Vertical axis wind turbines have a popular following. Which is better for you? This depends a little depending on what kind of wind you receive at your home, and how much area you have to work with. Vertical axis turbines seem to work better at lower speeds of wind. Also, they work better when you are limited to how you can place your windmill — be it close to ground level in a small yard that has a restricted amount of wind, or whether you have a yard that is restricted in space and the amount of wind it generally receives.

On the other hand, horizontal axis (the kind you regularly think of when you think of windmills) have various benefits that will most likely make them superior to vertical axis depending on your situation. This article focuses on helping you decide which is better for you.

If you are interested in vertical axis wind turbines, this blog has a good breakdown of how efficient vertical axis wind turbines are. I’ll give a summary though and add in my thoughts about which is better for any particular situation.

The wind has a certain amount of power within it that can be converted to mechanical power via a wind turbine. That amount is 59%, discovered by German scientist Albert Betz. When discussing horizontal wind turbines, windmills exist that can harvest nearly 50% of the power in the wind. However, when it comes to vertical wind turbines, that amount dramatically drops — the average vertical is about 5% to 10% efficient, whereas a superior designed vertical can be up to 15%.

Vertical = 15%, horizontal = 50%, its not hard to see which one is superior in most situations? (That being said, there are many horizontal wind turbines that are not constructed well and will only produce half of what it otherwise could generate.) If horizontal wind turbines (HAWT) are 3 times as efficient in generating power as vertical axis (VAWT), why would anyone want or need to fuss with a VAWT? Well there are a few instances where a VAWT can be a superior choice.

Benefits of Vertical Axis Wind Turbines

• VAWT are excellent for producing power in low wind. Sometimes the volume of electricity generated is not the main concern, but instead a consistent supply of electricity. VAWT are popular because they can spin in even the faintest wind. They are often promoted as being able to be mounted directly on the ground.
• VAWT can be lower maintenance in some circumstances. Not all VAWT are less maintenance (see below to see disadvantages of VAWT). One specific instance where VAWTs have been used successfully are small Savonius style design being used to power lights on a waterbuoy to help visibility at night (the model of vertical axis windmill pictured at the top of this article is Savonius).
• VAWT are a good choice when your average wind is not very strong. Regardless of how fast the wind blows at your home during periods of higher wind, if you consistently receive a low volume of wind, a VAWT can be a better choice as it will spin even in the lowest winds.
• VAWT make for great homemade windmills projects. A vertical axis wind turbine can be considered easier to make than a HAWT. The parts spin at only about a third of the speed, making it for less wear over time. There are many videos on youtube showing some fantastic vertical axis windmills, many of which can be made with a 55 gallon drum cut in half and made for $150 to $350 (depending on the quality of generator you decide to use). An Ametek alternator can run fairly cheap ($60), whereas a Windblue can run up to $250. The Windblue is capable of generating more electricity with a smaller RPM.

Those are the benefits of using a vertical axis wind turbine, but are there any disadvantages? There are plenty!

Vertical Axis Wind Turbines produce far less power than HAWT. They produce only one third of the amount of power.  If you have a decent consistent breeze, a horizontal axis will produce far more power.
VAWT can be higher maintenance in some circumstances. This section is not talking about the Savoinus style, instead it is referencing the Darrieus style.  The Darrieus style is the type of VAWT that looks like an egg-beater, with scoops extended from the base via bars.  For a very small windmill that deals with a low volume of wind, of course they will last quite some time.  However, if you are planning on sticking one of these in a situation where it will spin at a high speed frequently, it can cost more in maintenance.  Just because of the nature of the beast, the design of a VAWT leads to wear above and beyond what a HAWT would receive.  At issue are certain facts, for instance centrifugal force.  Both HAWT and VAWT are subject to centrifugal force as they spin.  With a HAWT, the greatest strain is where the blades meet the base, which happens to be where the blades are the thickest and sturdiest.  With a VAWT, the blades are extended away from the center.  The design does not call for a sturdiness where the blades are connected from the base to the blades — in fact the more this area is bulked up to account for the weakness of this style of VAWT, the less efficient it becomes, so it is a balancing act between generating power and lowering maintenance.
Never buy a commercially made VAWT. You are almost always certain to get a better deal on a conventional style horizontal axis windmill, with far more electricity produced for the wind it receives. VAWT should be made as a do-it-yourself project for situations where lower wind volume is expected. It would take a very long time to “pay off” a VAWT, the ROI on a commercially purchased vertical axis would be very slowly over decades.

The best argument for VAWT is for when there is low wind. However, if there is low wind, and you really want to tackle a rewarding do-it-yourself project, diy solar panels would be a better return on investment than a windmill.