Wind Turbine Payback in Marshall County, IA
Wind turbine payback in Marshall 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 Marshall County, IA averages 6.2 m/s (13.9 mph). A 10 kW turbine there would make about 21,187 kWh a year, worth $3,083 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 Marshall County
A home turbine is not worth buying for savings in Marshall County unless your spot is far windier than the county average, 8.1 m/s at the hub against 6.2 m/s here. Per kW, solar panels would make about 1,174 kWh a year here against the turbine's 2,119, 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 6.2. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of IA
Marshall County is the 588th 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 Marshall County
April is the strongest month here, at 7.15 m/s and about 2,310 kWh. August is the weakest, 4.92 m/s and 1,019 kWh, so the best month makes 2.3 times the worst. November to March brings in 47% of the year's output in Marshall County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 6.59 m/s | 2,043 kWh | $297 |
| February | 6.60 m/s | 1,850 kWh | $269 |
| March | 6.80 m/s | 2,175 kWh | $316 |
| April | 7.15 m/s | 2,310 kWh | $336 |
| May | 6.44 m/s | 1,948 kWh | $283 |
| June | 5.62 m/s | 1,387 kWh | $202 |
| July | 4.92 m/s | 1,019 kWh | $148 |
| August | 4.92 m/s | 1,019 kWh | $148 |
| September | 5.86 m/s | 1,532 kWh | $223 |
| October | 6.46 m/s | 1,965 kWh | $286 |
| November | 6.66 m/s | 2,020 kWh | $294 |
| December | 6.42 m/s | 1,937 kWh | $282 |
What a taller tower would buy
Measured at 10 m the wind in Marshall County averages 4.84 m/s; at 50 m it is 6.95 m/s. That gives a shear exponent of 0.225, typical of ordinary open country. Going from 20 m to 50 m takes output from 17,164 to 26,685 kWh a year, 55% 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 | 5.66 m/s | 17,164 kWh | 40 years |
| 30 m | 6.2 m/s | 21,153 kWh | 33 years |
| 40 m | 6.61 m/s | 24,213 kWh | 28 years |
| 50 m | 6.95 m/s | 26,685 kWh | 26 years |
Counties around Marshall County
2 of the 6 closest counties are windier at turbine height; the windiest, Hardin County, averages 6.32 m/s.
- Tama County, IA: 6.18 m/s, 21,039 kWh, payback 33 years (23 mi)
- Story County, IA: 6.21 m/s, 21,262 kWh, payback 32 years (25 mi)
- Jasper County, IA: 6.07 m/s, 20,223 kWh, payback 34 years (25 mi)
- Grundy County, IA: 6.17 m/s, 20,965 kWh, payback 33 years (27 mi)
- Hardin County, IA: 6.32 m/s, 22,077 kWh, payback 31 years (28 mi)
- Poweshiek County, IA: 6.07 m/s, 20,223 kWh, payback 34 years (34 mi)
Sun versus wind in Marshall County
Marshall County gets 4.02 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,174 kWh a year; one kW of the turbine above makes 2,119. 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.