Photovoltaic effect is a direct conversion of light into electricity, which as the name implies (photo meaning "light" and voltaic meaning "electricity") and this means converting sunlight directly into electricity. That was the brief definition of the Photovoltaic Effect.


- Photovoltaic materials:

 In order to understand the Photovoltaic effect, we need to know the materials which photovoltaics are made of.

 Photovoltaic materials are special materials called semiconductors such as silicon, which is currently used most commonly.
In order to get the photovoltaic effect we add some impurities to silicon.

First type of silicon used:
Consider silicon with some atoms of phosphorous here and there, maybe one for every million silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbor atoms, but in a sense, the phosphorous has one electron that doesn't have anyone to hold hands with. These electrons, called free carriers. The resulting silicon is called N-type ("n" for negative) N-type doped silicon is a much better conductor than pure silicon.

Second type of silicon used:

Consider silicon is doped with the element boron, which has only three electrons in its outer shell instead of four, to become P-type silicon. Instead of having free electrons, P-type ("p" for positive) has free openings and carries the opposite (positive) charge.

So Photovoltaic materials used to get photovoltaic effect are P-type & N-type silicon.

- Photovoltaic energy:

Sunlight contains packets of energy called 'photons'. When the sunlight strikes the N-type silicon layer, the energy that photons carry makes some electrons free and they move. They move to the P-type layer causing electrical current in the circuit. The electrical energy that we get with photovoltaic effect is called photovoltaic energy.


- What are photovoltaic cells :

 Photovoltaic cells are the units which is connected together to form a solar panel and we can say that a photovoltaic cell is the building unit in the solar system which made of photovoltaic materials and makes a photovoltaic effect under the sun to give solar energy.

- Photovoltaic array:
Photovoltaic array is a combination of solar panels connected together.
Photovoltaic panel or module is a combination of solar cells which is connected together in series or in parallel and collected in one frame. While there are many brands on the market, there are essentially just three types of technologies involved in making a solar panel – monocrystalline, polycrystalline and thin film.

Photovoltaic cells are made of special materials called semiconductors such as silicon, which is currently used most commonly. - See more at: http://www.solar-city.net/2013/10/what-is-photovoltaic-effect_7.html#sthash.lXIq2P6v.dpuf

which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity. - See more at: http://www.solar-city.net/2013/10/what-is-photovoltaic-effect_7.html#sthash.lXIq2P6v.dpuf

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when you decide going solar it's easy to pay for a specialist to install your solar device, but if you want to do it yourself, you are now in the right place.
there are two issues to know as a start.
1st: what is solar radiation and what data you will need? Answered in this topic.
2nd: position and best angle for solar panels or solar device to install? see here

simply...to answer the first question (solar radiation data). we need first to know What is solar radiation?
The Earth receives energy from the sun by way of radiated energy. This radiated energy is carried by tiny particles having no mass called photons. Photons behave like waves and, as such, have a characteristic wavelength, frequency, and energy. It is the energy of these photons that is used in photovoltaic cells to excite electrons so that an electrical current can be produced.

All energy carried by photons is referred to as electromagnetic (EM) energy and spans all possible values for wavelength and frequencies. Ranges of this spectrum—from shortest wavelength to longest—are referred to as gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, and radio waves.

However, different types of stars produce differing amounts of energy in each region of the spectrum. Our sun emits more photons in the visible light and surrounding regions than in any other part of the EM spectrum. This phenomenon may be why our eyes have evolved to see that part of the EM spectrum and not microwaves, gamma rays, or any of the other wavelengths that are emitted at lower intensities by our sun.

The Earth’s atmosphere protects us from the higher-energy forms of light, such as ultraviolet rays. In fact, the existence of life on Earth would be far less likely if these more damaging forms of energy were more abundant. The terrestrial spectrum in Left Figure describes the light that actually reaches the Earth’s surface after passing through the atmosphere. Notice that there are various wavelengths in which the number of photons is greatly reduced as compared to the space solar spectrum. This difference is due to photons being absorbed by atmospheric gases, the best known being ozone (O3), which absorbs higher-energy (lower-wavelength) ultraviolet light below 400 nm. Photons with wavelengths near 900, 1100, and 1400 nm are absorbed by water vapor in the atmosphere.

Now, how can we measure solar power (solar flux)? It's measured by the unit (Watt/m²) or (Btu/ft²*h) depending on the unit used commonly in your country.
To measure it - there is a digital device called (Solar power meter) It's shown in the Left figure and it has also other shapes but this one is common.
by using solar power meter you can measure solar power per square meter The sun gives at the moment and place you are now.(Watt/m²) Of course the amount of power changes by time all over the day.

If you want to be a professional it's recommended to own one - It's easy to get one online from a trusted market like Amazon and we recommend This solar power meter to you. But is there any other way to know nearly the solar power per square meter amount without owning a solar power meter? Of course yes. But you can't get an exact number with it. You can get a range.
Look at the annual world solar energy map below.

You can see that each color represents a range of energy that the place collects all over the year with the unit (KWh/m²) per year.
and to get more accurate number I recommend you to use this online tool.
If you have a problem with understanding any thing feel free to let your comment.

We never forget to recommend you that having a clean world and powerful energy sources is the responsibility of all of us. So as you are here you must play your role by sharing this topic with your friends. We know that your dream is to see our world as a large solar city.

