Backup

ABSTRACT The world cannot continue to rely for long on fossil fuels for its energy requirements. Fossil fuel reserves are limited. In addition, when burnt, these add to global warming, air pollution and acid rain. So solar photovoltaic systems are ideal for providing independent electrical power and lighting in isolated rural areas that are far away from the power grid. These systems are nonpolluting, don’t deplete the natural resources and are cheap in the long run. The aim of this project is to demonstrate how we can utilize solar light to electrify the remote areas, i.e., how we can store the solar energy and then use it for small-scale lighting applications.

CHAPTER 1 INTRODUCTION WHY DO WE NEED ALTERNATIVES? Fossil fuels are not, for all practical purposes, renewable. At current rates, the world uses fossil fuels 100,000 times faster than they can form. The demand for them will far outstrip their availability in a matter of centuries-or less. And although technology has made extracting fossil fuels easier and more cost effective in some cases than ever before, such is not always the case. As we deplete the more easily accessible oil reserves, new ones must be found and tapped into. This means locating oil rigs much farther offshore or in less accessible regions; burrowing deeper and deeper into the earth to reach coal seams or scraping off ever more layers of precious topsoil; and entering into uncertain agreements with countries and cartels with whom it may not be in our best political interests to forge such commitments. Finally, there are human and environmental costs involved in the reliance on fossil fuels. Drilling for oil, tunneling into coalmines, transporting volatile liquids and explosive gases-all these can and have led to tragic accidents resulting in the destruction of acres of ocean, shoreline and land, killing humans as well as wildlife and plant life. Even when properly extracted and handled, fossil fuels take a toll on the atmosphere, as the combustion processes release many pollutants, including sulfur dioxide-a major component in acid rain. When another common emission, carbon dioxide, is released into the atmosphere, it contributes to the "greenhouse effect," in which the atmosphere captures and reflects back the energy radiating from the earth's surface rather than allowing it to escape back into space. Scientists agree that this has led to global warming, an incremental rise in average temperatures beyond those that could be predicted from patterns of the past. This affects everything from weather patterns to the stability of the polar ice caps

WHAT IS SOLAR ENERGY Solar energy is the radiant light and heat from the Sun that has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for most of the available renewable energy on Earth. Only a minuscule fraction of the available solar energy is used. Solar power provides electrical generation by means of heat engines or photovoltaic. Once converted its uses are only limited by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation and disinfection, day lighting, hot water, thermal energy for cooking, and high temperature process heat for industrial purposes. Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute sunlight. Active solar techniques include the use of photovoltaic panels, solar thermal collectors, with electrical or mechanical equipment, to convert sunlight into useful outputs. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air ENERGY FROM THE SUN The Earth receives 174 petawatts (PW) of incoming solar radiation (insulations) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. Earth's land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle. The latent heat of water condensation amplifies

convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C.By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined. From the table of resources it would appear that solar, wind or biomass would be sufficient to supply all of our energy needs, however, the increased use of biomass has had a negative effect on global warming and dramatically increased food prices by diverting forests and crops into biofuel production. As intermittent resources, solar and wind raise other issues

CHAPTER 2 CIRCUIT DISCRIPTION

The figure shows the circuit diagram of solar lighting system. Here DPDT switch is used in order to get both supplies. The supply is connected to the primary of the transformer. Which is stepped down 12v 500mA..this supply is directly connected to the bridge rectifier circuit when the input connected to the left corner of the circle is positive, and the input connected to the right corner is negative, current flows from the upper supply terminal to the right along the positive path to the output, and returns to the lower supply terminal via the negative path A capacitor 2200 micro 35v connected across the rectifier output in order to get output smoothing. And also a 12v 200 ohms relay is connected across rectifier out to charge the battery through 7808 IC. Due to energisation of relay RL1, the positive terminal of the battery is connected to the output of regulator IC 7808.In this circuit IC 7808 is used to give a constant output of 8V.A diode is connected at output pin of 7808 Diode causes a drop of 0.7V, so we get approx. 7.3V to charge the battery 6V 4.5Ah lead acid battery is connected across common terminal of the relay and ground.During day time the battery is charged through relay and IC.At night time the relay will not energise and charging will not take place. The solar energy stored in the battery can then be used to light up the lamp.

