WINDMILLS

2008-06-13T05:25:00.000-07:00

A windmill is a machine that is powered by the energy of the wind. It is designed to convert the energy of the wind into more useful forms using rotating blades or sails. The term also refers to the structure it is commonly built on. In much of Europe, windmills served originally to grind grain, though later applications included pumping water and, more recently, generation of electricity. Recent electricity generating versions are referred to as wind turbines.

In Canada and the United States

An isometric drawing of the machinery of the Beebe Windmill. It was built in Bridgehampton, NY in 1820.Windmills feature uniquely in the history of New France, particularly in Canada, where they were used as strong points in fortifications.[8] Prior to the 1690 Battle of Québec, the strong point of the city's landward defenses was a windmill called Mont-Carmel, where a three-gun battery was in place.[8] At Fort Senneville, a large stone windmill was built on a hill by late 1686, doubling as a watch tower.[9] This windmill was like no other in New France, with thick walls, square loopholes for muskets, with machicolation at the top for pouring lethally hot liquids and rocks onto attackers.[9] This helped make it the "most substantial castle-like fort" near Montreal.[10]

In the United States, the development of the water-pumping windmill was the major factor in allowing the farming and ranching of vast areas of North America, which were otherwise devoid of readily accessible water. They contributed to the expansion of rail transport systems throughout the world, by pumping water from wells to supply the needs of the steam locomotives of those early times. Two prominent brands were the Eclipse Windmill developed in 1867 (which was later bought by Fairbanks-Morse) and the Aermotor, which first appeared in 1888 and is still in production. The effectiveness of the Aermotor's automatic governor, which prevents it from flying apart in a windstorm, led to its popularity over other models. Currently, the Aermotor windmill company is the only remaining water windmill manufacturer in the United States. They continue to be used in areas of the world where a connection to electric power lines is not a realistic option.[11]

The multi-bladed wind turbine atop a lattice tower made of wood or steel was, for many years, a fixture of the landscape throughout rural America. These mills, made by a variety of manufacturers, featured a large number of blades so that they would turn slowly with considerable torque in low winds and be self regulating in high winds. A tower-top gearbox and crankshaft converted the rotary motion into reciprocating strokes carried downward through a rod to the pump cylinder below.

Windmills and related equipment are still manufactured and installed today on farms and ranches, usually in remote parts of the western United States where electric power is not readily available. The arrival of electricity in rural areas, brought by the Rural Electrification Administration (REA) in the 1930s through 1950s, contributed to the decline in the use of windmills in the US. Today, the increases in energy prices and the expense of replacing electric pumps has led to an increase in the repair, restoration and installation of new windmills

Modern windmills

A modern Vestas windmill in SwedenMain article: Wind turbine
The most modern generations of windmills are more properly called wind turbines, or wind generators, and are primarily used to generate electricity. Modern windmills are designed to convert the energy of the wind into electricity. The largest wind turbines can generate up to 6MW of power (for comparison a modern fossil fuel power plant generates between 500 and 1,300MW).

With increasing environmental concern, and approaching limits to fossil fuel consumption, wind power has regained interest as a renewable energy source. It is increasingly becoming more useful and sufficient in providing energy for many areas of the world.

One area in which it is becoming rather popular is around the midwest of the United States where, due to great amounts of wind, turbines have become very useful.

Windmill Efficiency

Home owners need high efficiency, low speed windmills, so they can be placed at ground level, where they won't create an eyesore and a lot of noise. This means large diameter, large number of blades and low speed, instead of the 3 blade, small diameter, high speed windmills now being used by home owners. In some cases, they could be placed in attics with perpendicular tubes to the outside.

Large, commercial windmills cannot be efficient due to stress on the metal. Very larger size requires fewer blades, while the number of blades determines efficiency.

Efficiency is important for windmills, because the entire cost is in the technology, not the source of energy, which is wind.

The most significant factor determining the efficiency of windmills is the number of blades. This is because more blades capture more energy.

But large windmills must use few blades due to stress on the metal. When the diameter of rotation is 300 ft (100 m), two blade systems must be used. When the diameter is 150 ft, three blade systems can be used.

Yet windmills are unnecessarily large or too few in blades. Over sea coasts, they must be large; but most places, they could be smaller and use more blades. For homeowners, they are small, yet they are not using the large number of blades which would create high efficiency.

A large government study measured two blade systems only and showed moderate efficiency. Smaller, multi blades systems would have been much more efficient.

