Wind Turbine Payback in Story County, IA
Wind turbine payback in Story 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 Story County, IA averages 6.21 m/s (13.9 mph). A 10 kW turbine there would make about 21,262 kWh a year, worth $3,094 at IA's 14.55¢/kWh. Against an installed cost of about $100,000, that is a payback of 32 years, and the turbine is built to last about 20.
What to do in Story County
A home turbine is not worth buying for savings in Story County unless your spot is far windier than the county average, 8.1 m/s at the hub against 6.21 m/s here. Per kW, solar panels would make about 1,177 kWh a year here against the turbine's 2,126, 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 6.21. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of IA
Story County is the 576th 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 Story County
April is the strongest month here, at 7.13 m/s and about 2,301 kWh. August is the weakest, 4.95 m/s and 1,039 kWh, so the best month makes 2.2 times the worst. November to March brings in 47% of the year's output in Story County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 6.60 m/s | 2,049 kWh | $298 |
| February | 6.60 m/s | 1,851 kWh | $269 |
| March | 6.79 m/s | 2,165 kWh | $315 |
| April | 7.13 m/s | 2,301 kWh | $335 |
| May | 6.45 m/s | 1,954 kWh | $284 |
| June | 5.66 m/s | 1,414 kWh | $206 |
| July | 4.96 m/s | 1,044 kWh | $152 |
| August | 4.95 m/s | 1,039 kWh | $151 |
| September | 5.89 m/s | 1,554 kWh | $226 |
| October | 6.48 m/s | 1,977 kWh | $288 |
| November | 6.66 m/s | 2,021 kWh | $294 |
| December | 6.45 m/s | 1,954 kWh | $284 |
What a taller tower would buy
Measured at 10 m the wind in Story County averages 4.87 m/s; at 50 m it is 6.96 m/s. That gives a shear exponent of 0.222, typical of ordinary open country. Going from 20 m to 50 m takes output from 17,338 to 26,756 kWh a year, 54% 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 | 5.68 m/s | 17,338 kWh | 40 years |
| 30 m | 6.21 m/s | 21,290 kWh | 32 years |
| 40 m | 6.62 m/s | 24,316 kWh | 28 years |
| 50 m | 6.96 m/s | 26,756 kWh | 26 years |
Counties around Story County
2 of the 6 closest counties are windier at turbine height; the windiest, Hamilton County, averages 6.4 m/s.
- Boone County, IA: 6.21 m/s, 21,262 kWh, payback 32 years (24 mi)
- Marshall County, IA: 6.2 m/s, 21,187 kWh, payback 32 years (25 mi)
- Polk County, IA: 6.14 m/s, 20,742 kWh, payback 33 years (25 mi)
- Hardin County, IA: 6.32 m/s, 22,077 kWh, payback 31 years (27 mi)
- Hamilton County, IA: 6.4 m/s, 22,669 kWh, payback 30 years (27 mi)
- Jasper County, IA: 6.07 m/s, 20,223 kWh, payback 34 years (32 mi)
Sun versus wind in Story County
Story County gets 4.03 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,177 kWh a year; one kW of the turbine above makes 2,126. This is one of the rare places where a kilowatt of turbine out-produces a kilowatt of panels, by 1.8 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.