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Generating Electricity by Photoelectric Effect.

Hussain.Q, Uzair. A

January 1st, 2013

In modern civilization, the need for more environmentally friendly forms of energy has grown to an extent that the use of fossil fuels is now looked down upon. The negative environmental effect of fossil fuels has caused researchers to search for alternative types of energies to generate electricity. A prominent way to generate electricity through a greener medium is through the use of solar panels. Solar panels don’t pollute as much as fossil fuels and in the human timeline, the abundance of solar power will never run out, whereas fossil fuels will eventual run out of supply. Photovoltaic or solar cells in the solar panels convert the solar energy from the sun into usable electrical energy.

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Solar panels absorbing solar cells from the sun in order to generate electricity.

The photoelectric effect                                                                                                    

Einstein’s explanation on the photoelectric effect is that it takes a certain amount of energy to eject an electron from a metal surface. This energy is known as the work function (W), which depends on the metal that the electron is being ejected from. Electrons can gain energy by interacting with photons. If a photon has enough energy at least as big as the work function, the photon energy can be transferred to the electron and the electron will have enough energy to escape from the metal. A photon that’s energy is less than the work function will never be able to eject electrons.

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Electrons ejected by a metal surface provided that the frequency of the light is greater than the threshold frequency.

The photoelectric effect before Einstein’s explanation was really unknown. Scientists couldn’t really understand why light with low-frequency and high-intensity would not cause electrons to be produced, while light with higher-frequency and low-intensity would. But now it is easy to understand why this happens, since we know that light is made of photons, it is not the total amount of energy that’s important to the creation of electrons but it is the energy per photon that is important.

Problem                                                                                                                                           

A challenge in producing photovoltaic cells is increasing the efficiency as much as possible. The Sun’s rays include the electromagnetic spectrum and no material has a threshold frequency that can relate with the majority of the electromagnetic spectrum. Often the unconverted energy in the cell is given off as heat hence becoming extremely inefficient.

Solution

Scientists have come up with an idea of splitting the sunlight into smaller components and those smaller components will be sent to the different material that is designed to deal with each kind of threshold frequency. Before now, scientist had difficulty directing light at such a fine stage. Recent breakthroughs in optics and lenses have increased knowledge in this area and thus can be used to increase the efficiency of the Solar Panel.

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Splitting light to increase efficiency of photovoltaic cells

Real life Implications                                                                                                                    

As the growing need for a renewable source of energy drive human beings to search for other solutions, the usage of solar panels can be perfected to produce energy in daily lives. Using the application of photovoltaic cells, energy can be produced to power homes, cars, and even big offices. Photovoltaic cells have come a long way and are now being produced and installed for considerably cheap money. These cells are grouped into frames called Photovoltaic Module also known as, Solar Panels. These Modules are then placed into arrays, which are capable of producing colossal amounts of electricity. However of the efficiency of these cells is sometimes questioned. Recent breakthroughs are allowing these cells to produce fifty percent more energy than before.

Nowadays, solar energy has become extremely popular and ordinary citizens are prepared to mount Solar Panels on the roofing of their houses. These modules sometimes are responsible for creating partial or all of the energy required in the household. Since the cost of manufacturing photovoltaic cells and arranging them into modules has gone down over the years, more and more people are considering solar energy as a way of life. Soon most houses will run on solar energy.

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House partially powered by solar panels.

As the production of electric vehicles is rising, it is reducing dependence on gas powered combustion engines, which are one of the leading causes in greenhouse emissions. Since there is now competition in the motor market for producing more and more reliable electric cars, more and more research is being put into solar powered cars.

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Vehicle powered by solar panels.

Conclusion:

Since the environment needs to be conserved and burning fossil fuels are prone to diminishing, Solar Energy should be the next frontier since it is a form of renewable energy. The photoelectric effect will enable will enable scientists to harness the energy of the sum into photovoltaic cells which can be arranged into modules and ultimately arrays. Solar Panels will eventually be on top of every home, vehicle and even cities providing green and clean energy.

 References:

http://faculty.virginia.edu/consciousness/images/photoelectric%20effect.gif, retrieved January 1st, 2013

http://on3dprinting.com/wp-content/uploads/2012/06/20120616-Photovoltaic-PV.png, retrieved January 1st, 2013

http://why.knovel.com/all-engineering-news/2174-prism-power-solar-cells-could-dramatically-improve-by-splitting-light-into-parts.html, retrieved January 1st, 2013

http://static.ddmcdn.com/gif/solar-powered-vehicle-possibility-4.jpg, retrieved January 1st, 2013

http://physics.bu.edu/~duffy/PY106/PhotoelectricEffect.html, retrieved January 1st, 2013

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Alternative Energy: Harnessing Solar Energy

Katherine L., Alexis F.

