A good (hopefully, time will tell) tower for the 17 foot diameter wind turbine is very similar to the one we built for the 20 foot diameter wind turbine that powers our shop. The tower we'll discuss on this page is 64 feet tall, made from 10 inch diameter 12 gage steel tubing. It's important to note the difference between tubing, and pipe. Pipe is measured by inside diameter, tubing is measured by outside diameter. Pipe normally comes in 21 foot lengths, tubing normally comes in 20 foot lengths. Seamless 10 inch diameter pipe will fit tightly over 10 inch diameter tubing of any gage. The tower and its couplers are all built from tubing. The base, tower top and the end of the jin pole utilize pipe that the tubing slips into. Pictured above are 5, 20 foot sections of 10 inch tubing. The tower will utilize 3 pieces of tubing (60 feet) and the gin pole will utilize 34 feet of tubing. The remainder of the tubing is to be used for couplers.
The base of the tower is fabricated from angle iron and pipe. The gin pole and the tower will slip into the 10 inch diameter pipe, which is welded to a pivot so the tower can tip up and down. The whole tower will pivot on a 3 inch piece of pipe (the axis) and the 'bearing' is 4 inch diameter pipe. We don't want a 'tight' fit in the bearing. Since the base could never hold the tower up without guy wires, we like to have a good bit of play in the pivot. 4 inch pipe over 3 pipe works nicely in this application. The whole base is about 3 feet square.
The tower stub (this is the part that the wind turbine fits onto) is also built from pipe. The bottom part is 12 inches long, made from 10 inch diameter sched. 40 seamless pipe and it fits tightly over the tubing from which the tower is fabricated. On top of the 10 inch pipe we weld a 12 inch steel disk (cut from 1/4 inch steel). On top of that we weld the stub which is 40 inches long and made from 3 inch schedule 40 pipe. The yaw bearing for the wind turbine is 4 inch pipe and the fit between it and the 3 inch pipe is very loose. To take up slack we heat, hammer and weld 1 inch x 1/4 inch thick bar stock around the 3 inch pipe and grind it so the fit is good. There is not much slop, but the wind turbine turns freely on it. On top of the tower stub we weld a ring 3 inches outer diameter (this just fits inside the 3 inch pipe) and 1.75 inch inner diameter. This gives some surface area at the top and acts as somewhat of a bushing. Without this, in a short time the tower stub would wear into the top of the yaw bearing. That could make it hard for the machine to yaw and - even worse - furl.
Pictured above are the tower couplers. They're all the same, except the ones for the tower also have guy wire anchors. Two for the tower, one for the gin pole. They're each 2 feet long. We split the 10 inch tubing and weld bar stock to it with holes drilled so that they can be tightly clamped around the tubing with 3/8 inch bolts. The guy wire anchors are each basically just 2 triangles cut from 1/4 inch steel with 3/8 inch holes so that the guy wire loops around a 3/8 inch bolt. In the picture above the guy wire anchors have not been fabricated yet.
The picture above shows detail of the guy wire anchors welded to a coupler for my 20 foot diameter turbine.
Other stuff is required for the installation. In this installation we needed 75 feet of flexible stranded 8-3 (#8 AWG wire, 3 strands) to come down the tower.
We have 3 strands of #4 AWG wire, each 300 feet long to get from the tower base to the rectifier which is inside the house.
For tower anchors we built one dead man (a big heavy thing buried 4 feet under the ground) on one side, and the other 3 sides we were lucky to have solid granite. Into the granite we drilled 1 inch diameter holes 12 inches deep and used 1 inch diameter expansion bolts.
For the top guy wires we used 3/8 inch cable, we got two rolls, 360 feet. We also use 3/8 inch cable to pull the tower up with - which is why so much is required.
For the bottom guy wires we used 1/4 inch cable, 180 feet
8 turn buckles are required for this tower. For the top we used 5/8 inch / 12 inch jaw and eye drop forged turn buckles, qty 4. For the bottom we used 1/2 inch / 9 inch jaw and eye drop forged turnbuckles. Jaw and eye turn buckles are handy, as you can disconnect them with 1 bolt.
