Generation · Wind
The source most often oversold.
A turbine on a tall tower at an open site with steady wind is a fine machine that runs day and night. Every word in that sentence is doing work, and on most properties at least one of them is not true.
These seven guides are written so you can find out which one fails at your place before you spend anything. If none of them do, wind is worth building.
Before anything else
Four things have to be true at once.
A property qualifies for wind when it has open exposure with no obstacle close enough to spoil the air, room for a tower tall enough to reach that air, an ordinance that permits a tower of that height, and enough land that the setbacks and guy wires fit inside your own boundaries.
Miss any one of the four and the project stops, usually late and usually expensively. A sheltered yard has wind on the map and turbulence at the rotor. A good site under a 35 foot height limit gives up most of what makes it good. A parcel that cannot hold the setback circle cannot hold the machine.
None of this costs money to check. Two of the four are answered by a phone call to the county and an afternoon with your own deed. The first and second guides below work the other two, and between them they settle the question for most readers in a weekend.
If your site is sheltered, or your ordinance caps you at 35 feet
Then this section is worth reading and a poor place to spend money. The same budget in panels produces more on almost every property that wind disappoints, and that section is already written.
Solar at Property ScaleWhat the resource asks
Four facts that govern every page here.
Wind rewards height and punishes obstruction, in both cases far more steeply than most people expect. Understand these four and the rest of the section reads as consequence.
Power rises with the cube of speed
Doubling wind speed does not double the energy available, it multiplies it by eight. That is why a small difference in average speed between two sites a mile apart produces a large difference in what a turbine makes, and why regional wind maps settle nothing about a particular yard.
Height is most of the decision
The same 2.5 kilowatt machine screens at 1,912 kilowatt-hours a year on a 30 foot tower, 2,545 at 60 feet, 3,142 at 100 feet, and 3,646 at 140 feet. Going from 30 feet to 100 adds about 64 percent, from a machine that never changed. The tower is not the accessory.
The county often decides first
Department of Energy guidance notes that most zoning ordinances cap structures at 35 feet. Because limits are written against total height, a 12 foot rotor puts the hub at 29 feet, which leaves roughly 61 percent of the output the same machine would make at 100. The ordinance is worth reading before the brochures.
It is a structure before it is a generator
A guyed 100 foot tower anchors on a circle 50 to 75 feet out, which occupies between 0.18 and 0.41 of an acre and has to stay clear. Foundations resist overturning, not weight. Most of the money after the first year goes to reaching the machine, not to the machine.
What this hub covers
Seven guides, in the order the decisions actually come.
Measure the site, face the economics, choose the machine, raise it, control it, and satisfy the law. One 2.5 kilowatt turbine on a 100 foot tower runs as the worked example through all seven, so the numbers measured in the first guide are the numbers still being spent in the last.
Is your site worth it: assessing a wind resource
The clearance rule, the tower height ladder, four estimation methods ranked worst to best, and why a year of logging at hub height beats every shortcut.
2Why most residential wind disappoints
Measured capacity factors, real installed cost, roof mounting, and the four failure patterns behind the gap between expectation and output.
3Horizontal-axis turbines
The conventional machine: lift rather than push, why three blades, furling and overspeed protection, and the four questions to put to any manufacturer.
4Vertical-axis turbines
Savonius and Darrieus rotors, the generator at ground level, lower tip speed and less noise, and an honest look at the turbulence claim.
5Towers and maintenance
Guyed, self-supporting and tilt-down structures, the land each needs, what a foundation resists, and what reaching the machine costs across twenty years.
6Controlling a wind system
Why an unloaded rotor runs away, what a dump load does, the second independent overspeed protection the code requires, and the three kinds of brake.
7Zoning and permits
The 35 foot limit, how setbacks decide the land you need, sound and shadow flicker rules, covenants, interconnection, and when the FAA has to be told.
The screening number
Rotor size and average speed, and that is the estimate.
Before any brochure, a single piece of Department of Energy arithmetic tells you roughly what a machine will make at your site in a year[1].
kWh per year ≈ 0.01328 × rotor diameter (feet) squared × average wind speed (mph) cubed
The speed is the annual average at hub height, not at ground level and not from a regional map. A 12 foot rotor at a site averaging 11.8 miles per hour screens at about 3,142 kilowatt-hours. It is an estimate for deciding whether to keep going, not a design figure.
Whether that figure covers your household is a question you answer the way the whole Energy section answers it, from your own load list. The Power Needs Calculator works it out from your devices, and the four checks it runs do not change at property scale. Only the numbers do.
Measuring Power Use
What the household actually consumes in a day, measured rather than guessed.
Read the guidePower Needs Calculator
The four checks that size any system, wind included, from a device list.
Run the numbersMicro-Hydro and Water Power
The other source that runs at night, for the few properties with moving water and real drop.
See the sectionSources
Where these numbers come from.
- U.S. Department of Energy, Small Wind Guidebook (WINDExchange). The screening equation, the 30 foot rotor clearance above obstacles within 300 feet, tower families and their trade-offs, the guy radius range, and the observation that most zoning ordinances limit height to 35 feet.
- U.S. Department of Energy, Small Community Wind Handbook (WINDExchange). The same 30 foot clearance stated against a 500 foot radius, maintenance planning as a distinct project stage, and neighbour engagement ahead of permit applications.
- NFPA 70, National Electrical Code, Article 694, Wind Electric Systems. Scope, disconnecting means, the requirement for a second independent means of preventing overspeed where a diversion load controller is used, and wiring methods for turbine output circuits.
- 14 CFR Part 77, Federal Aviation Administration. Notice requirements for construction above 200 feet and for structures penetrating the imaginary surfaces near runways, and the Form 7460-1 filing window used in the permits guide.
Figures on this page are screening estimates worked from the running example used across the section. They are for deciding whether to look further. The governing answers come from your own measured wind data, your ordinance, your utility, and the manufacturer of the machine you are considering.
Continue reading
What’s next
Hydro
Micro-Hydro and Water Power
Eight guides on generating power from moving water, which unlike wind and solar runs continuously.
Energy
Generating Your Own Power
The property-scale generation section: solar, micro-hydro, wind, and what each one asks of a site.
Solar
When Household Solar Stops Being Enough
How to tell whether a household has outgrown its solar system, and the cheaper corrections worth trying first.
Land
Land and Self-Reliance
A household's relationship to land sets its self-reliance ceiling. Guides for renters, lots, and acreage.