Sunlight is a remarkable energy source – but one that can provide challenges to harness. One such challenge that often plagues solar panel installation is misalignment. Installations frequently use pricey solar tracking systems, for example multi-axis platforms that point a solar panel towards the sun, however this uses up electricity and often costs about 25% of a panel’s installation cost. Panels gather two types of light – diffused sunlight (negligible during energy collection) and direct sunlight (makes up about 90% of energy collected). A solar tracker helps to collect that direct sunlight, but its ultimate price proves it not to be a not very profitable solution.

In 2012, two recent Sir Winston Churchill High School graduates, Bruce Gao and Matt Privman, founded SimplySolar, a mobile application that allows people to align solar panels using GPS coordinates, after noticing many solar panel alignment programs required laptops and internet access, which is often hard to access in developing countries where alternative energy is needed the most. To read more, visit http://blogs.calgaryherald.com/2012/10/04/startup-of-the-week-simplysolar/.

The Photoelectric Effect

Solar panels are composed of solar cells, and the phenomenon that occurs in these solar cells is called the photoelectric effect. When light frequency and light intensity are manipulated, it can be observed that if the frequency were to fall below a certain value (different for different materials), nothing happens, no matter what the light intensity is. On the other hand, for frequencies above that certain value, electrons were observed on the surface of the material. In addition, if the intensity of the light were then raised, more electrons were ejected from the material and if the frequency was increased, this would occur with greater kinetic energy. This relationship is shown in Figure 1.

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Figure 1. During the photoelectric effect, the kinetic energy of electrons increases as the photon frequency increases above a certain value. If the photon frequency is below this value, then a vertical line occurs (indicating the photon energy is too low) and consequently, no electrons will be ejected from the material.

Einstein concluded that this provided evidence that light has the nature of a particle (bundles of light called photons). These photons would bear energy proportional to their frequency. It requires a particular minimum energy, called the ionization energy, to eject an electron fully out of an atom, and a quantity of energy below this ionization energy, called the work function, is needed to free an electron. If the energy of the photon is too low (in other words, the frequency is too low), then no matter how many photons strike the atom, the electron cannot be freed. On the other hand, if the energy of the photon is above the ionization energy level, an increase in the intensity increases the number of photons, which in turn increases the number of electrons ejected from the atoms.

Semiconductors, Bands, and Band Gaps

In a solar cell, the photoelectric effect works in a different way to produce electrons – they do not leave the surface of the material. Because recombination of the electron and ion is instantaneous in most materials, only the exceptions can be used to build solar cells. These materials are called semiconductors.

When atoms are trapped together in a solid, they usually become isolated by regular spacing in all directions, which forms a lattice, also known as a crystal structure. Because the atoms in the lattice influence one another, the electron energy levels of the atoms combine to become “bands.” These bands can either be partially or completely full, or empty. In metals, the band is partially full, and this allows electrons to wander within the material. These materials are called conductors. On the other hand, materials called insulators have all their bands filled. Therefore, since unfilled bands are at a higher energy level, electrons are not able to move unless external energy equivalent to the gap in energy between bands is applied, which is called the band gap (portrayed in Figure 2).

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Figure 2. Electron bands in a solid. The valence band exists below the band gap and the conduction band occurs above the band gap. Acceptor states would lie immediately above the valence band, while donor states would sit immediately below the conduction band.

In semiconductors, the filled band, also called the valence band, and the band in which electrons are free to move, or conduction band, are divided by a potential difference of approximately 1 volt. Therefore, incoming light can impel an electron from the valence band into the conduction band if it possesses energy of approximately 1 electron volt. Ultimately, if the electron in the conduction band doesn’t recombine, its energy can be surrendered in an external circuit prior to returning to the material.

Semiconductor Doping

To avoid the recombination discussed above, solar cells use two different types of ‘doped semiconductor’. Pure silicon is developed the presence of silicon vapor that is doped with acceptors or donors to insert layers of p-type or n-type material. For p-type semiconductors, atoms with fewer electrons in the outermost shell than in the rest of the atom are present on intermittent lattice sites, causing holes for electrons. Conversely, n-type semiconductor lattice sites have atoms possessing more electrons in the outermost shells than the rest of the atom. These extra electrons can move around in the n-type material when an external potential is applied, while in the p-type material, it is the holes that move around.

