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With gas prices rising, renewable energy is becoming increasingly important. Wind power is one of the most cost-effective options for renewable energy sources.
However, before you go out and buy a wind turbine, you need to know if the wind is strong enough where you live for wind energy to be helpful or a hindrance. Most of these turbines are efficient in wind farms.
This article will go into depth about the required wind speeds for small wind turbines and discuss a few popular wind turbines and their required wind speeds to generate power.
How Fast Must the Wind Blow For a Small Wind Turbine to Operate?
The wind must blow at a minimum of 9 mph (4 m/s) for a small wind turbine to function. Generally, the minimum wind speed required for a wind turbine to produce electricity is between 5.6 and 10 mph (2.5 and 4.5 m/s).
Continue reading for an overview of small wind turbines, a more in-depth examination of average wind speed requirements, and what to do if you want a small wind turbine and live in an area typically with less than nine mph winds (4 m/s).
The Average Wind Speed Requirements for Small Wind Turbines
Knowing your area’s wind speed is essential before buying a small wind turbine.
Knowing the annual wind speed will help you both determine whether or not a turbine is worth buying and which turbine is best to buy.
According to the US Energy Information Administration, small wind turbines require at least nine mph (4 m/s) wind speeds.
The cut-in wind speed, or the speed at which a wind turbine begins to generate electricity, is between 5.6 and 10 mph (2.5-4.5 m/s).
Other rates you might need to consider are the cut-off wind conditions and speed, the speed at which the wind turbine stops generating electricity, and the survival wind speed, which is the absolute fastest the wind can blow without damaging the turbine.
You can also consider a small wind turbine’s rated wind speed, which is the wind speed at which the turbine can generate the maximum energy output.
How Fast Does a Turbine Spin?
Now that you know how fast the wind needs to blow for the best results with your turbine, how fast does it spin to generate electricity?
The rotational speed of a wind turbine is measured in revolutions per minute (RPM) and absolute velocity.
Wind turbines can spin between 10 and 20 rotations per minute, translating to between 75 and 150 mph (120.70 and 241.40 km/h), depending on wind speed and blade size.
Understanding the Speed of a Wind Turbine
If you’ve observed a wind turbine closely, you may have realized that it rotates slowly. However, I just mentioned that these turbines can have absolute velocities of up to 150 mph (241.40 km/h). How is that possible?
You can understand how fast wind turbines spin by paying attention to various points on the blades.
For instance, imagine yourself at the tip of a wind turbine’s blade while your friend is closer to the blade’s root. Two facts emerge in this arrangement:
- The two of you will finish a full rotation at the same time
- You’ll cover different distances for every full rotation. The distance covered by each of you is equal to the circumference of the circle determined by the radius of each individual from the blade’s root.
To meet the above conditions, the one at the tip of the wind turbine’s blade must rotate faster than the one closer to the root.
Think of the above situation as being on a carousel. Being at the center of a carousel feels as if you’re moving slower.
However, as you move towards the edge, you feel as if the speed is increasing gradually. You eventually attain the highest speed at the edge, which translates to the tip of a wind turbine’s blade.
The above discussion brings in the concept of orbital velocity. This refers to the velocity at which a point on a rotating body orbits around the center.
The tip velocity is an essential factor when it comes to how fast a wind turbine spins. Engineers design wind turbines with optimal tip speed ratios for the maximum electrical energy output from the wind. How is that possible?
Well, a higher tip speed reduces the torque on the turbine’s drive train for a given power output. In turn, this reduces the drive drain’s mass and cost.
With that understanding, it’s evident that a wind turbine with an optimal tip speed ratio (TSR) guarantees the best results in power generation, keeping wind speed constant.
TSR is the ratio between wind velocity and the speed at which the tips of the wind turbines are rotating, expressed as follows:
TSR (λ) = The blade’s tip speed/Wind speed.
Use the below procedure to determine your wind turbine’s tip speed:
- Measure the length of one blade to find the rotor radius
- Calculate the speed by dividing distance by time {(Distance is the circumference (2∏r)}
Once you have the tip speed from the above procedure, divide it by wind speed to get your turbine’s TSR.
Factors That Affect How Fast a Wind Turbine Spins
Don’t expect your small wind turbine to always display constant rotational blade speed.
