Taking One to Texas

I have been meaning to write a blog entry about taking the wind turbine to Texas for a number of years now, but for some reason just haven’t set aside the time. It has sat nearly blank in my blogspot account for 3 years. But here it is…and I will try to keep it short, with it being father’s day and me wanting to spend some time with the kids and work on the aquaponics projects…

Back in October of 2011 I made a solo trip to Texas with one of the two 10 foot wind turbines. An old high school friend named Christian Seger, and wife Lisa, were interested in flying it at their goat farm in Hempstead called…

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It was very exciting for me because I knew Christian would make
it happen. Christian is definitely “smart and gets things done“, and getting the wind turbine completely set up on a tower would not be easy. And, all I wanted was to find the wind turbine a home where it would actually be able to fly. Well it is now June of 2014 and it is up and running! Better late than never Christian!!!  😉
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Back in 2011, I had disassembled the wind turbine in preparation for the journey to Texas. I laid it delicately next to me across the passenger seat of my crappy old 1999 Nissan Sentra. The pieces filled the entire car and gave me just enough room to change gears. I think the wind turbine was far more technologically advanced than my old car actually.

I hate driving, but the trip was not too bad. It was nice to have some time to think and listen to music that I hadn’t heard for years. I think I turned it into a three or four day trip and combined it with a few client visits. I can’t seem to go to Houston without doing some business.

It was a great trip because we turned it into a pretty big get-together at the farm and invited a bunch of mutual friends still living in Houston.

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Christian showed us the boat he is (was?) building from scratch! An awesome project indeed. I wonder if that project is complete now?

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And, we unloaded and setup the wind turbine in Christian’s garage. Nothing was damaged on the trip and it went together as expected.

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Anyway, it was a great trip. It was great to see everybody and hand off the wind turbine, but it went by too quickly.  Now tree years later Christian has it up on a tower…where it should be. I am looking forward to seeing video of it spinning and see it flying in person some day.

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I also can’t wait to hear all the details about building and setting up the tower, which is a really big job. Not only a big job but dangerous too.

This makes me want to pull wind turbine number 2 out of the garage and get it set up somewhere in the mountains of Colorado. Maybe someday soon!! I think this blog may have one more entry in it’s future before it gets shut down!!!

Carving Wooden Blades

I have been carving the blades for my second 10′ turbine over the summer. Wow this was really an interesting process and takes a lot of time to become good at it. You can mess up a blade in an instant if you are not careful. Here are a bunch of pictures of the process.

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You start with a set of blanks that you see above and end up with a complete set of blades mounted on a hub and ready to go. I still need to balance the blades on the actual wind turbine, but I can do that later.

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Powder Coating

I did a bit of research on how to best protect the steel parts from the elements. You can actually just leave the steel bare and let it rust. They say that it will not affect the performance in any way and will still last plenty long. Some people just spray the parts with a can of spray paint, and that prabably works fine too. Even better is to use these high quality industrial epoxy paints (like you find on street light poles), but I found from calling around that they were very toxic and expensive.

 

I think everyone would agree that the very best way to protect the steel parts is to have them powder coated, which is an electrically charged polyester powder that gets baked onto the steel at around 500 degrees. Anyway, I found a guy with rediculously good prices. He said he would powder coat 4 or 5 wind turbines for his minimum invoice amount of $100! That is half the price of doing the high end epoxy paint. So, I picked a textured green color and did both turines for this price…and he would have done like 5 or something for this price if I had that many! I went ahead and coated both turbines and they turned out great and look very professional. I am very pleased.
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One thing to remember next time is to make sure to have the steel disks for the magnet rotors powder coated before placing the magnets and resin on them. You can’t powder coat the finished magnet rotors because the resin would melt and the magnets would demagnetize from the high temperatures. So I decided to paint the magnet rotors using a steel primer and spray enamel paint. I think this will hold up fairly well for these parts.
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Building the Tower Stub Cont.

