A monopole tower consists of heavy large diameter tubes. The primary advantage of monopoles is that they take very little space. For this reason, many large turbines are installed on monopole towers. In the case of large turbines, the tube is large enough in diameter to provide internal stairs or an elevator to service the turbine while remaining out of the weather. Monopoles for small turbines such as the Aerostar 6 Meter are too small in diameter to offer this advantage.
The primary disadvantage of monopoles is their cost. They tend to cost 50% to 100% more than a lattice type freestanding tower. Another disadvantage is that because of their large surface area they tend to be more effective at radiating sound than other types of towers so noise from the turbine can be amplified. A crane is usually required for installation, although Aerostar has pioneered self erecting monopoles.
We are often asked for hydraulically raised monopoles. Raising a tower hydraulically sounds like a good idea, but it can actually be very expensive. Hydraulic cylinders large enough to raise a turbine the size of the Aerostar 6 Meter or Independence, can cost $10,000 or more. This substantially increases the cost of the installed wind system. There is also a need for a hydraulic power system to supply hudraulic pressure. If you happen to have a tractor, backhoe or other equipment it may be possible to use the equipment hydraulic system to supply pressure to the cylinders.
Safety and liability is another consideration. The force on the hinge and the hydraulic cylinder is huge. As an example, a typical 100 foot monopole might easily weigh 10,000 pounds. Add a small turbine and the weight can exceed 11,000 pounds. This results in a force moment about the tower hinge of about 600,000 foot pounds. If a hydraulic cylinder were located 3 feet from the tower hinge, the cylinder would have to exert a force of 200,000 pounds in order to lift the tower. This is a very large force. If we assume a typical hydraulic pressure of 3000 PSI, it would take a hydraulic cylinder over 9 inches in diameter to lift the tower. This is a huge and extremely costly cylinder. Because of the high cost, hydraulic towers are very difficult or impossible to justify economically.
Another problem is if a hydrulic piston seal or hose were to fail, the tower and turbine could come crashing down. If hydraulic monopoles were such a good idea, you would see commercial wind farms using them. You don't.