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Solar technology isn’t new. Its history spans from the 7th Century B.C. to today. We started out our dream of the solar city with concentrating the sun’s heat with glass and mirrors to light fires. Today, we have everything from solar-powered buildings to solar powered vehicles.

Here you can learn more about the milestones in the history of solar energy, century by century, and year by year. You can also glimpse the future.

Ancient Egypt.

Cleopatra’s needle

It has been speculated that ancient monuments such as Stonehenge were built to align with the position of the sun at certain times of the year.
The position of the sun is a reliable way to help us tell the time.
The Egyptians knew this, the three Cleopatra’s needles sited in London, Paris, and New York were originally from the Egyptian city of “Heliopolis” written in Greek as Ηλiου πoλις.

The name of the city effectively meant “solar city” and was the place of sun-worship.

It sounds like the destination for a pilgrimage for solar junkies worldwide!

We can be fairly sure that the obelisks that they erected, such as London’s Cleopatra’s needle shown in Figure , were used as some sort of device that indicated a time of day based on the position of the sun.

From 7th Century B.C. to 1200s A.D.

• Magnifying glass used to concentrate sun’s rays to make fire and to burn ants.
• Greeks and Romans use burning mirrors to light torches for religious purposes.
• As early as 212 BC, the Greek scientist, Archimedes, used the reflective properties of bronze shields to focus sunlight and to set fire to wooden ships from the Roman Empire which were besieging Syracuse. (Although no proof of such a feat exists, the Greek navy recreated the experiment in 1973 and successfully set fire to a wooden boat at a distance of 50 meters.)
• Chinese document use of burning mirrors to light torches for religious purposes.
• The famous Roman bathhouses in the first to fourth centuries A.D. had large south facing windows to let in the sun’s warmth.
• Sun rooms on houses and public buildings were so common that the Justinian Code initiated “sun rights” to ensure individual access to the sun.
• Ancestors of Pueblo people called Anasazi in North America live in south-facing cliff dwellings that capture the winter sun.

From 1767 to 1891.

1767
Swiss scientist Horace de Saussure was credited with building the world’s first solar collector, later used by Sir John Herschel to cook food during his South Africa expedition in the 1830s.

1816
On September 27, 1816, Robert Stirling applied for a patent for his economiser at the Chancery in Edinburgh, Scotland. By trade, Robert Stirling was actually a minister in the Church of Scotland and he continued to give services until he was eighty-six years old! But, in his spare time, he built heat engines in his home workshop. Lord Kelvin used one of the working models during some of his university classes. This engine was later used in the dish/Stirling system, a solar thermal electric technology that concentrates the sun’s thermal energy in order to produce power.

1839
French scientist Edmond Becquerel discovers the photovoltaic effect while experimenting with an electrolytic cell made up of two metal electrodes placed in an electricity-conducting solution—electricity-generation increased when exposed to light.

1860s
French mathematician August Mouchet proposed an idea for solar-powered steam engines. In the following two decades, he and his assistant, Abel Pifre, constructed the first solar powered engines and used them for a variety of applications. These engines became the predecessors of modern parabolic dish collectors.

1873
Willoughby Smith discovered the photoconductivity of selenium.

1876
1876 William Grylls Adams and Richard Evans Day discover that selenium produces electricity when exposed to light. Although selenium solar cells failed to convert enough sunlight to power electrical equipment, they proved that a solid material could change light into electricity without heat or moving parts.

1880
Samuel P. Langley, invents the bolometer, which is used to measure light from the faintest stars and the sun’s heat rays. It consists of a fine wire connected to an electric circuit. When radiation falls on the wire, it becomes very slightly warmer. This increases the electrical resistance of the wire.

1883
Charles Fritts, an American inventor, described the first solar cells made from selenium wafers.

1887
Heinrich Hertz discovered that ultraviolet light altered the lowest voltage capable of causing a spark to jump between two metal electrodes.

1891
Baltimore inventor Clarence Kemp patented the first commercial solar
water heater.

1900s.

1904
Wilhelm Hallwachs discovered that a combination of copper and cuprous oxide is photosensitive.

1905
Albert Einstein published his paper on the photoelectric effect (along with a paper on his theory of relativity).

1908
William J. Bailley of the Carnegie Steel Company invents a solar collector with copper coils and an insulated box—roughly, it’s present design.

1914
The existence of a barrier layer in photovoltaic devices was noted.

1916
Robert Millikan provided experimental proof of the photoelectric effect.

1918
Polish scientist Jan Czochralski developed a way to grow single-crystal silicon.

1921
Albert Einstein wins the Nobel Prize for his theories (1904 research and technical paper) explaining the photoelectric effect.

1932
Audobert and Stora discover the photovoltaic effect in cadmium sulfide (CdS).

1947
Passive solar buildings in the United States were in such demand, as a result of scarce energy during the prolonged W.W.II, that Libbey-Owens-Ford Glass Company published a book entitled Your Solar House, which profiled forty-nine of the nation’s greatest solar architects.

1953
Dr. Dan Trivich, Wayne State University, makes the first theoretical
calculations of the efficiencies of various materials of different band gap widths based on the spectrum of the sun.