I was having a hard time finding bushings that fit the tower stub so I decided to make them myself out of plastic. I did a bit of research and found that people were using Ultra High Molecular Weight (UHMW) plastic for this type of thing. UHMW appears to have a very low friction coefficient and is much cheaper than nylon or any other exotic and more expensive plastic. I figured it would also do less damage to the tower stub and frame than bronze. Here are the specs on the thrust bearing and bushings…
Thrust Bearings:
– 1/4″ Thick UHMW polyethylene plastic
– 1-1/8″ hole saw for the inner diameter
– 2″ hole saw for the outer
Bushings:
– 1″ Thick UHMW polyethylene plastic
– 2″ hole saw for the inner
– 2-5/8″ hole saw for the outer
I’ll probably use two of the 1/4 thrust bearings on top so they can rub against each other and they should last longer that way. Hopefully there isn’t too little friction though using this plastic instead of bronze. I don’t want the wind turbine to jitter back and forth seeking the exact direction of the wind. The wind turbine will apparently produce more power if it yaws less and just points more into the predominant wind. We will just have to see. Also, I’ll probably put PVC between the three bushings in order to hold them in best position. I think this plastic should last a good long time…at least between yearly maintenance. Here are a few pictures…
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Wind Power Equations

I don’t want to spend too much time writing about the math used to analyze wind turbines because it is not very interesting for most people to read and it has already been done a million times for these 10′ turbines. I just think it will be interesting to see how these numbers will compare to the real world numbers that I get out of my turbines when they are finally flying. I’m not really a big math guy so keep me honest here if you see any mistakes.

Ok, it seems that the math for estimating the power output goes somehing like this. First you can figure out the total power available in the wind using the first formula below.

Pa = 0.5 x rho x A x V³

This is the power available to your wind turbine and is determined by the air density, size of the blades (swept area), and speed of the wind. Notice that increasing the swept area (A) and the wind speed (V³) create substantial increases in available power. You can’t change the wind density so forget about that variable (rho). Doubling the diameter of the blades (which increases the swept area according to the formula π ), will increase the power output by a factor of 4. Also,doubling the wind speed will increase the power output by a factor of 8. So, you can greatly increase the power output by making the blades really big and getting the wind turbine as high as possible, since the wind increases substantially with height above ground.

All the indented stuff below is taken from a discussion at http://www.awea.org/faq/windpower.html that was written by Eric Eggleston on February 5, 1998. He explains all of this by saying…

Power in the area swept by the wind turbine rotor:

Pa = 0.5 x rho x A x V³

Pa = power available in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
rho = air density (about 1.225 kg/m3 at sea level, less higher up; about 1 in Denver, Co)
A = rotor swept area, exposed to the wind (m2)
V = wind speed in meters/sec (20 mph = 9 m/s) (mph/2.24 = m/s)

This yields the power in a free flowing stream of wind. Of course, it is impossible to extract all the power from the wind because some flow must be maintained through the rotor (otherwise a brick wall would be a 100% efficient wind power extractor). So, we need to include some additional terms to get a practical equation for a wind turbine.

Wind Turbine Power:

P = 0.5 x rho x A x V³ x Cp x Ng x Nb

P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
rho = air density (about 1.225 kg/m3 at sea level, less higher up)
A = rotor swept area, exposed to the wind (m2)
V = wind speed in meters/sec (20 mph = 9 m/s)
Cp = Coefficient of performance (.59 {Betz limit} is the maximum thoretically possible, .35 for a good design)
Ng = generator efficiency (50% for car alternator, 80% or possibly more for a permanent magnet generator or grid-connected induction generator)
Nb = gearbox/bearings efficiency (depends, could be as high as 95% if good)

Notice from the equations above (the Cp or Coefficient of performance variable) where he says the maximum power that a wind turbine can theoretically generate is ~59% of what is available in the wind. This value is called the Betz limit and was discovered in 1919. Above this value the wind appearently backs up in front of the blades or goes around them and just can’t be converted into power. This is basically the efficiency limit of the wind turbine blades. Appearently, most well done homebrew wind turbines are doing very well if they to approach a 30% Cp, unlike some commercial turbines, which are getting much closer to the Betz limit (I’m not sure how close to 59% they are getting).

