Campaign 137: Harness the Wind
The Complete Windmill Construction, Wind Power, and Mechanical Wind Energy Guide
A Sovereignty Module of the Practitioner Community
Preamble
Wind is free, perpetual, and available everywhere on Earth. For over 2,000 years, windmills have ground grain, pumped water, sawed lumber, and powered workshops. A single windmill can pump thousands of gallons of water per day from deep wells, grind enough grain to feed a village, or generate electricity for an off-grid homestead. Wind power requires no fuel, produces no emissions, and operates day and night when the wind blows. This campaign covers the complete design, construction, and operation of wind-powered machines from simple water pumpers to grain mills to electricity generators.
Part I: Wind Fundamentals
Chapter 1: Wind Power Physics
| Concept | Formula/Value | Practical Meaning |
|---|---|---|
| Power in wind | P = ½ρAV³ | Power increases with the CUBE of wind speed. Double the wind = 8x the power. |
| Swept area | A = πr² | Doubling blade length = 4x the swept area = 4x the power |
| Air density (ρ) | 1.225 kg/m³ at sea level | Higher altitude = lower density = less power |
| Betz limit | 59.3% maximum efficiency | No wind turbine can capture more than 59.3% of wind energy |
| Practical efficiency | 25-45% for well-designed turbines | Real-world losses from friction, generator, and blade design |
| Cut-in speed | 7-10 mph typical | Minimum wind speed to start generating useful power |
| Rated speed | 25-35 mph typical | Wind speed at which turbine reaches maximum rated output |
| Survival speed | 60-100 mph | Maximum wind speed the structure can withstand |
Chapter 2: Site Assessment
| Factor | Ideal | Measurement Method |
|---|---|---|
| Average wind speed | 10+ mph annual average | Anemometer for 1 year, or check wind maps |
| Prevailing direction | Consistent from one direction | Wind vane observation over months |
| Obstructions | None within 500 ft upwind | Trees, buildings, hills create turbulence |
| Tower height | 30+ ft above any obstruction within 500 ft | Higher = stronger, smoother wind |
| Ground conditions | Solid for tower foundation | Must support tower + wind loads |
Chapter 3: Wind Speed and Power Output
| Wind Speed (mph) | Wind Speed (m/s) | Power Available (watts per m² of swept area) | Practical Output (6 ft diameter rotor) |
|---|---|---|---|
| 5 | 2.2 | 6.5 | ~5 watts |
| 10 | 4.5 | 52 | ~40 watts |
| 15 | 6.7 | 176 | ~135 watts |
| 20 | 8.9 | 417 | ~320 watts |
| 25 | 11.2 | 815 | ~625 watts |
| 30 | 13.4 | 1,407 | ~1,080 watts |
Part II: Windmill Types
Chapter 4: Windmill Design Comparison
| Type | Complexity | Efficiency | Best For | Materials |
|---|---|---|---|---|
| Savonius (vertical axis, drag) | Very simple | 10-15% | Water pumping, low-speed applications | Oil drums, sheet metal |
| American farm windmill (multi-blade) | Moderate | 15-20% | Water pumping from wells | Steel, wood, or aluminum |
| Dutch-style post mill | Complex | 20-30% | Grain grinding, sawmill | Heavy timber, canvas sails |
| Horizontal axis (3-blade, modern) | Moderate-complex | 30-45% | Electricity generation | Wood, PVC, fiberglass, or metal blades |
| Cretan sail windmill | Simple | 15-25% | Grain grinding, water pumping | Wood frame, cloth sails |
Chapter 5: Building a Savonius Rotor (Simplest Design)
| Step | Action | Details |
|---|---|---|
| 1. Cut drums | Cut two 55-gallon drums in half lengthwise | Creates 4 half-cylinders |
| 2. Weld/bolt to shaft | Attach two half-drums to central vertical shaft, offset 90° | S-shape when viewed from top |
| 3. Mount shaft | Shaft in bearings at top and bottom | Vertical axis — works from any wind direction |
| 4. Connect to pump or generator | Belt, chain, or direct drive to load | Low RPM, high torque — ideal for pumping |
ADVANTAGE: Savonius rotors work from any wind direction (no yaw mechanism needed), start in very low winds, and are extremely simple to build. DISADVANTAGE: Low efficiency (10-15%), limited to low-speed applications.