Using n-type and p-type together results in the creation of a p-n junction, where the electrons in the n-type region combine with the holes in the p-type in the region close to the boundary. This eliminates free charges and forms an internal electric field there within the semiconductor that averts the movement of other charges. When an external electric field is applied, it could act in two ways: with or against the direction of the internal field at the boundary. A current can only flow due to an external electric field in the direction that allows the internal electric field to be minimized. Devices that allow this to occur are called diodes.

Connection Between Solar Cells and Photovoltaic Cells

The word photovoltaic is composed of ‘photo’, indicating light, and ‘voltaic’, indicating a potential difference from light. The light directly frees electrons, and the diode action makes certain that if one of the materials composing the junction undergoes the photoelectric effect and produces charges, the electrons can flow in only one direction. The current must pass through an external circuit to reach the other side of the p-n junction and join with the opposite charge.

Therefore, as long as light is incident on the solar cell, charges will be produced via the photoelectric effect and the current will flow. Needless to say, when there is no light, there is no current. This is the main problem with solar energy; when the Sun goes sets, or is covered by a cloud, the cell will cease to produce current.

Solar Cells

Solar cells work to directly transform light into electricity. As described above, when light strikes, electrons are liberated in the p-type region and holes are produced in the n-type region; this lowers the potential energy barrier at the p-n junction. A current flows and establishes an external potential difference. Solar cells act similar to diodes, forcing currents to flow in only one direction.

Standard solar cell cross-sections can be observed in Figure 3b and c. A solar cell from the outside is shown in Figure 3d. The thin lines in Figure 3d represent collectors of charge that have been separated within a solar cell. The ridges cover wires that carry the charge away from the thin strips. Excess energy from the band gap is converted to thermal energy in the solar cell, increasing its temperature. To minimize this, it is required to match the band gap to the available visible light.

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Figure 3 a. Solar cell drawing. b. Connections for a p-type solar cell. c. Connections for n-type solar cell. d. Actual solar cell.

 

 

 

 

 

 

 

 

 

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Figure 4. Drawing of a photons coming into contact with a solar cell.

 

 

 

The solar cells are single wafers of semiconductor. Each wafer can produce a small amount of power at the potential difference (voltage) determined by its band gap. To use the cells for mass energy collection, they must be assembled into larger structures, and then from into even larger structures.

Societal Implications

The use of solar panels in modern day society is crucial as a source of alternative and renewable energy. The sun (and solar energy) will be around much longer than fossil fuels will be and are much cleaner. In addition to being “clean” (or free of pollution), using solar panels is also much less time consuming and may be used with little maintenance – with the help of programs such as Simply Solar.

Solar panels would be extremely beneficial in rural or developing communities such as South Africa, Nepal, or some regions of China. These often remotes regions have trouble acquiring and utilizing electricity – even if these areas were near urban centers many lack the necessary funds to live sustainable lives when depending on electricity from outside companies. Solar panels after purchase (or donation) require little to no funds to upkeep apart from cleaning and realigning. This would provide many communities with the electricity to help purify water and heat homes. The potential that this technology has to improve the lives of individuals is endless – in just the last year alone over 3.4 million individuals have died from water-disease related deaths, and over 780 million individuals lack access to clean drinking water.

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Figure 5. A photo of students at the Kopan monastery

in Kathmandu, Nepal standing beside donated solar

panels.

 

 

 

 

On a global scale, solar panels will also help reduce pollution – a great deal of electricity is generated by burning fossil fuels or other methods that create pollution such as smog which are reported to have a multitude of harmful side-effects. In addition, the burning of fossil fuels results in the release of greenhouse gases, which trap heat in Earth’s atmosphere. This increase in greenhouse gases and temperature would result in global warming; the melting of ice caps and the subsequent rise in sea level and flooding.

In conclusion, solar panels though often thought of as expensive and as a high-maintenance technology are actually quite simple to upkeep – it’s benefits outweighing the expenses. With technologies such as Simply Solar, panels can be aligned to generate the greatest amount of electrical energy based on the angle in relation to the sun. On a societal aspect, this technology will also aid in reducing global warming and decrease the number of contaminated water related deaths. Overall, solar panels are an extremely useful and revolutionary piece of technology that can only change our society for the better.

References

Foroudastan, Saeed . Solar Power and Sustainability in Developing Countries. unknown: Engineering Technology and Industrial Studies College of Basic and Applied Sciences Middle Tennessee State University, 2006.

Knier, Gil. “How do Photovoltaics Work?  – NASA Science.” NASA Science. http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/ (accessed January 1, 2013).

