wind turbines use large neodymium magnets
wind turbines use large neodymium magnets

Buy Wind Turbine

The American Wind Energy Association estimates that residential wind turbines can reduce electrical bill charges by 50% to 90%. When in the market to buy wind turbine, take a close look at some wind-turbine components that might give clues as to the quality of the wind turbine.

The first important thing to consider when choosing a wind turbine is the type of the turbine. A wind turbine can be either a horizontal-axis type or a vertical-axis type of wind turbine. Horizontal-type turbine technology has accumulated more mileage compared to that of the vertical-type turbine. Vertical-axis wind turbines (or VAWTs) do not require tall and expensive support towers; they can produce electricity at lower wind speeds; and they generally emit less noise compared to the horizontal-axis wind turbines (HAWTs). But, VAWTs, because of their more complex design, can actually be more difficult to maintain and repair. Also, a VAWT cannot match the power output of a HAWT of the same size or price. For a given weight or size, HAWTs are more efficient at producing electricity from wind than VAWTs. VAWTs, though, are more space friendly compared to the HAWTs. Since VAWTs don’t need to be raised high above the ground, they are less visible; and, therefore, are less likely to attract the attention of the local building inspectors.

Having chosen the turbine mounting type (HAWT or a VAWT), the next important topic to consider is the make and the material of the propeller blades (or rotor blades in other countries). Unless you’re a bit familiar with aerodynamics, there’s not much you can ask regarding the shape of the blade. Remember, though, that the longer the blades, the larger the “swept” area, which in turn translates to more power. The problem with longer blades, of course, is that they require a taller (and larger) tower and also, usually, a larger alternator, etc. The size of the blades has been matched to the alternator and has been factored into the specified power rating of the turbine. Inspect the quality of the wood and of the finish. On some kits, the buyer is responsible for the final weatherproofing finish on the propeller hub/s and blades. Aircraft-quality laminated wood (e.g., Sitka spruce or Western red cedar) is the standard blade material on good-quality turbines. Fiberglass blades with large neodymium magnets are also popular. Look for those with added ultraviolet protection because unprotected fiberglass becomes progressively brittle with continual sun exposure. Paint that has been applied after the fiberglass has set can flake off. Superior quality fiberglass products have the coloring pigments and the anti-UV compounds added to the liquid resin before it is applied to the fiberglass mat. If carbon-fiber blades are available, they would be a good choice, as long as they’re not too expensive. Some blades are made of metal, such as aluminum, which can be more durable, but are also often heavier.

A tail vane is a rudder-like device that is attached to the end of the tail boom or directly at the rear end of the nacelle. Its purpose is to “furl” or turn the propeller such that its plane of rotation is parallel to the direction of the wind. Furling the propeller is necessary during high winds to reduce the stress on the blades and to prevent the propeller from over-speeding. Sustained over-speeding will damage the propeller, overheat the alternator, and cause excessive currents to flow towards the batteries.

Th next item to consider would be the gearbox, if one is present. Gearboxes are usually found in larger turbines. Its purpose is to keep the spindle (that attaches to the alternator) spinning at a constantly fast rate (about 1,200 to 1,800 rpm). Gearboxes can be mechanically complex and expensive. If pressed to choose between  two turbine models of the same power rating, the one without the gearbox would be the  better choice. The less components there are to break, the easier it would be to maintain or repair the turbine.

The alternator (or induction generator for some units) is another crucially important component. The alternator with the appropriate rating is chosen that matches the maximum and the average rotational speeds of the propeller. Automotive alternators and washing-machine motors (with some modifications) have been used on wind turbines with good results. Custom-made alternators are common on the ready-to-run wind turbines. DIY wind turbines sometimes come with alternators that need to have the neodymium magnets put in by the buyer. Choose a wind turbine with the newer brushless alternators if possible.

Most wind turbines with alternators have a shutdown switch which, if triggered, causes electromagnetic-induction braking  inside the alternator. The effect is a rapid increase in the resistance against the rotation of the propellers. The energy of the opposing currents is rapidly converted into heat. Once the propeller stops moving, the currents and the heat dissipates. Make sure to purchase a wind turbine that has this (or other propeller-braking) mechanism in place that can quickly stop the propeller from rotating in case of an emergency.

For turbines that output AC current, a rectifier sits between the emergency shutdown switch and the over-voltage input breaker. The rectifier converts the AC current into DC current.

The over-voltage input breaker is an emergency circuit breaker or fuse that immediately cuts off the current that flows from the rectifier into the batteries. This fuse or breaker protects the batteries from excessive currents. Once this breaker trips, the propeller will spin freely as the charge that is present in the batteries can no longer resist the current that comes from the alternator.

An excess load diversion controller is a device that drains power from the batteries once they have been fully charged. Excess charging will ruin a battery and this device simply removes the excess charge by sending a current to a resistor which then converts the excess current into heat. The excess load controller and the input breaker are two additional safety mechanisms that, along with the emergency shutdown switch, should be included with the electronics package of a wind turbine.

Do the research when it comes to choosing one brand of wind turbine over another. Ask for warranty information. If possible, talk to people who had purchased a certain brand and and have already spent a good number of months or years with that product. Safety mechanisms should always be included with a good quality wind turbine.

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