Understanding the components of a small wind turbine


Mariah Power Tilt Down Tower installation
Home wind energy systems generally consist of blades, a rotor, a generator or alternator mounted on a frame, a tail (usually), a tower, wiring, and “balance of system” components ie. controllers, inverters, and/or batteries. The spinning of the blades enables the rotor to capture the kinetic energy of the wind and convert the linear kinetic energy into rotary motion to drive the generator.
Wind Turbine
Most turbines manufactured today are horizontal axis upwind turbines with two or three blades, which are usually made of a composite material. Some systems will have more blades then two, but testing has proven that though more blades will increase the wind speed operating range it will ultimately decrease the power output.
The amount of power a wind turbine will produce is determined primarily by the diameter of its rotor. The diameter of the rotor defines its “swept area,” or the quantity of wind intercepted by the turbine. The wind turbine’s frame is the structure onto which the rotor, generator, and tail are attached. The purpose of the tail is to keep the turbine facing forward into the wind.
In general, wind speed and consistency of wind resources increase dramatically with height. Because wind resources increase with height, the turbine will be mounted on a tower. Generally, the higher the tower, the more power a given wind system can produce. The tower also raises the turbine above the air turbulence that can exist close to the ground because of obstructions such as hills, buildings, and trees. A rule of thumb is to install a wind turbine on a tower that is at least twice the height of any obstructions within 500 feet. For more on tower height and set backs read Determining Setback Distances and Height for Small Wind Turbines. Keep in mind, relatively small investments in increased tower height can yield very high rates of return in power production. For instance, to raise a 10 kilowatt generator from a 60 foot tower height to a 100 foot tower height involves a 10% increase in overall system cost, but it can produce as much as 29% more power.

There are two basic types of towers: self-supporting (free standing) and guyed (or anchored). Most home wind power systems use a guyed tower. Guyed towers, which are the least expensive, can consist of lattice sections, pipe, or tubing (depending on the design), and supporting guy wires. They are easier to install than self-supporting towers. However, because the guy radius must be one-half to three-quarters of the tower height, guyed towers require enough space to accommodate them. Although tilt-down towers are more expensive, they offer the consumer an easy way to perform maintenance on smaller light-weight turbines, usually 5 kW or less.
Tilt-down towers can also be lowered to the ground during hazardous weather such as hurricanes. Aluminum towers are prone to cracking and should be avoided. Most turbine manufacturers provide wind energy system packages that include towers.
Mounting turbines on rooftops is not recommended. All wind turbines vibrate and transmit the vibration to the structure on which they are mounted. This can lead to noise and structural problems with the building, and the rooftop can cause excessive turbulence that can shorten the life of the turbine.
Balance of System
The parts that you need in addition to the turbine and the tower, also known as the “balance of system” parts, will depend on your application.
Most manufacturers can provide you with a system package that includes all the parts you need for your application. For example, the parts required for a water pumping system will be much different than what you need for a residential application. The balance of system required will also depend on whether the system is grid-connected, stand-alone, or part of a hybrid system.
For a residential grid-connected application, the balance of system parts may include a controller, storage batteries, a power conditioning unit (inverter), and wiring. Some wind turbine controllers, inverters, or other electrical devices may be stamped by a recognized testing agency, like Underwriters Laboratories.
Stand-Alone Systems
Stand-alone systems (systems not connected to the utility grid) require batteries to store excess power generated for use when the wind is calm. They also need a charge controller to keep the batteries from overcharging. Deep-cycle batteries, such as those used for golf carts, can discharge and recharge 80% of their capacity hundreds of times, which makes them a good option for remote renewable energy systems. Automotive batteries are shallow-cycle batteries and should not be used in renewable energy systems because of their short life in deep-cycling operations.
Small wind turbines generate direct current (DC) electricity. In very small systems, DC appliances operate directly off the batteries. If you want to use standard appliances that use conventional household alternating current (AC), you must install an inverter to convert DC electricity from the batteries to AC. Although the inverter slightly lowers the overall efficiency of the system, it allows the home to be wired for AC, a definite plus with lenders, electrical code officials, and future homebuyers.
For safety, batteries should be iso-lated from living areas and electronics because they contain corrosive and explosive substances. Lead-acid batteries also require protection from temperature extremes.
Grid-Connected Systems
In grid-connected systems, the only additional equipment required is a power conditioning unit (inverter) that makes the turbine output electrically compatible with the utility grid. Usually, batteries are not needed.