CHAPTER 3 WORKING OF THE CIRCUIT Solar cells generate direct current, so make sure that DPDT switch S1 is towards the solar panel side. The DC voltage from the solar panel is used to charge the battery and control the relay. Capacitor C1 connected in parallel with a 12V relay coil remains charged in daytime until the relay is activated. Capacitor C1 is used to increase the response time of the relay, so switching occurs moments after the voltage across it falls below 12V. Capacitor C1 also filters the rectified output if the battery is charged through AC power. The higher the value of the capacitor, the more the delay in switching. The switching time is to be properly adjusted because the charging would practically stop in the early evening while we want the light to be ‘on’ during late evening. During daytime, relay RL1 energises provided DPDT switch S1 is towards the solar panel side. Due to energisation of relay RL1, the positive terminal of the battery is connected to the output of regulator IC 7808 (a 3-terminal, 1A, 8V regulator) via diode D1 and normally-open (N/O) contacts of relay RL1. Here we have used a 6V, 4.5Ah maintenance-free, lead-acid rechargeable battery. It requires a constant voltage of approx. 7.3 volts for its proper charging. Even though the output of the solar panel keeps varying with the light intensity, IC 7808 (IC1) is used to give a constant output of 8V. Diode D1 causes a drop of 0.7V, so we get approx. 7.3V to charge the battery.LED1 indicates that the circuit is work working and the battery is in the charging mode. At night, there will be no generation of electricity. The relay will not energise and charging will not take place. The solar energy stored in the battery can then be used to light up the lamp. A 3W lamp glows continuously for around 6 hours if the battery is fully charged. Instead of a 3W lamp, you can also use a parallel array of serially connected white LEDs and limiting resistors to provide sufficient light for even longer duration. In case the battery is connected in reverse polarity while charging, IC 7808 will get damaged. The circuit indicates this damage by lighting up LED2, which is connected in reverse with resistor R2. However, the circuit provides only the indication of reverse polarity and no measure to protect the IC. A diode can be connected in reverse to the common terminal of the IC but this would reduce the voltage available to the battery for

charging by another 0.7 volt. There is also a provision for estimating the approximate voltage in the battery. This has been done by connecting ten 1N4007 diodes (D2 through D11) in forward bias with the battery. The output is taken by LED3 across diodes D2, D3, D4 and D5, which is equal to 2.8V when the battery is fully charged.LED3 lights up at 2.5 volts or above. Here it glows with the voltage drop across the four diodes, which indicates that the battery is charged. If the battery voltage falls due to prolonged operation, LED3 no longer glows as the drop across D2, D3, D4 and D5 is not enough to light it up. This indicates that the battery has gone weak. Micro switch S1 has been provided to do this test whenever you want If the weather is cloudy for some consecutive days, the battery will not charge. So a transformer and full-wave rectifier have been added to charge the battery by using DPDT switch S1. This is particularly helpful in those areas where power supply is irregular; the battery can be charged whenever mains power is available

CHAPTER 4 USED COMPONENTS  Step down single phase transformer (230v/12v AC ,1A)  Integrated Circuit 7808  Solar panel(12V-16V)  Bridge rectifier  Diodes(IN 4007)  Capacitor (2200 micro farad 35V)  Resistor’s(1k,100)  Battery (6V,4.5 AH)  Relay (12v,200ohms)  DPDT switch  LED’s  Push to on switch  On/off switch  Lamp(3 W)

STEP DOWN SINGLE PHASE TRANSFORMER (230V/12V AC, 1A) A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer's coils or "windings". Except for air-core transformers, the conductors are commonly wound around a single iron-rich core, or around separate but magnetically-coupled cores. A varying current in the first or "primary" winding creates a varying magnetic field in the core (or cores) of the transformer. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary" winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will flow from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion

to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary to the number of turns in the primary as follows