“Solar Cells.” The NEED Project. solardat.uoregon.edu/download/Lessons/Appendix_E_HowSolarCellsWork.pdf (accessed January 1, 2013).

“Solar Energy Facts – Current Solar Energy Information from Solar Online | Solar Content.” Solar Shop – Solar Power, Solar Panels, Solar Systems, Inverters – Solar Online Australia – Solar Online Australia. http://www.solaronline.com.au/content/solar-energy-facts/ (accessed January 2, 2013).

“Solar Power Energy Information, Solar Power Energy Facts – National Geographic.” Environment Facts, Environment Science, Global Warming, Natural Disasters, Ecosystems, Green Living – National Geographic. http://environment.nationalgeographic.com/environment/global-warming/solar-power-profile/ (accessed January 2, 2013).

“Solar cells — the physics behind them.” Solarbotics.net — Home page. http://www.solarbotics.net/starting/200202_solar_cells/200202_solar_cell_physics.html (accessed January 2, 2013).

“The Physics of Sustainable Energy Generation.” UBC Physics & Astronomy Outreach – Home. http://outreach.phas.ubc.ca/phys420/p420_01/james/solarphysics.htm (accessed January 2, 2013).

“Water Facts: Water.” Water.org. http://water.org/water-crisis/water-facts/water/ (accessed January 2, 2013).

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The Power of Wind

The Power of Wind

Dilum W         Ian V

 

In the modern society, the need for greener forms of energy have grown. The use of fossil fuels is no longer looked upon as being efficient source for energy. The search for alternative types of energies have grown in the past years. One of the most popular sources of energy is wind energy. The wind power is clean and a plentiful source of energy. Wind is the result from the uneven heating of the Earth by the Sun and the tendency of temperature to attempt to reach an equilibrium. The kinetic energy of the wind is harnessed by a turbine. The turbine changes the kinetic energy into electrical energy. Generally, the bigger the surface of the turbine leads to more energy that gets produced.

As mentioned in the previous paragraph, the wind turbines turn the kinetic energy of the wind into electrical energy. This is similar to the principle of electromagnetic induction.  Electromagnetic induction works when the current is generated in a conductor by placing the conduction in a changing magnetic field.

The simplest wind energy turbine consists of the rotor blades, shaft, and generator. The blades and the hub together are called the rotor. When the wind hits the blades, it transfers some of the energy to the rotor. When the rotor spins, the shaft also spins. Therefore, the rotor transfers its mechanical energy to the shaft. The shaft enters an electrical generator on the other end. Inside the generator, the shaft connects to an assembly of permanent magnets that surrounds the conductor (a coil of wire). When the rotor spins the shaft, the shaft spins the magnet, generating voltage to the coil of wire. The voltage sends an electrical current (AC power) through the power lines. Through electromagnetic induction, the mechanical energy of wind is turned into electrical energy.

The benefits of using wind power are: it is a clean fuel source, does not pollute the air, and do not produce atmospheric emissions that cause acid rain or greenhouse gasses.  It is also a renewable source of energy and is one of the lowest-priced renewable sources of energy. Wind turbines can be built on rural areas, and do not use the land farmers and ranchers need. However, there are concerns over the impact of wind power on wildlife. Birds have been killed by flying too close to the rotating blades. There are also complaints of noise pollution by the noise that is produced by the blades.  In terms of cost, transmission lines need to be built to bring the electricity from the wind farm to the city.

Although there are some disadvantages to using wind power, the advantages of the source of energy surpass the disadvantages. As a result, currently, wind energy is the fastest growing energy source in the world.

References

Article about Wind power. Retrieved June 7, 2012, from

http://topics.nytimes.com/top/news/business/energy-environment/wind-power/index.html

Wind farm. Retrieved June 7, 2012, from

http://plainswindeis.anl.gov/guide/photos/index.cfm

Parts of a wind turbine. Retrieved June 7, 2012, from

http://www1.eere.energy.gov/wind/wind_how.html

Electromagnetic induction. Retrieved June 7, 2012, from

http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/electroinduction.htm

Wind turbines. Retrieved June 7, 2012, from

http://science.howstuffworks.com/environmental/green-science/wind-power1.htm

How do generators work? Retrieved June 7, 2012, from

http://www.ehow.com/how-does_5163045_do-generators-make-electricity.html

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The Photoelectric Effect and Power Generation from Solar Energy

By Nick K and Steven R                                                                    Submitted June 8, 2012

Photovoltaic cells (more commonly referred to as solar cells) convert solar energy from the sun directly into usable electrical energy. First developed for use in space (where solar energy was readily available and more cost-effective than alternative forms of power generation), photovoltaic cells are becoming more widespread here on earth, and are a promising candidate for generating renewable energy to meet the world’s future energy needs.

