Wind Turbine Payback in Coffee County, TN
Wind turbine payback in Coffee 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 Coffee County, TN averages 4.2 m/s (9.4 mph). A 10 kW turbine there would make about 7,623 kWh a year, worth $1,052 at TN's 13.8¢/kWh. Against an installed cost of about $100,000, that is a payback of 95 years, and the turbine is built to last about 20.
What to do in Coffee County
A home turbine is not worth buying for savings in Coffee County unless your spot is far windier than the county average, 8.4 m/s at the hub against 4.2 m/s here. Per kW, solar panels would make about 1,261 kWh a year here against the turbine's 762, so get a solar quote first.
What would have to change
- Power would have to cost 66¢/kWh, 4.8 times what TN pays now.
- Or the average wind at the hub would have to be 8.4 m/s instead of 4.2. A taller tower or an exposed ridge can add some of that; a rooftop never will.
Against the rest of TN
Coffee County is the 1,951st 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 Coffee County
March is the strongest month here, at 5.03 m/s and about 1,081 kWh. July is the weakest, 3.01 m/s and 223 kWh, so the best month makes 4.8 times the worst. November to March brings in 58% of the year's output in Coffee County.
| Month | Wind at 30 m | Output | Worth |
|---|---|---|---|
| January | 4.89 m/s | 1,003 kWh | $138 |
| February | 5.04 m/s | 981 kWh | $135 |
| March | 5.03 m/s | 1,081 kWh | $149 |
| April | 4.98 m/s | 1,018 kWh | $140 |
| May | 4.07 m/s | 591 kWh | $82 |
| June | 3.38 m/s | 319 kWh | $44 |
| July | 3.01 m/s | 223 kWh | $31 |
| August | 3.10 m/s | 247 kWh | $34 |
| September | 3.58 m/s | 382 kWh | $53 |
| October | 4.13 m/s | 617 kWh | $85 |
| November | 4.58 m/s | 806 kWh | $111 |
| December | 4.72 m/s | 909 kWh | $125 |
What a taller tower would buy
Measured at 10 m the wind in Coffee County averages 2.98 m/s; at 50 m it is 4.93 m/s. That gives a shear exponent of 0.313, typical of rough, sheltered ground: trees or buildings slow the low wind a lot. Going from 20 m to 50 m takes output from 5,168 to 12,065 kWh a year, 133% 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 | 3.7 m/s | 5,168 kWh | over 100 years |
| 30 m | 4.2 m/s | 7,632 kWh | 95 years |
| 40 m | 4.6 m/s | 9,931 kWh | 73 years |
| 50 m | 4.93 m/s | 12,065 kWh | 60 years |
Counties around Coffee County
1 of the 6 closest counties is windier at turbine height; the windiest, Cannon County, averages 4.35 m/s.
- Moore County, TN: 4.2 m/s, 7,623 kWh, payback 95 years (21 mi)
- Warren County, TN: 3.42 m/s, 4,018 kWh, payback over 100 years (21 mi)
- Bedford County, TN: 4.2 m/s, 7,623 kWh, payback 95 years (21 mi)
- Grundy County, TN: 3.42 m/s, 4,018 kWh, payback over 100 years (22 mi)
- Cannon County, TN: 4.35 m/s, 8,460 kWh, payback 86 years (22 mi)
- Franklin County, TN: 3.8 m/s, 5,614 kWh, payback over 100 years (23 mi)
Sun versus wind in Coffee County
Coffee County gets 4.32 kWh of sunshine per square metre a day on average. One kW of solar panels here would make roughly 1,261 kWh a year; one kW of the turbine above makes 762. Kilowatt for kilowatt, panels make 1.7 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.