The overall efficiency of a windmill has to be directly measured, it cannot be calculated, because there are too many interacting factors. A good guess at design efficiency can be made by direct observation. Only measurements under operating conditions can improve upon direct observation.

For this reason, the US government spent a large amount of money (probably more than a billion dollars) during the late seventies and eighties creating experimental windmills for testing their practicality. But researchers only studied two blade systems. The results were worthless, in spite of having tested dozens of windmills. None of the experimental windmills were designed for good overall efficiency, and the most important questions were not studied. The test designs were so large that the structures made them impractical, and such designs are never used. Three blade systems are used on wind farms.

Overall efficiency means the amount of electricity that can be generated over time on a cost basis. In other words, will a kilowatt hour cost ten cents, twenty cents, or what?

Two factors are important in determining overall efficiency of a windmill. One is its ability to use low velocity wind, and the other is its conversion efficiency.

The ability to use low velocity wind determines whether the windmill is working or doing nothing while wind velocities are low, which is a large part of the time.

For example, an locale might have wind of 15 miles per hour (mph) or greater 20% of the time, and 10 mph or greater 40% of the time. A windmill that can use 10 mph wind is operating 40% of the time, while one requiring 15 mph wind is only operating 20% of the time.

The windmills tested by the experimenters would not use low velocity wind. The minimum wind speed required by their "best" designs required more than 15 mph wind speed. There is no reason why 5-10 mph winds could not be utilized to create highly efficient windmills for generating electricity.

To utilize low velocity wind effectively, there has to be more blades. The researchers studied two blade systems. They never even made comparisons to systems with more blades.

Conversion efficiency also requires more than two blades. More blades allows lower rpms, which results in less turbulence, so conversion is more efficient.

A quagmire of technicalities does not change these overall facts. Arguers will talk about torque and velocity trying to prove something, but it proves nothing, because there are infinite options in integrating all of those factors.

For example, they repeatedly say high rpm rotors are needed for generating electricity. That's mindlessness, because the rpms (revolutions per minute) are determined by diameter—the larger the slower.

The tip speed of the blade increases as the circular diameter of motion increases. In the government experiments, two blade systems were used, with rotors up to 300 ft long. Tip speeds were in excess of 200 mph, which created problems with noise and vibrations. Normal rotation was 18 rpm. This means more than 3 seconds per revolution.

Notice that the rpms have to decrease as the diameter of motion increases. Otherwise tip speeds would be excessive. So the rpms are determined by the diameter of motion, not the number of blades.

Arguers say high rpm at low torque is needed for generating electricity, instead of low rpm and high torque. Supposedly, they are saying, use fewer blades for higher rpms. But the diameter has more influence on rpms than the number of blades, and no one is suggesting small diameters.

They need a gear box regardless, and they make low velocity winds unusable with fewer blades. A gear box makes the torque-speed question irrelevant. And they contradict themselves to an extreme by using large diameters of motion, which is what really requires low rpms.

They could get the same rpms by using a smaller diameter of motion with more blades. They would then need more rotors per unit output, but more small ones are cheaper and more efficient than fewer large ones. Throwing away the low velocity wind and creating turbulence result in loss of efficiency.

Also, metal stress becomes the limiting factor with large size. Smaller windmills reduce that problem. One of the most significant facts about size is that steel gets like rubber when large. Excessive steel and heavy mass create the overriding expenses for large windmills.

The government experimenters said they could produce electricity at the usual price by using their large two blade systems, which required wind speeds in excess of 15 mph. This means that if systems were designed to use lower velocity winds with less turbulence, they would have produced electricity cheaper than other sources.

The design of the government windmills was extremely expensive due to the large size. Supposedly, the larger the size, the greater the efficiency. That point was not tested, but general appearance indicates that the technical difficulties of getting control of forces that high off the ground was not as cost-effective as smaller designs would be.

Let me say this in plain English. Anyone can look at an old-fashioned farm windmill, which had about 18 blades, and compare it to an experimental windmill, which had 2 blades, and see that the farm windmill was extremely efficient, and the experimental windmill is extremely inefficient. It is quite visible that unused wind goes between the blades with two and three blade systems. Propagandists use a lot of numbers and jargon to deny the obvious, but their numbers are not fact.

Modern wind farms use three blade systems, which is a major improvement over the two blade systems which were studied. Diameter is reduced from about 300 ft to about 120 ft, which reduces tip speeds and cumbersome stress forces. Whether four or five blades would be an improvement depends upon mechanical factors and reliability; but if smaller diameter and multi-blade systems were designed, they would be more practical for small users and home owners.

Wind Mills

WINDMILLS