Solar power is attracting greater attention as a source of alternative energy.

In 1839, French Physicist Antoine-César Becquerel discovered that light falling upon a solid electrode in an electrolyte solution produced a phenomenon now known as the photoelectric effect, whereby electrons were released from the electrode surface (this process will be explained in greater detail later on). Further experiments with these so called solar cells continued throughout the 19th and 20thcenturies, however, the energyconversion efficiency of these photovoltaic cells remained under 1 percent. A major breakthrough finally came in 1954, when American researchers G.L. Pearson, Daryl Chapin, and Calvin Fuller working for Bell Telephone Laboratories developed the first practical solar cell, which was capable of a 6 percent energy conversion efficiency when placed in direct sunlight. Since then, developments in technology have allowed for further improvements in the efficiency of photovoltaic cells.

Modern photovoltaic cells are commonly grouped together into a frame, called a photovoltaic module (or more often, simply a solar panel), and these modules in turn can be grouped into large solar arrays capable of generating enormous quantities of electricity. The cells themselves are made of semiconductor materials, such as silicon. In what is known as the photoelectric effect, photons of light from the sun’s electromagnetic radiation strike the surface of the photovoltaic cell and if the frequency (and thus energy) of these photons is sufficiently high, they will knock electrons loose from the semiconductor material.

The emission of electrons from a surface by photons of light striking that surface is known as the photoelectric effect.

The minimum energy which must be transferred by a photon to the material for this to occur is known as the work function of the material (a value which varies depending on the material used) and this also represents the minimum frequency, or threshold frequency, of the photon needed. Photons with sufficient energy interact with the electrons in the material in a one to one ratio, thus a single photon causes the emission of a single electron, with any surplus energy of the photon above the work function contributing to the kinetic energy of the emitted electron. The resulting free-flowing electrons are what make up the electrical current produced by the photovoltaic cell.

However, these electrons will not simply move (i.e. become electricity) on their own without an external force to influence them. This is where an electric field comes into play. In a photovoltaic cell made of silicon for instance, two types of silicon are used. Each type of silicon contains specific impurities, which alter its structure and behaviour. The process of adding these impurities is known as doping. The exterior (top) layer is composed of N-type silicon, which is doped with phosphorous atoms to produce a type of silicon with an overall negative charge (thus the name N-type). The second (bottom) layer consists of P-type silicon which is doped with boron atoms, which lend this silicon an overall positive charge (hence P-type).  The difference in charge between these two layers of silicon now produces an electric field which pushes and pulls the free electrons ejected from the N-type silicon towards the layer of P-type silicon (the bottom layer).

Layers of N- and P-type silicon create an electric field which draws the emitted electrons into contacts, creating an electrical current.

As these electrons begin to flow through the electric field, they pass into electrical contacts (composed of a conductive material, usually metal) embedded within the P-type silicon and from there they are routed through a circuit. Thus the electrons emitted by the top layer of silicon begin to flow due to the electrical field between the two layers of silicon, and this subsequent electron flow is captured to produce an electrical current.  Also known as electricity, this current can now be used to power everything from homes, to cars, to entire cities.

Since they were first invented, photovoltaic cells have become far more efficient and considerably less expensive to manufacture. In recent years, photovoltaic cells have become a much more common sight as solar panels are increasingly used to (partially or even entirely) power homes.

Solar powered houses are becoming increasingly more common.

Another use for electricity from photovoltaic cells is in powering vehicles. So called “Solar Parking Lots” (a few of which already exist) would utilize solar arrays to recharge electric cars in parking lots, which would greatly improve the feasibility of electric vehicles and reduce the need for traditional gas-powered cars, which run on non-renewable energy and are responsible for significant emissions of greenhouse gases.

Solar parking lots can power our vehicles.

However, the true potential for photovoltaic technology lies in large solar arrays, or solar power plants, which are capable of generating massive quantities of energy. In May 2012, German solar power plants produced a record 22 gigawatts of electricity in a single day. Roughly equivalent to the daily output of 20 nuclear reactors, this record-breaking quantity of solar energy was sufficient to generate a third of the daily power needed by one of the world’s leading industrial nations.

Large scale solar power plants, such as Spain’s revolutionary Gemasolar plant, are capable of supplying the vast quantities of energy required by our modern society.

