Alternative energy Wind energy in the upwind By

Alternative energy Wind energy in the upwind By: Vasilescu Tiberiu Aurel And Brata Sorin

Contents 1. Short presentation 2. History of wind energy 3. Wind Turbines: Upwind Machines 4. How wind machines work 5. Types of wind turbines 5. 1. Vertical-axis wind turbines 5. 1. 1. Presentation 5. 1. 2. Advantages and disadvantages 5. 2. Horizontal-axis wind turbines 5. 2. 1. Presentation 5. 2. 2. Advantages and disadvantages 6. Small wind turbines 7. Turbine design and construction 8. The benefits of wind energy 9. Wind and the environment 10. The costs of wind energy

Short presentation n n n Wind is simple air in motion. It is caused by the uneven heating of the earth’s surface by the sun. Wind energy converts kinetic energy that is present in the wind into more useful forms of energy such as mechanical energy or electricity. During the day, the air above the land heats up more quickly than the air over water. The warm air over the land expands and rises, and the heavier, cooler air rushes in to take its place, creating winds. At night, the winds are reversed because the air cools more rapidly over land than over water. In the same way, the large atmospheric winds that circle the earth are created because the land near the earth's equator is heated more by the sun than the land near the North and South Poles. Today, wind energy is mainly used to generate electricity. Wind is called a renewable energy source because the wind will blow as long as the sun shines. Windmills that were used to grind grain are an example of early uses of wind energy. Modern uses of wind energy include generation of electricity and pumping water. Current wind energy machines are called "wind turbine generators", "wind pumps", or more generally, "wind turbines".

n n n History of wind and wind energy Since ancient times, people have harnessed the winds energy. Over 5, 000 years ago, the ancient Egyptians used wind to sail ships on the Nile River. Later, people built windmills to grind wheat and other grains. The earliest known windmills were in Persia (Iran). These early windmills looked like large paddle wheels. Centuries later, the people of Holland improved the basic design of the windmill. American colonists used windmills to grind wheat and corn, to pump water, and to cut wood at sawmills. As late as the 1920 s, Americans used small windmills to generate electricity in rural areas without electric service. The oil shortages of the 1970 s changed the energy picture for the country and the world. It created an interest in alternative energy sources, paving the way for the re-entry of the windmill to generate electricity. In the early 1980 s wind energy really took off in California, partly because of state policies that encouraged renewable energy sources. Humans have used wind energy for thousands of years. Ancient Persians used wind energy to pump water before the birth of Christ. The current interest in wind energy was started by the need to develop clean, sustainable energy systems that can be relied on for the long-term future.

Wind Turbines: Upwind Machines n n n Upwind machines have the rotor facing the wind. The basic advantage of upwind designs is that one avoids the wind shade behind the tower. By far the vast majority of wind turbines have this design. On the other hand, there is also some wind shade in front of the tower, i. e. the wind starts bending away from the tower before it reaches the tower itself, even if the tower is round and smooth. Therefore, each time the rotor passes the tower, the power from the wind turbine drops slightly. The basic drawback of upwind designs is that the rotor needs to be made rather inflexible, and placed at some distance from the tower (as some manufacturers have found out to their cost). In addition an upwind machine needs a yaw mechanism to keep the rotor facing the wind.

How wind machines work n n Like old fashioned windmills, today’s wind machines use blades to collect the wind’s kinetic energy. Windmills work because they slow down the speed of the wind. The wind flows over the airfoil shaped blades causing lift, like the effect on airplane wings, causing them to turn. The blades are connected to a drive shaft that turns an electric generator to produce electricity. With the new wind machines, there is still the problem of what to do when the wind isn’t blowing. At those times, other types of power plants must be used to make electricity.

n Types of wind turbines There are two types of wind machines (turbines) used today based on the direction of the rotating shaft (axis): horizontal–axis wind machines and vertical-axis wind machines. The size of wind machines varies widely. Small turbines used to power a single home or business may have a capacity of less than 100 kilowatts. Some large commercial sized turbines may have a capacity of 5 million watts, or 5 megawatts. Larger turbines are often grouped together into wind farms that provide power to the electrical grid. Vertical-axis Types Horizontal-axis

Vertical-axis n n Vertical-axis wind turbines (or VAWTs) have the main rotor shaft running vertically. Key advantages of this arrangement are that the generator and/or gearbox can be placed at the bottom, near the ground, so the tower doesn't need to support it, and that the turbine doesn't need to be pointed into the wind. Drawbacks are usually pulsating torque that can be produced during each revolution and drag created when the blade rotates into the wind. It is also difficult to mount vertical-axis turbines on towers, meaning they must operate in the often slower, more turbulent air flow near the ground, resulting in lower energy extraction efficiency. Exemples of vertical-axis wind turbines: n n Darrieus wind turbine Savonius wind turbine Darrieus wind turbine

Vertical-axis wind turbines n n n n n Advantages: Easier to maintain because most of their moving parts are located near the ground. This is due to the vertical wind turbine’s shape. The airfoils or rotor blades are connected by arms to a shaft that sits on a bearing and drives a generator below, usually by first connecting to a gearbox. As the rotor blades are vertical, a yaw device is not needed, reducing the need for this bearing and its cost. Vertical wind turbines have a higher airfoil pitch angle, giving improved aerodynamics while decreasing drag at low and high pressures. Low height useful where laws do not permit structures to be placed high. Smaller VAWTs can be much easier to transport and install. Does not need a free standing tower so is much less expensive and stronger in high winds that are close to the ground. Does not need to be pointed into the wind, can turn regardless of the direction of the wind. They can potentially be built to a far larger size than HAWT's , for instance floating VAWT's hundreds of meters in diameter where the entire vessel rotates , can eliminate the need for a large and expensive bearing. n n n Disadvantages : Most VAWTs produce energy at only 50% of the efficiency of HAWTs in large part because of the additional drag that they have as their blades rotate into the wind. This can be overcome by using structures to funnel more and align the wind into the rotor or the "vortex" effect of placing straight bladed VAWTs closely together There may be a height limitation to how tall a vertical wind turbine can be built and how much sweep area it can have. However , this can be overcome by connecting a multiple number of turbines together in a triangular pattern with bracing across the top of the structure. Thus reducing the need for such strong vertical support , and allowing the turbine blades to be made much longer. Most VAWTS need to be installed on a relatively flat piece of land some sites could be too steep for them but are still usable by HAWTs. Most VAWTs have low starting torque, and may require energy to start the turning.

