martes, 29 de abril de 2008

Wind Energy (eolic energy)

Wind is simple air in motion. The origin of wind is complex. The Earth is unevenly heated by the sun resulting in the poles receiving less energy from the sun than the equator does. Also the dry land heats up (and cools down) more quickly than the seas do. The differential heating powers a global atmospheric convection system reaching from the Earth?s surface to the stratosphere which acts as a virtual ceiling.

Wind can be used to do work. The kinetic energy of the wind can be changed into other forms of energy, either mechanical energy or electrical energy. Wind energy is ample, renewable, widely distributed, clean, and mitigates the greenhouse effect if used to replace fossil-fuel-derived electricity.

History of wind as energy source

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. They gave it propeller-type blades, still made with sails. Holland is famous for its windmills.

American colonists used windmills to grind wheat and corn, to pump water, and to cut wood at sawmills. As late as the 1920s, Americans used small windmills to generate electricity in rural areas without electric service. When power lines began to transport electricity to rural areas in the 1930s, local windmills were used less and less, though they can still be seen on some Western ranches.

The oil shortages of the 1970s 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 1980s wind energy really took off in California, partly because of state policies that encouraged renewable energy sources. Support for wind development has since spread to other states, but California still produces more than twice as much wind energy as any other state.

How do we turn wind into energy?

Blowing wind spins the blades on a wind turbine ? just like a large toy pinwheel. This device is called a wind turbine and not a windmill. A windmill grinds or mills grain, or is used to pump water.

The blades of the turbine are attached to a hub that is mounted on a turning shaft. The shaft goes through a gear transmission box where the turning speed is increased. The transmission is attached to a high speed shaft which turns a generator that makes electricity.

If the wind gets too high, the turbine has a brake that will keep the blades from turning too fast and being damaged. 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.

In order for a wind turbine to work efficiently, wind speeds usually must be above 12 to 14 miles per hour. Wind has to be this speed to turn the turbines fast enough to generate electricity. The turbines usually produce about 50 to 300 kilowatts of electricity each. A kilowatt is 1,000 watts (kilo means 1,000). You can light ten 100 watt light bulbs with 1,000 watts. So, a 300 kilowatt (300,000 watts) wind turbine could light up 3,000 light bulbs that use 100 watts!

Wind Energy

An estimated 1% to 3% of energy from the Sun that hits the earth is converted into wind energy. This is about 50 to 100 times more energy than is converted into biomass by all the plants on Earth through photosynthesis. Most of this wind energy can be found at high altitudes where continuous wind speeds of over 160 km/h (100 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat throughout the Earth?s surface and atmosphere.

Wind power plants

Wind power plants, or wind farms as they are sometimes called, are clusters of wind machines used to produce electricity. A wind farm usually has dozens of wind machines scattered over a large area. The Big Spring Wind Power Project in Texas has 46 wind turbines that generate enough electricity to power 7,300 homes. Unlike power plants, many wind plants are not owned by public utility companies. Instead they are owned and operated by business people who sell the electricity produced on the wind farm to electric utilities. These private companies are known as Independent Power Producers.

Operating a wind power plant is not as simple as just building a windmill in a windy place. Wind plant owners must carefully plan where to locate their machines. One important thing to consider is how fast and how much the wind blows. As a rule, wind speed increases with altitude and over open areas with no windbreaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funneling.

Wind speed varies throughout the country. It also varies from season to season. In Tehachapi, California, the wind blows more from April through October than it does in the winter. This is because of the extreme heating of the Mojave Desert during the summer months. The hot air over the desert rises, and the cooler, denser air above the Pacific Ocean rushes through the Tehachapi mountain pass to take its place. In a state like Montana, on the other hand, the wind blows more during the winter. Fortunately, these seasonal variations are a good match for the electricity demands of the regions. In California, people use more electricity during the summer for air conditioners. In Montana, people use more electricity during the winter months for heating.

Small scale production

Wind turbines have been used for household electricity generation in conjunction with battery storage over many decades in remote areas. Household generator units of more than 1 kW are now functioning in several countries. To compensate for the varying power output, grid-connected wind turbines may utilise some sort of grid energy storage. Off-grid systems either adapt to intermittent power or use photovoltaic or diesel systems to supplement the wind turbine.

Wind turbines range from small four hundred watt generators for residential use to several megawatt machines for wind farms and offshore. The small ones have direct drive generators, direct current output, aeroelastic blades, lifetime bearings and use a vane to point into the wind; while the larger ones 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 and direct current generators are sometimes used.

