Projected Numbers?

[Hoskald]

As I begin planning my turbine, I was wondering that if those more expereniced could look over my numbers and see if they are kosher...

My first shot was with Betz at 20% but I am thinking this is too high, am I correct? My next plan was with 15%...but at 20% I still show a small surplus.  I have pulled the last four years of data from NOAA for the site closest  to the build site (60 miles West) and these are numbers I came up with:

With an anualized wind average of 11.2 mph, assuming a 75' tower, 20% efficiency a ten foot rotor would just cover our estimated 6000 KW/year (7997.9 KWH from the spreadsheet).

On my 4 year average wind speeds for this area I see that Aug is the only bad month with a speed of 8.6 mph.  Not too much there to play with!

Do these numbers look close to the mark for a homemade turbine? I had to make a few assumptions...

Thoughts?

Thanks,

Hos

[wdyasq]

Hos,

You need to look a bit more about the wind speed distribution and if you are in a 'hidden' area, a spot where it will get less wind. You may be on a small ridge and get more. As I left my clairvoyancy cap at the cafe this morning, I'm just not sure.

The closest data to my area shows 12mph 'on the ridges' and 8 mph every where else. Just using those 'yearly agerage' numbers there is over 3 times the power in 12 mph wind as there is in 8 mph wind.

The wind distribution goes something like this; the wind blows at 20 mph for 6 hours a day then dies or it blows 5 mph for 24 hours. Both show 5 mph average. The 20mph x 6 hours has 3.2 times the energy.

6000kWh/year is ~16.5 kWh/day. It requires about 1/2 of that to run a refrigerator and small freezer. I have no idea of your lifestyle or if your figures are even close to correct.

Have fun,

Ron

[The Crazy Noob]

Wow, our freezer and fridge combined only use like 3-4 kWh/day and I tought that that was a lot!

[Flux]

I am not sure how relevant wind data from 60 miles away is. Local factors could make it drastically different.

You are not likely to change Betz limit, I am not sure if your 20% is 20% of Betz or a Cp of 20%. You are not likely to achieve a Cp of more than 20% over much of the range.

Even so your figure seems high.

I tried 11 mph into Michael Klemen's table for a good turbine, which is better than anything you are likely to get.

11mph is 2.67 kWH per month per square foot. 10 ft dia is 78.5 sq ft.

giving 209.6 kWH per month.  Per year you have  2515 kWH. Assuming the standard measuring height is 30 ft and you are working at 75 ft you will do better, but as the figures are optimistically high to start with, probably not much better.

Local wind conditions could throw this way out. If your life depends on it you should have done 5 years of wind survey at your site.

Michael Klemen's figures are based on a Rayleigh distribution, you may not have that but you will never know without extensive measurement.

Flux

[Hoskald]

I thought they seemed high as well.  That is why I wanted others to look at them. I understand that wind data from 60 miles isn't a true indication of wind at the site, but it is a general reference to the trend of wind in this area and it gives me something to start with that isn't totally guesswork. Looking at the wind trend data from several points, I think the variation could well be +/- 20% not counting the imediate terrain.

Your numbers are more in line with what I expected. The spread sheet that I used is percent of Betz if I am reading the formula correctly.  

Since no ones life is at stake, and that this is mostly for my entertainment (grid power will be available to us) and the fact that we have not yet taken possession of the land extensive site measurements aren't required (they would be nice, and once we have possession we intend to start monitoring the local wind).

Thanks for info!  

Hos

[Flux]

I have just checked and Michael Klemen's figures are based on 35% of Betz.

I am not sure why the spreadsheet you used is giving such high figures for 20% of Betz.

I trust Klemen's figures and most sites do get close to a Rayleigh distribution.

Be interesting to see how your real wind compares with the recorded site. Best to be realistic for a start and be pleased when you get better than expected.

Flux

[Hoskald]

Ron,

JUst an FYI...

we currently live in a very energy inefficent home (all eletric) and removing the  A/C load and the water heater, we use 600 KWh per month now...and that includes a large fridge and freezer.  Unlike most people I guess we don't use a lot of juice. When we move into the new home, we intend on replacing most of the applicances with efficent ones, so I think that 500KW is good for us.

Cheers,

Hos

[drober23]

That was my spreadsheet.  I don't claim to be an expert, so I'm open to constructive criticism on the sheet.  Here it is for those not familiar with it.

Wind Power Calcs.xls

I did not see anything like it on this site, so I worked it up.  It has two parts.  One part is to figure out how much power a commercial unit will deliver.  This was easy to figure, since the manufacturer's power curve tells you how much power it delivers at a given wind speed.

I tried a second sheet for homebrew machines.  It attempts to use a percentage of the Betz limit to figure how much power the machine would produce at any given average wind speed.  It is possible that I borked up the power calculations here.

The calculations use the Rayleigh distribution to estimate how much time the wind blows at any given speed based on the average windspeed entered.  It also factors in the height and terrain.

The home brew sheet includes a cut in speed and a furling speed.  It then discounts any potential energy from wind below the cut in and over the furling speeds.

I will review the formulas I used to put it together.  I certainly don't want to mislead folks into over-optimistic power projections.  If those who commented on the numbers could take a look at the sheet I would appreciate any feedback.

The benchmark of 35% of Betz limit for a 'good machine' is good information already!

DJ Roberts

[elt]

I've noticed that I have to put efficiency numbers like 6% to 10% in to get the power output reported for Hugh's axial flux machines. Also, when I double the rotor size, I see double the power; shouldn't it show four times the power?

- Ed.