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Wind Turbine payback calculator for an irish back garden

wind_speed_upperchurch.jpg
I have recently measured wind speed in my back garden for 1 year from April 23rd 2008 to April 23rd 2009 at 4 m. We live in Upperchurch in Co. Tipperary and the area would be considerd by locals and visitors a windy place all year round, and bleak spot in the winter.

I then applied a scaling factor of 0.61 (i.e. divide the reading by 0.61) to bring the wind speed up to 10 m height this figure was based on data provided by http://www.sustainability.ie/microwind.html and had a higher shear factor than RETscreen recommended i.e. I was generous in my estimation.

Accorrding to the wind maps the wind speeds for Upperchurch are 6 – 6.25 m/s at 50 meters. At 10 meters my average measured wind speed was 3.83 ms (this is upscaled) the measurement at 4 meters was 2.3363 m/s .

Number of hours for each wind speed were as follows.

April 23 2008 – April 23 2009 extimated wind
speed at 10 meters height
m/s Hours
0 1261.833
1 747.4167
2 890.8333
3 1443.333
4 1395
5 1040.583
6 393.4167
7 597.5833
8 390.75
9 243.9167
10 84.91667
11 110.9167
12 75.16667
13 40.91667
14 23.25
15 20.16667

Using Mike Sagrillos Wind Swept Area Calculations I generated a payback table based on wind turbine diameter only I calculated the income that would be generated from selling back to the grid. The first 3,000 KW hrs are priced at 19 cents and the remainder at 9 cents.

The results are as follows:

Diameter
(meters)
Turbine Output at 10m/s Kw Hrs Income
2 0.77 1159 220
2.2 0.93 1402 266
2.4 1.1 1669 317
2.6 1.3 1958 372
2.8 1.5 2271 431
3 1.7 2608 495
3.2 1.96 2967 563
3.4 2.2 3349 601
3.6 2.48 3755 638
3.8 2.78 4184 676
4 3 4636 717
4.2 3.4 5111 760
4.4 3.38 5111 804
4.6 4 6131 851
4.8 4.4 6676 900
5 4.8 7244 952
5.2 5.18 7835 1005
5.4 5.59 8450 1060
5.6 6.02 9087 1117
5.8 6.45 9784 1177
6 6.9 10432 1238

These figures should help you to estimate the payback time. Look up the turbine’s diameter and look across to the income.

A breakdown for a 3 meter radius turbine is provided below

3 meter radius turbine
Rotor M Rotor feet m/s mph Power (kW) Hrs Energy (kWh)
3 10 3 6.75 0.046624 1443.333 67.29332
3 10 4 9 0.110515 1395 154.1685
3 10 5 11.25 0.21585 1040.583 224.6096
3 10 6 13.5 0.372988 393.4167 146.7398
3 10 7 15.75 0.592292 597.5833 353.9436
3 10 8 18 0.884121 390.75 345.4701
3 10 9 20.25 1.258836 243.9167 307.051
3 10 10 22.5 1.726798 84.91667 146.6339
3 10 11 24.75 2.298368 110.9167 254.9273
3 10 12 27 2.983907 75.16667 224.2903
3 10 13 29.25 3.793775 40.91667 155.2286
3 10 14 31.5 4.738334 23.25 110.1663
3 10 15 33.75 5.827943 20.16667 117.5302
Total Kw  2608.053
Income 495.53

If you are interested in learning some more on Wind Energy, you might consider reading this book.