The speed at which wind turbine blades spin is influenced by several factors, which can be broadly categorized into environmental, turbine design characteristics, and operational considerations factors.
Here are the main factors that affect the rotational speed of a wind turbine blade:
Wind Speed
As we’ve already discussed, wind speed is the most critical factor in determining the blade speed.
The power output of a wind turbine is proportional to the cube of the wind speed. As the wind speed increases, the blades spin faster to capture more energy.
Conversely, when wind speeds decrease, the blades will slow down.
It’s worth noting that the wind turbine starts reacting and thus generating electricity as the wind speed approaches 9 miles per hour (4 miles per second).
However, most small wind turbines attain their rated capacities at a maximum wind speed of 35 mph (56.33 km/h).
At 55 mph (88.51 km/h) wind speed, most turbines attain their cut-off point. This means they don’t generate any extra electricity, no matter how fast the wind moves.
The turbine cuts off at such wind speeds to prevent mechanical damage to internal components.
Blade Length and Design
The length of your turbine’s blades affects wind speed directly.
Longer blades have higher tip speeds because they can capture more kinetic energy. On the other hand, the blade design affects their aerodynamic efficiency.
The more wind power captured by longer blades generates higher rotational speeds, leading to the production of more electricity.
Modern turbine blades are designed to be longer and aerodynamically efficient to extract maximum kinetic energy from the wind.
Also, you’ll notice that large wind turbines for industrial applications have longer blades for the same reason.
Air Density
The denser the air, the faster the turbine will spin.
Denser means there are more air particles per unit volume of wind, translating to more energy. It’s this energy that eventually translates to more rotational power.
That said, you can expect that small wind turbines in regions with denser air generate more electricity than those in areas with less dense air.
What Are Small Wind Turbines?
Small wind turbines are turbines with a typical power of between 400 watts and 20 kilowatts (kW). These turbines can power homes and small buildings either in addition to or instead of an electrical grid.
When deciding if you want to buy a small wind turbine, you need to consider much more than just the average annual wind speed of your area. Location is critical when it comes to utilizing wind energy.
Suppose you live in an area with a lot of obstructions. In that case, your wind turbine might not receive the amount of wind or speed necessary for enough electricity to make a difference.
The best areas to put your wind turbine are on the tops of hills, near clear plains, by a water source, and in the crevices of valleys. These areas all have excellent access to wind, helping your turbine generate the most power possible.
Popular Small Wind Turbines
There are numerous different wind turbine models and brands out there, and choosing the best one depends on many factors, including:
- What you will be using the small wind turbine for
- Whether or not it will be connected to the electric grid
- How much power you need to generate
- Where you live
The US Department of Energy states that the average home uses about 10,649 kilowatt-hours (kWh)/year, or around 877 kWh/month.
Suppose you are getting your small wind turbine to live off-grid or not in conjunction with the national grid. In that case, you need a higher-powered turbine since you will have no backup source of electricity.
Since so many factors go into deciding on a small wind turbine, let’s look at some of the best models for residences and discuss their best applications.
Aeolos-H 500W Wind Turbine
Aeolos-H 500W Wind Turbine is a terrific 500W small wind turbine. Aeolos is a well-known and well-respected wind turbine brand, so you know you’ll get reliability.
This 500W wind turbine has a permanent magnet generator with a maximum efficiency of 96%. It is best to use it alongside the national grid because it is a lower-powered turbine. For that reason, this turbine is best for home lighting and street light projects.
Here are the cut-in, rated, and survival wind speeds for the Aeolos-H 500W:
- Cut-in wind speed: 5.6 mph (2.5 m/s)
- Rated wind speed: 26.8 mph (12 m/s)
- Survival wind speed: 100.7 mph (45 m/s)
Windspire 1kW Vertical Axis Wind Turbine
Windspire 1kW Vertical Axis Wind Turbine is an excellent 1kW small wind turbine. It is a vertical-axis wind turbine (VAWT). Instead of looking like a propeller, like a horizontal-axis turbine (HAWT), it looks like vertical rods rotating around a post.