Clearly photovoltaic technology, when utilized en masse in large scale solar power plants has the potential to meet much of our future energy needs. A major benefit of solar power is that it is completely clean; there is no emission of greenhouse gases and no production of radioactive wastes unlike coal and nuclear power plants respectively. The only apparent drawbacks of large solar power plants are the large amount of space required (although solar panels strategically attached to the sides of buildings could provide large quantities of energy as well), their dependence on sunny weather, and their perceived inefficiency in nations far from the equator. However, while the amount of available sunlight certainly decreases the farther one is from the equator, most nations should have little difficulty acquiring sufficient sunlight, considering Germany’s accomplishment despite a relatively northerly latitude. Aside from these minor drawbacks, solar power generation holds tremendous promise as it provides a free, clean, and endless supply of energy. With further development of photovoltaic technology and investment into solar power plants, solar energy has the potential to power our world for years to come.

 References:

How Stuff Works. (2012). How Solar Cells Work. Retrieved May 19, 2012, from: http://science.howstuffworks.com/environmental/energy/solar-cell.htm

Proffessor’s House. (2012). Solar Panels for Homes. Retrieved May 27, 2012, from: http://www.professorshouse.com/Your-Home/Environment/Energy-Efficient/Articles/Solar-   Panels-for-Homes/

NASA Science. (2011). How do Photovoltaics work? Retrieved June 3, 2012, from:  http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/

Encyclobeamia Solarbotics. (2012). Solar Cells. Retrieved June 3, 2012, from: http://encyclobeamia.solarbotics.net/articles/solar_cell.html

 Article:

The Globe and Mail. (2012). Germany sets solar power record, institute says. Retrieved May 19, 2012,    from: http://www.theglobeandmail.com/report-on-business/international-business/european-         business/germany-sets-solar-power-record-institute-says/article4216973/

Image Credits:

http://news.cnet.com

http://science.howstuffworks.com

http://www.ourbreathingplanet.com

http://homemadesolarpanelsite.com/

http://www.sciencetech.technomuses.ca

http://physics-tutor.site90.net

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Solar Energy

Solar Energy

By Jason C, Brad S

June 5th, 2012

A very widespread and effective way to generate electricity is by harnessing the sun’s power and converting it into electricity. This alternative is very desirable: every minute, enough energy in the form of sunlight arrives on the earth to meet our energy demands for an entire year – the only problem is we cannot harness all of it – yet. The main way to generate electricity is by using photovoltaic cells – these are the bluish colored cells seen in everything from calculators to rooftops of homes.

A small solar cell.

Physics Concepts

Photovoltaic or solar cells generate power by converting light to electricity at an atomic level: the photoelectric effect is responsible for this. In a solar cell, a thin layer of a semiconductor is treated and gains an electric field. This means that the semiconductor is positive on one side and negative on the other. When light (photons) strikes this semiconductor material, electrons are knocked loose and can form an electric current if passed through a circuit. The result is the generation of electricity. The current produced by a photoelectric array is directly proportional to the amount of light that strikes array; the voltage will remain the same as each cell is designed to a specification of voltage generated.

The basis for operation of the Photovoltaic cell is the photoelectric effect. From a high-level view, the photoelectric effect is very simple: light goes in, electrons come out. What happens here is the light photon strikes a certain material, giving energy to the electrons of the material (similar to a collision, photons act as particles). The electrons then have enough energy to free themselves from the material, and fly away. These electrons can now be made to flow in a circuit, generating electricity.

Illustration of the Photoelectric Effect : Ejection of Electrons

In order to generate a lot of electricity, Photovoltaic cells are often combined in large amounts, forming a solar panel.  These solar panels can be placed on a rooftop, and can then be connected directly to a battery or appliance.

A Solar Panel mounted on a household rooftop.

Social Impacts

Further development and use of solar energy would be able to make a huge positive impact on society. Compared to currently widespread methods of electricity generation, such as the burning of fossil fuels, solar power is far more sustainable. The earth has a limited supply of fossil fuels, while the sun will continue to give humans energy for many millions of years to come. Burning fossil fuels creates a large amount of pollution, reducing air quality and contributing to increased carbon dioxide levels in the atmosphere, while active solar cells produce none of this. Solar cells also require less water to make than other methods of electricity generation do to function. While some people think that solar cells are inefficient in that they require more energy to produce than they themselves produce, modern solar cells ‘break even’ in energy after six months to two years of use, and continue to generate energy for many more years. Solar cells will soon have a large impact on society. Homes and businesses will have solar cells on roofs and windows, and large solar plants are likely to be set up in deserts. Despite the general lack of knowledge about solar power, and the initial cost of the cells, in the not too distant future, solar power will be a very large part of how we as a society generate energy, and it will be good for us as well as the earth.