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making NS greater than NP, or "stepped down" by making NS less than NP. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical

Fig An ideal step-down transformer showing magnetic flux in the core BRIDGE RECTIFIER A diode bridge or bridge rectifier is an arrangement of four diodes in a bridge configuration that provides the same polarity of output voltage for either polarity of input voltage. When used in its most common application, for conversion of alternating current

(AC) input into direct current (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave rectification from a two-wire AC input, resulting in lower cost and weight as compared to a center-tapped transformer design The essential feature of a diode bridge is that the polarity of the output is the same regardless of the polarity at the input. BASIC OPERATION According to the conventional model of current flow originally established by Benjamin Franklin and still followed by most engineers today, current is assumed to flow through electrical conductors from the positive to the negative pole.[2] In actuality, free electrons in a conductor nearly always flow from the negative to the positive pole. In the vast majority of applications, however, the actual direction of current flow is irrelevant. Therefore, in the discussion below the conventional model is retained. In the diagrams below, when the input connected to the left corner of the diamond is positive, and the input connected to the right corner is negative, current flows from the upper supply terminal to the right along the red (positive) path to the output, and returns to the lower supply terminal via the blue (negative) path.

When the input connected to the left corner is negative, and the input connected to the right corner is positive, current flows from the lower supply terminal to the right along the red path to the output, and returns to the upper supply terminal via the blue pathIn each case, the upper right output remains positive and lower right output negative. Since this is true whether the input is AC or DC, this circuit not only produces a DC output from an AC input, it can also provide what is sometimes called "reverse polarity protection". That is, it permits normal functioning of DC-powered equipment when

batteries have been installed backwards, or when the leads (wires) from a DC power source have been reversed, and protects the equipment from potential damage caused by reverse polarity. OUTPUT SMOOTHING For many applications, especially with single phase AC where the full-wave bridge serves to convert an AC input into a DC output, the addition of a capacitor may be desired because the bridge alone supplies an output of fixed polarity but continuously varying or "pulsating" magnitude

The function of this capacitor, known as a reservoir capacitor (or smoothing capacitor) is to lessen the variation in (or 'smooth') the rectified AC output voltage waveform from the bridge. One explanation of 'smoothing' is that the capacitor provides a low impedance path to the AC component of the output, reducing the AC voltage across, and AC current through, the resistive load. In less technical terms, any drop in the output voltage and current of the bridge tends to be canceled by loss of charge in the capacitor. This charge flows out as additional current through the load. Thus the change of load current and voltage is reduced relative to what would occur without the capacitor. Increases of voltage correspondingly store excess charge in the capacitor, thus moderating the change in output voltage / current. IC7808 Description: The LM78XX series of three terminal positive regulators are available in the TO-220 package and with several fixed output voltages, making them useful in a wide range of applications. Each type employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output current..

FEATURES Output Current up to 1A Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24 Thermal Overload Protection Short Circuit Protection Output Transistor Safe Operating Area Protection

LEAD-ACID BATTERY The lead-acid battery is an electrical storage device that uses a reversible chemical reaction to store energy. Lead-acid batteries have a capacity of six or more volts, enough to power a vehicle or boat Description Application: 6v 4.5ah rechargeable fan battery Specifications: Nominal voltage: 6V Nominal capacity: 4.5Ah (20 hour rate) Dimensions(L*W*H*TH): 70*47*101*106mm Approximate weight: 0.71kg Capacity: (25 º C, 1.75V/cell) 4.5Ah (20 hours rate) 4.27Ah (10 hours rate) 3.6Ah (5 hours rate) 2.93Ah (1 hour rate Special Features: 1. Long service life: 3 years design life 2. Low self discharge: Lower than 3% of rated capacity per month under normal operating temperature 3. ABS case (can be made with flame retardant V0) 4. No memory effect after repetitious usage or discharges 5. Maintenance free operation 6. Sealed construction and leakproof