1954
Photovoltaic technology is born in the United States when Daryl Chapin,Calvin Fuller, and Gerald Pearson develop the silicon photovoltaic (PV) cell at Bell Labs—the first solar cell capable of converting enough of the sun’s energy into power to run everyday electrical equipment. Bell Telephone Laboratories produced a silicon solar cell with 4% efficiency and later achieved 11% efficiency.

1955
Western Electric began to sell commercial licenses for silicon photovoltaic (PV) technologies. Early successful products included PV-powered dollar bill changers and devices that decoded computer punch cards and tape.

Mid-1950s
Architect Frank Bridgers designed the world’s first commercial office building using solar water heating and passive design. This solar system has been continuously operating since that time and the Bridgers-Paxton Building, is now in the National Historic Register as the world’s first solar heated office building.

1956
William Cherry, U.S. Signal Corps Laboratories, approaches RCA Labs’ Paul Rappaport and Joseph Loferski about developing photovoltaic cells for proposed orbiting Earth satellites.

1957
Hoffman Electronics achieved 8% efficient photovoltaic cells.

1958
T. Mandelkorn, U.S. Signal Corps Laboratories, fabricates n-on-p silicon photovoltaic cells (critically important for space cells; more resistant to radiation).

1958
Hoffman Electronics achieves 9% efficient photovoltaic cells.

1958
The Vanguard I space satellite used a small (less than one watt) array to power its radios. Later that year, Explorer III, Vanguard II, and Sputnik-3 were launched with PV-powered systems on board. Despite faltering attempts to commercialize the silicon solar cell in the 1950s and 60s, it was used successfully in powering satellites. It became the accepted energy source for
space applications and remains so today.

1959
Hoffman Electronics achieves 10% efficient, commercially available
photovoltaic cells. Hoffman also learns to use a grid contact, reducing the series resistance significantly.

1959
On August 7, the Explorer VI satellite is launched with a photovoltaic array of 9600 cells (1 cm x 2 cm each). Then, on October 13, the Explorer VII satellite is launched.

1960
Hoffman Electronics achieves 14% efficient photovoltaic cells.

1960
Silicon Sensors, Inc., of Dodgeville, Wisconsin, is founded. It starts producing selenium and silicon photovoltaic cells.

1962
Bell Telephone Laboratories launches the first telecommunications satellite, the Telstar (initial power 14 watts).

1963
Sharp Corporation succeeds in producing practical silicon photovoltaic modules.

1963
Japan installs a 242-watt, photovoltaic array on a lighthouse, the world’s largest array at that time.

1964
NASA launches the first Nimbus spacecraft—a satellite powered by a 470-watt photovoltaic array.

1965
Peter Glaser conceives the idea of the satellite solar power station.

1966
NASA launches the first Orbiting Astronomical Observatory, powered by a 1-kilowatt photovoltaic array, to provide astronomical data in the ultraviolet and X-ray wavelengths filtered out by the earth’s atmosphere.

1969
The Odeillo solar furnace, located in Odeillo, France was constructed. This featured an 8-story parabolic mirror.

1970s
Dr. Elliot Berman, with help from Exxon Corporation, designs a significantly less costly solar cell, bringing price down from $100 a watt to $20 a watt. Solar cells begin to power navigation warning lights and horns on many offshore gas and oil rigs, lighthouses, railroad crossings and domestic solar applications began to be viewed as sensible applications in remote locations where grid connected utilities could not exist affordably.

1972
The French install a cadmium sulfide (CdS) photovoltaic system to operate an educational television at a village school in Niger.

1972
The Institute of Energy Conversion is established at the University of Delaware to perform research and development on thin-film photovoltaic (PV) and solar thermal systems, becoming the world’s first laboratory dedicated to PV research and development.

1973
The University of Delaware builds “Solar One,” one of the world’s first photovoltaic (PV) powered residences. The system is a PV/thermal hybrid. The roof-integrated arrays fed surplus power through a special meter to the utility during the day and purchased power from the utility at night. In addition to electricity, the arrays acted as flat-plate thermal collectors, with fans blowing the warm air from over the array to phase-change heat-storage bins.

1976
The NASA Lewis Research Center starts installing 83 photovoltaic power systems on every continent except Australia. These systems provide such diverse applications as vaccine refrigeration, room lighting, medical clinic lighting, telecommunications, water pumping, grain milling, and classroom television.

1976
David Carlson and Christopher Wronski, RCA Laboratories, fabricate first amorphous silicon photovoltaic cells.

1977
The U.S. Department of Energy launches the Solar Energy Research Institute “National Renewable Energy Laboratory”, a federal
facility dedicated to harnessing power from the sun.

1977
Total photovoltaic manufacturing production exceeds 500 kilowatts.

1978
NASA’s Lewis Research Center dedicates a 3.5-kilowatt photovoltaic (PV) system it installed on the Papago Indian Reservation located in southern Arizona—the world’s first village PV system. The system is used to provide for water pumping and residential electricity in 15 homes until 1983, when grid power reached the village. The PV system was then dedicated to pumping water from a community well.

1980
ARCO Solar becomes the first company to produce more than 1 megawatt of photovoltaic modules in one year.

1980
At the University of Delaware, the first thin-film solar cell exceeds 10% efficiency using copper sulfide/cadmium sulfide.

