Wind Turbine Payback in Clarke County, IA
Wind turbine payback in Clarke 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 Clarke County, IA averages 6.16 m/s (13.8 mph). A 10 kW turbine there would make about 20,891 kWh a year, worth $3,040 at IA's 14.55¢/kWh. Against an installed cost of about $100,000, that is a payback of 33 years, and the turbine is built to last about 20.
What to do in Clarke County
A home turbine is not worth buying for savings in Clarke County unless your spot is far windier than the county average, 8.1 m/s at the hub against 6.16 m/s here. Per kW, solar panels would make about 1,194 kWh a year here against the turbine's 2,089, so get a solar quote first.
What would have to change
- Power would have to cost 24¢/kWh, 1.6 times what IA pays now.
- Or the average wind at the hub would have to be 8.1 m/s instead of 6.16. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of IA
Clarke County is the 630th windiest of 3,144 US counties at turbine height; the national middle is 4.79 m/s. The windiest in IA is Dickinson County at 6.59 m/s, payback 29 years.
Month by month in Clarke County
April is the strongest month here, at 6.99 m/s and about 2,217 kWh. August is the weakest, 4.85 m/s and 982 kWh, so the best month makes 2.3 times the worst. November to March brings in 48% of the year's output in Clarke County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 6.62 m/s | 2,061 kWh | $300 |
| February | 6.59 m/s | 1,846 kWh | $269 |
| March | 6.80 m/s | 2,177 kWh | $317 |
| April | 6.99 m/s | 2,217 kWh | $323 |
| May | 6.24 m/s | 1,826 kWh | $266 |
| June | 5.60 m/s | 1,378 kWh | $200 |
| July | 4.93 m/s | 1,027 kWh | $149 |
| August | 4.85 m/s | 982 kWh | $143 |
| September | 5.82 m/s | 1,507 kWh | $219 |
| October | 6.44 m/s | 1,949 kWh | $284 |
| November | 6.70 m/s | 2,042 kWh | $297 |
| December | 6.45 m/s | 1,955 kWh | $284 |
What a taller tower would buy
Measured at 10 m the wind in Clarke County averages 4.8 m/s; at 50 m it is 6.92 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 16,911 to 26,469 kWh a year, 57% 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 | 5.62 m/s | 16,911 kWh | 41 years |
| 30 m | 6.16 m/s | 20,908 kWh | 33 years |
| 40 m | 6.58 m/s | 23,982 kWh | 29 years |
| 50 m | 6.92 m/s | 26,469 kWh | 26 years |
Counties around Clarke County
1 of the 6 closest counties is windier at turbine height; the windiest, Union County, averages 6.22 m/s.
- Decatur County, IA: 6.05 m/s, 20,075 kWh, payback 34 years (20 mi)
- Lucas County, IA: 6.1 m/s, 20,446 kWh, payback 34 years (24 mi)
- Warren County, IA: 6.14 m/s, 20,742 kWh, payback 33 years (24 mi)
- Union County, IA: 6.22 m/s, 21,336 kWh, payback 32 years (24 mi)
- Madison County, IA: 6.14 m/s, 20,742 kWh, payback 33 years (24 mi)
- Wayne County, IA: 5.93 m/s, 19,186 kWh, payback 36 years (31 mi)
Sun versus wind in Clarke County
Clarke County gets 4.09 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,194 kWh a year; one kW of the turbine above makes 2,089. 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.