Spar, I put this 80 footer up because of our township's ordinance prohibiting towers with guy wires. I replaced a 72 foot tower that was originally designed as free-standing but for a smaller less powerful turbine. I had added guy wires to it for the larger machines. I submitted engineering specs and tower and foundation drawings for it when it was originally put up. But it was not "grandfathered in" by adding guy wires to it for a larger turbine.
I looked at various commercially available tower options, but virtually no tower manufacturer will supply an engineering approval to use their towers for wind turbines. And for good reason - most of them (aside from the Rohn SSV) are not suitable for wind turbines.
This tower is 460 lbs heavier than a Rohn SSV80, even though it uses the same basic design. Rohn will not allow more than a 5 foot mast on the SSV and that's because the top sections of the SSV are too light. For smaller wind turbines (3-5 meters) you need that mast to get blade tip clearance because the top of the lattice still forms an equilateral triangle with 24" sides. It would require a radical re-design of the turbine to get blade clearance, since my turbines do not have as much forward rotor lead as, say, a Bergey Excel. So I had to add extra iron to the tower, that a SSV does not have, to support that 8 foot mast. Most of that extra weight is in the columns, or legs. And I used 55 Kpsi mechanical tubing for the columns, where a SSV uses 33 Kpsi structural tubing.
This tower is designed and certified to meet Revision G, which now has 90 mph survival, 3 second gust, as the minimum requirement. It could handle a larger turbine than 3 kW rated output, but not at 80 feet height with the foundation it has, and definitely not with an 8 foot mast on it.
More and more townships are passing these tower ordinances, and almost all of them now require an engineering certification on the tower, and foundation approved by a state licensed engineer. And that certification is only good for one particular turbine - if you decide to throw a different turbine on it you have to go thru the entire process again, including FEA on the tower, and re-certify it. And to certify a tower for wind power, it requires certified loading data for the turbine, also done by a licensed engineer.
As I stated earlier, the old standby guyed pipe tower that most homebuilders use will eventually become a dinosaur. A good chunk of the $12,000 cost of this tower is in engineering work, and paperwork and drawings, that have to filed with the township, county and state to get it approved.
Experienced wind power people already know this, but for the newbies looking at wind power the tower is the single most expensive item involved with installing a wind power system.
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Chris