In urban locations, where it is difficult to obtain large amounts of wind energy, smaller systems may still be used to run low power equipment. Distributed power from rooftop mounted wind turbines can also alleviate power distribution problems, as well as provide resilience to power failures. Equipment such as parking meters or wireless internet gateways may be powered by a wind turbine that charges a small battery, replacing the need for a connection to the power grid and/or maintaining service despite possible power grid failures.

Small-scale wind power in rural Indiana.Small scale turbines are available that are approximately 7 feet (2 m) in diameter and produce 900 watts. Units are lightweight, e.g. 16 kilograms (35 lbs), allowing rapid response to wind gusts typical of urban settings and easy mounting much like a television antenna. It is claimed that they are inaudible even a few feet under the turbine. Dynamic braking regulates the speed by dumping excess energy, so that the turbine continues to produce electricity even in high winds. The dynamic braking resistor may be installed inside the building to provide heat (during high winds when more heat is lost by the building, while more heat is also produced by the braking resistor). The proximal location makes low voltage (12 volt, or the like) energy distribution practical. An additional benefit is that owners become more aware of electricity consumption, possibly reducing their consumption down to the average level that the turbine can produce.

According to the World Wind Energy Association, it is difficult to assess the total number or capacity of small-scaled wind turbines, but in China alone, there are roughly 300,000 small-scale wind turbines generating electricity.

Enviromental concerns

Wind energy offers a viable, economical alternative to conventional power plants in many areas of the country. Wind is a clean fuel; wind farms produce no air or water pollution because no fuel is burned.

The most serious environmental drawbacks to wind machines may be their negative effect on wild bird populations and the visual impact on the landscape. To some, the glistening blades of windmills on the horizon are an eyesore; to others, they?re a beautiful alternative to conventional power plants.

Sources: wikipedia, http://www.eia.doe.gov/kids/energyfacts/sources/renewable/wind.html

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Gu�a tur�stica de Zaragoza durante la Expo 2008

Para todo el que quiera conocer un poco m�s Zaragoza y no quedarse s�lo en comprar frutas de Arag�n y ver El Pilar, he preparado esta gu�a tur�stica que ya he colgado en Internet.

La gu�a est� pensada para el viajero que s�lo dispone de un d�a entero para conocer Zaragoza. Comienza a las 10 de la ma�ana en la Aljafer�a y como los libros que le�amos de cr�os de "elige tu propia aventura",.... hay tres finales posibles seg�n las ganas de andar del turista. El final que yo recomiendo en la gu�a es de fuegos artificiales, ya que propongo terminar en el Patio de la Infanta sobre las 19:15 horas

La gu�a est� estructurada en tres partes

- Ayer, Hoy y Ma�ana: d�nde comento pasado, presente y futuro de la ciudad.
- En la calle: D�nde describo la ruta tur�stica
- De tapeo: D�nde comento zonas de tapeo y hago una selecci�n de lugares con la que seguro que ninguno estar�is de acuerdo,.. por lo que invito al turista a no hacerme ni caso y descubrir sus preferidos por s� mismo.

Por favor, para todos los aficionados a la historia como Aragonesche o Bauer, agradecer� much�simo cualquier cr�tica o comentario sobre la informaci�n que incluyo. Me he informado en la web del ayuntamiento y en Wikipedia, pero eso no quiere decir que lo all� puesto sea fiable al 100%. Si he puesto algo mal prefiero saberlo para no seguir cont�ndoselo a los amigos a los que acompa�e por la ciudad en la Expo.

Gu�a tur�stica: ( Grapa a un lado )

Desde estos link os pod�is descargar el pdf con la versi�n para imprimir y poner una grapa a un lado, o bien para ver y leer directamente en la pantalla del ordenador. Con esta versi�n la gu�a queda como cuando fotocopias un libro y te quedan dos p�ginas seguidas del libro por cada cara del folio. Son unos 6,5 MB en total.

http://www.mediafire.com/?mbsx3jbs3zi

http://www.megaupload.com/es/?d=I6X9WXTV

http://www.gigasize.com/get.php?d=mzlrdzj61cb

Gu�a tur�stica: ( Grapas en medio )

Desde estos link os pod�is descargar el pdf con la versi�n para imprimir y poner dos grapas en medio o directamente encuadernarla como he hecho yo poniendo un canutillo y cortando las hojas por la mitad con una guillotina. Esta es la versi�n con la que pod�is crearos un libro y si os gusta, guardar�slo para despu�s de la Expo. Son tambi�n unos 6,5 MB

http://www.mediafire.com/?mmredunxrjn

http://www.megaupload.com/es/?d=DUETF6F6

http://www.gigasize.com/get.php?d=2t9bcbllsvb

A modo de muestra os pongo algunas p�ginas de la gu�a como Im�genes


















Bueno, espero que os guste. Para finalizar un par de consejos para imprimir la gu�a, imagino que ya lo conocer�is de sobra, pero por si os ayuda a alguno os lo comento.... a m� me cost� hasta que lo consegu� imprimir como yo quer�a...:bash:

El primero es como imprimirlo para que el m�rgen blanco alrededor sea el menor posible, elegir la opci�n de " Ajustar a los m�rgenes de la impresora ".