So from this discussion we are now able to figure out roughly what our power output will be if we build everything right on this wind turbine. It is important to point out though that you have to make sure to account for the loss of efficiency in the bearings and alternator, as well as the blades, which is where Cp, Ng, and Nb come from. From what I have read, it seems that the blades, bearings, and alternator all need to be very efficient to get even 30% overall efficiency and this is about where people say these 10′ homebrew wind turbines tend to run. The numbers I have used in the formulas below give it about 30% overall efficiency for this reason. I don’t really know exactly how efficient these individual values are in reality, but I think these are close. So the numbers for this wind turbine would look something like this…

P = power in watts
rho = 1.05 (density of air around denver, co)
A = 10 foot diameter (which equals 9.57 meters squared)
V = 10 miles per hour ( which is 4.47 meters per second)
Cp = 40% (so we have a very efficient rotor)
Ng = 80% (since we are using good quality bearings)
Nb = 95% (since we have a very efficient direct drive alternator)

P = 0.5 x rho x A x V³ x Cp x Ng x Nb
P = 1/2 x 1.05 x 9.57 x (4.47)³ x 0.40 x 0.80 X 0.95 = 136.41136.41 (watts in 10 mile/hour wind)
P = 1/2 x 1.05 x 9.57 x (6.71)³ x 0.40 x 0.80 X 0.95 = 461.44461.43 (watts in 15 mile/hour wind)
P = 1/2 x 1.05 x 9.57 x (8.94)³ x 0.40 x 0.80 X 0.95 = 1091.331091.33 (watts in 20 mile/hour wind)

Another helpful equation is one that helps you calculate the RPMs of your wind turbine at a given wind speed. You must be able to calculate RPMs over a range of wind speeds in order to build the alternator appropriately, so this is very important. The tip speed ratio (TSR) in the equation below is simply the ratio of the speed that the tip of the wind turbine blade is travelling divided by the wind speed.

Revolutions / Minute (RPM) = V x TSR x 60 / (6.28 x R)

V = Wind speed (m/s)
TSR = Tip Speed Ratio
R = Radius of rotor (meters)

So, for the 10′ turbines we will have…

V = Lets us 10 miles per hour, which is 4.47 meters per second
TSR = 6
R = We have 5 foot radius which is 1.52 meters

RPM = 4.47 x 6 x 60 / (6.28 x 1.52) = 168.58 (in 10 mile/hour wind)
RPM = 6.71 x 6 x 60 / (6.28 x 1.52) = 253.06 (in 15 mile/hour wind)
RPM = 8.94 x 6 x 60 / (6.28 x 1.52) = 337.16 (in 20 mile/hour wind)

Now you can compare these numbers to the real world power curve from the otherpower.com folks below. I believe this graph was produced from a real world test of their alternator performance, probably mounting it to a drill press or something. “Alternator 1″ below is the same alternator that I have built for these two turbines (using 2 x 1 x 1/2 inch magnets, 12” disks, and 140 turns of 17 gauge wire). Comparing the numbers we computed above, you can see that the numbers are a bit different but not too badly off. This approach would give us numbers within the relm of what the wind turbine will produce. I think the values drop off in this real world test primarily because the alternator becomes less efficient at higher RPMs. I guess you loose more power to friction in the bearings as well. Anyway, that is enough math…building the turbines is much more fun…

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Sustainable Living Festival 2009

Here are some pictures of the Rocky Mountain Sustainable Living Festival this past weekend. Wow, I had a great time! I signed up again for all 4 wind turbine building workshops hosted by the Otherpower.com guys. I wanted to take these classes again just to fill in the gaps in my knowledge. Last year I took all 4 classes but concentrated primarily on building the stator, magnet rotors, and assembly. Somehow I missed out almost completely on the blade carving. So, this time I spent almost the entire time carving the blades. It is really an art and requires a certain amount of guidance, so it was really great. I feel very confident now that I can carve some good blades for one or both of the turbines. I realized that I didn’t really have the knowledge or tools that I needed to do this before.
Anyway, here are some miscellaneous pictures from the two day event…
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Building the Tower Stub