1981
Paul MacCready builds the first solar-powered aircraft—the Solar
Challenger—and flies it from France to England across the English Channel. The aircraft had over 16,000 solar cells mounted on its wings, which produced 3,000 watts of power.

1982
The first, photovoltaic megawatt-scale power station goes on-line in Hisperia, California. It has a 1-megawatt capacity system, developed by ARCO Solar, with modules on 108 dual-axis trackers.

1982
Australian Hans Tholstrup drives the first solar-powered car—the Quiet Achiever—almost 2,800 miles between Sydney and Perth in 20 days—10 days faster than the first gasoline-powered car to do so.

1982
The U.S. Department of Energy, along with an industry consortium, begins operating Solar One, a 10-megawatt central-receiver demonstration project. The project established the feasibility of power-tower systems, a solar-thermal electric or concentrating solar power technology. In 1988, the final year of operation, the system could be dispatched 96% of the time.

1982
Volkswagen of Germany begins testing photovoltaic arrays mounted on the roofs of Dasher station wagons, generating 160 watts for the ignition system.

1983
ARCO Solar dedicates a 6-megawatt photovoltaic substation in central
California. The 120-acre, unmanned facility supplies the Pacific Gas & Electric Company’s utility grid with enough power for 2,000-2,500 homes.

1983
Solar Design Associates completes a stand-alone, 4-kilowatt powered home in the Hudson River Valley.

1983
Worldwide photovoltaic production exceeds 21.3 megawatts, with sales of more than $250 million.

1984
The Sacramento Municipal Utility District commissions its first 1-megawatt photovoltaic electricity generating facility.

1985
The University of South Wales breaks the 20% efficiency barrier for silicon solar cells under 1-sun conditions.

1986
The world’s largest solar thermal facility, located in Kramer Junction, California, was commissioned. The solar field contained rows of mirrors that concentrated the sun’s energy onto a system of pipes circulating a heat transfer fluid. The heat transfer fluid was used to produce steam, which powered a conventional turbine to generate electricity.

1986
ARCO Solar releases the G-4000—the world’s first commercial thin-film power module.

1988
Dr. Alvin Marks receives patents for two solar power technologies he developed: Lepcon and Lumeloid. Lepcon consists of glass panels covered with a vast array of millions of aluminum or copper strips, each less than a micron or thousandth of a millimeter wide. As sunlight hits the metal strips, the energy in the light is transferred to electrons in the metal, which escape at one end in the form of electricity. Lumeloid uses a similar approach but substitutes cheaper, film-like sheets of plastic for the glass panels and covers the plastic with conductive polymers, long chains of molecular plastic units.

1991
President George Bush redesignates the U.S. Department of Energy’s Solar Energy Research Institute as the National Renewable Energy Laboratory.

1992
University of South Florida develops a 15.9% efficient thin-film photovoltaic cell made of cadmium telluride, breaking the 15% barrier for the first time for this technology.

1992
A 7.5-kilowatt prototype dish system using an advanced stretched-membrane concentrator becomes operational.

1993
Pacific Gas & Electric completes installation of the first grid-supported photovoltaic system in Kerman, California. The 500-kilowatt system was the first “distributed power” effort.

1994
The National Renewable Energy Laboratory (formerly the Solar Energy Research Institute) completes construction of its “Solar Energy Research Facility”, which was recognized as the most energy-efficient of all U.S. government buildings worldwide. It features not only solar electric system, but also a passive solar design.

1994
First solar dish generator using a free-piston Stirling engine is tied to a utility grid.

1994
The National Renewable Energy Laboratory develops a solar cell—made from gallium indium phosphide and gallium arsenide—that becomes the first one to exceed 30% conversion efficiency.

1996
The world’s most advanced solar-powered airplane, the Icare, flew over Germany. The wings and tail surfaces of the Icare are covered by 3,000 super-efficient solar cells, with a total area of 21 m2.

1996
The U.S. Department of Energy, along with an industry consortium, begins operating Solar Two—an upgrade of its Solar One concentrating solar power tower project. Operated until 1999, Solar Two demonstrated how solar energy can be stored efficiently and economically so that power can be produced even when the sun isn’t shining. It also fostered commercial interest in power towers.

1998
The remote-controlled, solar-powered aircraft, “Pathfinder” sets an altitude record, 80,000 feet, on its 39th consecutive flight on August 6, in Monrovia, California. This altitude is higher than any prop-driven aircraft thus far.

1998
Subhendu Guha, a noted scientist for his pioneering work in amorphous silicon, led the invention of flexible solar shingles, a roofing material and state-of-the-art technology for converting sunlight to electricity.

1999
Construction was completed on 4 Times Square, the tallest skyscraper built in the 1990s in New York City. It incorporates more energy-efficient building techniques than any other commercial skyscraper and also includes building-integrated photovoltaic (BIPV) panels on the 37th through 43rd floors on the southand west-facing facades that produce a portion of the buildings power.

1999
Spectrolab, Inc. and the National Renewable Energy Laboratory develop a photovoltaic solar cell that converts 32.3 percent of the sunlight that hits it into electricity. The high conversion efficiency was achieved by combining three layers of photovoltaic materials into a single solar cell. The cell performed most efficiently when it received sunlight concentrated to 50 times normal. To use such cells in practical applications, the cell is mounted in a device that uses lenses or mirrors to concentrate sunlight onto the cell. Such “concentrator” systems are mounted on tracking systems that keep them pointed toward the sun.