7. Safety valve regulated system 8. Operating in any position 9. Deep discharge recovery 10. Wide operating temperature range

ELECTROCHEMISTRY Each cell contains (in the charged state) electrodes of lead metal (Pb) and lead (IV) dioxide (PbO2) in an electrolyte of about 33.5% v/v (6 Molar) sulphuric acid (H2SO4). In the discharged state both electrodes turn into lead(II) sulfate (PbSO4) and the electrolyte loses its dissolved sulphuric acid and becomes primarily water. Due to the freezing-point depression of water, as the battery discharges and the concentration of sulphuric acid decreases, the electrolyte is more likely to freeze The chemical reactions are (charged to discharged): Anode (oxidation):

Cathode (reduction):

MEASURING THE CHARGE LEVEL Because the electrolyte takes part in the charge-discharge reaction, this battery has one major advantage over other chemistries. It is relatively simple to determine the state of charge by merely measuring the specific gravity (S.G.) of the electrolyte, the S.G. falling as the battery discharges. Some battery designs have a simple hydrometer built in using coloured floating balls of differing density. When used in diesel-electric submarines, the S.G. was regularly measured and written on a blackboard in the control room to apprise the commander as to how much underwater endurance the boat had remaining. RELAY In the diagram a relay with asset of normally open contacts (NO) shown in figure when power is applied to the control circuit the electromagnetic coil will be energized. The resultant electromagnetic field pulls the armature and contacts toward the electromagnetic, closing the contacts. This allows current to flow through the contacts.when power is removed spring tension pushed the armature away, opening the contacts

.

OPERATION When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current to the coil is switched off, the armature is returned by a force that is half as strong as the magnetic force to its relaxed position. Usually this is a spring, but gravity is also used commonly in industrial motor

starters. Relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing. If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a spike of voltage and might cause damage to circuit components. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle The contacts can be either Normally Open (NO), Normally Closed (NC), or change-over contacts Normally-open contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called Form A contact or "make" contact. Form A contact is ideal for applications that require to switch a high-current power source from a remote device. Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called Form B contact or "break" contact. Form B contact is ideal for applications that require the circuit to remain closed until the relay is activated. Change-over contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called Form C contact or "transfer" contact.

CHAPTER 5 OTHER IMPORTANT USED COMPONENTS SOLAR CELL really called "photovoltaic", "PV" or "photoelectric" cells) that convert light directly into electricity. In a sunny climate, you can get enough power to run a 100W light bulb from just one square metre of solar panel.

solar cell or photovoltaic cell is a device that converts sunlight directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar panels, solar modules, or photovoltaic arrays. Photovoltaics are 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 Solar panels (arrays of photvoltaic cells) make use of renewable energy from the sun, and are a clean and environmentally sound means of collecting solar energy. THREE GENERATIONS OF SOLAR CELLS Solar Cells are classified into three generations which indicates the order of which each became important. At present there is concurrent research into all three generations while the first generation technologies are most highly represented in commercial production, accounting for 89.6% of 2007 production FIRST GENERATION

