Wind Energy is Available for Everybody
During the day, the air above the land heats up faster than the air over water. The warm air over the land expands and rises up in the atmosphere, and the heavier, cooler air rushes in to take its place, creating winds. At night, the small-scale winds are reversed because the air is getting cool more rapidly over land than over water.
In the same way, the large scale atmospheric winds that circle the Earth are created because the land and sea near the earth’s equator is heated more by the sun than the land and sea near the North and South Poles.
HISTORY OF THE USE OF WIND ENERGY
The history of the use of wind energy is very ancient. The great ancient Greek poet Homer recounts the tale of trapping the winds in the goatskin bag of Aiolos, the Greek god of the winds. Since the tale indicates the humans’ need to control the winds, the wind energy is referred as Aiolic (or Acolic) energy.
Archaeologists have evidences that sails already existed and used for navigation about 5,000 years ago in the Eastern Mediterranean Sea and the Nile River. For thousands of years, the movement of boats depended mainly on the strength of the winds, until the end of the 19th Century. A windwheel operating a music organ was described as early as the 1 st Century AD by engineer and inventor Heron of Alexandria, Egypt, marking probably the first instance of a wind powered machine in history. Information about windmills bring us to Persia (Iran) sometime between the 7th and 9th Century AD; Persians used windmills for grinding wheat or for pumping water, as described in manuscripts of old Muslim geographers. These were vertical axle windmills, which had long vertical shafts with rectangle shaped blades or sails.
The use of the wind as a prime mover ceased only in the 20th Century, the age when coal and conventional liquid fuels were expanding rapidly and electricity was being extended even to the most remote areas.
The oil crisis and the Ecological Movements at the beginning of the 1970s brought Aiolic energy to prominence again. From that time up to the present, there has been very rapid development which has been reinforced by the urgent need to protect and save the environment due to threat of world climate change. More and more people realized that the wind is a clean and inexhaustible source of energy and not at all “old fashioned”. After all, wind is called a “renewable energy source” and it will blow as long as the sun exists.
DO IT YOURSELF
This article focuses on windmills for farming applications like water pumping or small electric generators, and contains guidelines on constructing windmills. However, this is not a complete construction manual.
Building a wind generator is not that difficult. You will need a shop with basic power and hand tools and, of course, dedication.
Large wind generators of 2,000 watts and up are a major projects needing very strong construction and exact calculations, but smaller ones up to 1,000 watts with 3-4 m diameter range can be built easily from scrapped car parts and be up and flying in a week. It is highly recommend that you make a smaller windmill before even thinking of building a large one.
The research on windmills derived many types of machines which can be separated into two major categories: windmills of vertical axle and windmills of horizontal axle.
THE VERTICAL AXLE WINDMILLS
Following the style of the Persian ancestors, the vertical axle offers some great advantages: they can work with wind from any direction, no need to turn them to the wind direction. Its materials and construction are also cheaper than horizontal axle machines. Its generator and gearbox, for instance, can be placed on the floor - just protect these from rain and floods - that’s why it is easy to maintain. Moreover, it doesn’t need a tower but it is still advisable to place it on an elevated position.
Only three types vertical axle windmills are still in use, with minor or greater variations:
• The anemometer-type for very light applications.
• The Savonius-type for low speed applications.
• The Darius-type generators.
Anemometer-type. This is the easiest to construct. Its four cups (usually of
hemispherical or truncated cone shape) are mounted and all facing at the same direction at the ends of a horizontal cross, which can turn around a vertical axle passing through its center. Today, it is used almost exclusively for measuring wind speed.
Savonius-type. The Savonius vertical axle windmill was invented by Sigrid Savonius, a Finn racing driver in 1930s. Although less efficient than a conventional horizontal axle design, it is simpler and has less moving parts. This design also has an advantage, it has an aerodynamic effect called the “Magnus principal” wherein the air moving over the convex face of the rotor forms suction, while in the concave face a pushing force is developed. This means that there is force acting on the face of the rotor pulling it into the wind.
This is very easy to construct. A unit can be made by attaching two halves of vertically split barrel to a vertical axle; this produces a low speed, high torque unit that can be used for pumping water, or for generating electricity with a car alternator or dynamo which will give up to 200 watts for charging a car battery. A car alternator is not the most efficient generator-type for this purpose, but it is certainly cheap and widely available (Safety notice for the amateurs: Do not use a metal barrel of oil or gasoline, as it may explode while cutting with electric cutter or welding it. You can safely work with a metal brand-new barrel or a metal one used for water or a plastic one. Please consult a technician about this subject.).
On the other hand, the Savonius-type is more suitable for mechanical applications like pumping water. The frame must be very strong, providing also some way to immobilize the rotor. Possibly, double ball bearings are needed, and these bearings need lubricating maintenance. Small Savonius wind turbines are sometimes used as advertising signs wherein the rotation helps draw attention to the item advertised. It is also used as a ventilation device - a small Savonius wind turbine is driving an extractor fan - on the roofs of vans and buses.
