What are the two basic types of towers for wind turbines?

There are two basic types of towers for wind turbines:

Fixed – The kind you have to climb. If you (or a friend, or a professional wind turbine installer) don't mind high climbing and know the necessary safety precautions, harnesses, and knots, a lattice tower with 3 guy wires can be very cost effective.

The tower sections, and finally the wind turbine, are raised one at a time using a gin pole and davit, or the whole thing at once with a crane. Lattice tower sections are often available used or as surplus. Freestanding, fixed towers are more expensive:

wider at the base and narrow up towards the top, but they need no guy wires. At very steep, craggy or tree-filled sites, fixed and freestanding towers have the advantage that a much smaller ‘footprint’ of level ground free of trees is needed.

Tilt-up – This is a great alternative for non-climbers, though it is often more expensive. A tilt-up tower has the big advantage that you can do all your adjustment and maintenance to the turbine while its on the ground, instead of while you are hanging from the tower top. It also uses a ‘gin pole’ to raise it, but in this case the gin pole is a lever arm that stands straight up when the tower is down, and lays along the ground when the tower is up.

Tilt up towers use 4 guy wire locations instead of 3, and the guy anchors must be perfectly square to the tower base. Tilt-up towers are generally made of steel pipe, which is heavier and more expensive than lattice. The prospect of high climbing a fixed tower might convince you that the added expense (and required large level area, clear of trees and obstructions) of a tilt-up is justified.

Tower Bases and Guy Anchors

The tower base actually does not receive much stress compared to the guy anchors once the tower is erected, all of the force on the base is straight down, from the weight of the turbine and tower. Fixed towers require a chunk of concrete at the base, and the manufacturer's specs will tell you how much mud to pour.

A metal plate is bolted into the concrete and the lattice sections attached to the plate. Freestanding towers need even more concrete – with no guy wires, the weight and depth of the base are critical. Again, follow the tower manufacturers recommendations.

Tilt-up towers benefit from a concrete base because of the side forces when raising or lowering the tower, but some perfectly good commercial designs use a flat metal base that’s simply spiked directly into the dirt.

What's most important is the strength of the guy wire anchors, which are usually either concrete or (when digging is impossible) large metal pitons sunk into holes drilled into the rock, and further secured with masonry epoxy. Fixed towers give you a little leeway on exactly where the 3 guy anchors are placed, but tilt-ups don't.

If the 4 guy anchors on a tilt-up are not perfectly square and level with the base and each other, the side guy wires may alternately tighten and loosen during raising and lowering.

This requires diligence and very slow action by the owner during erection; because wire rope guys don't give any visible indication of how much tension they are under they look the same whether there's 100 pounds of force on them or 1000.

A broken guy wire can be a disaster for the turbine, tower, and could even kill the owner. Seek expert advice if you've never raised a tilt-up tower before! It would be wise to do the same if you're thinking of a fixed one, too.