JAK
12-06-2006, 07:52 AM
A couple of weekends past I helped raise a 200' NRG met tower in a wooded area. It made me think about the economics of masts for smaller wind turbines. How much do they weight and cost as a function of height and generator weight? How tall should they be for a given generator and wind regime? I am going to add to this post as I figure stuff out. Feel free to chime in. By small wind turbine I mean a total capital cost under $10,000 including batteries, mast, generator, and blades, with a hopes to generate an average of as much as 1kw.
Initial thoughts:
1. In wooded areas there is high average wind shear, so you really need a good hill, and I think you would need to give it a good haircut, enough so that there are no trees tops above the base of the mast. You could still grow blueberries and perhaps firewood using the coppice method.
2. There will be an optimal mast height for a project. This should be higher for larger turbines. As a rule the mast might be half the cost of the project, but this is something I want to examine more closely. In wooded areas the mast I think the mast should be taller and cost relatively more than in smoother terrain, because of the higher wind shear.
3. In northern regions icing is a serious issue. In any region extreme winds can be an issue. For those reasons, and for maintenance purposes, it would be useful if a mast can be raised and lowered by one person once it is up. This might change the way a mast should be guyed. The four corners and gin-pole approach is still a good one, but the business of transfering the guy wires to and from the gin pole can get tricky. It might make sense to have a somewhat modified gin-pole method with a more permamant gin-pole and dedicated guy wires, or perhaps even some sort of hybrid fixed tripod mast for the bottom 20-40 feet, that also serves as a gin pole for the top mast.
4. Given a 20-30 year lifespan for such a tower, aluminum pipe might be cheaper than steel pipe by the time you include corrosion protection and so forth, but you would need to insulate between steel and aluminum parts.
Initial thoughts:
1. In wooded areas there is high average wind shear, so you really need a good hill, and I think you would need to give it a good haircut, enough so that there are no trees tops above the base of the mast. You could still grow blueberries and perhaps firewood using the coppice method.
2. There will be an optimal mast height for a project. This should be higher for larger turbines. As a rule the mast might be half the cost of the project, but this is something I want to examine more closely. In wooded areas the mast I think the mast should be taller and cost relatively more than in smoother terrain, because of the higher wind shear.
3. In northern regions icing is a serious issue. In any region extreme winds can be an issue. For those reasons, and for maintenance purposes, it would be useful if a mast can be raised and lowered by one person once it is up. This might change the way a mast should be guyed. The four corners and gin-pole approach is still a good one, but the business of transfering the guy wires to and from the gin pole can get tricky. It might make sense to have a somewhat modified gin-pole method with a more permamant gin-pole and dedicated guy wires, or perhaps even some sort of hybrid fixed tripod mast for the bottom 20-40 feet, that also serves as a gin pole for the top mast.
4. Given a 20-30 year lifespan for such a tower, aluminum pipe might be cheaper than steel pipe by the time you include corrosion protection and so forth, but you would need to insulate between steel and aluminum parts.