In this tutorial, you will learn how to use a small wind turbine and how to take the most amount of it in terms of electrical output. It can be used to charge a battery pack, or direct electrical consumption at your house or at your camping spot. Since renewables are gaining ground and it is always great to know how to be sustainable and generate your own energy all of the information given below will be extremely helpful.
You can also check our other tutorial about the basics of photovoltaics and who knows you will be able to combine both in the future and do a combined renewable system.
- Available Outside Space or roof;
- Location with Wind;
- Small Wind turbine;
- DC/AC inverter;
- Charge controller;
What is it?
The small ones we will talk about today are no different than the big and tall Wind turbines observed in the fields and mountains. At first glance, the size is an obvious difference but also some particular details related to the blades are key to taking them apart.
Small wind turbines often have passive Yaw systems as a tail fin to point into the wind, a direct drive generator, and no pitch. They usually produce between 250 W and 10 kW.
At a basic level Wind turbines work on a simple principle: instead of using electricity to make wind, like a fan, wind turbines use the wind to make electricity. The wind turns the propeller-like blades of a turbine around a rotor, which spins a generator, which creates electricity. That’s very simple. It is possible due to the aerodynamics of the blades, which work like an airplane wing or helicopter rotor blade. When wind flows across the blade, the air pressure on one side of the blade decreases. The difference in air pressure across the two sides of the blade creates both lift and drag. The force of the lift is stronger than the drag and this causes the rotor to spin.
Also, by looking at the Figure above we can see that the angle at which the “blade collects the wind” have a direct influence on the lift force. That angle is called Pitch. The angle regulation is normally done via an electric motor at the axis of the blade, very identically to airplanes. However, this is not very common in small-scale Wind turbines like the ones in this tutorial but is good to mention that they can regulate themselves by aerodynamic deformations proportional to the wind speed.
Then, the rotor connects to the generator, either directly (if it’s a direct drive turbine) or through a shaft and a series of gears (a gearbox). This translation of aerodynamic force to the rotation of a generator creates electricity.
As we can imagine the more aligned to the wind a turbine is the better. For that to be possible a Yaw mechanism must be implemented.
There exist two types:
- Passive there are no actuators involved electrical or mechanical, the turbine is aligned to the wind via a fixed tail.
- Active There are in general electric motors responsible to align to the wind accordingly to external sensor information.
Basically, the mechanical output is given by the following equation. It can be included the actual pitch angle but not taken into account in small turbines:
The majority of wind turbines fall into two basic types:
- Horizontal-axis wind turbines most commonly, have three blades and operate “upwind,” with the turbine pivoting at the top of the tower so the blades face always the wind.
- Vertical-axis wind turbines these turbines are omnidirectional, meaning they don’t need to be adjusted to point into the wind to operate.
Most small wind turbines are horizontal-axis wind turbines (HAWT), but vertical-axis wind turbines (VAWT) may have benefits in maintenance and placement, although they are less efficient at converting wind to electricity.
Also, they can be categorized by the place they are installed and how they are connected to the grid:
- OnShore – Implemented at land fields ranging around 100 meters and larger power output and when grouped together make a wind farm.
- Offshore – Implemented at vast open sea similar to Onshore but normally with larger power output due to available stronger winds.
- Distributed – Wind turbines of any size are installed at or near the place where the energy they produce will be used.
After the previous explanation, let’s choose our Wind Turbine. We will proceed with an Onshore Horizontal-axis wind turbine implemented as a distributed system since it will be installed in the backyard and near the consumption with a passive Yaw and no active Pitch systems, like the model below.
The quality of the local wind conditions is a significant factor in determining if a turbine will be economically viable.
In all wind turbines, they must reach a certain wind speed, called the cut-in speed, to start generating electricity. This speed is usually around 4 – 5 ms for small turbines. To avoid obstacles and to catch higher winds, turbines are often placed on towers above anything, between 10 and 20 meters. Better locations for turbines are far from large and high/tall obstacles, as wind tunnel studies show significant negative effects from nearby obstacles. Below we can see a hypothetical case of the power output related to the height that the rotor is located and the wind speed. So, the higher the height and winds the better.
Another option for placing a small turbine is using a model based on actual wind measurements to predict how nearby obstacles will affect local wind conditions at the potential turbine location, considering the size, shape, and distance to the obstacles.
Small-scale rooftop turbines can be installed on a roof but may face issues such as vibration and turbulence caused by the roof ledge as well as the roof shape, which can impact their power generation. If you know the location as you live there it is easier, however, if you do not live there we can take advantage of tools like the Global Wind Atlas database to use values for your desired location.