Y por �ltimo, imprimir a doble cara volteando por el lado corto.





Bueno, y ahora a recorrer Zaragoza....


Origen: http://www.skyscrapercity.com/showthread.php?t=611887

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lunes, 28 de abril de 2008

Electricity

Electricity is actually made up of extremely tiny particles called"electrons", that you cannot see with the naked eye unless you havebeen drinking.

The five main kinds of electricity arealternating current, direct current, lightning, static, and European.Most American homes have alternating current, which means that theelectricity goes in one direction for a while, then goes in the otherdirection. This prevents harmful electron buildup in the wires.

Hereis a simple experiment that will teach you an important electricallesson: On a cool, dry day, scuff your feet along a carpet, then reachyour hand into a friend's mouth and touch one of his dental fillings.Did you notice how your friend twitched violently and cried out inpain? This teaches us that electricity is a very powerful force, but wemust never use it to hurt others unless we need to learn an importantelectrical lesson. It also teaches us how an electrical circuit works.When you scuffed your feet, you picked up batches of "electrons", whichare very small objects that carpet manufacturers weave into carpets sothey will attract dirt. The electrons travel through your bloodstreamand collect in your finger, where they form a spark that leaps to yourfriend's filling, then travels down to his feet and back into thecarpet, thus completing the circuit. Amazing Electronic Fact: If youscuffed your feet long enough without touching anything, you wouldbuild up so many electrons that your finger would explode! But this isnothing to worry about unless you have carpeting.

Although wemodern persons tend to take our electric lights, radios, mixers, etc.,for granted, hundreds of years ago people did not have any of thesethings, which is just as well because there was no place to plug themin. Then along came the first Electrical Pioneer, Benjamin Franklin,who flew a kite in a lightning storm and received a serious electricalshock. This proved that lightning was powered by the same force ascarpets, but it also damaged Franklin's brain so severely that hestarted speaking only in incomprehensible maxims, such as "A pennysaved is a penny earned." Eventually he had to be given a job runningthe Post Office.

After Franklin came a herd of ElectricalPioneers whose names have become a part of our electrical terminology:Myron Volt, Mary Louise Amp, James Watt, Bob Transformer, etc. Thesepioneers conducted many important electrical experiments. For example,in 1780 Luigi Galvani discovered (this is the truth) that when heattached two different kinds of metal to the leg of a frog, anelectrical current developed and the frog's leg kicked, even though itwas no longer actually attached to the frog, which was dead anyway.Galvani's discovery led to enormous advances in the field of amphibianmedicine. Today, skilled veterinary surgeons can take a frog that hasbeen seriously injured or killed, implant pieces of metal in itsmuscles, and watch it hop back into the pond just like a normal frog,except for the fact that it sinks like a stone.

But the greatestElectrical Pioneer of them all was Thomas Edison, who was a brilliantinventor despite the fact that he had little formal education and livedin New Jersey. Edison's first major invention in 1877, was thephonograph, which could soon be found in thousands of American homes,where it basically sat until 1923, when the record was invented. ButEdison's greatest achievement came in 1879, when he invented theelectric company. Edison's design was a brilliant adaptation of thesimple electrical circuit: the electric company sends electricitythrough a wire to a customer, then immediately gets the electricityback through another wire, then (this is the brilliant part) sends itright back to the customer again. This means that an electric companycan sell a customer the same batch of electricity thousands of times aday and never get caught, since very few customers take the time toexamine their electricity closely. In fact the last year any newelectricity was generated in the United States was 1937; the electriccompanies have been merely re-selling it ever since, which is why theyhave so much free time to apply for rate increases.

So, thanksto men like Edison and Franklin, and frogs like Galvani's, we receivealmost unlimited benefits from electricity. For example, in the pastdecade scientists developed the laser, an electronic appliance thatemits a beam of light so powerful that it can vapourize a bulldozer2,000 yards away, yet so precise that doctors can use it to performdelicate operations on the human eyeball, provided they remember tochange the power setting from "Vapourize Bulldozer" to "Delicate".

Dave Barry
, U.S. humor columnist, 1988 Pulitzer Prize winner in commentary journalism, "What is Electricity?" (1990).

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