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Part VIII: Wind, Water, and BiofuelsChapter 12. Small Wind and Micro-Hydro

Small Wind Turbines: Towers, Safety, and Expectations

Tower height, guy anchors, and the output you should believe from a small turbine.

Difficulty
Advanced
Cost
Varies widely
published

A small wind turbine is a rotor on a tower, and the tower is most of the project. The rotor only sees the wind that arrives at its height. On a house lot that wind is often slow, turbulent, and not worth the steel. If the assessment did not survive the cube of a realistic speed, stop on that page. This page is what a real installation demands when the site is actually windy, and why the expectations people bring from a rated wattage are too high.

This is not a plan for fabricating a rotor, sizing guy cable, or mixing anchor concrete. Those are engineered for the soil, the wind load, and the machine. The links below are other builders' projects. They are not repeated here.

Difficulty

Level
Advanced
Time
A permitted structure, not a weekend mast
Skills
Treating the tower as the project and the turbine as a load on it

Cost estimate

Varies widely

A toy rotor on a roof bracket is the cheap end and usually the disappointing end. A guyed or freestanding tower with engineered anchors, a listed turbine, and a permitted interconnection is a construction project that can dwarf the turbine price. Get local quotes. This page has no national price.

Materials

ItemQtyNotes
A site that passed the assessment1Including a height you are allowed to build. Zoning and a neighbor's view are part of the site.
An engineered tower and anchors1Matched to the turbine loads. A stake in the lawn is not an anchor.
A permitted electrical path1Same boundary as photovoltaic wiring. The utility and the inspector are in this list.

Height, turbulence, and the house

Wind speed usually rises with height, and turbulence falls once you clear the obstacles. A rotor down among eaves and crowns sees gusts from odd directions, which wears bearings and makes less energy. A roof mount puts that turbulence and that vibration into the house. The usual siting advice is to get the whole rotor well above nearby trees and roofs. A short pole in a pretty yard does not get there. The local ordinance and the manufacturer set the actual limits. A rule of thumb is not a permit.

The tower has to be designed for the thrust of the rotor in a storm, for ice, and for fatigue. Guyed towers need anchors placed where the design says, in soil that can hold them, with cables that stay tensioned. Freestanding towers need a foundation the same way. This book will not invent those sizes. If a seller tells you the turbine is "self supporting on a 2-inch pipe," ask for the engineering and the wind speed it was checked at. Then ask your building department.

Tower, guys, and a fall distanceA guyed mast with anchors, and a house drawn outside the height of the tower.AnchorsAnchorsAssume it can fall its full height. Do not climb it.
Guys go to real anchors. The fall distance is the height of the tower, in every direction.

What output to believe

Believe the assessment sketch at the speed your site holds, not the largest number on the curve. A machine that makes a kilowatt at a speed you see a few hours a year will spend most of its life making far less. Maintenance, noise, and a failed bearing are part of the yield. So is icing, which can stop the rotor and can throw ice as it sheds. Small turbines on residential lots have a long public record of producing less than their owners hoped. Treat a sunny anecdote as a story, and treat your own wind data as the estimate.

Interconnection does not get easier because the source is wind. A grid-tied inverter, protection, and a utility agreement are the same class of work as the photovoltaic wiring page. An off-grid battery is the battery page, and it still does not make a calm week windy.

Composite: the roof bracket

This is an invented composite, not a product recall or a real street. A household clamps a small rotor to the roof because a tower sounded like a bigger project. The rotor lives in the turbulence over the ridge. It vibrates the ceiling, annoys the next house, and makes little energy at the low speeds between gusts. A storm loosens the bracket. Without the tower, the rotor never reached the wind, so if you cannot build the tower you cannot use the turbine. No brand name belongs on this composite.

  1. Stop if the assessment failed

    Buying a turbine does not add wind to a site that failed. Revisit the cube at your speed.

  2. Permit the tower before you buy the rotor

    Settle height, setback, noise, and the utility first. Already owning the machine does not get you a variance.

  3. Buy tower, anchors, and turbine as one engineered set

    Foundations and guy anchors are designed, not improvised. The fall zone stays clear of people, lines, and the neighbor.

  4. Hand the wires to the same standard as a photovoltaic array

    Listed equipment, a permit, and an electrician for anything that can meet the grid or a house panel.

Further reading

These links go to outside sources. This book cites them by link and does not copy their words or pictures.

General education, not a permit or a stamped design. Follow the safety note in the guide, read the safety disclaimer, and hire a licensed trade when the work requires one.