Turnbuckles with loops are also OK - slightly less convenient though. Never use turn buckles with hooks.
Of course every loop in the cable should have a thimble, so we need 8 3/8 inch thimbles and 8 1/4 inch thimbles.
We require 30, 3/8 inch cable clamps, 24 for the tower, 6 for the cable we pull it up with. (every loop in the cable should have 3 cable clamps)
24, 1/4 inch cable clamps are required for the lower guy wires.
Shackles are handy for connecting the turn buckles to the ground anchors, so we got 10, 1/2 inch shackles.
We leveled the base and put it in position, and pinned it to the ground. The ground is hard here, but I'd have rather seen concrete poured first and a nice level pad. Instead - (not pictured) we welded lots of re-bar to the base and poured concrete around it after the fact. Once the tower base is positioned we assemble the gin pole.
Pictured above is the coupler on the gin pole. This couples a 20 foot piece of tubing to a 14 foot piece, the overall length of the gin pole is 34 feet which is also the distance away from the base that the guy wire anchors are.
The end of the gin pole has accommodation for two guy wires to be anchored, and a large pulley at the end. The cable we use to pull the tower up with will be anchored right beneath the end in granite, go through the pulley at the end of the gin pole, back down to the ground (also very near the end of the gin pole) through another pulley - and then to whatever vehicle (in this case a small bull dozer) we use to pull the tower up. I prefer to use a permanently mounted winch but in this case... we used a bull dozer. A large truck with low gears would also work fine. When using a vehicle to pull a tower up it's important that it be facing the tower so that the driver can see what's going on and see hand signals from helpers.
Once the gin pole is assembled, it should be guyed -- just like the tower, so that it cannot fall over. The guy wires that go from the gin pole to the tower should also be attached with turnbuckles (once the jin pole is raised it's too late!) Often times a temporary gin pole should be built to raise the real gin pole.
In this case we used a backhoe to pull the gin pole up. Once the gin pole is raised we can start building the tower.
Always test raise the tower before putting anything on it. At the top of the tower (along with the top guy wires) we've attached a rope.
When raising, people need to pull on the rope as the tower gets nearly erect to overcome the weight of the gin pole, otherwise it will up so high and then the gin pole will 'fall' to the ground making for a rather violent erection. The test raise is always a bit scary. We try to figure our guy wire lengths as accurately as possible but usually we cut/adjust them so the tower is slack on the first raise, and some adjustment is necessary. This is also a good time to mention that a towers guy wires should *always* tighten as it goes up and slack a bit when it goes down. This is accomplished by putting the side anchors a small distance (in this case about 6 inches) in front of the tower (in the direction it the tower tips)
On the first test raise it's important to get the tower plumb, and get the cables properly adjusted. After that, assuming it does slack on the way down as it should, it should work well and always come back up into adjustment.
Pictured above is detail of the gin pole while raising the tower. If you look closely you can see a bulldozer in the background. You can see how the cable we pull it up with comes from the ground, through a pulley at the end of the gin pole, back down to the ground through another pulley and then to the tractor.
Once the tower is finished we assemble the machine on it, hook up the wires and balance the blades. For a large machine like this it's handy to have a ladder (or stand in the back of a pickup truck) for blade balancing. You need to balance the blades on a calm day, as too much wind will make it difficult or impossible.
Very carefully and slowly raise the tower and hope for the best! Be sure during raising that the turbine is shorted out (the stop switch is 'on') so it can't start running during the process.
This time we had a few folks pulling on the rope to overcome the weight of the gin pole.
Usually when you raise a wind turbine you stop all the wind sometimes for weeks. This time, it was a windy day and it started up immediately, making over 3kW and furling a bit.
The system featured in these last few pages probably cost about $2500 for the turbine itself, and about the same for the tower - so $5000 over all and a lot of hours. Well worth it I think!
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