Project Table of Contents
- What kind of energy should I harvest?
- City ordinance and neighborhood considerations
- Installing the tower base
- Building and securing the tower
- Building and installing the wind turbine
- Selecting the type of turbine (this article)
- Choosing AC or DC
- Prototype, aka “Mark 1”
- Building the “Mark 2”
- Video of the finished Mark 2 in action
- Preventing “reverse flow”
- Regulating and controlling the charge
- Dump Loads
I’ve got to be honest, the order in which I’ve been writing these articles, and the order in which I actually undertook this project haven’t paralleled each other. I actually started with deciding what kind of energy to harvest, then jumped right to prototyping a wind turbine. I decided to write the articles in this order because it’s a more natural progression, and there’s nothing more disappointing than having a turbine atop a 10-foot pole that rarely spins, or in storage in your garage, or learning that the whole attempt was for naught due to city restrictions, etc. That having been said, let’s get to the really fun part of this project!
Selecting the type of Wind Turbine
Vertical Axis Wind Turbines (VAWTs) have some distinct advantages over their Horizontal Axis Wind Turbine (HAWT) cousins, but they operate on the same basic principles: air moves past the “blades” which causes them to rotate, this rotation is then converted into electrical energy (via a motor, generator, dynamo, alternator, or similar device) or physical energy (for pumping, grinding, “milling,” etc. – hence the term “wind mill”). VAWTs usually have fewer moving parts than HAWTs do, which equates to less to maintain and repair. You never have to worry about a VAWTs electrical wiring getting twisted in the tower, unlike HAWTs. VAWTs usually can harvest more power from the same wind as HAWTs.
There are two type of VAWTs: those that operate using lift (faster), and those that operate using drag (slower). There are also some hybrids between the two.
Lift-based VAWTs include the savonius, darrieus, giromill and cycloturbine varieties. When they rotate they have an enormous pulsatory torque that can be produced during each revolution and the huge bending moments on the blades. This happens when the lift on one blade is increase as it comes into the wind, effectively “slinging” it around to the other side, where another blade picks up the wind and exhibits the same behavior. Later designs like turby, quietrevolution and aerotecture address this torque issue by using the helical twist of the blades, similar to Gorlov’s water turbines, which exposes the same amount of blade to the wind at any point in the revolution, thus equalizing the toque though the entire revolution.
Drag-type VAWT, such as the Savonius rotor, typically operate at lower tipspeed ratios than lift-based VAWTs. These are similar to anemometers and typically don’t spin faster than the wind that is pushing it. These turbines can generally produce large amounts of torque, so they can be geared to spin a generator faster than the wind, or can spin much larger generators. A major down-side to VAWTs is that they cannot be furled out of the wind, which is bad when high-winds come up and threaten to destroy the turbine. In these cases physical or electronic braking systems are used to keep the turbine from spinning too quickly.
Horizontal Axis Wind Turbines (HAWTs), on the other hand, are what you commonly think of when you hear the word “windmill.” These are typically on large towers and have blades that protrude from a central hub and spin perpendicularly to the wind, much like the propeller on an airplane spins.
This design has been used and improved upon for centuries. From pumping water from the Dutch lowlands, to grinding mill and cutting wood, to pumping water on the plains of the USA, and finally, to generating power (either on a small, or very large scale).
I decided to go with the tried-and-true HAWT for its simplicity, the ready availability of pre-built turbines and parts, and for the ease of recognition (people will look at it and know what it is, whereas a VAWT people would just wonder about it).
To Build or To Buy, That is the Question
At this point in your process you’ll be faced with the question: Should I build my own turbine, or should I purchase one. If you’re in a very windy location, or if you aren’t mechanically inclined, you’re probably better off buying a pre-built turbine.
If you’re a tinkerer, like me, or if you want be able to build these for when “the system falls apart and we cannot afford electricity – or it’s simply not available,” or if you want to know how it works so you’ll be able to service it and fix it if it breaks, why not build your own?