CROATIAN CENTER of RENEWABLE ENERGY SOURCES
3 RENEWABLE SOURCES
|Energy from the Wind
Wind is simply air in motion. It is caused by the uneven heating of the Earth’s surface by the sun. Because the Earth’s surface is made of very different types of land and water, it absorbs the sun’s heat at different rates. One example of this uneven heating can be found in the daily wind cycle.
The daily wind cycle
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 wind. At night, the winds are reversed because the air cools more rapidly over land than over water.
In the same way, the 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.
Wind Energy for Electricity Generation
Today, wind energy is mainly used to generate electricity. Wind is a renewable energy source because the wind will blow as long as the sun shines.
How Wind Turbines Work
Like old fashioned windmills, today’s wind machines (also called wind turbines) use blades to collect the wind’s kinetic energy. The wind flows over the blades creating lift, like the effect on airplane wings, which causes 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.
In 2008, wind machines in the United States generated a total of 52 billion kilowatthours, about 1.3% of total U.S. electricity generation. Although this is a small fraction of the Nation’s total electricity production, it was enough electricity to serve 4.6 million households or to power the entire State of Colorado.
The amount of electricity generated from wind has been growing rapidly in recent years. Generation from wind in the United States nearly doubled between 2006 and 2008.
New technologies have decreased the cost of producing electricity from wind, and growth in wind power has been encouraged by tax breaks for renewable energy and so called “green pricing programs”. Many utilities around the country offer green pricing options that allow customers the choice to pay more for electricity that comes from renewable sources to support new technologies.
Where Wind is harnessed
Wind Power Plants Require Careful Planning
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. It is important to consider how fast and how much the wind blows at the site.
As a rule, wind speed increases with altitude and over open areas that have no windbreaks. Good sites for wind plants are the tops of smooth, rounded hills, open plains or shorelines, and mountain gaps that produce wind funnelling.
Wind Speed is not the same across any country
Wind speed varies throughout any 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.
Major wind power locations
Most of the wind power plants in the world are located in Europe and in the United States where government programs have helped support wind power development. As of 2008, the United States ranks first in the world in wind power capacity, followed by Germany, Spain, and China. Denmark ranks ninth in the world in wind power capacity, but generates about 20% of its electricity from wind.
Large wind turbines (sometimes called wind machines) generated electricity in 34 different States in 2008. The top five wind power producing States with the most wind production were Texas, California, Minnesota, Iowa, and Washington.
Offshore Wind Power
Conditions are well suited along much of the coasts of the United Kingdom to use wind energy. However, there are people who oppose putting turbines just offshore, near the coastlines, because they think the wind turbines will spoil the view of the ocean. There is a plan to build an offshore wind plant off the coast of Cape Cod, Massachusetts, USA.
Wind is a renewable energy source that does not pollute, so some people see it as a good alternative to fossil fuels.
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.
Horizontal-axis Turbines Look Like Windmills
Most wind machines being used today are the horizontal-axis type. Horizontal-axis wind machines have blades like airplane propellers. A typical horizontal wind machine stands as tall as a 20-story building and has three blades that span 200 feet across. The largest wind machines in the world have blades longer than a football field. Wind machines stand tall and wide to capture more wind.
Vertical-axis Turbines Look Like Egg Beaters
Vertical-axis wind machines have blades that go from top to bottom. The most common type — the Darrieus wind turbine, named after the French engineer Georges Darrieus who patented the design in 1931 — looks like a giant, two-bladed egg beater. This type of vertical wind machine typically stands 100 feet tall and 50 feet wide. Vertical-axis wind machines make up only a very small share of the wind machines used today.
Wind Power Plants Produce Electricity
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 world’s largest wind farm, the Horse Hollow Wind Energy Centre in Texas, has 421 wind turbines that generate enough electricity to power 220,000 homes per year.
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.
History of Wind Power
The Oldest Windmills Were in Ancient Persia
Since early recorded history, people have been harnessing the energy of the wind. Wind energy propelled boats along the Nile River as early as 5000 B.C. By 200 B.C., simple windmills in China were pumping water, while vertical-axis windmills with woven reed sails were grinding grain in Persia and the Middle East.
New ways of using the energy of the wind eventually spread around the world. By the 11th century, people in the Middle East were using windmills extensively for food production; returning merchants and crusaders carried this idea back to Europe. The Dutch refined the windmill and adapted it for draining lakes and marshes in the Rhine River Delta. When settlers took this technology to the New World in the late 19th century, they began using windmills to pump water for farms and ranches, and later, to generate electricity for homes and industry.
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.
Windmills Make a Comeback in the Wake of Oil Shortages
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.
Wind Energy & the Environment
In the 1970s, oil shortages pushed the development of alternative energy sources. In the 1990s, 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 power plants (also called wind farms) produce no air or water pollution because no fuel is burned to generate electricity. Growing concern about emissions from fossil fuel generation, increased government support, and higher costs for fossil fuels (especially natural gas and coal) have helped wind power capacity in the United States grow substantially over the past 10 years.
Drawbacks of Wind Machines
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.
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|Energy from Water
Hydropower Generates Electricity
Hydropower is the renewable energy source that produces the most electricity in the United States. It accounted for 6% of total U.S. electricity generation and 67% of generation from renewable in 2008.
Hydropower relies on the Water Cycle
Understanding the water cycle is important to understanding hydropower. In the water cycle:
Mechanical Energy is harnessed from moving water
The amount of available energy in moving water is determined by its flow or fall. Swiftly flowing water in a big river, like the Columbia River in the United States that forms the border between Oregon and Washington, carries a great deal of energy in its flow. Water descending rapidly from a very high point, like Niagara Falls in New York, also has lots of energy in its flow.
