Wind Turbine Payback in Knox County, TN
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, TN averages 3.36 m/s (7.5 mph). A 10 kW turbine there would make about 3,794 kWh a year, worth $524 at TN's 13.8¢/kWh. Against an installed cost of about $100,000, that is a payback of over 100 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, 8.4 m/s at the hub against 3.36 m/s here. Per kW, solar panels would make about 1,259 kWh a year here against the turbine's 379, so get a solar quote first.
What would have to change
- Power would have to cost 132¢/kWh, 9.5 times what TN pays now.
- Or the average wind at the hub would have to be 8.4 m/s instead of 3.36. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of TN
Knox County is the 2,665th windiest of 3,144 US counties at turbine height; the national middle is 4.79 m/s. The windiest in TN is Lake County at 5.54 m/s, payback 44 years.
Month by month in Knox County
March is the strongest month here, at 4.00 m/s and about 559 kWh. August is the weakest, 2.48 m/s and 111 kWh, so the best month makes 5.0 times the worst. November to March brings in 58% of the year's output in Knox County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 3.85 m/s | 497 kWh | $69 |
| February | 4.02 m/s | 514 kWh | $71 |
| March | 4.00 m/s | 559 kWh | $77 |
| April | 4.02 m/s | 551 kWh | $76 |
| May | 3.33 m/s | 314 kWh | $43 |
| June | 2.82 m/s | 172 kWh | $24 |
| July | 2.60 m/s | 133 kWh | $18 |
| August | 2.48 m/s | 111 kWh | $15 |
| September | 2.76 m/s | 160 kWh | $22 |
| October | 3.24 m/s | 287 kWh | $40 |
| November | 3.50 m/s | 356 kWh | $49 |
| December | 3.68 m/s | 430 kWh | $59 |
What a taller tower would buy
Measured at 10 m the wind in Knox County averages 2.26 m/s; at 50 m it is 4.04 m/s. That gives a shear exponent of 0.361, typical of rough, sheltered ground: trees or buildings slow the low wind a lot. Going from 20 m to 50 m takes output from 2,321 to 6,780 kWh a year, 192% 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 | 2.9 m/s | 2,321 kWh | over 100 years |
| 30 m | 3.36 m/s | 3,792 kWh | over 100 years |
| 40 m | 3.73 m/s | 5,285 kWh | over 100 years |
| 50 m | 4.04 m/s | 6,780 kWh | over 100 years |
Counties around Knox County
None of the 6 closest counties is windier than Knox County.
- Anderson County, TN: 3.05 m/s, 2,751 kWh, payback over 100 years (17 mi)
- Union County, TN: 3.14 m/s, 3,034 kWh, payback over 100 years (21 mi)
- Blount County, TN: 3.25 m/s, 3,402 kWh, payback over 100 years (21 mi)
- Sevier County, TN: 3.36 m/s, 3,794 kWh, payback over 100 years (27 mi)
- Loudon County, TN: 3.07 m/s, 2,813 kWh, payback over 100 years (28 mi)
- Jefferson County, TN: 3.36 m/s, 3,794 kWh, payback over 100 years (28 mi)
Sun versus wind in Knox County
Knox County gets 4.31 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,259 kWh a year; one kW of the turbine above makes 379. Kilowatt for kilowatt, panels make 3.3 times as much here as the turbine. 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.