s|

Shaft

 * Define common shaft dimensions and interfaces for easy rotor/generator interchangeability

Bearing: old wheel bearings from the automotive sector may be suitable. not plastic covered -RS type (Rubber Sealed), but ZZ type, with steel covers on both sides..

Electrics

 * Rectifying at production site and only providing 2 pole 16-48V to POL (Point of Load)
 * Leaving room for the possibility of higher system voltages in case of very long distances from windpark to POL
 * Define a common, simple but reliable connector system which is incompatible to others, to avoid accidents

Modular Generators

 * Multi-Stacking Modules
 * Build a common model for generator scaling according to rotor size
 * The generator module should always be at the bottom of the mast, reducing the top load of the mast and also making the generator more accessible for maintenance.

hdd-magnet based generator

TODO: collect old hard disk drives, dissassemble and gather the pair of neodymium magnets. There are 4 magnets in one HDD Alte Festplattenmagnete können eine Basis für ein Generatordesign bilden, weil oft überflüssig und verfügbar -> Recycling. Nachteil: Begrenzte Flussdichte bedingt durch die flache Bauform. Die Größe ist aber ideal für einen mehrpoligen Generator.

entirely new 2-stage design

never been done: tubular, cylindrical rare earth magnets aligned in a circle pattern, hold by two plates made out of a non ferrous, non magnetic material. magnets are entirely suspended in those plate or in one thick plate, then covered by a sheet of plastic material on both ends. This part is coupled via a universal hole pattern to the VAWT's main shaft and forms the rotor of the generator. above and below this permanent magnet disc lays a stator consisting of either generator-coil-form-

   a three phase, multi pole coil pattern, each coil wound with an inner spacing of about the size of one magnet or

   a serpentine style pattern with one coil being bent into a star shape forming one phase, then another star shaped coil on top with a phase shift. this pattern may be repeated from 3 up to 5 phases. the star shaped coils are easier to wind vs. the many single rather round coils. the star shaped phases consist of just one piece of copper wire and don't have to be daisy-chained like the many coils in 1.

(graphics to be made, especially for the magnet holder.)

Flexible System Configuration

Allow for flexible consumption/wind specific load/source parameter based switching of different star/triangle and parallel/serial configurations

Star/Triangle Configuration

Examples and schematics

Parallel/Serial Configuration

draft for a control loop: example values: V_out = 16V fixed V_sys = variable, depending on load V_gen = variable, depending on wind input and switching and system voltage

   watchdog V_out. if V_sys less than Vout, then

   serialize the windings,

   still to little voltage? -> if generator-coil-form-1 and many points are broken out of the coil, then serialize them in a pattern to gain more voltage

   too much voltage? nevermind, either wait for a small period of time because the rotor has a mass and stores kinetic energy, which first has to be converted by the "new serial-wound-generator". the speed will drop eventually and the voltage will stabilize itself, OR

   rapidly switch between parallel and serial modes (if the load, e.g. the synchronous rectifier, can cope with the spikes (inductive..) and has appropiate switiching abilities) and thus form an sort of automatic pulse width modulated, regulated, operation mode.

   if V_sys + Vdelta,hysteresis >Vout, then

   switch to parallel mode

other cases: any of the voltages exceed e.g. 56V: emergency mode: - either make the generator windings float or short them. !! shorting may not be an option. only with temperature control of the generator and the semiconductors due to the heat generated at a shortcut.!! If all batteries are loaded and the current user power consumption level is minimal, the power surplus of the turbine should be fed into high power LEDs, pointing upwards from the base, lighting the turbine. This adds to protect the system of an unbalanced situation, when more power is generated than reasonably consume- or storable and at the same time to signal, that we still have more energy to share, inviting people to join, in a friendly and beautiful manner. In general, LEDs should also be incorporated at the controller: the controller should have a mosfet-switched control output, one 3W RGB led should display the wind speed or the battery voltage.. (on a scale from red to green and strobe patterns) - 'high-tech' electronic idea: dual rotor on single pole design, counterrotating, brushless royer converter, doubled rpm, less poles, switching power supply is already build in due to the royer converter, coil-in-coil, core coupling, voltage output may be quite high from the start. lower electrical efficiency? downside: needs IP67 protected circuits on both the rotor and the stator of the royer converter. upside: output voltage could be regulated on-board. also, input voltage may be very low depending on the setup. - variation: a rotor with lift-type wings on top and a rotor with drag-type wings at the bottom. thus the lower rotor gains speed at lower wind speeds but has a top end speed of approx. lift-type/2, while the lift-type wing still accelerates in high wind speed conditions.