Well I finally have a tower stub put together. This is the part that the wind turbine (the yaw bearing actually) slides over at the very top of the tower. The wind turbine needs to pivot or yaw in order to point towards the wind. You may be surprised to find out that people don’t often use ball bearings for this moving part. I assumed at first that pillow block bearing or something like that would be best, but not so. They mostly use this kind of tube over tube design with lots of axle greese and sometimes a bronze or plastic bushing between the steel tubes. It turns out this design will keep the metal parts lasting plenty long, and it is actually prefered because the added friction keeps the turbine from nervously jittering back and fourth to face the changing winds. This way the turbine appearently stays pointed in the direction of the prevailing winds and produces more power. I like this keep it simple stupid approach since it is cheap and extremely easy to build…sometimes it is better not to over engineer something simple that just works.

I decided to build my tower stub a bit different from the design in the Homebrew Wind Power book. Instead of simply sliding the yaw bearing over a 2 inch pipe with some grease, I decided to use a slightly smaller diameter tube so I can slide a bronze or plastic bushing down the entire length of the tower stub and place a bronze washer at the top.

Below you can see the 2 inch piece of tube I started with. The outer diameter is exactly 2 inches. Look how crazy thick the walls are on this tube!!! This is expensive tube that I found in the scrap yard for only 40 cents a pound. The yaw bearing would never wear through this even if there were no bushings. It took 15 minutes to make one cut of this tube with my new steel cut-off saw!!!!

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Anyway, I welded it to a 1/4 inch thick sqaure plate that can be bolted or welded to the top of the tower.

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Below is the steel cap I welded that slides over the top of the tower stub. You put this on after sliding a section of 2 inch bronze or plastic down the length of the tower stub. This keeps there from being any steel on steel contact down the vertical legnth of the yaw being. I am going to order a bronze bushing tonight that should fit just right. I am also ordering a bronze thrust bushing that sits on top of the steel cap and keeps there from being any steel on steel at the top of the yaw bearing.

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Above you can see the tower stub with a section of PVC and the steel cap. PVC was my first idea, but since I found a website you can order bronze from I have decided to use it.

When we are ready to set this thing up we will grease the entire tower stub, add the bushing, and finally slide the entire alternator assembly over the top. That is all there is to it. The grease and bushings will allow the wind turbine to spin around and face the wind.

I just ordered the bushing from the website below…

Vertical Bushing

Horizontal Bushing (Fluid Bearing)

Putting it all together

Take a look!!!! I put the first turbine together the other day in order to get a feel for how it will eventually look. It seems really big to me. I would not want to be in the way when it is spinning for sure. I definitely understand why this is not legal in the city…I would never put this up in my backyard. You could kill someone.
In these pictures it is assembled with the fiberglass blades that I ordered a while back, which actually put it at 9 1/2 feet in diameter. I have started carving a set of wooded blades according to the Homebrew Wind Power book design. These new blades will be 10 feet in diameter and will prabably perform much better. I was disappointed that the blades seemed very heavy and unbalanced. I am guessing that the extra weight and the smaller angle of attack will make it much harder to start up and get to cutin speed. I will give them a try but am not too hopeful.
Anyway, the wood parts still need to be coated with linseed oil and the metal parts still need to be protected. I am thinking about powder coating the steel since I found someone that will help me get a discount on this process. We will see if that actually makes it affordable. It is getting really close and I can’t wait to get her flying and tested.
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Shout out to my peeps!

So I realize that this blog has been just a bunch of dry boring technical wind turbine stuff. So far I have just been documenting the technical side of this experience? I have worked really hard to figure out how to build these turbines and to truly understand how they work. It has been much harder and taken much longer than I thought it would, but very rewarding too. I tend to get so obsseded with projects that I often just don’t even come up for air. I am a bit idealistic and detail oriented and sometimes just want to see it through at any cost. Anyway, the point is that I am embarassed because I have not given any “props” to a few people that have supported me on this project regardless of how silly it seems…

My investor, “Mommy 2.0” down in Texas, was kind enough to sponsor the building of 2 of these 10 foot wind turbines and I would like to thank her greatly for that. I can’t wait to have these turbines perfected and set one of them up on her land. Hopefully it will even be cost effective to set it up as a grid-tie system and watch her meter run backwards! I hope it will pay her back many times over in the long run. I thank her for being patient too since this is taking longer than I had hoped.

