Wind Turbine Payback in Sully County, SD
Wind turbine payback in Sully 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 Sully County, SD averages 6.35 m/s (14.2 mph). A 10 kW turbine there would make about 22,299 kWh a year, worth $3,251 at SD's 14.58¢/kWh. Against an installed cost of about $100,000, that is a payback of 31 years, and the turbine is built to last about 20.
What to do in Sully County
A home turbine is not worth buying for savings in Sully County unless your spot is far windier than the county average, 8.1 m/s at the hub against 6.35 m/s here. Per kW, solar panels would make about 1,221 kWh a year here against the turbine's 2,230, so get a solar quote first.
What would have to change
- Power would have to cost 22¢/kWh, 1.5 times what SD pays now.
- Or the average wind at the hub would have to be 8.1 m/s instead of 6.35. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of SD
Sully County is the 402nd windiest of 3,144 US counties at turbine height; the national middle is 4.79 m/s. The windiest in SD is Todd County at 6.77 m/s, payback 27 years.
Month by month in Sully County
April is the strongest month here, at 6.89 m/s and about 2,160 kWh. July is the weakest, 5.73 m/s and 1,507 kWh, so the best month makes 1.4 times the worst. November to March brings in 42% of the year's output in Sully County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 6.41 m/s | 1,930 kWh | $281 |
| February | 6.13 m/s | 1,585 kWh | $231 |
| March | 6.62 m/s | 2,065 kWh | $301 |
| April | 6.89 m/s | 2,160 kWh | $315 |
| May | 6.62 m/s | 2,065 kWh | $301 |
| June | 6.09 m/s | 1,676 kWh | $244 |
| July | 5.73 m/s | 1,507 kWh | $220 |
| August | 5.78 m/s | 1,535 kWh | $224 |
| September | 6.51 m/s | 1,928 kWh | $281 |
| October | 6.78 m/s | 2,160 kWh | $315 |
| November | 6.40 m/s | 1,863 kWh | $272 |
| December | 6.27 m/s | 1,846 kWh | $269 |
What a taller tower would buy
Measured at 10 m the wind in Sully County averages 5.05 m/s; at 50 m it is 7.07 m/s. That gives a shear exponent of 0.209, typical of ordinary open country. Going from 20 m to 50 m takes output from 18,505 to 27,542 kWh a year, 49% 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 | 5.84 m/s | 18,505 kWh | 37 years |
| 30 m | 6.35 m/s | 22,329 kWh | 31 years |
| 40 m | 6.75 m/s | 25,223 kWh | 27 years |
| 50 m | 7.07 m/s | 27,542 kWh | 25 years |
Counties around Sully County
4 of the 6 closest counties are windier at turbine height; the windiest, Walworth County, averages 6.51 m/s.
- Potter County, SD: 6.43 m/s, 22,891 kWh, payback 30 years (24 mi)
- Hughes County, SD: 6.35 m/s, 22,299 kWh, payback 31 years (25 mi)
- Hyde County, SD: 6.4 m/s, 22,669 kWh, payback 30 years (35 mi)
- Stanley County, SD: 6.31 m/s, 22,003 kWh, payback 31 years (37 mi)
- Dewey County, SD: 6.39 m/s, 22,595 kWh, payback 30 years (45 mi)
- Walworth County, SD: 6.51 m/s, 23,481 kWh, payback 29 years (49 mi)
Sun versus wind in Sully County
Sully County gets 4.18 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,221 kWh a year; one kW of the turbine above makes 2,230. 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.