Wind Turbine payback calculator for an irish back garden

| | Comments (4)
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.


4 Comments

colm mc grath said:

very interesting i had heard that windmills don't pay for themselves i was looking into buying one but with this kinda information i don't think i will bother

p.s.
well done it must have taken alot of time and effort to produce this information

Hi, Well done on the research - we need more of this.

I wonder if you tried plotting the shear using the calculator at http://www.windpower.org/en/tour/wres/calculat.htm - I can't do it without having some idea of the roughness class of your land, but it would be interesting to see how the plot using SEI's wind map figure of 6m/s at 50m and your roughness class and using the plot there to see how close that comes to your actual readings at 4m and your shear estimate at 10m?

I think most turbines with a 3m blade would have some control to prevent them giving over 5kw. This is always a design issue as the output really ramps up when you get above 11 or 12 m/sec, and most have an inverter that would blow a gasket if you sent 5kw down the line.

However, unless you live at a very windy site, the lost power from cutting out at 14 m/sec isn't that much, and your figures bear that out. Although the power output at 15m/sec at 5kw is very tempting, 117kwhr per year probably doesn't justify the cost of a larger inverter etc., especially if this additional power only brings in revenue at 9c / kwhr

Q

Cormac said:

Liam,
I have just read some of your earlier posts and have tried to follow through on your later ones.

The measurement of the wind speeds is something that i have wondered about.

One of the questions raised by Quentin in his post is the roughness class and i would also be interested in knowing what the local factors were. As you measured the wind at a height of only 4m it is likely that this would be significantly influenced by any obstructions. Where was your anemometer mounted?

As you say the local wind speed from the wind atlas is 6m/s @ 50m. Using the shear formula and a roughness class of 0.1 (Agricultural land with some houses and 8 metre tall sheltering hedgerows with a distance of approx. 500 metres) the wind speed at 10m is 4.446m/s and at 4m is 3.5615m/s.

Using a roughness of 0.4 the speeds further drop to 4m/s and 2.864m/s much closer to your measured 2.33m/s.

So it would be interesting to see what your opinion on the roughness of the location is and an actual description or sketch of the measurement set up.

A quick backward calc seems to say that your measured speed would mean the roughness class would be around 1.24 which would put it above an city centre figure!!

So, is it the maps, the measurment, the location? Or are we missing something...

Regardless well done on putting in the effort. Would be good to hear your thoughts on the above.

liam noonan said:

Hi Cormac,

Thanks for your comments.

You are right about the shear factor and this is something I am painfully aware off.

The issue I think is that the weather station was 30 meters from the house.

The idea behind the measuring was to assess if a windy back garden could support a wind turbine, local knowledge would say yes but measurement says no as the exact spot was not open to the winds from the south east to the north west.

Unfortunately our house blocks wind from the west and wind from the south west has to contend with a 8 metre house 80 meters away. There is a constant breeze/wind where we live but buildings do wreck havoc.

So even though its not the city centre the rule of thumb of being 20 times the height of your house away from a turbine does apply and make sense in this instance.

Regards

Liam

Leave a comment

About this Entry

This page contains a single entry by liam noonan published on April 27, 2009 1:53 PM.

Free PDF creation software for Windows was the previous entry in this blog.

Pay back time for Wind Turbines - show us the calculations is the next entry in this blog.

Find recent content on the main index or look in the archives to find all content.

Influenced by:

Irish Eyes
Jabit
Mike Maunsell
Buzzblog
Tom Raftery I.T. views
Damien Mulley
James Corbett (Eirepeneur)
Powered by Movable Type 4.12