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.


Wind Production

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.

More info at: solarserdar@gmail.com


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:

  • Solar energy heats water on the surface, causing it to evaporate.
  • This water vapor condenses into clouds and falls back onto the surface as precipitation (rain, snow, etc.).
  • The water flows through rivers back into the oceans, where it can evaporate and begin the cycle over again.


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.

More info at: solarserdar@gmail.com


Energy from the Sun

The sun has produced energy for billions of years. Solar energy is the sun’s rays (solar radiation) that reach the Earth. This energy can be converted into other forms of energy, such as heat and electricity.

In the 1830s, the British astronomer John Herschel famously used a solar thermal collector box (a device that absorbs sunlight to collect heat) to cook food during an expedition to Africa. Today, people use the sun’s energy for lots of things.

Solar Energy can be used for heat and electricity

When converted to thermal (or heat) energy, solar energy can be used to:

  • Heat water — for use in homes, buildings, or swimming pools
  • Heat spaces — inside homes, greenhouses, and other buildings

Solar energy can be converted to electricity in two ways:

  • Photovoltaic (PV devices) or “solar cells” change sunlight directly into electricity. Individual PV cells are grouped into panels and arrays of panels that can be used in a wide range of applications ranging from single small cells that charge calculator and watch batteries, to systems that power single homes, to large power plants covering many acres.
  • Concentrating Solar Power Plants generate electricity by using the heat from solar thermal collectors to heat a fluid which produces steam that is used to power the generator. Out of the 11 known concentrating solar power generating units operating in the United States at the end of 2008, 9 of these are in California, 1 in Arizona, and 1 in Nevada.

Two drawbacks of solar energy are:

  • The amount of sunlight that arrives at the Earth’s surface is not constant. It depends on location, time of day, time of year, and weather conditions.
  • Because the sun doesn’t deliver that much energy to any one place at any one time, a large surface area is required to collect the energy at a useful rate

Where solar is found

Solar Energy is everywhere the sun shines.

Solar energy is by far the Earth’s most available energy source. Solar power is capable of providing many times the total current energy demand. But it is an intermittent energy source, meaning that it is not available at all times. However, it can be supplemented by thermal energy storage or another energy source, such as natural gas or hydropower.

California has the world’s biggest solar power plant

Nine solar power plants, in three locations, in California’s Mojave Desert comprise the Solar Energy Generating Systems (SEGS). SEGS VIII and IX (each 80 megawatts), located in Harper Lake, are, individually and collectively, the largest solar power generating plants in the world. SEGS plants are concentrating solar thermal plants.

Concentrating solar power technologies use mirrors to reflect and concentrate sunlight onto receivers that collect the solar energy and convert it to heat. This thermal energy can then be used to produce electricity via a steam turbine or heat engine driving a generator.


Europe has a lot of large photovoltaic power plants

Another solar generating technology uses photovoltaic cells (PV) to convert sunlight directly into electricity. PV cells are made of semiconductors, such as crystalline silicon or various thin-film materials. Photovoltaic can provide tiny amounts of power for watches, large amounts for the electric grid, and everything in between.

Recently multi-megawatt photovoltaic plants have also been built. The Moura photovoltaic power station in Portugal and the Waldpolenz Solar Park in Germany, both completed in 2008, represent the trend toward larger photovoltaic power stations.

Over 100,000 grid-connected PV systems are already installed in Germany, Austria and Italy. The alternating current generated is fed into the local power grid via a separate feed meter. In Germany, the local grid operator purchases the solar power fed into the grid according to the Renewable Energy Sources Act (EEG). This provides the supplier with cash for every generated kilowatt hour fed into the grid. The same happened in Italy (GSE is the government own company in charge of the subsidies).

A grid-connected PV system includes:

  • PV modules for converting light into electrical power
  • An inverter for converting the solar power to mains grid power. The inverter converts the direct current into alternating current and controls the entire system. This is necessary if the public mains grid fails or is switched off.
  • AC meter / Feed meter for recording the power yields.
  • Safety components providing electrical protection for the PV system.


Solar Power can be used almost anywhere at a variety of scales

Low-temperature solar collectors also absorb the sun’s heat energy, but instead of making electricity, use the heat directly for hot water or space heating in homes, offices, and other buildings.

Even larger plants than exist today are proposed for construction in the coming years. Covering 4% of the world’s desert area with photovoltaic could supply the equivalent of all of the world’s electricity. The Gobi Desert alone could supply almost all of the world’s total electricity demand.