1999
The National Renewable Energy Laboratory achieves a new efficiency record for thin-film photovoltaic solar cells. The measurement of 18.8 percent efficiency for the prototype solar cell topped the previous record by more than 1 percent.

1999
Cumulative worldwide installed photovoltaic capacity reaches 1000 megawatts.

solar technology in the 2000s.

2000
First Solar begins production in Perrysburg, Ohio, at the world’s largest photovoltaic manufacturing plant with an estimated capacity of producing enough solar panels each year to generate 100 megawatts of power.

2000
At the International Space Station, astronauts begin installing solar panels on what will be the largest solar power array deployed in space. Each “wing” of the array consists of 32,800 solar cells.

2000
Sandia National Laboratories develops a new inverter for solar electric systems that will increase the safety of the systems during a power outage. Inverters convert the direct current (DC) electrical output from solar systems into alternating current (AC), which is the standard current for household wiring and for the power lines that supply electricity to homes.

2000
Two new thin-film solar modules, developed by BP Solarex, break previous performance records. The company’s 0.5-square-meter module achieves 10.8 % conversion efficiency—the highest in the world for thin-film modules of its kind. And its 0.9-square-meter module achieved 10.6% conversion efficiency and a power output of 91.5 watts — the highest power output for any thin-film module in the world.

2001
Home Depot begins selling residential solar power systems in three of its stores in San Diego, California. A year later it expands sales to include 61 stores nationwide.

2001
NASA’s solar-powered aircraft—Helios sets a new world record for non-rocket powered aircraft: 96,863 feet, more than 18 miles high.

2001
The National Space Development Agency of Japan, or NASDA, announces plans to develop a satellite-based solar power system that would beam energy back to Earth. A satellite carrying large solar panels would use a laser to transmit the power to an airship at an altitude of about 12 miles, which would then transmit the power to Earth.

2001
TerraSun LLC develops a unique method of using holographic films to
concentrate sunlight onto a solar cell. Concentrating solar cells typically use Fresnel lenses or mirrors to concentrate sunlight. TerraSun claims that the use of holographic optics allows more selective use of the sunlight, allowing light not needed for power production to pass through the transparent modules. This capability allows the modules to be integrated into buildings as skylights.

2001
PowerLight Corporation places online in Hawaii the world’s largest hybrid system that combines the power from both wind and solar energy. The gridconnected system is unusual in that its solar energy capacity—175 kilowatts— is actually larger than its wind energy capacity of 50 kilowatts. Such hybrid power systems combine the strengths of both energy systems to maximize the available power.

2001
British Petroleum (BP) and BP Solar announce the opening of a service station in Indianapolis that features a solar-electric canopy. The Indianapolis station is the first U.S. “BP Connect” store, a model that BP intends to use for all new or significantly revamped BP service stations. The canopy is built using translucent photovoltaic modules made of thin films of silicon deposited onto glass.

2002
NASA successfully conducts two tests of a solar-powered, remote-controlled aircraft called Pathfinder Plus. In the first test in July, researchers demonstrated the aircraft’s use as a high-altitude platform for telecommunications technologies. Then, in September, a test demonstrated its use as an aerial imaging system for coffee growers.

2002
Union Pacific Railroad installs 350 blue-signal rail yard lanterns, which incorporate energy saving light-emitting diode (LED) technology with solar cells, at its North Platt, Nebraska, rail yard—the largest rail yard in the United States.

2002
ATS Automation Tooling Systems Inc. in Canada starts to commercialize an innovative method of producing solar cells, called Spheral Solar technology. The technology—based on tiny silicon beads bonded between two sheets of aluminum foil—promises lower costs due to its greatly reduced use of silicon relative to conventional multicrystalline silicon solar cells. The technology is not new. It was championed by Texas Instruments (TI) in the early 1990s. But despite U.S. Department of Energy (DOE) funding, TI dropped the initiative.

2002
The largest solar power facility in the Northwest—the 38.7-kilowatt
White Bluffs Solar Station—goes online in Richland, Washington.

2008, Subsidy Reduction in Spain
Due to the global financial crisis in the year 2008, the Spanish government reduced subsidies on ongoing solar power production in the country. This had a negative effect on the industry across the world.

2010, Evergreen Solar and Solyndra Fail
Two leading solar companies failed. This was due to lack of market for their high technology produced products.

2012, Record Breaking Solar Plants
The past few years have seen enormous investment in utility-scale solar plants, with records for the largest frequently being broken. As of 2012, the history’s largest solar energy plant is the Golmud Solar Park in China, with an installed capacity of 200 megawatts. This is arguably surpassed by India’s Gujarat Solar Park, a collection of solar farms scattered around the Gujarat region, boasting a combined installed capacity of 605 megawatts.

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One of solar energy facts  that the position of the sun in the sky changes from hour to hour, day to day, and year by year. While this might be interesting, it is not very helpful to prospective solar energy users— where exactly do we point our solar device?
How the position of the sun changes over the day
If you dig a stick into the ground, you will see that as the sun moves through the sky, so the shadow will change Figure below.In the morning the shadow will be long and thin; however, toward the middle of the day, the position of the shadow not only changes, but the shadow shortens. Then at the end of the day, the shadow again becomes long.
Of course, this effect is caused by the earth spinning on its axis, which causes the position of the sun in the sky to change relative to our position on the ground.