First generation cells consist of large-area, high quality and single junction devices. First Generation technologies involve high energy and labor inputs which prevent any significant progress in reducing production costs. Single junction silicon devices are approaching the theoretical limiting efficiency of 33%[7] and achieve cost parity with fossil fuel energy generation after a payback period of 5–7 years. SECOND GENERATION Second generation materials have been developed to address energy requirements and production costs of solar cells. Alternative manufacturing techniques such as vapour deposition, electroplating, and use of Ultrasonic Nozzles are advantageous as they reduce high temperature processing significantly. It is commonly accepted that as manufacturing techniques evolve production costs will be dominated by constituent material requirements,[7] whether this be a silicon substrate, or glass cover. Second generation technologies are expected to gain market share in 2008 The most successful second generation materials have been cadmium telluride (CdTe), copper indium gallium selenide, amorphous silicon and micromorphous silicon.[6] These materials are applied in a thin film to a supporting substrate such as glass or ceramics reducing material mass and therefore costs. These technologies do hold promise of higher conversion efficiencies, particularly CIGS-CIS, DSC and CdTe offers significantly cheaper production costs Among major manufacturers there is certainly a trend toward second generation technologies, however commercialisation of these technologies has proven difficult.[9] In 2007 First Solar produced 200 MW of CdTe solar cells making it the fifth largest producer of solar cells in 2007 and the first ever to reach the top 10 from production of second generation technologies alone.[9] Wurth Solar commercialised its CIS technology in 2007 producing 15 MW. Nanosolar commercialised its CIGS technology in 2007 with a production capacity of 430 MW for 2008 in the USA and Germany.[10]Honda, also began to commercialize their CIGS base solar panel in 2008.In 2007, CdTe production represented 4.7% of total market share, thin-film silicon 5.2% and CIGS 0.5% THIRD GENERATION

Third generation technologies aim to enhance poor electrical performance of second generation (thin-film technologies) while maintaining very low production costs Current research is targeting conversion efficiencies of 30-60% while retaining low cost materials and manufacturing techniques. They can exceed the theoretical solar conversion efficiency limit for a single energy threshold material that was calculated in 1961 by Shockley and Queisser as 31% under 1 sun illumination and 40.8% under maximal concentration of sunlight (46,200 suns, which makes the latter limit more difficult to approach than the former). There are a few approaches to achieving these high efficiencies including the use of Multifunction photovoltaic cells, concentration of the incident spectrum, the use of thermal generation by UV light to enhance voltage or carrier collection, or the use of the infrared spectrum for night-time operation. HOW DO PHOTOVOLTAICS WORK? Photovoltaic are the direct conversion of light into electricity at the atomic level. Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons. When these free electrons are captured, an electric current result that can be used as electricity. The photoelectric effect was first noted by a French physicist, Edmund Bequerel, in 1839, who found that certain materials would produce small amounts of electric current when exposed to light.The first photovoltaic module was built by Bell Laboratories in 1954. It was billed as a solar battery and was mostly just a curiosity as it was too expensive to gain widespread use. In the 1960s, the space industry began to make the first serious use of the technology to provide power aboard spacecraft. Through the space programs, the technology advanced, its reliability was established, and the cost began to decline. During the energy crisis in the 1970s, photovoltaic technology gained recognition as a source of power for non-space applications.

The diagram above illustrates the operation of a basic photovoltaic cell, also called a solar cell. Solar cells are made of the same kinds of semiconductor materials, such as silicon, used in the microelectronics industry. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current -- that is, electricity. This electricity can then be used to power a load, such as a light or a tool. A number of solar cells electrically connected to each other and mounted in a support structure or frame is called a photovoltaic module. Modules are designed to supply electricity at a certain voltage, such as a common 12 volts system. The current produced is directly dependent on how much light strikes the module

Multiple modules can be wired together to form an array. In general, the larger the area of a module or array, the more electricity that will be produced. Photovoltaic modules and arrays produce direct-current (dc) electricity. They can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination Today's most common PV devices use a single junction, or interface, to create an electric field within a semiconductor such as a PV cell. In a single-junction PV cell, only photons whose energy is equal to or greater than the band gap of the cell material can free an electron for an electric circuit. In other words, the photovoltaic response of singlejunction cells is limited to the portion of the sun's spectrum whose energy is above the band gap of the absorbing material, and lower-energy photons are not used One way to get around this limitation is to use two (or more) different cells, with more than one band gap and more than one junction, to generate a voltage. These are referred to as "multijunction" cells (also called "cascade" or "tandem" cells). Multijunction devices can achieve a higher total conversion efficiency because they can convert more of the energy spectrum of light to electricity