VAWTs are a great choice if you don’t want to rearrange your wind turbine every time the wind direction changes, as wind flow from any direction can generate electricity. These turbines are often shorter than HAWTs so maintenance may be more straightforward.
Here are the cut-in, cut-out, and survival wind speeds for the Windspire 1kW Vertical Axis Wind Turbine:
- Cut-in wind speed: 8 mph (3.6 m/s)
- Cut-out wind speed: 35 mph (15.6 m/s)
- Survival wind speed: 110 mph (49.2 m/s)
Bornay Wind 25.3+
Bornay Wind 25.3+ is a fantastic 5kW wind turbine. When working at a 42% capacity factor (the average capacity factor for most wind turbines), 5kW turbines can generate about 18,393 kWh annually or 1,533 kWh a month.
This turbine offers more power than the average home consumes, so you can use a Bornay Wind 25.3+ as your sole source of electricity if you live in a suitable area with the proper wind speeds. You can also use this turbine to pump your water or for telecommunications.
Here are the cut-in, rated, cut-out, and survival wind speeds for the Bornay Wind 25.3+:
- Cut-in wind speed: 4.5 mph (2 m/s)
- Rated wind speed: 26.8 mph (12 m/s)
- Cut-out wind speed: 67.1 mph (30 m/s)
- Survival wind speed: 134.2 mph (60 m/s)
Ryse E-10 HAWT
The Ryse E-10 HAWT is a fantastic 10kW small wind turbine. It is incredibly safe and reliable and can potentially displace greenhouse gas emissions equivalent to 60 acres of forest annually.
This turbine is also incredibly quiet, ranging from 46 decibels at 196.9 feet (60 meters) to 33 decibels at 590.6 feet (180 meters).
For reference, according to the American Academy of Audiology, 30 decibels is equivalent to a whisper, and 50 decibels is equal to moderate rainfall.
Here are the cut-in, rated, cut-out, and survival wind speeds for the Ryse E-10 HAWT:
- Cut-in wind speed: 4.5 mph (2 m/s)
- Rated wind speed: 20.1 mph (9 m/s)
- Cut-out wind speed: 67.1 mph (30 m/s)
- Survival wind speed: 156.6 mph (70 m/s)
What To Do For an Area That Doesn’t Get Enough Wind
As said, annual average wind speed is essential when deciding if you want to buy a small wind turbine or not. If you live in an area that doesn’t get the average wind speed, there isn’t much of a point in spending a considerable amount of money on a wind turbine.
Still, suppose your household, or wherever you want to set up a turbine, doesn’t get the necessary minimum average annual wind speed. In that case, you can consider getting a hybrid solar and wind power system.
Use a Hybrid Solar/Wind Power System
Average wind speeds vary with the seasons, with it being windier in autumn and winter compared to summer and spring.
Conversely, solar power is best in the summer and spring rather than in winter or autumn. Therefore, a hybrid solar/wind power system may be advantageous.
During the darker seasons, when there is little sun but more wind, your wind turbine can be the primary energy source. On the other hand, when it is sunnier and less windy, your solar panels can be the primary energy source.
To sum it up, a hybrid solar/wind power system is terrific when you don’t get enough wind for a small wind turbine to be useful or have good, consistent power all year round.
Conclusion
Before buying a small wind turbine, check if your area has a high enough average annual wind speed. If your location does not get the wind speeds best for small wind turbines, it is not ideal to buy a wind turbine.
The minimum average annual wind speed for a small wind turbine is nine mph (4 m/s). Most small wind turbines begin to generate electricity between 5.6 to 10 mph (2.5 to 4.5 m/s).
If your heart is set on getting a small turbine, then you may also be concerned with the costs. Luckily, our articles on Are They Affordable and What Is The Average Payback Period will give you a rough idea of this topic!
Sources
- US Energy Information Administration: Wind explained: Where wind power is harnessed
- US Department of Energy: Installing and Maintaining a Small Wind Electric System
- Aeolos Wind Turbine: Aeolos-H 500 W Wind Turbine
- Windspire: 1kw Vertical Axis Wind Turbine
- Bornay: Wind +
- Ryse Energy: E-10 HAWT
- American Academy of Audiology: LEVELS OF NOISE In decibels (dB)
- AltE: Residential Wind Turbines: Are They Practical for You?
