WIND ENERGY
Wind energy systems
Wind turbines can have three, two or just one rotor blade. Most small wind turbines have three. The blades are usually made of fiberglass-reinforced polyester or wood-epoxy.
Because the wind speed varies most modern wind turbines have microprocessor controlled governors which adjust the turbine speed. These governors are essential because extremely high wind gusts can cause the rotors to turn too fast which can damage the turbine due to excessive vibration.
Most wind turbines have gearboxes though increasingly manufacturers are turning to turbines with direct drives because they are much simpler and easier to maintain.
Wind turbines have a wind vane mounted on the housing to keep the turbine facing into the wind. This is also sometimes referred to as a "yaw mechanism".
Wind turbines may also have a small anemometer on them which is a small spinning wind gage which can feed information to the controller on the current wind speed.
Every wind turbine has a rotor or propeller with blades which harvest the energy from the wind. The rotor is connected to a hub which in turn is connected to the main drive shaft. The drive shaft connects to the generator which generates the electricity.
The rotor blades are usually made of plastic, fiberglass or wood covered with an epoxy or urethane coating.
The rotor blade edge is similar to that of an airplane wing and creates lift because of the differential air pressure between the flat side and the rounded side of the blade. However, since the blade is turned at an angle the lift causes the blade to turn rather than rise. Lift-powered wind turbines have much higher rotational speeds than drag types and therefore are well suited for electricity generation.
The reason is that number of blades that make up a rotor and the total area they cover affect wind turbine performance. Rotors that use the lift-principle need for the wind to flow smoothly over the blade. If the blades are too close together the turbulence from one blade can disrupt the flow of air to the blade next to it. So the blades must be far enough apart given there overall size so that this does not happen.
Blade size is important in determining the amount of energy you can generate. The larger the blade size the more of the kinetic energy of the wind you can capture.
Another factor that is looked at in rotor design is what is called the Tip Speed Ratio, the tip being the tip of each blade on the rotor. The larger this ratio, the faster the rotation of the wind turbine rotor at a given wind speed. Lift-type wind turbines have maximum tip-speed ratios of around 10, while drag-type ratios are approximately 1. The tips of a wind turbine rotor can reach speeds of up to 300 mph. Since electrical generators require the shaft to turn at a high speed, high tip speed ratios are needed.
The hub is connected to a gearbox and generator, which are located inside the nacelle. The nacelle houses the electrical components and is mounted at the top of the tower.
The Generator
The generator is the device inside the turbine that actually generates the electricity. It can also be referred to as a permanent magnet alternator. It takes the kinetic energy generated by the rotor and translates it into electricity. Inside the generator, coils of copper wire called the armature are rotated in a magnetic field to produce electricity.
Generators can be designed to produce either alternating current (AC) or direct current (DC), and they are available in a large range of output power ratings.
If the turbine is designed to produce DC current it will have an additional component inside the housing called a rectifier which will convert the originating AC current to DC current. Another approach for getting DC current is to pass the AC current to a separate device called an inverter which can convert the AC current to DC current.
Grid-tied and off-the-grid systems have different requirements when it comes to wind turbines. In a grid tied system you will want AC output which matches that of the electrical grid itself. Most home and office appliances operate on 120 volt (or 240 volt), 60 cycle AC.
if you are using your wind turbine as part of an off-the-grid standalone system you will need to store the power it generates in batteries when not using it directly.
Batteries run on DC current. Battery voltages are voltages of between 12 volts and 120 volts. DC generators are normally used in battery charging applications and for operating DC appliances and machinery in a business.
The Transmission
Generators typically require 1,200 to 1,800 revolutions per minute (RPM's) to operate efficiently. However, the RPM's of a wind rotor are usually more in the range of 40 to 400 RPM's. In order to make up this difference wind turbines will usually have a gear-box transmission to increase the rotation of the generator to the speeds necessary for efficient electricity production. The gear is connected to a second high speed shaft which because of the gear ratio turns at the higher speed the generator requires.
In a grid-tied configuration the electricity from the generator is routed to an inverter which converts the electricity from direct current (DC) to the alternating current (AC) that electrical grids use.
The AC electricity is then fed into the grid through the home's control panel. The diagram below shows a typical grid-tied configuration
Types of Wind Turbines
Wind turbines are classified into two general types: horizontal axis and vertical axis. A horizontal axis machine has its blades rotating on an axis parallel to the ground. A vertical axis machine has its blades rotating on an axis perpendicular to the ground
The area where the wind mill is set up should be optimum enough to enable proper functioning of theblades by capturing maximum wind that comes along its way. The main requirement is that the area shouldspan up to more than one acre of land.
The first question that should always be asked when choosing a site is "Does it have enough wind?". Fortunately this is a question that is fairly easy to answer. Wind maps which show both annual and seasonal wind speeds are available from a variety of source like wind maps.
