Wind Turbine Payback in Knox County, IL
Wind turbine payback in Knox 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 Knox County, IL averages 6.03 m/s (13.5 mph). A 10 kW turbine there would make about 19,926 kWh a year, worth $3,832 at IL's 19.23¢/kWh. Against an installed cost of about $100,000, that is a payback of 26 years, and the turbine is built to last about 20.
What to do in Knox County
A home turbine is not worth buying for savings in Knox County unless your spot is far windier than the county average, 6.8 m/s at the hub against 6.03 m/s here. Per kW, solar panels would make about 1,186 kWh a year here against the turbine's 1,993, so get a solar quote first.
What would have to change
- Power would have to cost 25¢/kWh, 1.3 times what IL pays now.
- Or the average wind at the hub would have to be 6.8 m/s instead of 6.03. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of IL
Knox County is the 791st windiest of 3,144 US counties at turbine height; the national middle is 4.79 m/s. The windiest in IL is Cook County at 6.73 m/s, payback 21 years.
Month by month in Knox County
April is the strongest month here, at 7.01 m/s and about 2,228 kWh. August is the weakest, 4.64 m/s and 866 kWh, so the best month makes 2.6 times the worst. November to March brings in 49% of the year's output in Knox County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 6.57 m/s | 2,033 kWh | $391 |
| February | 6.55 m/s | 1,826 kWh | $351 |
| March | 6.71 m/s | 2,116 kWh | $407 |
| April | 7.01 m/s | 2,228 kWh | $428 |
| May | 6.12 m/s | 1,748 kWh | $336 |
| June | 5.38 m/s | 1,247 kWh | $240 |
| July | 4.65 m/s | 870 kWh | $167 |
| August | 4.64 m/s | 866 kWh | $167 |
| September | 5.42 m/s | 1,273 kWh | $245 |
| October | 6.33 m/s | 1,882 kWh | $362 |
| November | 6.65 m/s | 2,016 kWh | $388 |
| December | 6.38 m/s | 1,916 kWh | $368 |
What a taller tower would buy
Measured at 10 m the wind in Knox County averages 4.7 m/s; at 50 m it is 6.77 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 16,027 to 25,384 kWh a year, 58% 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 | 5.5 m/s | 16,027 kWh | 32 years |
| 30 m | 6.03 m/s | 19,917 kWh | 26 years |
| 40 m | 6.44 m/s | 22,932 kWh | 23 years |
| 50 m | 6.77 m/s | 25,384 kWh | 21 years |
Counties around Knox County
None of the 6 closest counties is windier than Knox County.
- Warren County, IL: 6.02 m/s, 19,852 kWh, payback 26 years (22 mi)
- Stark County, IL: 6.03 m/s, 19,926 kWh, payback 26 years (25 mi)
- Peoria County, IL: 6.03 m/s, 19,926 kWh, payback 26 years (25 mi)
- Henry County, IL: 5.99 m/s, 19,630 kWh, payback 27 years (29 mi)
- Fulton County, IL: 5.94 m/s, 19,260 kWh, payback 27 years (32 mi)
- Mercer County, IL: 6.02 m/s, 19,852 kWh, payback 26 years (33 mi)
Sun versus wind in Knox County
Knox County gets 4.06 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,186 kWh a year; one kW of the turbine above makes 1,993. 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.