Small wind power: your checklist before buying

You no longer have to live in a remote location for wind energy to work for you. Thanks to major improvements in technology and a general awareness of the benefits of making your own energy from clean and free wind, small wind power is going mainstream. According to the American Wind Energy Association (AWEA), the US small wind market grew by 78% last year with many new turbines hitting the market.

But more options don’t make finding the right wind power solution easy. If you are interested but not sure how to even get started, here are some things to know as you consider wind power.

Vertical wind turbines are ideal for generating power in tight spaces

Small vertical wind turbines can be broken into two main technologies:

Horizontal Axis Wind Turbines (HAWTs) or Vertical Axis Wind Turbines (VAWTs).

HAWTs are propeller based turbines that are traditionally mounted on tall poles and are commonly used in large wind farm settings. HAWTs have blades which rotate vertically around a horizontal axis, similar to a propeller on an airplane.

VAWTs include two main classes: a tall vertical airfoil style (Darrieus), and a solid winged style (Savonius).

Darrieus turbines come in a few varieties. Some have rotors with curved blades that look like an eggbeater and rotate about a vertical axis. Another variation uses straight-sided airfoils and is called a Giromill. Like propeller turbines, Darrieus turbines utilize some lift to capture wind energy.

Savonius Turbines have rotors with solid vanes or “scoops” which rotate about a vertical axis.

Small wind, big category

There is no exact definition for small wind, but it usually applies to machines with less than 100 kilowatt (kW) ratings. The ratings refer to how much power the turbine can instantaneously generate at a specific wind speed.

AWEA recently adopted small wind standards, but it will be 12–18 months before any manufacturers are certified against those standards, thus manufacturers are still able to set their ratings at varying wind speeds. It is not uncommon to find one turbine rated at 25mph and another one rated at 48mph. Obviously the higher wind speed used will result in a higher kW rating, so its not a completely useful figure to go by.

Size doesn’t really matter

While kW ratings can give you a general sense for the size of a turbine, what really matters is how much energy it will produce over a period of time. Wind turbine companies provide energy curves that tell how many kilowatt hours (kWhs) you can expect to generate at specific average wind speeds.

You can check your monthly electric bills to gain an understanding of how many kWhs you use. Electricity use varies by season and time of day, so ideally you should add up the kWhs of the last 12 months.

Every turbine has it’s cut-in wind speed

Obviously, you need wind to create wind power. All turbines have a minimum required wind speed at which they will start to generate power, this is also known in the wind world as the cut-in wind speed. It is possible for a turbine to spin at speeds below the cut-in speed, but those rotations won’t be fast enough to actually create energy.

The majority of small wind turbines require a minimum of 10mph average annual winds to generate significant energy. Several new low-wind turbines claim to be able to generate power from as little as 6mph. Wind power is a cubic function of wind speed, which means that a little more wind can create a lot more power. When determining average annual wind speeds, a 10mph average annual wind does not mean it blows 10mph all day everyday.

Because of the cubic function, a day of high wind can generate enough power to make up for multiple days of low wind.

Find out how much wind you have in your area

How do you know if you have enough wind to make wind power a feasible option?

The best way to know is to install an anemometer where you want to place your turbine. You can get a good anemometer for around $500 and take an annual reading. If you don’t want to wait a year, you can do shorter anemometer tests but you need to realize that wind speeds change with the seasons.

Not ready to invest $500 in your research? Check out local weather sites which should provide data on average wind speeds. Local airports are also wonderful resources for this information. The DOD provides wind maps, but these are measured at 50 meter heights and are not always localized enough for small wind installations which are very site specific. You can also call a local wind turbine dealer and request a site visit.

What about a site?

The site is the place on your property where you install your turbine. Site location is a crucial element, and will have a major impact on which turbine you can consider. Turbines are best placed with enough open space to allow the wind direct access to the rotor. This does not necessarily require a specific lot size or a totally open and clear site.

Many small wind turbines are designed to work in a variety of settings. HAWTs will work if you can put up a large tower and have consistent wind direction, and VAWTs may be a better option if your wind changes direction often and/or you cannot put up a structure taller than 30 feet.

Wind speed can also vary drastically on one piece of property due to structures and topography. Always choose the site with the most access to wind.

Power output versus cost per kilowatt hour

It’s common for people to put up multiple turbines in order to meet their energy needs. Two big factors to consider are the expected power output and the running cost of the unit when fully installed.

Consult the energy curve of each wind turbine to determine how much energy it is likely to create with your average wind speeds over the course of a year. Compare the kWhs at the same wind speeds across wind turbines, while keeping in mind total cost of the unit.

A wind turbine that generates 400kWhs for $2,000 is a lot more expensive than a wind turbine that generates 2,000kWhs for $6,500.

Also, don’t be fooled by energy curves that show amazing results at 30mph average winds. It is highly unlikely that you live in an area with wind speeds of that level.

Independent testing

As I mentioned above, AWEA standards are still being applied to turbine certification and until they are in place we recommend focusing your search on independently tested wind turbines.

Power curves, which turbine companies use to estimate power ratings and energy curves, can be supposed from complex calculations. But, the truest power curves are created from units being independently tested in real world scenarios.

It is very easy for manufacturers to create their own power curves, so it is important to look for wind turbines with independently tested data. I recommend avoiding any turbines that do not have their data verified by an independent test facility.

In this way you will be ready when you install your own vertical wind turbine for your home.

Noise

When you have chosen a turbine or turbines, try to visit a live installation of the model you’ve chosen (or find a video of it in action) so you can hear what it sounds like when operating.

This is a big purchase decision, so do your research and find a dealer or manufacturer you’re comfortable working with. The more thorough you are with your research, the happier you will be with your purchase.