Horizontal-axis n n Horizontal-axis wind turbines have the main rotor shaft and electrical generator at the top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to drive a generator. Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. Turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount. Downwind machines have been built, despite the problem of turbulence, because they don't need an additional mechanism for keeping them in line with the wind, and because in high winds, the blades can be allowed to bend which reduces their swept area and thus their wind resistance. Since turbulence leads to fatigue failures, and reliability is so important, most HAWTs are upwind machines. Types of Horizontal-axis wind trubines: n n Modern Rural Windmills Common modern wind turbines

Horizontal-axis wind turbines n n n n Advantages: n Blades are to the side of the turbine's n center of gravity, helping stability. Tall tower allows access to stronger wind n in sites with wind shear. In some wind shear sites, every ten meters up, the wind speed can increase by 20% and the power output by 34%. Tall tower allows placement on uneven n land or in offshore locations. Can be sited in forests above the tree line. Most are self-starting. Can be cheaper unit of output n because of higher production volume, larger sizes and, in general, higher capacity factors and efficiency. n Disadvantages: HAWTs have difficulty operating in near ground, turbulent winds. The tall towers and long blades (up to 180 feet (55 m) long) are difficult to transport on the sea and on land. Transportation can now cost 20% of equipment costs. Supply of HAWTs is less than demand between 2004 and 2006, turbine prices increased up to 60%. At the end of 2006, all major manufacturers were booked up with orders through 2008. The FAA has raised concerns about tall HAWTs effects on radar near Air Force bases. Their height can create local opposition based on impacts to viewsheds.

Small wind turbines n n Small wind turbines may be as small as a four hundred watt generators for residential use. The small ones often have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind. Larger, more costly turbines generally have geared power trains, alternating current output, flaps and are actively pointed into the wind. Direct drive generators and aeroelastic blades for large wind turbines are being researched. A small wind turbine can be installed on a roof. Installation issues then include the strength of the roof, vibration, and the turbulence caused by the roof ledge.

Turbine design and construction n n Wind turbines are designed to exploit the wind energy that exists at a location. Aerodynamic modeling is used to determine the optimum tower height, control systems, number of blades, and blade shape. Virtually all modern wind turbines convert wind energy to electricity for energy distribution. As described, the modern wind turbine is a system that comprises three integral components with distinct disciplines of engineering science. The rotor component, which is approximately 20% of the wind turbine cost, includes the blades for converting wind energy to an intermediate low speed rotational energy. The generator component, which is approximately 34% of the wind turbine cost, includes the electrical generator, the control electronics, and most likely a gearbox component for converting the low speed rotational energy to electricity. The structural support component, which is approximately 15% of the wind turbine cost, includes the tower for optimally situating the rotor component to the wind energy source.

The benefits of wind energy n Wind energy is an ideal renewable energy because: n n n n n It is a pollution-free, infinitely sustainable form of energy It doesn’t require fuel It doesn’t create greenhouse gasses It doesn’t produce toxic or radioactive waste. Wind energy is quiet and does not present any significant hazard to birds or other wildlife. When large arrays of wind turbines are installed on farmland, only about 2% of the land area is required for the wind turbines. The rest is available for farming, livestock, and other uses. Landowners often receive payment for the use of their land, which enhances their income and increases the value of the land. Ownership of wind turbine generators by individuals and the community allows people to participate directly in the preservation of our environment. Each megawatt-hour of electricity that is generated by wind energy helps to reduce the 0. 8 to 0. 9 tonnes of greenhouse gas emissions that are produced by coal or diesel fuel generation each year.

Wind and the environment n n In the 1970 s, oil shortages pushed the development of alternative energy sources. In the 1990 s, the push came from a renewed concern for the environment in response to scientific studies indicating potential changes to the global climate if the use of fossil fuels continues to increase. Wind energy is an economical power resource in many areas of the country. Wind is a clean fuel; wind farms produce no air or water pollution because no fuel is burned. Growing concern about emissions from fossil fuel generation, increased government support, and higher costs for fossil fuels have helped wind power capacity in the United States grow substantially over the last 10 years. The most serious environmental drawbacks to wind machines may be their negative effect on wild bird populations and the visual impact on the landscape.

The costs of wind energy n The cost of wind energy is determined by: n n n The initial cost of the wind turbine installation The interest rate on the money invested The amount of energy produced Any wind turbine that is installed in a very windy area generates less expensive electricity than the same unit installed in a less windy area. So it’s important to assess the wind at the potential site. Modern wind turbine generators cost between $1500 and $2000 per kilowatt for wind farms that use multiple-unit arrays of large machines. Smaller individual units cost up to $3000 per kilowatt. In good wind areas, the costs of generating electricity range between five and ten cents per kilowatt hour. That cost is somewhat higher than the costs associated with an electrical facility, but wind energy costs are decreasing every year, whereas most conventional generation costs continue to increase.