No matter what measurement system or tool is used, it is a must to have recorded data for a minimum of 1 year and compare it with another source of data. It is very important that the measurement equipment is set at hub height.
Our chosen location is a random high place where at first glance it appears to have a good average wind speed. On this website, you can also include the type of turbine you have or even upload the data from the manufacturer, so it is possible to plot the power curve of the turbine.
So, in this location, we can see that it is possible to produce 727 w/m2 at a height of 10 meters in the windiest areas. We can also observe the temporal data at a yearly, monthly, and daily variation thus we can get a glimpse of the estimated wind behavior.
Is it worth it?
After reaching the conclusion that our location is windy for placing a turbine we may need to estimate the amount of electrical energy output generated in an average day and compare if the overall cost to produce the electricity is less than the cost of electricity from other grid sources. If you are just pointing for self-generated electricity it can either be entirely consumed by the property owner or exported to a local distribution grid for credit under a net metering arrangement with an electricity distributor may be always worth it.
The project cost depends on market location, but we know that the system costs can be 50% higher or more, due to site conditions, remote location, interconnections costs, permits, and fees. The cost of wind power, unlike other sources of electrical power, is almost entirely due to the cost of purchasing and installing the system. Once the turbine is installed, there is no fuel cost associated with its operation, only the cost of maintaining the wind turbine, a low one.
For example, in the next chapter, we can see the energy generated by the wind turbine with the load analysis to have a basic idea of how the energy produced is related to the savings.
Electric Load Analysis
Much similar to our previous photovoltaics tutorial, now we may need to consider which loads we want to supply or how much we want to reduce our monthly bill. For that let’s take an example of constant load. The reason is to simplify our analysis.
Below, is displayed our constant hypothetical load as red, and at the same time the imaginary Power output of a 250 W max power Wind turbine is green color.
Since our load has a constant consumption, for example, a ventilation system, every energy generated by the wind turbine will be subtracted to the red line, as observed below. Then the red area on the right side is less which means the energy consumed by the grid supplier is also reduced. This is the scenario where our Wind turbine is supplying most of the demand and in some cases exceeds production (Green pics) that can be sold to the grid operator or used to charge the battery bank.
Now we can calculate how much we save for this scenario above without considering any energy sold to the grid operator. Remember that better days will produce better savings, but for the long-term calculation we must use an average day/values:
- 140Wx24h = 3360 Wh day without Wind turbine
- Approx. 650 Wh day with a wind turbine for the scenario above
- (Energy savings of 2710 Wh day) x (price kwh of your grid operator) = Savings
- Payback time days = (Installation + Turbine price)/Day savings
- Good investment for maximum payback of 4/5 years.
Installation and Electrical Setup
Have a licensed electrical contractor perform all electrical work to ensure it is done safely and meets the safety requirements code. Use a tower approved by the wind turbine manufacturer, otherwise, the warranty may become invalid. Also, ensure the tower is grounded for protection in case of a lightning strike.
A disconnect switch is required that can electrically isolate the wind turbine from the rest of the wind energy system. It may be an automatic or manual one to allow for maintenance and system modifications to be safely made to the turbine. Should be placed right after the output cable of the Wind turbine.
Following the figure below, hereby we describe the basic components to fully enjoy the output.
Since the wind turbine generates DC output it is required a charge controller regulates voltage and current to then proceed safely and stable to the inverter. Also, the charge controller may be connected to the battery bank if applicable and DC appliances in case you are dealing with camping equipment mainly at 12V.
Remember that the battery bank is only required if you want to consume energy during periods of low wind and they may have a certain capacity to supply your load to a certain desired duration. The turbine may be capable of charging the batteries at the same time that deals with live load consumption. If you want to know more about how to dimension batteries bank and joined them with this kind of system, it is a good idea to check our tutorial chapter “Joining with batteries”. It is the same logic but now with a wind turbine and different output curves.
The DC/AC inverter is responsible to convert the DC output from the charge controller, so that can be used in our house. In addition, a bidirectional meter can be installed in a pre-existing grid so that the energy produced can flow to the grid when not used by our AC appliances.
Before proceeding, be sure that the project meets all regulatory requirements with the local municipal building/zoning department for more information. They provide clear, consistent rules and standardized technical requirements to protect human health and the environment.
Depending on the location and nature of the project, there may be other approvals, permits, and/or authorizations required from other ministries and approving bodies. Renewable energy projects can be subject to a variety of approvals and permits, depending on project type and size. Speaking from my personal experience, small wind projects less than or equal to 3 kW do not require anything, but this may not be the case for your country.
Here is a list of some references used and where you can also learn even more. There are some credible information and good analysis from other amazing people. Go check them.
- Smal guide for US on small Wind Turbines