Otherpower - EWB DenverObjective: produce electricity Savonious: Mostly drag based VAWT with very...

Otherpower.com

Dan Bartmann and Dan Fink

Copyright 2008 by Otherpower.com

Wind is the most difficult energy resource to harvest

Solar, hydro, and fossil fuel sources give smooth and steady energy, so efficient generators for them are easy to design.

The wind varies wildly and unpredictably, with an exponential power curve.

Power available in the wind (in watts) =

½ x air density x swept area x wind speed³

(kg/m³, m², m/s)


The objective: Slow down the wind, and transfer this energy into a spinning shaft

Wind quantity and quality are both important

Most winds come to us at low speeds

Tall towers are essential—you wouldn't mount a solar panel in the shade!

Turbulence is also a problem


HAWT vs. VAWT1kw HAWT

1kw VAWT

½ of a VAWTs rotor is moving in the wrong direction

VAWT blades are also ½ as efficient as HAWTs

Therefore VAWTs must be 4 times as large as HAWTs to make the same energy

VAWTs experience severe cyclical stresses every rotation

VAWTs cannot be yawed out of the wind to control them

VAWTs are not more quiet than HAWTs, nor are they safer for birds

VAWTs do NOT perform better near the ground, on turbulent sites, or in low winds, than HAWTs—despite the advertising hype


Comparison of wind turbine rotor design efficiency and Tip Speed Ratios

No wind turbine power coefficient (cP) can exceed the Betz Limit of 59.26%

Drag-based turbines are very inefficient, suitable only for grinding grain or pumping water

High-solidity rotors have a very high drag component, and are also not suitable for producing electricity

3-blade, low drag, lift-based turbines operating at TSRs of 5-7 are the most efficient, and are easiest and cheapest to build.

Graph source: NREL

Before you try to think “outside the box,” find out what's IN the box and why.


Objective: produce electricity

Savonious: Mostly drag based VAWT with very low RPM

Waterpumper: Lift-based but high solidity and high drag give low RPM

The lower the shaft RPM, the heavier and more expensive the alternator must be

Gearing to increase RPM is undesirable due to friction, which hurts low wind performance

Using electromagnets to produce magnetic flux hurts low-wind performance

Ferrous coil cores increase magnetic flux, but hurt low-wind performance by cogging

In winds of 7-28 mph that we want to capture, turbine RPM of 80-500 is ideal for TSR=5-7 and therefore maximum cP

POOR POOR

FANTASY

There are many reasons this is a graphic and not an actual photo!


Wind turbine alternators No effective commercial or surplus

products exist:

Vehicle alternators need 1000 RPM plus; too fast

Servo motors are wired wrong: very inefficient, with high possibility of burnout

Induction motors and surplus gasoline generators need constant RPM

The only effective solution:Build your own low-RPM alternator.

Just like what all legitimate wind turbine companies do!

NO

NO


Axial flux air gap alternator Low RPM, specifically designed for

individual system voltage

Permanent magnets eliminate parasitic losses from electromagnets

Large mass of very powerful magnetic material makes up for large air gap and no ferrous coil cores

Start-up cogging losses are eliminated

Easy to build using standard vehicle parts and/or flat steel sheets, even in remote areas

Common in commercial wind turbine designs


Furling Systems Wind turbines must cope

with an exponential increase in power from the wind to survive

Alternators react to power input on a mostly linear curve

Matching the turbine rotor to the alternator is critical

Reducing the swept area is the best way to regulate small wind turbine output

The most reliable, elegant, easy to fabricate, and effective solution is the furling tail


Renewable energy systems Hybrid solar/wind systems

produce the most energy, in kwh per month, at most locations

Rated output is overrated

You cannot compare solar and wind systems by “rated output”

Solar PV rated output assumes full sun, fairly common

Wind rated output assumes 28 mph wind speeds, very rare

The critical figure is ENERGY production in watt-hours, not instantaneous POWER output in watts. Instantaneous power output does not matter much—what matters is for how long you gained or used it.


Local Manufacture and Training

Local manufacture is possible, these photos from Bluefields, Nicaragua, Blue Energy Group NGO

Skills and equipment needed include welding, metalworking, electrical wiring, resin casting, wood carving


Frame Fabrication Flat steel parts can be cut

with torch or hacksaw

Strong welding is absolutely essential

Standard trailer bearings are available worldwide


Stator Fabrication

The stator must be a solid resin casting


Magnet Rotor Fabrication

Again, a strong casting is needed


Blade Carving Wood--the original

carbon-graphite composite!

The main advantage of fiberglass is in mass production


Towers Towers must be both

tall and sturdy Turbines must fly 30

feet above anything within 300 feet in any direction

Tower cost and time to build it is at least equal to that of the turbine itself

Climb or tilt up—depends on your skill set and training


Regular Maintenance A regular, yearly maintenance schedule

is essential with ALL wind turbines, not just homebrew ones.

Maintenance training is critical with inexperienced turbine owners

Climate affects the maintenance schedule of turbines and towers tremendously

Attention to detail is critical!

The “EVENT CASCADE” is the start of almost all wind turbine failures.

For example, a $5 rectifier fails from a heat sink that's too small. The turbine runs single phase, and the stator overheats. The stator melts and swells, causing magnets to rub it. Friction heating brings the magnets past their Curie temperature. The magnets no longer adhere to the rotors, and fly out, hitting the blades. You are left with a pile of junk!


Homebrew wind turbine books

Windpower Workshop by Hugh Piggott

Axial Flux Wind Turbine Plans by Hugh Piggott

Homebrew Wind Power by us


Wind turbine seminars Hands-on experience for

educators is essential

Develop your own curriculum to suit the ultimate location, no matter how remote

Custom tailor the curriculum to the skill level of your students


Wind energy should be:

- Cost effective- Reliable- Silent- Easy to live with- Fun!


Date post:	23-Mar-2020
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

Otherpower - EWB DenverObjective: produce electricity Savonious: Mostly drag based VAWT with very...

Documents