How the position of the sun changes over the year
The earth is slightly tilted on its axis; as the earth rotates about the sun on its 365_1⁄4 -day cycle, different parts of the earth will be exposed to the sun for a longer or shorter period. This is why our days are short in the winter and long in the summer.
The seasons in the northern hemisphere will be exactly the opposite to that in the southern hemisphere at any one time.
We can see in Figure below that because of this tilt, at certain times of year, depending on your latitude you will receive more or less sunlight per day. Also if you look at your latitude relative to the sun, you can see that as the earth rotates your angle to the sun will be different at any given time of day, depending on the season.

We can see in Figure below an example house in the southern hemisphere we can see that the sun shines from the north rather than the south . . . obviously if your house is in the northern hemisphere, the sun will be in the south!
This graphically demonstrates how the sun’s path in the sky changes relative to your plot at different times of year, as well as illustrating how our rules for solar positioning are radically different depending on what hemisphere we are in. What does this mean for us?
Essentially, it means that we need to change the position of our solar devices if we are to harness the most solar energy all year round.
 
Which direction should my solar device face?
Regardless of where you are on the planet and regardless of the time of year, the sun will of course always rise in the east and set in the west. Let’s say that you live in the northern hemisphere therefore, the sun is above the equator, your solar panels will work best if they are south facing. This is because they will be facing the sun all day long. North facing panels will be facing away from the sun and will be inefficient.
What is the best angle for my solar device?
Whilst everyone can easily agree upon the optimum direction for solar panels, the question of angle of tilt is less straightforward. On the equator it is simple – horizontal is best as the sun will be directly above. At the poles the sun will always be near to the horizon so vertical is best. At other latitudes, such as Egypt, the sun will appear at a different angle relative to the Earth at different times of year (i.e. it will be lower in the sky in winter and higher in summer). This means that if you point your device at where the sun will be at midday on the summer solstice (midsummer) then you may maximize summer efficiency but you’ll lose out in winter when your array will be pointing “over” the sun.
For the Northern hemisphere, your device should be facing as close to south as possible.
In the Southern hemisphere, you want to orientate your solar device to the North.
The best angle for your solar panels to be at is the angle of your latitude.

You can also set your solar device for optimum performance in summer and winter. In summertime, the solar panel should be at a lower angle. This is because the sun is higher over head.
In wintertime, the sun moves across the sky at a lower angle. So by angling your solar panels higher, you will catch more sun rays.
If you plan to adjust your solar array tilt angle seasonally, a good rule of thumb is:

• latitude minus 15° in the summer
• latitude in the spring/fall
• latitude plus 15° in the winter

The latitude of some cities for example:
Cairo Egypt : 30.04449
New York USA :40.7143528
London UK : 51.5112139
Keeping your solar panels out of the Shade
Shade is the thing that will have the biggest negative effect on the efficiency of solar device, and it can even cause damage. Before deciding how to position them therefore you should assess the area to see whether there are any surrounding structures or trees as well as moving throughout the day, shadows will be in different positions throughout the year due to changes in the angle of the sun, so if you are in doubt you may need to make an assessment over a six month period in order to see the full range of shadows. You’ll also need to check at different times of the day.
There are computer models available that will give a virtual picture, which would avoid the need to measure over an extended period.
Solar tracking devices
The best way to ensure that you get maximum efficiency from your solar panels is to use a solar tracking device. A dual axis system (one that tracks the sun across the sky and adjust the angle of the panels according to the height of the sun in the sky) could increase efficiency by 30% – 40%. Such systems are expensive however and it may be more cost effective to either purchase additional panels or simply accept the lesser efficiency of a fixed array.
As well as the initial expense, solar tracking devices tend to need more maintenance than fixed arrays because they have more moving parts.

As you saw making our world a big solar city isn’t very difficult; Just little knowledge, little experience and a lot of work then it could be done .

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Electric power is getting much more expensive with the increase in the cost of fossil fuel. Most people’s electric bills are increasing by at least 6% per year. Solar city is the solution!
One of solar energy facts is that Solar panels can be situated almost anywhere there is direct sunlight available. They can be placed on the roof of a house or in an open unused area, as long as they can come in contact with direct sunlight. If you offset a majority of your electric usage with solar energy, you end up paying at a lower tier level. Therefore, what electricity you do use, is at the lowest price.

Advantages of solar energy

A solar system will actually increase the value of your home.

Solar energy can be a very efficient source of energy in a very large area of our planet.

On overcast days, there can still be production with some of the newer technologies that are in existence.
It is very costly to lay new high voltage lines across new territory, where solar panels can be placed in any remote location at a fraction of the cost.
There is no pollution put into the atmosphere from solar panels.
Although the initial investment on solar is fairly high, there is very little upkeep expense.
Another great pro for solar energy is the ability to gather from the largest energy source available, the sun from the most remote areas of the planet, many of which are not even linked to a national grid system.

Even in space, solar panels can be utilized to gather energy to power spacecraft.
Solar can be installed on top of residential roofs or above parking structures, eliminating the problem of finding the required space for solar panels.
The warranty on most solar panels is 20 years or more. The solar inverters are typically guaranteed for at least 10 years.
Solar reduces the use of fossil fuel and our dependency on it. Solar is truly a green source of energy.
There is no noise pollution generated during solar production. It is the quietest way to produce energy.