These maps can help you determine if wind speeds in your area are strong enough to justify investing in a wind system
Another approach is to actually take wind readings at your site yourself using a recording anemometer. Anemometers are small and simple devices. A number of the newer units are digital hand held recorders which allow you to easily check wind conditions in different parts of your property. The anemometers aren't hard to set up and many can record not only wind speed but temperature and humidity as well. If your schedule allows you may wish to take recordings at different times of the year in order to get a complete picture of how the wind changes at your location by season
Never underestimate the impact even a small reduction in wind velocity will have on your ability to generate power. Wind power increases exponentially relative to speed (V3). A site with an annual average wind speed of about 12.6 miles per hour (5.6 meters per second), has twice the energy available as a site with a 10 mile per hour (4.5 meter per second) average.
Even if you have what appears to be a perfect site for wind power, you should always check state and local regulations before investing money in a wind energy solution. Take the time to research local zoning requirements.
Many communities have put up strong restrictions on the height of structures. Wind turbines perform better the higher they are placed but you may find that a 75 or 100 foot tower may violate local zoning requirements.
the average wind speed should be around 18 Km per hour and the source should be consistent. The windspeed is important because it should be sufficient enough to move the blades against its inertial mass.
The blades are used to capture thewind directly, the shaft on the other hand connects the blades to the tower, the tower is the structure thatholds the blades at a height, and the base supports the entire structure.
The 6 Key Elements of a Successful Wind
Wind –1 mph difference is make or break
Energy is function of cube of wind speedAvg. wind speeds of 16-19 mph in most areasAt higher altitudes, air density drops-requires a higher wind speed for same outputDepends on region’s market price for power No mitigation for low wind speed!
Start-up Speed - This is the speed at which the rotor and blade assembly begins to rotate.
Cut-in Speed - Cut-in speed is the minimum wind speed at which the wind turbine will generate usable power. This wind speed is typically between 7 and 10 mph for most turbines.
Rated Speed - The rated speed is the minimum wind speed at which the wind turbine will generate its designated rated power. For example, a "10 kilowatt" wind turbine may not generate 10 kilowatts until wind speeds reach 25 mph. Rated speed for most machines is in the range of 25 to 35 mph. At wind speeds between cut-in and rated, the power output from a wind turbine increases as the wind increases. The output of most machines levels off above the rated speed. Most manufacturers provide graphs, called "power curves," showing how their wind turbine output varies with wind speed.
Cut-out Speed - At very high wind speeds, typically between 45 and 80 mph, most wind turbines cease power generation and shut down. The wind speed at which shut down occurs is called the cut-out speed, or sometimes the furling speed. Having a cut-out speed is a safety feature which protects the wind turbine from damage. Shut down may occur in one of several ways. In some machines an automatic brake is activated by a wind speed sensor. Some machines twist or "pitch" the blades to spill the wind. Still others use "spoilers," drag flaps mounted on the blades or the hub which are automatically activated by high rotor rpm's, or mechanically activated by a spring loaded device which turns the machine sideways to the wind stream. Normal wind turbine operation usually resumes when the wind drops back to a safe level.
One of the key things to know about wind speed is that the amount of energy which wind can generate is not a one to one function. Rather energy increases by the cube of the wind speed. If you double the wind speed, you get eight times the energy. That is one reason that looking at wind maps is so useful. Even a small difference in wind speed within a given area can have a big impact on the amount of energy a wind turbine can generate. It is also one of the reasons why a taller wind tower can make so much of a difference. If the wind speed increases even a few miles an hour by going with a taller tower the energy generation potential goes way up
Betz Limit
It is the flow of air over the blades and through the rotor area that makes a wind turbine function. The wind turbine extracts energy by slowing the wind down. The theoretical maximum amount of energy in the wind that can be collected by a wind turbine's rotor is approximately 59%. This value is known as the Betz limit. If the blades were 100% efficient, a wind turbine would not work because the air, having given up all its energy, would entirely stop. In practice, the collection efficiency of a rotor is not as high as 59%. A more typical efficiency is 35% to 45%. A complete wind energy system, including rotor, transmission, generator, storage and other devices, which all have less than perfect efficiencies, will (depending on the model) deliver between 10% and 30% of the original energy available in the wind.
Land –need willing landowners
Need large, contiguous parcels. Compatible land uses -e.g. ranching, dry land (un-irrigated) agriculture, open space
Permits –wildlife
Transmission (capacity and proximity)
Typically connect to 115/230/345 kV linesMust have capacity availableFeeder lines typically < 5 -10 miles Ability to finance feeder lines, upgrades depends on project size and economics. Bigger projects with better winds can afford longer feeder lines and more upgradesLong feeder lines may be difficult and expensive to acquire and permit
Buyer (Power Purchase Agreement)
Financing –need all 5 above to get it
Unlike natural gas, coal or nuclear power plants, we can not transport our “fuel” (wind) to a desirable location –we have to go to where the
