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Wind-power equipment can supply electricity in distant, off-grid locales, or right in town when linked to the service grid. They tend to require more upkeep than solar-electric, solar-hot water, or even micro hydro-electric systems. However, if you are ready to invest up front in a good apparatus, plan well, and select the right wiring setup, wind-electric arrangements can make economical and ecological sense. They also provide a good deal of contentment. Nothing is more satisfying than observing your wind generator changing a sultry summer breeze or a blustery winter wind into electrical energy.
In simple terms, the principle of wind power is that the rotating blades of a wind generator converts the kinetic energy of the wind into revolving force on the shaft of a generator or alternator. The power thus generated is transmitted via wires down the tower to its final use.
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Wind Turbine Terminology
There are some details involved during the selection process. Here are some of the terms that you're likely to hear or may want to ask about.
Break-in Wind Speed
The wind speed at which the wind generator starts generating is the break- in wind speed. Bear in mind that the wind speeds under 6 to 7 mph (3 m/s) supply slight or no operational energy, although the blades may be rotating. Presently there are several high-tech controllers with the capacity to “store” the small quantity of energy obtainable at low wind speeds in the alternator windings after which the energy is pulsed to the batteries using a pulse width modulated charge controller.
Rated Wind Speed
This is the wind speed at which the wind generator attains its rated output, which most companies specify as anywhere from 18 to 31 mph (8–14 m/s). Here you will have to understand that a potential 511% extra power can be generated in a 31 mph wind. The power of the wind accessible to a wind generator can be computed with the help of the equation
P = 1/2 d x A x V3
where P is power, d is density of the air, A stands for the swept area of the rotor, and V means the wind speed. This formula shows that P ~ V3 meaning P is directly proportional to the cube of the wind speed. Remember that if the rated wind speed is less then the actual wind, the generator will produce more energy, given its rated output.
This capacity is assumed at a random wind speed that the producer aims for. It inclines to be at or just under the leading wind speed of the wind generator. Any windmill generator may max out at a higher output than the rated output. The more rapidly you spin a wind generator, the more it will generate, until it overproduces to the degree that it cuts out. For the same amount of rated wind speed, a turbine having a high rated wind speed will be priced less than the one with a lower rated wind speed. You can check this with the help of the equation mentioned above.
This may be the similar to the rated output, or it may be higher. According to Hugh Piggott [as quoted in Estimating Wind Energy, Aug/Sep 2004 (#102) pp. 42-44], “Peak or rated output specifications for small wind turbines can be red herrings unless you take the rated wind speed into account, and yet these specs are all the customers seem to want to know about.”
Maximum Design Wind Speed
Most wind generators are intended to endure wind speeds of 120 mph (54 m/s) or more. Whether this statement is true or false is left for you to find out since it is very difficult to test.
Rated Output RPM
This is the alternator RPM at which rated output takes place. Broadly speaking, the smaller the rotor coil, the quicker the blades spin. Generator RPM will have an impact on the total noise that the wind producer makes. High RPM wind generators get more stress due to centrifugal forces, which are continuously attempting to split the machine apart. Also the life of the bearings is impacted by RPM.
Even though lot of new materials have been used recently to make wind generator blades, wood stands as the best and the most used material for small home units. Sitka spruce is the best material for wood blades.
TSR (Tip Speed Ratio)
The operation of a blade’s airfoil (contour) is a function of the ratio of the speed of the tip of a blade to the wind speed. A TSR of 5 or 6 to 1 can be found in a low-speed blade, while a TSR of 10 or 11 to 1 can be seen in a high-speed blade. This means that if the blades spin faster, then they will generate more noise. So research and then buy the turbine which best suits your area.
There are three kinds of electrical generators which can be used in wind electric systems: DC generators, permanent magnet (PM) alternators, and brushless alternators. There is no difference in performance of all the three as they all do a fine job of generating electricity. It is only in their internal make-up and wiring that they differ.
A governing system is required for two reasons:
- To protect the generator itself from overproducing and burning off
- To protect the complete system from flying apart in high winds.
Governing Wind Speed
The wind speed at which the prevailing mechanism is completely functional takes place anywhere between the wind generator’s rated power output and its highest power output, which is the governing wind speed.
One of the major considerations which you will have to think about when buying a wind turbine is the shut-down mechanism. Halting the rotor and shutting down the generator is worthy for preservation or repairs, or at any time when you feel that the rotor should not be turning, like in a storm or when you are away for some time. The mechanism of shut-down are of two types: mechanical and electrical. In the mechanical shut-down method, the tail is folded in such a way so that it is parallel to the blades.
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To conclude I would like to draw your attention towards the safety concerns of your wind turbines. Remember that all wind turbines have a limiting wind speed, known as the survival speed, beyond which the operation of the turbine stops. An internal break occurs when the wind is at its maximum speed and prevents the blade from spinning faster. If the conditions are very cold, then be ready to de-ice as mandatory, and be sure to store your batteries in a protected place.
3. Willie Scott - Residential Wind Turbines – A Survey of Types
Tswind - TechnoSpin rooftop wind turbines