I also want to thank Heather for putting up with my S#*@. I have turned the entire garage into a workshop…the garage is no longer for cars and Heather has not been happy with this situation. I have spent a small fortune on tools and supplies and that just ain’t cool either. Heather has been more understanding than I could have imagined. I am glad that Heather is a knitter and not a wind turbine builder! Cloth is way cheaper than steel and copper.

Thanks to Kelly as well for helping me to put together a shop full of tools. The welder has worked great! You have also been helpful with some of the design issues.

Ok, so enough mushy stuff, I want to talk about metal, plastic, and things spinning really fast! I am starting to build the second 10′ turbine now and should have it done much more quickly than the first. I haven’t quite finished the first one yet, but it is getting very close. This way I can get some things done on the second one while I am waiting for parts for the first one in the mail and stuff like that. I think the second one will be of better quality since I am learning from my mistakes. There are a few little things I will do differently this time around that should speed up the process and simply make better, more efficient wind turbine.

I am really looking forward to getting these wind turbines up in the air and start testing them out. I will need to really start thinking about how best to measure and log the output from these things. This will be a whole new project in and of itself.

So What is Left?

It has been a little while since my last wind turbine post because we have been working on the house a bunch lately…mostly landscaping the front yard. I should be able to get back to work on the turbine here again soon. I ‘ve been thinking about what I have left to do though and it is not that much really.
I ‘ve been thinking about where I can set this turbine up in order to test it. We have been thinking it would be nice to fly it at a friends house in Toas but that is not looking like such a good option now. His off-grid system is a bit small and a different voltage from the 10’ turbine stator. I built this wind turbine for a 48 volt system, which has become kind of the standard for battery banks. My friends batteries are wired for 12 volts. Down the road, when I have the building of this type of turbine down, I would like to look for a small piece of land and use this turbine to power a small cabin on it. But, right now I just need a place, prefereably near by, to test it out and make sure that this design actually works well.
Anyway, here is my list of things I have left to do on the first turbine…
1. Finish the tower stub. The stub needs to be cut to size, reinforced at the bottom, and cleaned up since it is very rusty. I might as well go ahead and build the tower stub for the second wind turbine while I’m at it. I also need to order a few bronze or plastic bushings for the yaw bearing. I think the sides of the tower stub will be covered with a piece of 2 inch PVC to protect the steel along the sides of the tower stub. I’m not sure this is the best material for a side bushing, but will give it a try.
2. Put a couple of layers of boiled linseed oil on the wooden parts of the blade assembly and tail. I also need to quickly make sure the blade assembly actually fits on the alternator. I think the 1/2 inch stainless threaded rod is plenty long but need to double check. I used 3/4 inch disks instead of 1/2 inch so it might be tight.
3. Order flat plastic stock for building a new stator mold. I need another one for building the stator for the second 10′ turbine. I need 2 pieces of 18″ squares of plastic that are 1/2 inch thick.
4. Test alternator RPMs using the new laser tachometer. I quickly tested it out and it looks like the cutin is at 130 RPMs for 48 volts. This is already a bit under the RPMs that the Homebrew Wind Turbine book says it should be. The shorter blades will probably cause it to hit this RPM too quickly. Perhaps I will add washers to increase the air gap distance in the alternator. I think the air gap will need to be larger since the blades I am using are shorter. If the alternator over powers the blades then it will not spin up fast enough to avoid stalling in low winds.
5. Finally, I need to figure out the best way to protect the steel parts. I would like to powder coat the entire thing, but I hear that is very expensive. I will call around but it is probably cost prohibitive. So perhaps I will try to call some automotive body shops and see if they can paint it for cheap using the last bit of paint from a run. If I can’t find someone else to paint it I will just paint it myself with steel etching primer and acrylic enamel paint.
Also, here are a few posts on the www.fieldlines.com discussion forum that I posted in the last couple of weeks or so…
Cheers