DIY Small Wind Turbine: Power from Moving Air

Assess Your Site First

Build before you assess your wind resource and you may build a very expensive ornament.

Wind speed data is available from the National Renewable Energy Laboratory's wind map tool (windexchange.energy.gov) for most US locations. These give annual averages at 30 and 100 meters. Your actual ground-level site will be lower than these averages — trees, buildings, and terrain create turbulence that dramatically reduces output.

Rules for a good small wind site:

• Average annual wind speed at your planned tower height of at least 10-12 mph (4.5-5.5 m/s)
• Tower location at least 300 feet from major obstructions (trees, buildings) in the prevailing wind direction
• Clear open fetch — the wind travels over open land before reaching your turbine
• No nearby noise-sensitive neighbors — wind turbines make mechanical noise at speed

If you cannot establish at least 10 mph average, solar is a better investment. Below 7 mph average, wind power is rarely worth the effort and maintenance.

Generator Selection

The generator is the heart of the system. Two practical choices for DIY builders:

Permanent magnet DC motor (repurposed as generator): Treadmill motors, DC PM motors salvaged from industrial equipment, and purpose-sold PM generators all work. A treadmill motor rated for 90-130 volts DC produces useful voltages at low RPM — critical for a wind turbine that may not spin very fast in light winds.

Key specs to look for: permanent magnet (not wound field), voltage output per RPM (higher is better for low-RPM applications), and amperage capacity.

Dedicated wind turbine generators: Suppliers like Windblue Power, Missouri Wind and Solar, and several international sellers offer PM alternators specifically designed for wind turbine use. These are purpose-built for low RPM, high voltage per turn, and weather resistance. They cost $150-500 but eliminate most of the guesswork.

What to avoid: Automotive alternators require high RPM (3,000+) and field excitation. They work for belt-driven applications but are poorly suited for directly-coupled wind turbines.

Blade Design and Materials

Blades are aerodynamic structures. They are not flat paddles. The shape matters.

Blade physics: A well-shaped blade uses lift (like an airplane wing) rather than drag (like a sail) to spin the turbine. Lift-based designs are far more efficient. The key dimensions are the angle of attack at each point along the blade (the twist) and the chord width (how wide the blade is at each point).

PVC pipe blades: Cut from 4-inch or 6-inch PVC pipe, shaped with a grinder or sander. Plans for PVC blade cutting are available from Scoraig Wind Electric and numerous DIY sources. PVC blades are practical for turbines up to 4-5 feet diameter.

Carved wood blades: More work, better performance. Use straight-grained pine, cedar, or fir. Wood carving gives better aerodynamic shape than PVC but requires tools and skill. Fiberglass coat the finished blades for weather resistance and to prevent moisture absorption.

Key blade variables:

• Tip speed ratio (TSR): The ratio of blade tip speed to wind speed. Most efficient small turbines run a TSR of 5-7. This affects blade count (2-3 blades typical) and pitch angle.
• Blade count: Two blades run faster (higher TSR), three blades are smoother and quieter. Three is more common for permanent installations.
• Balance: Blades must be balanced both statically (all blades same weight) and dynamically (weight distribution along each blade matched). Unbalanced blades cause vibration that destroys bearings.

Building the Hub and Frame

The hub connects the blades to the generator shaft. The frame holds the generator, tail, and mounting.

Hub construction: A circular steel plate, 1/4-inch minimum thickness, drilled for blade mounting bolts and bored center for the shaft. Weld or bolt blades at the calculated attachment angle. Blades should be pitched (tilted) at about 15-20 degrees from the plane of rotation at the root, twisting to near-flat at the tip.

Generator frame: Steel angle iron welded into a simple bracket that bolts the generator facing into the wind, with a pivot (yaw bearing) to allow the turbine to rotate and face changing wind direction.

Tail: A flat aluminum or plywood tail, roughly the same area as the blade swept circle divided by 4, mounted on an arm extending behind the generator. The tail passively yaws the turbine to face the wind.

Furling: In strong winds, an uncontrolled turbine overspeeds and destroys itself. A simple mechanical furling system uses an offset tail hinge to cause the turbine to turn sideways (furl) when wind exceeds a set speed, reducing the swept area and slowing rotation. Piggott's books describe furling geometry in detail.

Tower Selection and Installation

The tower determines how much wind you actually intercept. A turbine on a 20-foot tower in a location with trees is dramatically underperforming the same turbine on a 40-foot tower above the turbulence zone.

Tower types:

Tilt-up guyed tower: The simplest DIY tower. A steel pipe (2-inch schedule 40 or heavier) hinged at the base, held upright by 3-4 guy wire anchors. Tip the tower up with a gin pole, tilt it back down for maintenance. No climbing required. Works well to 30-40 feet.

Free-standing tower: Heavier, more expensive, more rigid. Required for turbines over 500 watts where vibration is significant.

Mounting height: Rule of thumb — tower should be at least 30 feet tall and at least 10 feet above any obstruction within 300 feet. Taller is almost always better. Each doubling of height roughly doubles wind speed at the top (in turbulent near-ground air layers).

Electrical System

Wire sizing: Use correct gauge wire for the full run from turbine to charge controller and batteries. At 12 volt, 10 amp output (120 watts), a 100-foot run requires 8 AWG wire to keep voltage drop under 3%. Voltage drop wastes power and heats wire. Size up, not down.

Charge controller: A wind-specific charge controller (or a dump load controller) is mandatory. Unlike solar controllers that simply disconnect when the battery is full, a wind turbine must always have a load or it overspeeds. A wind charge controller diverts excess power to a dummy load (resistor bank) instead of disconnecting. Standard solar PWM or MPPT controllers do not work for wind — they will allow overspeed and damage the turbine.

Rectifier: If your generator produces AC output (most PM alternators do), you need a 3-phase bridge rectifier to convert to DC before the charge controller and battery. Size the rectifier for at least 150% of the alternator's rated current.

Surge protection: Wind turbines in lightning-prone areas need surge protection. A simple arrester across the battery terminals, and another between the turbine and the controller, protects thousands of dollars of equipment from a transient.

Realistic Expectations

A well-built 6-foot diameter turbine (3 meters of swept diameter, roughly 7 square feet of swept area) in a 12 mph average wind location produces approximately:

• Average power: 50-100 watts
• Daily energy: 1.2-2.4 kWh/day
• Monthly energy: 36-72 kWh

That is enough to keep a 200Ah battery bank charged for basic lighting, a phone, a small radio, and occasional laptop use. It is not enough to run a refrigerator, electric heating, or power tools continuously.

Wind and solar together are better than either alone. Wind often blows hardest at night and during storms — exactly when solar is producing nothing.