1. Alex: wir sollten für den generator vielleicht ein separates pad haben für verschiedene ideen.. ?

Formeln zum Royer Converter

source: mikrocontroller.net todo: mit werten überschlagen ob wir einen kleinen leistungsbereich damit abdecken können. wichtig: startspannung. todo-2: wie gut könnte der koppelfaktor sein? kann man eventuell die ganze achse als kern nehmen? und/oder nested coils?

• <m>f_r=\frac{1}{2 \pi \sqrt{L_{pri} C_2}}</m>
• <m>U_p = \pi \cdot U_{ein}</m>
• <m>I_p = U_{ein} \cdot \pi \sqrt{\frac{C}{L}}</m>
• <m>k = \frac {U_{aus}}{\pi \cdot U_{ein}} \cdot \frac {N_{pri}}{N_{sek}}</m> (im Leerlauf gemessen)
• <m>k = \sqrt{1-\frac{L_{Pri-K}}{L_{Pri-0}}}</m> (mit L-Meter gemessen)
• <m>R1 \sim \frac{\beta _{I_N} \cdot U_{ein}}{I_N}</m>
• <m>N_{steu} \le \frac{5 \cdot N_{Pri}}{2\pi \cdot U_{ein}}</m>
• <m>P_{max}=\frac{(\pi \cdot U_{ein} \cdot k)^2 \sqrt{L_{pri} \cdot C_2 (1-k^2)}}{4 \cdot L_{pri} \cdot (1-k^2)}</m> (Näherungsformel)
• <m>R_{opt}=(1-k^2)(\frac{N_{sek}}{N_{pri}})^2 L_{pri} \cdot 2\pi \cdot f</m>

| Variable | Description | | <m>\!\, f_r</m> | Resonanzfrequenz im Leerlauf | | <m>\!\, L_{Pri}</m> | Induktivität der Primärwicklung | | <m>\!\, C2</m> | Kapazität des Primärschwingkreises | | <m>\!\, U_p</m> | Spitzenspannung im Resonanzkreis | | <m>\!\, I_p</m> | Spitzenstrom im Resonanzkreis | | <m>\!\, k</m> | Koppelfaktor zwischen Primär- und Sekundärwicklung | | <m>\!\, L_{Pri-0}</m> | Primärinduktivität bei Leerlauf der Sekundärwicklung | | <m>\!\, L_{Pri-K}</m> | Primärinduktivität bei Kurzschluss der Sekundärwicklung | | <m>\!\, U_{ein}</m> | Eingangsspannung des Royer Converters (Gleichspannung) | | <m>\!\, U_{aus}</m> | Ausgangsspannung des Royer Converters (Wechselspannung, Spitzenwert) | | <m>\!\, R1</m> | Basiswiderstand | | <m>\!\, I_N</m> | Nennstrom des Royer Converters am Eingang | | <m>\!\, \beta _{I_N}</m> | Stromverstärkung der Transistoren bei Nennstrom
Achung! Die Stromverstärkung sinkt bei höheren Strömen deutlich, ins Datenblatt schauen. | | <m>\!\, N_{steu}</m> | Windungszahl der Steuerwicklung | | <m>\!\, P_{max}</m> | Maximale Ausgangsleistung bei Leistungsanpassung | | <m>\!\, R_{opt}</m> | Optimaler Lastwiderstand für Leistungsanpassung |

Controlled - 4 MOSFET Rectifier

active synchronous rectifier "gesteuerter Synchrongleichrichter" Examples, Schematics & Links to concept

DIY Schotky-Cheap-O-Rectify

Examples, Schematics & Links to concept NICE TO HAVE: Someone with the ability to establish FEM simulations of different rotor type models and mechanics to analyze stress points in the

mechanics and to optimize the rotors performance.