The use of fossil and even other renewable fuels, such as wind and hydro production can be very noisy.

Disadvantages of solar energy

The biggest con of solar power is the cost of solar panels. The initial cost, or start-up expense, is pretty high.
Solar can only be produced during daylight hours. Therefore, for 50% or more of the time, your system isn’t producing any power.
Cloudiness or anything that blocks the sun from hitting the solar device can affect the efficiency of the system.
The more pollution or dust that gets on a solar panel, the less productive it will be. Solar panels need to be cleaned off periodically to keep a system at its maximum efficiency.
Some areas of the planet aren’t as conducive to sunny weather. The more rainy an area is, the less solar production you can have.

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What is a Solar City ?
A solar city is an urban community that is committed to the development of sustainable energy to power its development, rather than the continuing reliance on fossil and nuclear fuels. It is a world wide movement that seeks to share knowledge and best practice on tackling some of the major issues of the early 21st century - that of climate change and peak oil.

Benefits of Solar

• Save on Electricity Costs
  solar energy will dramatically reduce your electric bill. Any excess power your solar system generates during the day will flow back to the utility grid and your meter literally spins backward! Utility companies will pay or credit you for this electricity,reducing your electric bill even further.(The matter may not be as such optimism, but you certainly will save a lot of money)
• Protect Yourself From Rising Prices
  Residential electricity prices have risen 38% since 2000. Utility companies are dependent on fossil fuels such as oil and natural gas,which are vulnerable to volatile foreign markets. When you switch to solar power,you can lock in low, predictable electricity costs for years into the future. As utility rates continue to rise, your savings will grow every year.
• Protect the Environment
  Every solar system has a significant environ-mental impact. An average sized solar system reduces CO₂emissions equivalent to the amount absorbed by 60 trees, or released by driving a car over 125,000 miles.
• Increase Your Home Value
  A recent study from the Appraisal Institute demonstrated that the selling price of homes increased by $20 for every $1 decrease in annual utility bills.

--> Founded solar cities around the world :
Sacramento

                                                 






Dezhou

Australian Solar Cities



UAE Masdar solar city



Solar City Tower


Indian Solar Cities

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We have seen before what goes on at the sun as a source of our energy, we now need to explore what happens after that solar energy travels all the way through space to reach the earth’s orbit and see these solar energy facts.
Outside the earth’s atmosphere, at any given point in space, the energy given off by the sun (insolation) is nearly constant. On earth, however, that situation changes as a result of:
● The earth changing position in space
● The earth rotating
● The earth’s atmosphere (gases, clouds, and dust) 
 
The gases in the atmosphere remain relatively stable. In recent years, with the amount of pollution in the air, we have noticed a phenomenon known as global dimming, where the particulate matter resulting from fossil fuels, prevents a small fraction of the sun’s energy from reaching our solar city (the earth).
Clouds are largely transient, and pass from place to place casting shadows on the earth.
In most places on Earth, the weather changes with the seasons. We generally associate winter with cold, ice, and snow. We think of showers, green grass, and new flowers when we think of spring. Summer brings to mind hot, humid, sunny weather. Autumn means falling leaves with cooler temperatures.
A season, then, is one of the four parts of the year (winter, spring, summer, and fall), each associated with a particular type of weather and happenings in nature.
Most of us have been comfortable with this knowledge since we were very young.
We’ve observed it year after year. Why do we have the seasons?
To understand the reason for seasonal temperature differences, we must consider the following diagram. (See figure below for the seasons in the Northern hemisphere.)
Specifically, we must pay attention to the angle of the tilt of the Earth as it relates to the sun in each of the four seasons. It helps to start with this information: The Earth’s axis is not sitting perfectly vertical. That is, if the Earth was a big, fat, juicy apple and you stuck a popsicle stick (axis) through its South Pole and passed it up through its North Pole, it wouldn’t sit flat. It would lean over. The amount it would lean is 23.5 degrees from vertical. Our big, fat, juicy Earth is leaning 23.5 degrees from vertical, too, regardless of the season. What changes from one season to the next is not the amount or the direction the Earth is tilted, but the orientation of the Earth’s tilt with respect to the sun.