In either instance, the water flows through a pipe, or penstock, then pushes against and turns blades in a turbine to spin a generator to produce electricity. In a run-of-the-river system, the force of the current applies the needed pressure, while in a storage system, water is accumulated in reservoirs created by dams, then released as needed to generate electricity.
History of Hydropower
Early uses of waterpower date back to Mesopotamia and ancient Egypt, where irrigation has been used since the 6th millennium BC and water clocks had been used since the early 2nd millennium BC. Other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient China.
Hydropower has been used for hundreds of years. In India, water wheels and watermills were built; in Imperial Rome, water powered mills produced flour from grain, and were also used for sawing timber and stone; in China, watermills were widely used since the Han Dynasty. The power of a wave of water released from a tank was used for extraction of metal ores in a method known as hushing. The method was first used at the Dolaucothi gold mine in Wales from 75 AD onwards, but had been developed in Spain at such mines as Las Medulas. Hushing was also widely used in Britain in the Medieval and later periods to extract lead and tin ores. It later evolved into hydraulic mining when used during the California gold rush.
In China and the rest of the Far East, hydraulically operated “vigina wheel” pumps raised water into irrigation canals. At the beginning of the Industrial revolution in Britain, water was the main source of power for new inventions such as Richard Arkwright’s water frame.Although the use of water power gave way to steam power in many of the larger mills and factories, it was still used during the 18th and 19th centuries for many smaller operations, such as driving the bellows in small blast furnaces and gristmills, such as those built at Saint Anthony Falls, utilizing the 50-foot (15 m) drop in the Mississippi River.
In the 1830s, at the peak of the canal-building era, hydropower was used to transport barge traffic up and down steep hills using inclined plane railroads.
Hydropower is one of the oldest sources of energy. It was used thousands of years ago to turn a paddle wheel for purposes such as grinding grain. U.S. first industrial use of hydropower to generate electricity occurred in 1880, when 16 brush-arc lamps were powered using a water turbine at the Wolverine Chair Factory in Grand Rapids, Michigan.
The first U.S. hydroelectric power plant opened on the Fox River near Appleton, Wisconsin, on September 30, 1882.
Because the source of hydroelectric power is water, hydroelectric power plants must be located on a water source. Therefore, it wasn’t until the technology to transmit electricity over long distances was developed that hydropower became widely used.
Where Hydropower is generated
Hydroelectric power now supplies about 715,000 megawatts or 19% of world electricity. Large dams are still being designed. The world’s largest is the Three Gorges Dam on the third longest river in the world, the Yangtze River. Apart from a few countries with an abundance of hydro power, this energy source is normally applied to peak load demand, because it is readily stopped and started. It also provides a high-capacity, low-cost means of energy storage, known as “pumped storage”.
Most dams were not built for power
Only a small percentage of all dams in the world produce electricity. Most dams were constructed solely to provide irrigation and flood control.
Small Scale hydropower
Small scale hydro or micro-hydro power has been increasingly used as renewable energy source, especially in remote areas where other power sources are not viable. Small scale hydro power systems can be installed in small rivers or streams with little or no discernible environmental effect on things such as fish migration. Most small scale hydro power systems make no use of a dam or major water diversion, but rather use water wheels. Many areas of the North Eastern United States have locations along streams where water wheel driven mills once stood. Sites such as these can be renovated and used to generate electricity. Also, small scale hydro power plants can be combined with other energy sources as a supplement. For example a small scale hydro plant could be used along with a system of solar panels attached to a battery bank. While the solar panels may create more power during the day, when the majority of power is used, the hydro plant will create a smaller, constant flow of power, not dependent on the sunlight.
There are some considerations in a micro-hydro system installation. The amount of water flow available on a consistent basis, since lack of rain can affect plant operation. Head, or the amount of drop between the intake and the exit. The more head, the more power that can be generated. There can be legal and regulatory issues, since most countries, cities, and states have regulations about water rights and easements.
Micro-hydro power can be used directly as “shaft power” for many industrial applications. Alternatively, the preferred option for domestic energy supply is to generate electricity with a generator or a reversed electric motor which, while less efficient, is likely to be available locally and cheaply.
Hydropower and the Environment
Most dams in the world were built mainly for flood control and supply of water for cities and irrigation. A small number of dams were built specifically for hydropower generation. While hydropower (hydro-electric) generators do not directly produce emissions of air pollutants, hydropower dams, reservoirs, and the operation of generators can have environmental impacts
A dam to create a reservoir may obstruct migration of fish to their upstream spawning areas. A reservoir and operation of the dam can also change the natural water temperatures, chemistry, flow characteristics, and silt loads, all of which can lead to significant changes in the ecology (living organisms and the environment) and rocks and land forms of the river upstream and downstream. These changes may have negative impacts on native plants and animals in and next to the river, and in the deltas that form where rivers empty into the ocean. Reservoirs may cover important natural areas, agricultural land, and archaeological sites, and cause the relocation of people.
Greenhouse gases, carbon dioxide and methane, may also form in reservoirs and be emitted to the atmosphere. The exact amount of greenhouse gases produced from hydropower plant reservoirs is uncertain. The emissions from reservoirs in tropical and temperate regions may be equal to or greater than the greenhouse effect of the carbon dioxide emissions from an equivalent amount of electricity generated with fossil fuels.
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