How it works simplified: a wind generator´s rotating blades convert the wind´s kinetic energy into rotational momentum in a shaft. The rotating shaft turns an alternator, which makes electricity. This electricity is transmitted through wiring down the tower to its end use.
The blades use airfoils matched to the alternator, that capture the wind´s energy. Together, the blades and the hub are attached to the rotor, which is the collector of the system, intercepting winds that pass by. Most turbines on the market today are upwind machines—their blades are on the windward side of the tower. A few downwind machines are available, but neither configuration has a clear performance advantage over the other.
In most small-scale designs, the rotor is connected directly to the shaft of a permanent magnet alternator, which creates three-phase AC. Three-phase electricity means that the voltage and frequency vary continuously with the wind speed. They are not fixed like the 60 Hz, 120 VAC electricity coming out of common household outlets. The wind output is rectified to DC to either charge batteries or feed a grid-synchronous inverter. In most designs (up to 15 KW in peak capacity), the rotor is usually connected directly to the alternator, which eliminates the additional maintenance of gears. In systems 20 KW and larger, as well as some smaller wind systems, a gearbox is used to increase alternator speed from a slower turning rotor.
The blades must turn to face the wind, so a yaw bearing is needed, allowing the wind turbine to track the winds as they shift direction. The tail directs the rotor into the wind. Some sort of governing system limits the rotor rpm as well as generator output to protect the turbine from high winds. A shutdown mechanism is also useful to stop the machine when necessary, such as during an extreme storm, when you do not need the energy, or when you want to service the system.
What to look for when purchasing? Well one might look at the rated output However this can be misleading… Why? Because rated output is pegged to a particular wind speed, and different manufacturers use different wind speeds to determine rated output. Also, the power available in the wind varies with the cube of its speed, so small increases in wind speed result in large increases in power available to the rotor. A 10 percent increase in wind speed yields a 33 percent increase in power available in the wind. Conversely, this means that a turbine rated at 1,000 watts at 28 mph might produce only 125 watts or less at half that wind speed, 14 mph. Therefor I suggest you Ignore the peak output and the power curve. Look for the monthly or annual energy numbers for the turbine, estimated for the average wind speed you expect or measure at your site. These will be given in KWH per month (or year) in the manufacturer´s specifications for each turbine. Energy is what you´re after, not peak power! If, for example, you are looking for a turbine that can produce 300 KWH per month, and you know that you have a 10 mph average wind speed at the proposed turbine height, you can shop for a turbine that is predicted to generate that much energy in that average wind speed. More things to consider when purchasing is a turbine that has a very good track record and a good warranty—five years is preferable but not always available in the small wind industry. A warranty is one indication of the manufacturer´s confidence in their product, and their intention to stand behind it. Keep in mind that just buying a wind turbine will not get you any wind-generated electricity. You´ll also need most or all of the components mentioned elsewhere. Also budget for equipment rental, like a backhoe and crane, concrete and re bar, electrical components, shipping, and sales tax. Unless you do all of the work yourself, also factor in installation labor expenses. These costs can add up significantly, so make sure that you research and understand all of the associated expenses
Note: that a number of the wind turbines listed here are relatively new introductions with not very much customer run-time in North America. These turbines include the ARE, Eoltec, Kestrel, and Sky stream. We recommend that you contact either your local wind turbine installer, or the manufacturers or importers and find out how many of these machines are actually operating in North America. Then contact the owners, and inquire about their experience and satisfaction with both the machine and the manufacturer or importer. While many first-time wind turbine buyers may be looking for a bargain, second-time wind turbine buyers are seeking the most rugged machine they can afford. You can avoid a painful “learning experience″ by focusing on durability, production, warranty, and track record, and not on price alone, or on peak output. You don´t want to depend on the low bidder for something as important to you as your long-term energy investment.
Be sure to check back for my next article where we will discuss the various types of wind Energy Systems and their components.
Tags: Add new tag, THE BASICS, WIND ENERGY, WIND TURNBINES
