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How much power does a small wind turbine actually produce?
A 1 kW turbine does not produce 1 kW. It produces about 2,000 kWh a year in a decent site, 800 kWh in a poor one, and almost nothing in a suburb. Here is the arithmetic behind that, so you can size a machine honestly.
Rated power is a wind speed, not an output
Every small turbine has a rated wind speed — usually 11 m/s — at which the generator reaches its nameplate figure. Below that, output falls with the cube of wind speed: at half the rated wind speed you get roughly one eighth of the rated power, not half.
That cubic relationship is the whole story of small wind. A site averaging 4 m/s and a site averaging 6 m/s differ by 50 % in wind speed but by more than 200 % in energy. It is why the annual mean wind speed at hub height is the only number worth arguing about before you buy.
Annual output by size and wind speed
| Turbine | 4 m/s | 5 m/s | 6 m/s | 7 m/s |
|---|---|---|---|---|
| 300 W | 300 kWh | 600 kWh | 1,050 kWh | 1,600 kWh |
| 500 W | 500 kWh | 1,000 kWh | 1,750 kWh | 2,700 kWh |
| 1 kW | 1,100 kWh | 2,000 kWh | 3,000 kWh | 4,200 kWh |
| 2 kW | 2,200 kWh | 4,000 kWh | 6,000 kWh | 8,400 kWh |
| 3 kW | 3,300 kWh | 6,000 kWh | 9,000 kWh | 12,600 kWh |
| 5 kW | 5,500 kWh | 10,000 kWh | 15,000 kWh | 21,000 kWh |
| 10 kW | 11,000 kWh | 20,000 kWh | 30,000 kWh | 42,000 kWh |
These are gross figures at hub height for a well-sited machine with a good power curve, before inverter and battery losses (subtract 8–12 %). Treat them as a planning estimate, not a guarantee — a measured power curve and your own wind data beat any table.
Capacity factor: why 20 % is normal and 30 % is excellent
Dividing annual output by (rated power × 8,760 hours) gives the capacity factor. A 1 kW turbine producing 2,000 kWh a year runs at 23 %. Anything above 25 % means an excellent site and a well-matched rotor; below 15 % means the machine is too big for the wind you have.
This is also why buying a bigger turbine is a bad way to fix a low-wind site. A 5 kW machine on a 4 m/s site has a capacity factor near 12 % and produces less per dollar than a 2 kW machine on the same tower.
The seasonal shape matters as much as the total
In temperate climates, 60 % of annual wind energy arrives between October and March — exactly when solar produces least. That is the argument for wind-solar hybrid systems: the two sources are anti-correlated, so a combined system needs a much smaller battery than either alone.
In monsoon climates the pattern reverses and wind becomes a wet-season supplement. Ask for a monthly output table for your site before you commit; an annual total hides the three months when the machine does nothing.
Estimating your own site in ten minutes
Start with a wind atlas or a nearby airport mast for a first guess, then apply two corrections: height (wind rises about 10 % per doubling of height in open terrain) and obstacles (if a tree or building within 100 m is taller than the hub, expect 20–40 % less). If the result is below 4.5 m/s, stop and look at solar instead.
For anything above 1 kW, spend the money on a three-month measurement at hub height with a calibrated anemometer and a wind vane. It costs a few hundred dollars and it is the difference between a system that pays back and one that does not.
