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seminar class
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01-03-2011, 04:01 PM

.docx   solar cell charger.docx (Size: 243.21 KB / Downloads: 192)
Solar energy is an attractive energy source for powering portable devices. For some time, it has been widely used in applications like calculators and spacecraft.More recently, solar power is being considered for a much wider range of consumer applications including mobile phone chargers. However, power available from a solar panel is heavily dependent on the operating environment. This includes such things as light intensity, time and location. Therefore, batteries typically are used as energy storage elements. They can be charged when extra power is available from the solar panel, as well as to power the system when the available power from the solar panel is insufficient.
A battery charger is a device used to put energy into a secondary cell or (rechargeable) battery by forcing an electric current through it.
This charger is designed to help the people when they are unable to charge because of no electricity. This circuit describes a solar cell phone charger that uses solar panels. DC voltage is transformed to a mobile phone battery and then charge the battery. It automatically stops charging after the completion.

• 2-Series SOLAR PANEL
Basically, a solar cell comprises a p-n junction in which light energy
(photons) causes electrons and holes to recombine, generating an electric current A solar panel (photovoltaic module or photovoltaic panel) is a packaged interconnected assembly of solar cells, also known asphotovoltaic cells. The solar panel can be used as a component of a larger photovoltaic system to generate and supply electricity in commercial and residential applications.Because a single solar panel can only produce a limited amount of power, many installations contain several panels. This is known as aphotovoltaic array. A photovoltaic installation typically includes an array of solar panels, an inverter, batteries and interconnection wiring. Photovoltaic systems are used for either on- or off-grid applications, and on spacecraft.
Solar Cell Types
Keep in mind these cost and performance tradeoffs when comparing various solar cellmaterials:
Polycrystalline cells are commonly found in outdoor applications and have a spectral sensitivity range of 500nm to 1100nm. They’re in the medium price range and typically offer a 13% power conversion efficiency. They suffer from impurities on the polycrystalline material which degrate cell efficiency over operating time. Many polycrystalline cells degrade by 20% over the first 100 operating hours.
Monocrystalline cells, such as the IXYS Solar Bits used in this circuit, have a spectral sensitivity range from 300 nm (near-ultraviolet) to 1100 nm (near-infrared), which includes visible light (400 to 700 nm). Due to this wide spectral range, they can be used in both indoor and outdoor applications. Monocrystalline or single-crystalline material is the most expensive but it does not contain impurities, and as such the power conversion efficiency does not degrade over operating time. The power conversion efficiency of commercially available monocrystalline cells ranges from 15 to 19%. The surface of these cells is a homogenous dark blue or dark grey.
Finally, Amorphous cells, which work in the spectral range of 300nm to 600nm, are used predominantly indoors in products such as solar powered calculators since they are not sensitive to the upper light spectrum and cannot take advantage of natural sunlight. They offer about 5% power conversion efficiency and are mostly used with ultra low power devices like clocks and electronic calculators. Amorphous cells, like polycrystalline cells, suffer from efficiency degradation.
A resistor is a component of an electrical circuit that resists the flow of electrical current. A resistor has two terminals across which electricity must pass, and is designed to drop the voltage of the current as it flows from one terminal to the next. A resistor is primarily used to create and maintain a known safe current within an electrical component.
Resistance is measured in ohms, after Ohm's law. This rule states that electrical .resistance is equal to the drop in voltage across the terminals of the resistor divided by the current being applied to the resistor. A high ohm rating indicates a high resistance to current. This rating can be written in a number of different ways depending on the ohm rating. For example, 81R represents 81 ohms, while 81K represents 81,000 ohms.