 References

NASA Science : Photoelectrics. Retrieved June 5th, 2012, http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/.

Photoelectric Effect, retrieved June 5th, 2012 http://physics.bu.edu/~duffy/PY106/PhotoelectricEffect.html .

Scribd: Environmental and Social impact of Solar Photovoltaics, retrieved June 5th, 2012,

http://www.scribd.com/doc/34182066/Environmental-and-Social-Impact-of-Solar-Photovoltaics

Photo References

http://gomakesolarpanels.com/wp-content/uploads/2011/06/Solar-Panel-Electricity.jpg

http://www.physicsforums.com/mgc_gloss/30/img_1.png

http://upload.wikimedia.org/wikipedia/commons/9/90/Solar_cell.png

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Solar Energy as Alternative to Fossil Fuels

Submitted June 8th, 2012

Nina C., Vanessa J., Jessica W.

Although the burning of fossil fuels is very efficient and cheap, there are many drawbacks as well. The burning of fossil fuels release large quantities of carbon dioxide, which is a great contributor to the issue of global warming. Moreover, the mining of fossil fuels also results in the destruction of natural habitats. Scientists have been seeking alternative sources of fuel, and solar energy is a popular choice for development.

Photovoltaic cells were first discovered in 1839 when a 19 years old French Physicist, Edmund Becquerel, discovered the photovoltaic effect when experimenting with a two metal electrode electrolytic cell. Many of the great scientists including Heinrich Hertz and Albert Einstein further studied this idea, providing an explanation to the photoelectric effect. Photovoltaic technologies started appearing in the market during around 1955, and were modified to maximize efficiency from then on. Today, photovoltaic systems are present everywhere from light switches, charge batteries, and almost all satellites cycling around Earth uses photovoltaic cells. A single photovoltaic device can only generate around 1V of electricity; therefore, they are usually connected into a solar panel to generate a larger potential difference. A solar panel is made up of basic building blocks of photovoltaic devices. Commonly seen solar panels are usually in dark colors, black and blue. They are designed to reflect as little visible light as possible for the intention to ‘absorb’ a larger number of photons. The size of current generated depends on the intensity of the incident light.

Photovoltaic systems are clean, quiet, and visually unobtrusive. It requires only sunlight to function; this indicates that it is a locally renewable resource since it does not require transportation of energy. The photovoltaic systems are very environmental friendly because it does not produce any harmful gases such as carbon dioxide. It is able to function for long periods of time and requires very little repair. Solar panels are more sustainable than common DC batteries. A DC battery’s ability to generate electricity depends on the electrochemical potential difference between the cathode and the anode. Although the process is more stable and consistent, it is not permanent because it is possible for one phase to be used up. Solar cells are constantly recharged by light, in other words, it is able to generate electricity as long as the sun is present.

There are some drawbacks of using photovoltaic systems, however. Firstly, the photovoltaic production process still releases toxic chemicals into the atmosphere such as arsenic, but the quantity of toxic chemicals produced this way is much less than burning fossil fuels. Chemicals such as arsenic can be controlled via recycling and other types of treatments while carbon dioxide cannot. In industries, the common goal of investors is to maximize the shareholder value. However, the use of solar energy is more expansive from the production of equipment to the conversion of energy. Many industries are not willing to pay the price in return for a cleaner environment. The photovoltaic system is capable of producing power in all types of weathers. It can produce up to 80% of their maximum energy output on cloudy days and around 25% during days where the sun is virtually not present. However, the 25% is sometimes not enough to run, leading to periods of electricity shortages. The inconsistency of power supply became the third reason why photovoltaic systems are not hugely favoured.

To make a long story short, we are able to understand the basic concepts of solar panels by applying knowledge from physics 30 course. First of all, recalling the concepts from the quantum theory, light is made up of packets of energy called photons. When sufficient energy is present during collision with a metal surface, these photons are capable of excite and release the inherent electrons within the metal. This procedure is known as the photoelectric effect. Although electrons will escape to higher energy levels, they return to their ground state quickly.

Observing the behavior of the electrons, scientists came up with the photovoltaic device in order to obtain electricity before the electrons reach their ground state. Electricity is then transported into an external circuit in which a potential difference is created that allows work to be done. The work is then used to supply the heating and lighting system of building and houses.