Photovoltaic Cells convert sunlight into electricity

A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power. A photovoltaic cell is a no-mechanical device usually made from silicon alloys.

Photons carry Solar Energy

Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum.

When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material’s atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.


The flow of electricity

When the electrons leave their position, holes are formed. When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell’s front and back surfaces creates a voltage potential like the negative and positive terminals of a battery. When the two surfaces are connected through an external load, such as an appliance, electricity flows.

How Photovoltaic Systems operate

The photovoltaic cell is the basic building block of a photovoltaic system. Individual cells can vary in size from about 0.5 inches to about 4 inches across. However, one cell only produces 1 or 2 watts, which isn’t enough power for most applications.

To increase power output, cells are electrically connected into a packaged weather-tight module. Modules can be further connected to form an array. The term array refers to the entire generating plant, whether it is made up of one or several thousand modules.

The number of modules connected together in an array depends on the amount of power output needed.

Weather affects photovoltaic

The performance of a photovoltaic array is dependent upon sunlight. Climate conditions (such as clouds or fog) have a significant effect on the amount of solar energy received by a photovoltaic array and, in turn, its performance. Most modern modules are about 10% efficient in converting sunlight. Further research is being conducted to raise this efficiency to 20%.

Commercial applications of Photovoltaic Systems

The success of PV in outer space first generated commercial applications for this technology. The simplest photovoltaic systems power many of the small calculators and wrist watches used every day. More complicated systems provide electricity to pump water, power communications equipment, and even provide electricity to our homes.

Some advantages of photovoltaic systems are:

  1. Conversion from sunlight to electricity is direct, so that bulky mechanical generator systems are unnecessary.
  2. PV arrays can be installed quickly and in any size.
  3. The environmental impact is minimal, requiring no water for system cooling and generating no by-products.

Photovoltaic cells, like batteries, generate direct current (DC), which is generally used for small loads (electronic equipment). When DC from photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid, it must be converted to alternating current (AC) using inverters, solid state devices that convert DC power to AC.

History of the Photovoltaic Cell

The first practical photovoltaic (PV) cell was developed in 1954 by Bell Telephone researchers examining the sensitivity of a properly prepared silicon wafer to sunlight. Beginning in the late 1950s, PV cells were used to power U.S. space satellites. PV cells were next widely used for small consumer electronics like calculators and watches and to provide electricity in remote or “off-grid” locations were there were no electric power lines. Technology advances and government financial incentives have helped to greatly expand PV use since the mid-1990s.

The first solar module

In 1963, Sharp Corporation developed the first usable photovoltaic module from silicon solar cells. The biggest photovoltaic system at the time, the 242 W module field was set up in Japan. In 1966, Sharp installed its solar modules in the word’s largest lighthouse at that time.

Solar Energy & the Environment

Using solar energy produces no air or water pollution and no greenhouse gases, but does have some indirect impacts on the environment. For example, there are some toxic materials and chemicals, and various solvents and alcohols that are used in the manufacturing process of photovoltaic cells (PV), which convert sunlight into electricity. Small amounts of these waste materials are produced.

In addition, large solar thermal power plants can harm desert ecosystems if not properly managed. Birds and insects can be killed if they fly into a concentrated beam of sunlight, such as that created by a “solar power tower.” Some solar thermal systems use potentially hazardous fluids (to transfer heat) that require proper handling and disposal.

Concentrating solar systems may require water for regular cleaning of the concentrators and receivers and for cooling the turbine-generator. Using water from underground wells may affect the ecosystem in some arid locations.

More info at: solarserdar@gmail.com



CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES)• was founded in 1988 as the non-profit European Association for Renewable Energy that conducts its work independently of political parties, institutions, commercial enterprises and interest groups, • is dedicated to the cause of completely substituting for nuclear and fossil energy through renewable energy, • regards solar energy supply as essential to preserve the natural resources and a prerequisite for a sustainable economy,• acts to change conventional political priorities and common infrastructures in favor of renewable energy, from the local to the international level, • brings together expertise from the fields of politics, economy, science, and culture to promote the entry of solar energy, • provides the opportunity to play a part in the sociocultural movement for renewable energy by joining the association for everyone, • considers full renewable energy supply a momentous and visionary goal - the challenge of the century to humanity. CCRES Željko Serdar Head of association solarserdar@gmail.com

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