-->Look at the diagram again. Notice that the Earth is spinning on its axis. (our solar city is spinning on its axis.) making rotational movement. It has nothing to do with the seasons, but makes a night and day difference in our lives! When our part of the Earth rotates to face the sun (regardless of the season), it’s day. When we face away (again regardless of the season), it’s night.
Getting back to the cause for the seasons, we now know what the reason for the seasons isn’t the rotation of the Earth on its axis. And it’s not the tilt of the Earth by itself; the Earth tilts 23.5 degrees from vertical all the time. Look at the diagram again. Notice that as we go from one season to the next, the Earth revolves around the sun.
It makes one complete revolution around the sun in one year, actually in 365 1/4 days and 8 minutes.
Viewed from upper Figure, this path makes a circle.
It’s when we combine the ideas of axial tilt and one complete revolution around the sun that things get interesting. They get interesting because the end result is that during one season the Earth leans toward the sun, during one season the Earth leans away from the sun, and during two seasons the Earth leans neither toward nor away from the sun.
Assuming you live in the Northern hemisphere. ( I think most of us do . Tell us if you don’t.)
The season when the Earth leans toward the sun is Summer.
The season when the Earth leans away from the sun is Winter.
The seasons when the Earth leans neither toward nor away from the sun are Spring and Fall.
Check out the diagram one more time. When the Earth tilts towards the sun, the Earth receives the sun’s most direct rays. What does that mean for us? Have you ever been riding in the car on a long trip when the passengers in the car start to argue about how cool the air conditioner should be? The passengers sitting in the “sunny” parts of the car--where the sun’s rays are the most direct--are HOT. They want the AC cranked. Those who are sitting where the sun’s rays are not as direct want it a little warmer. It’s the same with the seasons. During the season when our part of the solar city (Earth) tilts towards the sun, the sun’s rays strike us most directly and we’re hot. (There are also more hours of daylight, which means more time for our part of the planet to absorb solar energy, which again means hot.)
As a result of the sun appearing to be in a different place in the sky, we may need to move our solar devices to take account of this. Figure below shows how a flat plate collector may need to be moved at different times of the year to take account of the change in the sun’s position in order to harness energy effectively.

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Sun is the largest object in our solar system and contains approximately 98% of the total solar system mass.
It is 92.95 × 10⁶ miles away from us (149.6 × 10⁶ km) .
It has a diameter of 864,950 miles (1.392 million km.)
the amount of solar energy that reaches us is equal to 10,000 times the annual global energy consumption. On average, 1,700 kWh per square meter every year.
How does the sun work?
One of solar energy facts is that the sun is effectively a massive nuclear reactor. When you consider that we have such an incredibly huge nuclear reactor in the neighborhood already, it seems ridiculous that some folks want to build more!
The sun is constantly converting hydrogen to ­helium, minute by minute, second by second.­­­
But what stops the sun from exploding in a massive thermonuclear explosion?—simple gravity! The sun is caught in a constant struggle between wanting to expand outwards as a result of the energy of all the complex reactions occurring inside it, and the massive amount of gravity as a result of its enormous amount of matter, which wants to pull everything together. All of the atoms inside the sun are attracted to each other, this produces a massive compression which is trying to “squeeze” the sun inwards.
Meanwhile, the energy generated by the nuclear reactions taking place is giving out heat and energy which wants to push everything outwards. Luckily for us, the two sets of forces balance out, so the sun stays constant!
Structure of the sun.
Figure below illustrates the structure of the sun—now let’s explain what some of those long words mean! Starting from the center of the sun we have the core, the radiative zone, the convective zone, the photosphere, the chromosphere, and the corona.
The core
The core of the sun possesses two properties which create the right climate for nuclear fusion to occur—the first is incredibly high temperature 15 million degrees Celsius (I don’t envy the poor chap who had to stand there with a thermometer to take the reading) and the second is incredibly high pressure. As a result of this nuclear fusion takes place. In nuclear fusion, you take a handful of hydrogen nuclei—four in fact, smash them together and end up with one helium nucleus. There are two products of this process—gamma rays which are high-energy photons and neutrinos, one of the least understood particles in the universe, which possess no charge and almost no mass.
The radiative zone
Next out from the core is the radiative zone. This zone is so named because it is the zone that emits radiation. A little bit cooler, the temperature in the radiative zone ranges from 15 million to 1 million degrees Celsius (even at that temperature though, I still wouldn’t have liked to have been the one holding the thermometer).
What is particularly interesting about the radiative zone, is that it can take millions of years for a photon to pass through this zone to get to the next zone, aptly named the convective zone!
The convective zone
This zone is different, in that the photons now travel via a process of convection—if you remember high school physics, you will recollect that convection is a process whereby a body makes its way to a region of lower temperature and lower pressure. The boundary of this zone with the radiative zone is of the order of a million degrees Celsius; however, toward the outside, the temperature is only a mere 6,000°C (you still wouldn’t want to hold the thermometer even with asbestos gloves)
The photosphereThe next region is called the photosphere. This is the bit that we see, because this is the bit that produces visible light. Its temperature is around 5,500°C which is still mighty hot. This layer, although relatively thin in sun terms is still around 300 miles thick.
The chromosphere.Sounding like a dodgy nightclub, the chromosphere is a few thousand miles thick, and the temperature rises in this region from 6,000°C to anywhere up to 50,000°C. This area is full of excited hydrogen atoms, which emit light toward the red wavelengths of the visible spectrum.
The coronaThe corona, which stretches for millions of miles out into space, is the outer layer of the sun’s atmosphere. The temperatures here get mighty hot, in fact up to a million degrees Celsius. Some of the features on the surface of the sun can be seen in Figure below.
Features of the sun
Now we might like to take a look at what goes on the surface of the sun, and also outside it in the immediate coronal region.( Take a look at the upper figure )
Coronal holes form where the sun’s magnetic field lies. Solar flares, also known as solar prominences, are large ejections of coronal material into space. Magnetic loops suspend the material from these prominences in space. Polar plumes are altogether smaller, thinner streamers that emanate from the sun’s surface.

After all of this don’t you think that we can depend on solar energy as a main source of our energy consumption and don’t you believe that Earth is a solar city !

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