References

Advantages and Disadvantages of Photovoltaics. (2008). Retrieved Jun 2nd, 2012 from the internet: http://www.cetonline.org/Renewables/PV_pro_con.php

D. Anderson. Clean Elecricity from Photovoltaics, eds. (2001). London:Imperial College Press.

Fossil Fuels: Their Advantages and Disadvantages. (2012). Retrieved Jun 2nd, 2012 from the internet: http://www.alternativeenergysecret.com/fossil-fuels.html

Mary Bellis. History: Photovoltaics Timeline. (2012). Retrieved Jun 2nd, 2012 from the internet: http://inventors.about.com/od/timelines/a/Photovoltaics.htm

Matt Mozer. Solar Cell Panels and the Photovoltaic Effect. (Oct. 09, 2010). Retrieved June 2nd 2012 from the internet: http://ezinearticles.com/?Solar-Cell-Panels-And-The-Photovoltaic-Effect&id=5178365

Photovoltaic Cells: Electricity from Sunlight. (2012). Retrieved Jun 2nd, 2012 from the internet: http://www.dasolar.com/solar-energy/photovoltaic-cells

Solar Photo Voltaic. Image retrieved Jun 8th, 2012 from http://www.rids-nepal.org/index.php/Solar_Photo_Voltaic.html

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Plastic Solar Cells

             Technological advancements are accelerating every year, and energy requirements are increasing as most applications run on electricity. With the demand for energy increasing each year, our generation is in a race to increase the efficiency of energy production greater than before, and we have found the key.

            Professor Ted Sargent from the University of Toronto and his graduate students have discovered a new plastic solar cell that generates electricity with infrared light. Plastic solar cells, like the original photovoltaic cells, use the photoelectric effect. The semiconductor material, such as silicon, becomes conductive when light hits. Because there are energy levels within the atom where the electrons exist, when a photon of an electromagnetic wave with energy above or at a certain work function hits an electron, the electron is set free. This in effect creates electron flow, electricity. The electricity generated by solar cells can be stored in rechargeable batteries, which can be used later when sufficient infrared or convertible wave sources are unavailable.

            Energy of a photon from sun light is generally based on the wavelength. There is a threshold wavelength, the longest wavelength that can trigger the photoelectric effect. Wavelengths shorter than the threshold wavelength will have enough energy to free the electron. What makes plastic solar cells surpass PV cells is that the plastic material is made of quantum dots, which detect infrared light. Thus, from this concept we can see that plastic solar cells have a larger threshold wavelength value covering the infrared wavelengths. In comparison, PV cells have smaller threshold wavelength, limiting these cells to wavelengths shorter than infrared.

            Presently, there are some disadvantages to plastic solar cells. One of the major cons is the low efficiency of 6%, nothing in comparison to PV cells which are at least 30% efficient. As well, although prices are predicted to drop eventually, plastic solar cells are extremely expensive, for they use nanotechnology and quantum dots. Lastly, because they are composed of organic materials, the lifespan of plastic solar cells is considerably shorter than PV cells.

            However, this new technology provides many benefits. One being the limited space and installation needed. They can be sprayed onto various materials in a thin layer, such as clothes, essentially turning those items into batteries. Another advantage is the range of accepted wavelengths. Plastic cells can use infrared light to produce electricity, meaning it can generate energy even when cloudy. It has been predicted that plastic solar cells can reach an efficiency of 30% or higher, making it a possible energy method to replace fossil fuels. Not only could plastic solar cells be more efficient than fossil fuels, but they produce little waste, unlike fossil fuels which produce many greenhouse gasses.

            As the world uses increasing amounts of energy, new methods of energy production are required. Plastic solar cells are a viable option for future energy generation. Although much work is needed to make plastic cells worthwhile, perhaps a decade can bring forth this technology. The cells, if developed, promise a cleaner environment and future.

References

 Kharif, O. (2005) Solar Cells: The New Light Fantastic. Retrieved May 22nd, 2011 from
http://www.businessweek.com/technology/content/jan2005/tc20050131_1084_tc024.htm

Lovgren, S. (2005) Spray-On Solar-Power Cells Are True Breakthrough. Retrieved on May 22nd, 2011 from http://news.nationalgeographic.com/news/2005/01/0114_050114_solarplastic.html

University of Dalaware. (2007) UD-led team sets solar cell record, joins DuPont on $100 million project. Retrieved May 22nd, 2011 from http://www.udel.edu/PR/UDaily/2008/jul/solar072307.html


Picture References
http://www.konarka.com/

Written by Melissa W. and Ji Yoon K. Submitted June 5, 2011.

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