Chapter 6: Building a 3-Blade Wind Turbine for Electricity
| Component | Material | Details |
|---|---|---|
| Blades (3) | Carved wood, PVC pipe, or fiberglass | 3-6 ft long each. Airfoil shape critical for efficiency. |
| Hub | Steel plate or flange | Connects blades to generator shaft at correct pitch angle |
| Generator | Permanent magnet DC motor (treadmill motor) or car alternator | Treadmill motors are ideal: low RPM, high output |
| Tail/vane | Sheet metal or plywood on boom | Keeps rotor facing into wind |
| Tower | Steel pipe, wood poles, or lattice | 20-40 ft minimum. Guy-wired for stability. |
| Charge controller | Electronic (purchased or built) | Prevents battery overcharge |
| Batteries | Deep-cycle lead-acid or lithium | Store energy for calm periods |
| Inverter | DC to AC converter | If powering AC appliances |
Chapter 7: Blade Design (Airfoil)
| Parameter | Value | Why |
|---|---|---|
| Number of blades | 3 (optimal for electricity) | Balance of efficiency, smoothness, and structural balance |
| Tip speed ratio (TSR) | 5-7 for 3-blade | Blade tips move 5-7x faster than wind speed |
| Blade width (root) | 8-12% of blade length | Wider at root for strength |
| Blade width (tip) | 4-6% of blade length | Narrower at tip for speed |
| Twist angle (root) | 20-25° | Steeper angle at root (slower section) |
| Twist angle (tip) | 5-8° | Shallower angle at tip (faster section) |
| Airfoil profile | Flat bottom, curved top (like airplane wing) | Creates lift that drives rotation |
Part III: Water Pumping Windmills
Chapter 8: American Farm Windmill Design
| Component | Function | Details |
|---|---|---|
| Multi-blade rotor (12-18 blades) | Captures wind energy | Many blades = high torque at low speed (ideal for pumping) |
| Tail vane | Points rotor into wind | Also serves as overspeed protection (folds in high wind) |
| Gearbox | Converts rotary to reciprocating motion | Crank mechanism drives pump rod up and down |
| Pump rod | Transfers motion to well pump | Steel rod runs down inside well casing |
| Cylinder pump (at bottom of well) | Pumps water | Piston pump with check valves |
| Tower | Elevates rotor above obstructions | 20-40 ft steel lattice or wood |
Chapter 9: Pumping Capacity
| Rotor Diameter | Well Depth | Wind Speed | Approximate Output |
|---|---|---|---|
| 6 ft | 50 ft | 15 mph | 200-400 gallons/day |
| 8 ft | 100 ft | 15 mph | 300-600 gallons/day |
| 10 ft | 150 ft | 15 mph | 400-800 gallons/day |
| 12 ft | 200 ft | 15 mph | 500-1,000 gallons/day |
| 14 ft | 250 ft | 15 mph | 600-1,200 gallons/day |
Part IV: Grain Grinding Windmills
Chapter 10: Windmill-Powered Grain Mill
| Component | Function | Details |
|---|---|---|
| Sails/blades | Capture wind energy | 4 sails with canvas covering (adjustable for wind speed) |
| Main shaft | Transfers rotation from sails | Heavy timber or steel |
| Great spur gear | Changes rotation axis from horizontal to vertical | Large wooden or cast gear |
| Stone spindle | Drives upper millstone | Vertical shaft from gear to stone |
| Millstones (2) | Grind grain between surfaces | Lower stone fixed (bedstone), upper rotates (runner stone) |
| Hopper | Feeds grain to center of stones | Vibrating feed mechanism |
| Meal spout | Collects ground flour | Flour exits at edge of stones |
Chapter 11: Grinding Capacity
| Wind Speed | Sail Span | Approximate Output |
|---|---|---|
| 15 mph | 20 ft | 50-100 lbs flour/hour |
| 20 mph | 20 ft | 100-200 lbs flour/hour |
| 15 mph | 30 ft | 150-300 lbs flour/hour |
| 20 mph | 30 ft | 300-500 lbs flour/hour |
Part V: The Practitioner Wind Power Reference Card
WIND CUBES: Power in wind increases with the cube of wind speed. 10 mph wind has 8x more power than 5 mph wind. Site selection and tower height are the most important factors — get into stronger, smoother wind.
HEIGHT MATTERS: Every 10 feet of additional tower height increases wind speed by approximately 10-20%. A 40-foot tower captures significantly more energy than a 20-foot tower at the same location.
3 BLADES FOR ELECTRICITY, MANY BLADES FOR PUMPING: Three-blade rotors spin fast with low torque (good for generators). Multi-blade rotors (12-18 blades) spin slowly with high torque (good for pumps). Match the rotor to the task.
SAVONIUS FOR SIMPLICITY: If you need a wind-powered water pump and have access to 55-gallon drums, a Savonius rotor can be built in a day. It works from any wind direction and starts in the lightest breeze.
TREADMILL MOTORS ARE IDEAL GENERATORS: Permanent magnet DC motors from treadmills generate useful voltage at low RPM (200-500 RPM), making them perfect for direct-drive wind turbines without gearboxes.
REMEMBER: Wind is the most accessible renewable energy source. It requires no fuel, no grid connection, and no ongoing cost. A Practitioner with a wind turbine has water from deep wells, ground grain, and electricity — all from thin air. Wind power built civilizations before fossil fuels existed, and it will power them long after fossil fuels are gone.
Council Approval
Council Result: 12/12 APPROVED.