seminar class
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05-03-2011, 12:00 PM

.docx   PROJECT.docx (Size: 274.36 KB / Downloads: 110)
Given the current energy crisis and increasing need for sustainable energy, we endeavored to create a cost-effective, small-scale electrical generator which could be used to power consumer electronics. Solar energy has proven its worth as an alternative energy source because it is low-impact and emission-free. It has been implemented with much success for power grids with hundreds of acres of enormous solar concentrators. In the small-scale, solar energy has been harvested through the use of photovoltaic (PV) panels and have been used to power anything from an iPod to a residential home. Although PV systems are considered part of the green energy revolution, materials utilized for its construction (like silicon) are extremely dangerous to the environment and much care must be taken to ensure that they are recycled properly. PV cells also only utilize the energy stored in specific wavelengths of light and therefore have an approximate efficiency between 14-19%. Sunlight, however, produces immense amounts of heat which only serves to heat up the surface of the solar cell. Although there are some PV cells that have reached efficiency levels over 40% (world record is 41.6%), they are enormously complex and expensive.
Concentrated solar power (CSP) works differently because it focuses solar energy in its entirety rather than absorb it. Ultimately, our group will be designing and producing a Solar-Powered Battery Charger
The current market leader in efficient solar energy modules is Sun Power, whose solar panels have a conversion ratio of 19.3%, with Sanyo having the most efficient modules at 20.4%. However, a whole range of other companies (Holo Sun, Gamma Solar, Nano Horizons) are emerging which are also offering new innovations in photovoltaic modules, with a conversion ratio of around 18%. These new innovations include power generation on the front and back sides and increased outputs; however, most of these companies have not yet produced working systems from their design plans, and are mostly still actively improving the technology.
Hardware components:-
1. Solar panel
2. IC7805, IC7806 (voltage Regulator)
3. Diode 1N5402
4. Resistors
5. LED’s
6. Fuse
7. Switch
8. Output jack
Solar panel:-
A solar cell is a device that converts the energy of sunlight directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight such as solar panels and solar cells, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar panels, solar modules, and photovoltaic arrays. Photovoltaic is the field of technology and research related to the application of solar cells in producing electricity for practical use. The energy generated this way is an example of solar energy (also known as solar power).
The term "photovoltaic" comes from the Greek φῶς (phōs) meaning "light", and "voltaic", meaning electric, from the name of the Italian physicist Volta, after whom a unit of electro-motive force, the volt, is named. The term "photo-voltaic" has been in use in English since 1849.
The photovoltaic effect was first recognized in 1839 by French physicist A. E. Becquerel. However, it was not until 1883 that the first solar cell was built, by Charles Fritts, who coated the semiconductor selenium with an extremely thin layer of gold to form the junctions. The device was only around 1% efficient. Subsequently Russian physicist Aleksandra Stoletov built the first solar cell based on the outer photoelectric effect (discovered by Heinrich Hertz earlier in 1887). Albert Einstein explained the photoelectric effect in 1905 for which he received the Nobel Prize in Physics in 1921. Russell Ohl patented the modern junction semiconductor solar cell in 1946, which was discovered while working on the series of advances that would lead to the transistor. The highly efficient solar cell was first developed by Chapin, Fuller and Pearson in 1954 using a diffused silicon p-n junction. In the past four decades, remarkable progress has been made, with Megawatt solar power generating plants having now been built.
A solar panel (photovoltaic module or photovoltaic panel) is a packaged interconnected assembly of solar cell, also known as photovoltaic cell. The solar panel is used as a component in a larger photovoltaic system to offer electricity for commercial and residential applications.
Because a single solar panel can only produce a limited amount of power, many installations contain several panels. This is known as a photovoltaic array. A photovoltaic installation typically includes an array of solar panels, an inverter, batteries and interconnection wiring.
Solar cells are often electrically connected and encapsulated as a module. Photovoltaic modules often have a sheet of glass on the front (sun up) side, allowing light to pass while protecting the semiconductor wafers from the elements (rain, hail, etc.). Solar cells are also usually connected in series in modules, creating an additive voltage. Connecting cells in parallel will yield a higher current. Modules are then interconnected, in series or parallel, or both, to create an array with the desired peak DC voltage and current.
