HAWT and VAWT
Small wind turbines occupy two main families: Horizontal-axis wind turbines (HAWTs), which comprise the vast majority of all small wind turbines, and vertical-axis wind turbines (VAWTs), which comprise a far smaller group. For the most part, people looking for a small wind turbine for their property will be reviewing their options in the HAWT family.
Upwind and Downwind
HAWT turbines have two primary subclasses: Upwind and downwind turbines. A downwind turbine has no tail and the wind blows into it from behind. Upwind turbines have tails, and they face into the wind.
Upwind turbines have the benefit of increased wind responsiveness. That is, they respond to wind direction and maximize the potential of the wind’s speed and power. Additionally, they tend to be quieter than downwind turbines; as the wind is hitting the blades first, the resonant sound is typically a white noise, rather than a strobing or chopping sound that can result from a downwind turbine, in which the wind hits the tower before hitting the blades.
Blades and rotor hub
Most small HAWT turbines use a three-blade design. The blades are affixed to a central assembly called the rotor hub. The rotor hub serves two functions: It holds the blades together, and it attaches to the spindle that drives the alternator.
The alternator is the key mechanical element of the turbine, and it’s what generates electricity as the blades spin. It is housed inside the nacelle of the turbine.
The turbine’s nacelle is the body of the turbine that is connected at its front to the blades and rotor hub, at is base to the yaw assembly, and at its rear to the tail assembly (for an upwind turbine). The nacelle for large industrial wind turbines is the housing for the gear box and all other major power components of the machine. For a small wind turbine, the nacelle can house very few electronics in some cases, or much more circuitry in others.
If you’ve ever learned about aviation, you’ll recall that yaw is the pivoting action of the aircraft on a horizontal plane, left to right. Similarly, a wind turbine’s yaw is its horizontal planing motion. The yaw assembly attaches the nacelle to the tower while allowing the turbine to spin freely about the horizontal plane.
Tail assembly and vanes
Upwind turbines feature a tail assembly that includes tail vanes, which keep the turbine’s blades faced into headwinds.
Inverters and charge controllers
A home wind turbine won’t do much for you if you don’t connect it to anything. Like solar arrays, small wind turbines connect to inverters, and in the case of off-grid or battery-backup homes, battery charge controllers. These typically house the system electronics that let you retrieve, store, and output energy as needed, whether to your appliances, your battery bank or out to the grid.
In our next episode, we’ll get into the nitty-gritty on a major home wind turbine system component: The tower.
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