Wind Turbine Payback in Rock County, WI
Wind turbine payback in Rock County
No. The turbine wears out before it pays for itself.
At 30 m, the height a home turbine tower usually reaches, the wind in Rock County, WI averages 5.98 m/s (13.4 mph). A 10 kW turbine there would make about 19,556 kWh a year, worth $3,725 at WI's 19.05¢/kWh. Against an installed cost of about $100,000, that is a payback of 27 years, and the turbine is built to last about 20.
What to do in Rock County
A home turbine is not worth buying for savings in Rock County unless your spot is far windier than the county average, 6.9 m/s at the hub against 5.98 m/s here. Per kW, solar panels would make about 1,145 kWh a year here against the turbine's 1,956, so get a solar quote first.
What would have to change
- Power would have to cost 26¢/kWh, 1.3 times what WI pays now.
- Or the average wind at the hub would have to be 6.9 m/s instead of 5.98. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of WI
Rock County is the 873rd windiest of 3,144 US counties at turbine height; the national middle is 4.79 m/s. The windiest in WI is Manitowoc County at 7.32 m/s, payback 18 years.
Month by month in Rock County
April is the strongest month here, at 6.85 m/s and about 2,133 kWh. August is the weakest, 4.62 m/s and 856 kWh, so the best month makes 2.5 times the worst. November to March brings in 49% of the year's output in Rock County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 6.54 m/s | 2,011 kWh | $383 |
| February | 6.62 m/s | 1,861 kWh | $355 |
| March | 6.51 m/s | 1,994 kWh | $380 |
| April | 6.85 m/s | 2,133 kWh | $406 |
| May | 6.05 m/s | 1,703 kWh | $324 |
| June | 5.31 m/s | 1,205 kWh | $230 |
| July | 4.73 m/s | 913 kWh | $174 |
| August | 4.62 m/s | 856 kWh | $163 |
| September | 5.50 m/s | 1,320 kWh | $251 |
| October | 6.28 m/s | 1,849 kWh | $352 |
| November | 6.50 m/s | 1,924 kWh | $367 |
| December | 6.29 m/s | 1,854 kWh | $353 |
What a taller tower would buy
Measured at 10 m the wind in Rock County averages 4.66 m/s; at 50 m it is 6.71 m/s. That gives a shear exponent of 0.227, typical of ordinary open country. Going from 20 m to 50 m takes output from 15,676 to 24,947 kWh a year, 59% more, before counting the extra cost of the taller tower. Why tower height decides it explains the shear behind these numbers.
| Hub height | Average wind | Output | Payback |
|---|---|---|---|
| 20 m | 5.45 m/s | 15,676 kWh | 34 years |
| 30 m | 5.98 m/s | 19,521 kWh | 27 years |
| 40 m | 6.38 m/s | 22,511 kWh | 23 years |
| 50 m | 6.71 m/s | 24,947 kWh | 21 years |
Counties around Rock County
4 of the 6 closest counties are windier at turbine height; the windiest, Jefferson County, averages 6.09 m/s.
- Winnebago County, IL: 5.98 m/s, 19,556 kWh, payback 27 years (23 mi)
- Green County, WI: 5.98 m/s, 19,556 kWh, payback 27 years (27 mi)
- Walworth County, WI: 6.05 m/s, 20,075 kWh, payback 26 years (27 mi)
- Boone County, IL: 6.05 m/s, 20,075 kWh, payback 26 years (27 mi)
- Jefferson County, WI: 6.09 m/s, 20,371 kWh, payback 26 years (28 mi)
- Dane County, WI: 6.08 m/s, 20,297 kWh, payback 26 years (32 mi)
Sun versus wind in Rock County
Rock County gets 3.92 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,145 kWh a year; one kW of the turbine above makes 1,956. This is one of the rare places where a kilowatt of turbine out-produces a kilowatt of panels, by 1.7 times. Panel output assumes an 80% system performance ratio. Wind or solar runs the same comparison for every county.
How this is worked out
Wind is NASA's Power climate record, the 2001-2025 average at 10 m and 50 m for the county's centre, carried to 30 m with this county's own measured wind shear and spread into hours with a Rayleigh distribution. The turbine is a generic 10 kW, 7 m rotor machine with 10% losses. Cost is $10,000 per kW installed with no tax credit, because the federal one ended in 2025. One county-centre number cannot see your hilltop or your tree line, so treat it as the starting point for a site survey, not a substitute. The full method and its weak spots are in how the numbers are made.