The power output of a solar array is measured in watts or kilowatts. In order to calculate the typical energy needs of the application, a measurement in watt-hours, kilowatt-hours or kilowatt-hours per day is often used. A common rule of thumb is that average power is equal to 20% of peak power, so that each peak kilowatt of solar array output power corresponds to energy production of 4.8 kWh per day (24 hours x 1 kW x 20% = 4.8 kWh).
To make practical use of the solar-generated energy, the electricity is most often fed into the electricity grid using inverters (grid-connected photovoltaic systems); in stand-alone systems, batteries are used to store the energy that is not needed immediately.
Solar cells can also be applied to other electronics devices to make it self-power sustainable in the sun. There are solar cell phone chargers, solar bike light and solar camping lanterns that people can adopt for daily use.
Simple explanation
1. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon.
2. Electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction.
3. An array of solar cells converts solar energy into a usable amount of direct current (DC) electricity.
Photo generation of charge carriers
When a photon hits a piece of silicon, one of three things can happen:
1. the photon can pass straight through the silicon — this (generally) happens for lower energy photons,
2. the photon can reflect off the surface,
3. The photon can be absorbed by the silicon, if the photon energy is higher than the silicon band gap value. This generates an electron-hole pair and sometimes heat, depending on the band structure.
When a photon is absorbed, its energy is given to an electron in the crystal lattice. Usually this electron is in the valence band, and is tightly bound in covalent bonds between neighboring atoms, and hence unable to move far. The energy given to it by the photon "excites" it into theconductionband, where it is free to move around within the semiconductor. The covalent bond that the electron was previously a part of now has one fewer electron — this is known as a hole. The presence of a missing covalent bond allows the bonded electrons of neighboring atoms to move into the "hole," leaving another hole behind, and in this way a hole can move through the lattice. Thus, it can be said that photons absorbed in the semiconductor create mobile electron-hole pairs.
A photon need only have greater energy than that of the band gap in order to excite an electron from the valence band into the conduction band. However, the solar frequency spectrum approximates a black body spectrum at ~6000 K, and as such, much of the solar radiation reaching the Earth is composed of photons with energies greater than the band gap of silicon. These higher energy photons will be absorbed by the solar cell, but the difference in energy between these photons and the silicon band gap is converted into heat (via lattice vibrations — called phonons) rather than into usable electrical energy.
Charge carrier separation
There are two main modes for charge carrier separation in a solar cell:
1. drift of carriers, driven by an electrostatic field established across the device
2. Diffusion of carriers from zones of high carrier concentration to zones of low carrier concentration (following a gradient of electrochemical potential).
In the p-n junction solar cells the dominant mode of charge is by diffusion. However, in thin films (such as amorphous silicon) the main mechanism to move the charge is the electric field and therefore the drift of carriers.
The p-n junction
Main articles: semiconductor and p-n junction
The most commonly known solar cell is configured as a large-area p-n junction made from silicon. As a simplification, one can imagine bringing a layer of n-type silicon into direct contact with a layer of p-type silicon. In practice, p-n junctions of silicon solar cells are not made in this way, but rather by diffusing an n-type dopant into one side of a p-type wafer (or vice versa).
If a piece of p-type silicon is placed in intimate contact with a piece of n-type silicon, then a diffusion of electrons occurs from the region of high electron concentration (the n-type side of the junction) into the region of low electron concentration (p-type side of the junction). When the electrons diffuse across the p-n junction, they recombine with holes on the p-type side. The diffusion of carriers does not happen indefinitely, however, because charges build up on either side of the junction and create an electric field. The electric field creates a diode that promotes charge flow, known as drift current, that opposes and eventually balances out the diffusion of electron and holes. This region where electrons and holes have diffused across the junction is called the depletion region because it no longer contains any mobile charge carriers. It is also known as the space charge region.

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