SOLAR COLLECTOR solar collector is a device for extracting the energy of the sun directly into a more usable or storable form. The energy in sunlight is in the form of electromagnetic radiation from the infrared (long) to the ultraviolet (short) wavelengths. The solar energy striking the earth's surface at any one time depends on weather conditions, as well as location and orientation of the surface, but overall, it averages about 1000 watts per square meter under clear skies with the surface directly perpendicular to the sun's rays SOLAR COLLECTORS FOR ELECTRIC GENERATION Parabolic troughs, dishes and towers described in this section are used almost exclusively in solar power generating stations or for research purposes. The conversion efficiency of a solar collector is expressed as eta0 or η0 PARABOLIC TROUGH This type of collector is generally used in solar power plants. A trough-shaped parabolic reflector is used to concentrate sunlight on an insulated tube (Dewar tube) or heat pipe, placed at the focal point, containing coolant which transfers heat from the collectors to the boilers in the power station A parabolic trough is a type of solar thermal energy collector. It is constructed as a long parabolic mirror (usually coated silver or polished aluminum) with a Dewar tube running its length at the focal point. Sunlight is reflected by the mirror and concentrated on the Dewar tube. The trough is usually aligned on a north-south axis, and rotated to track the sun as it moves across the sky each day Alternatively the trough can be aligned on an east-west axis, this reduces the overall efficiency of the collector, due to cosine loss, but only requires the trough to be aligned with the change in seasons, avoiding the need for tracking motors. This tracking method works correctly at the spring and fall equinoxes with errors in the focusing of the light at other times during the year (the magnitude of this error varies throughout the day, taking a minimum value at solar noon). There is also an error introduced due to the daily motion of the sun across the sky, this error also reaches a minimum at solar noon. Due to these

sources of error, seasonally adjusted parabolic troughs are generally designed with a lower solar concentration ratio Heat transfer fluid (usually oil) runs through the tube to absorb the concentrated sunlight. The heat transfer fluid is then used to heat steam in a standard turbine generator. The process is economical and, for heating the pipe, thermal efficiency ranges from 6080%. The overall efficiency from collector to grid, i.e. (Electrical Output Power)/(Total Impinging Solar Power) is about 15%, similar to PV (Photovoltaic Cells) but less than Stirling dish concentrators. Current commercial plants utilizing parabolic troughs are hybrids; fossil fuels are used during night hours, but the amount of fossil fuel used is limited to a maximum 27% of electricity production, allowing the plant to qualify as a renewable energy source. Because they are hybrids and include cooling stations, condensers, accumulators and other things besides the actual solar collectors, the power generated per square meter of space ranges enormously

PARABOLIC DISH It is the most powerful type of collector which concentrates sunlight at a single, focal point, via one or more parabolic dishes -- arranged in a similar fashion to a reflecting telescope focuses starlight, or a dish antenna focuses radio waves. This geometry may be used in solar furnaces and solar power plants

There are two key phenomenena to understand in order to comprehend the design of a parabolic dish. One is that the shape of a parabola is defined such that incoming rays which are parallel to the dish's axis will be reflected toward the focus, no matter where on the dish they arrive. The second key is that the light rays from the sun arriving at the earth's surface are almost completely parallel. So if dish can be aligned with its axis pointing at the sun, almost all of the incoming radiation will be reflected towards the focal point of the dish -- most losses are due to imperfections in the parabolic shape and imperfect reflection Losses due to atmosphere between the dish and its focal point are minimal, as the dish is generally designed specifically to be small enough that this factor is insignificant on a clear, sunny day. Compare this though with some other designs, and you will see that this could be an important factor, and if the local weather is hazy, or foggy, it may reduce the efficiency of a parabolic dish significantly In some power plant designs, a stirling engine coupled to a dynamo, is placed at the focus of the dish, which absorbs the heat of the incident solar radiation, and converts it into electricity POWER TOWER A power tower is a large tower surrounded by small rotating (tracking) mirrors called heliostats. These mirrors align themselves and focus sunlight on the receiver at the top of tower, collected heat is transferred to a power station below

SOLAR PYRAMIDS Another design is a pyramid shaped structure, which works by drawing in air, heating it with solar energy and moving it through turbines to generate electricity. Solar pyramids have been built in places like Australia.

