Small wind turbines, step by step
Interactive lesson: when wind makes sense, how to measure it, rotor and turbine, mast and site, power with a dump load for the surplus, and maintenance.
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The whole lesson as text
1. When wind makes sense
A small wind turbine works at night, in winter and when it's cloudy, but only in the right place.
- The cube of speed — Wind at 6 m/s doesn't carry twice as much as wind at 3 m/s, but eight times as much energy.
- The 4–5 m/s threshold — Below roughly 4 m/s (9 mph) average at rotor height a small turbine rarely pays. From 4–5 m/s (9–11 mph) it's a useful top-up to solar and helps in winter.
- Ridge, not dip — A turbine 50 m away, on the ridge instead of in the dip, can give twice as much. Sheltered valleys are still and foggy in winter, and there a turbine is most often a failure.
- Storms mislead — People remember three stormy nights in March, not the average. A month of measuring often shows only 2–3 m/s. That's why the wind is measured before you buy.
Why: Many farms sit in valleys and sheltered hollows where the average wind is weak. Wind power rises with the cube of the speed, so the site is everything.
- Half a metre per second difference in the average means 30–40 % more or less electricity.
- Below a 3 m/s (7 mph) average, forget wind: panels and a battery are better.
2. How much wind you have
Wind is measured, not guessed.
- Wind atlas — The Global Wind Atlas is free and gives a rough average at 10, 50 and 100 m; in the US there are also NREL wind maps. For small turbines take the 10 m figure and be careful.
- Anemometer on a mast — A logging anemometer at the height of the future rotor, for at least 6 months, winter included, ideally 12.
- Wind rises with height — The atlas says 4.0 m/s at 10 m, terrain with an orchard and hedges. At 20 m (65 ft): 4.0 × 1.15 = 4.6 m/s, roughly 50 % more electricity.
- A tree as a flag — A crown shaped like a flag, with branches growing to one side, means roughly 4–6 m/s. A good first check, but it doesn't replace measuring.
Why: The atlas and the weather station give a rough figure, but they don't see your trees and buildings. Only an anemometer on your own site gives the real answer.
- A logging anemometer on a 10 m (33 ft) pole costs roughly a tenth of a small turbine.
- Without a logger, record the Beaufort force three times a day: at 7 am, 2 pm and 9 pm.
3. Rotor and turbine · Locked
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4. Mast and site · Locked
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5. Power and the dump load · Locked
Buy the Small wind turbines module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.
6. Maintenance · Locked
Buy the Small wind turbines module and you get the PDF to download and print, plus lifetime access to this interactive lesson: all 6 chapters, 24 steps.