Darius-type. This windmill is much different from the others. Instead of using cups or blades to collect the wind power by dragging them around, this turbine has aerofoils that are vertically mounted onto the framework. The “secret” of the aerofoils is their cross-section shape, like a “drop” or a “fish body”.
Invented by French engineer Georges Darrieus in 1931, the Darius windmill has a vertical shaft, which does not need the wind to be blowing into it, and two to three “C shape” vanes around it. Generally, it looks like a kitchen blender.
The interesting thing is that you can construct this type of wind generator which can produce 3,000 watts from parts readily available in your home and hardware. This generator has been tested to be more suitable for sites where winds are not strong; but in standby position, it can also withstand even strong storms.
There are many benefits in using this type of turbine. Although it does not generate as much torque as a Savonius windmill does, it spins faster, that is why it is more suited to electricity generation than to water pumping or other mechanical applications.
Moreover, vertical axle wind turbines produce less noise than the standard horizontal axle turbines because the speed ratios are lower. Although they are not as efficient as the common horizontal axle windmills, they are safer, easier to build, and handle turbulence a lot better.
However, Darius wind generators are not self-starting; to initiate rotation, a small powered motor or a small Savopius windmill must be attached to these. Since the windmill is on the ground and not on a tower, it needs i: lot of free space around it, especially on the directions of the principal winds of the region, and this is not always possible in a small farm. Besides, the wind speed near the ground is lesser compared with the wind speed on a tower as high as 20 meters or more. A remedy for this is to install the Darius windmill on top of a strong building or on a hill.
THE HORIZONTAL AXLE WINDMILLS
This category comprises the classic windmills we all have in mind. Centuries after the Persian constructions that looked like large paddle wheels, Hollanders changed and improved the basic design of the windmill. They gave it propeller-type blades, sometimes made with sails.
Holland is famous for its windmills. Most of these impressive and beautiful traditional structures situated along the edge of water-channels, are actually water-pumps designed to drain the land. These are important because much of the Netherlands lies below sea level.
Similar constructions were developed in other countries for other purposes, like grinding wheat for flour production.
We still have to mention another place which offers some interesting constructions of this kind, in Lasithi Plateau, Crete Island, Greece. Venetian engineers in 1464 - the era of the famous engineer and artist Leonardo da Vinci - designed a scenic way of draining the water of the plateau, and a big number of water pumping windmills was constructed. About 25 of the old constructions still survive and some of them are restored as monuments. In the meantime, thousands of newer windmills were erected, so in mid 20″ Century, there were about 10,000 on this plateau. This is how the plain used to be drained and irrigated.
Although many windmills are not in use anymore today, they are still splendid sight against the mountains. Lasithi Plateau is still well known for the hundreds of white sailed windmills and recently, the tradition started reviving, because of the oil price hike.
Two types of horizontal axle windmills are mostly in commercial use today:
1. The multi-blade fan-type, mainly used for water pumping, and
2. The propeller-type for high-power electricity production.
Multi-blade fan-type. An evolution of the traditional conventional design, this windmill consists of a rotor with 16 to 20 blades driving a generator or a pump, either directly or through a gearbox or a chain or a belt system. A tail vane, or fantail, is-required to direct the machine into the wind. When the windmill is not in use, the fantail can be folded to one side, so that the fan is directed parallel to the wind and the turning force is practically reduced to zero. It is quite easy to construct this type of windmill. Some amateurs use a bicycle wheel (without the tire), and a bicycle chain to transfer the rotary movement to a pump or generator.
Propeller-type. For amateurs, this type is difficult to construct. Propeller-type windmills are today, dominant for industrial use and can have huge dimensions. Just for reference, typical dimensions of an industrial wind generator of 500,000 watts (500kW) are 40m diameter, placed on a tower of 40-50m high, while for 3,000,000 watts (3MW) the above dimensions are doubled. Small or extended Aiolic Parks for industrial production of electric power exist today in many countries. Small-scale commercial models of this type for pumping water can also be found in the market.
POINTS TO CONSIDER
Wind is a “free fuel” for everybody. Aiolic energy applications are, based on very simple principles and high technology is not needed in small applications. Of course, a higher technology and precision is necessary in making complex windmill designs. That is why you should select the type and design of a windmill according to your purpose. It is also advisable to consult an engineer or technician about your plans, conduct experimental construction, and double-check the strength of your materials because the winds in countries like Kenya and Malawi are not so strong, compared with the typhoons in Philippines.
On the other hand, it is not advisable to work your windmill in extreme conditions, but even in stand-by position you have to protect your construction during strong winds and heavy rains depending on your location and daily conditions.