ADVANTAGES Very high temperatures reached. High temperatures are suitable for electricity generation using conventional methods like steam turbine or some direct high temperature chemical reaction. Good efficiency. By concentrating sunlight current systems can get better efficiency than simple solar cells. A larger area can be covered by using relatively inexpensive mirrors rather than using expensive solar cells. Concentrated light can be redirected to a suitable location via optical fiber cable. For example illuminating buildings, like here DISADVANTAGES Concentrating systems require sun tracking to maintain Sunlight focus at the collector. Inability to provide power in diffused light conditions. Solar Cells are able to provide some output even if the sky becomes a little bit cloudy, but power output from concentrating systems drop drastically in cloudy conditions as diffused light cannot be concentrated passively

The following process will give you

ADVANTAGES Solar energy is free - it needs no fuel and produces no waste or pollution In sunny countries, solar power can be used where there is no easy way to get electricity to a remote place. Handy for low-power uses such as solar powered garden lights and battery chargers, or for helping your home energy bills. DISADVANTAGES Doesn't work at night Very expensive to build solar power stations. Solar cells cost a great deal compared to the amount of electricity they'll produce in their lifetime. Can be unreliable unless you're in a very sunny climate. In the United Kingdom, solar power isn't much use for high-power applications, as you need a large area of solar panels to get a decent amount of power. However, technology has now reached the point where it can make a big difference to your home fuel bills Our planet receives enough raw energy in the form of sunlight in sixty minutes to illuminate all of the worlds lights for a full year. Unfortunately, a very small part of it can be harnessed so most of the population still gets most of its energy from power plants that burn fossil fuels. Fortunately for our environment, we have recently seen an increasing trend in the demand for solar energy. This is partly due to the fact that solar panels are becoming cheaper as technology advances. At the equator, the Sun provides approximately 1000 watts of energy per square meter on the earths surface. That means that 1 square meter of each panel can generate approximately 100 GW of raw power per year. That amount of power is enough to illuminate more than 50,000 houses. The entire area that would need to be covered by solar panels to power the entire world for a year would be the equivalent to one percent of the entire space of the Sahara Desert. The amount of power solar panels can generate

on a given day depends on a few variables like smog, cloudy days, low temperatures and humidity. Solar panel farms are a lot like other normal power plants with the only big difference being that most power plants get their energy from fossil fuels. And when conventional plants burn fossil fuels, they generate the by products which are contributing to global warming. Solar panel farms or solar heat plants (or CSP plants) absorb the rays of the sun to generate electrical energy. This process of energy conversion in solar heat plants rather simple. The panels absorb the rays of the sun, which then shines on the power receiver. In this receiver, the energy is converted into steam from the suns rays. The steam is taken to tanks where it will be used to spin turbines and generate electricity. The process is clean because it requires no fossil fuels to be burned. It is safe for the environment and doesn't contribute to global warming like conventional power plants. If more solar panel farms are implemented, the demand for oil will be reduced sharply. Today, there are many households that use solar panels for energy and more people are adding panels every day. When this demand for solar energy and other alternatives goes up, fewer people will use gas and fossil fuels, and the prices for these will surely drop as well. If you use solar energy, you may actually be able to use "negative energy". Because every house is connected to the city's power system, the extra energy that your panels produce will go back into the grid and can be consumed by other households. This will result in you being sent a check by the electric company for the energy you put back in. Even if you panels are small, you will see a huge reduction in your bill. These solar panels, aside from being good for the environment, are good for your pocket! Even though the initial investment into your solar panel system is a bit expensive, the panels will undoubtedly pay for themselves in the long run. Not only do you save money and perhaps even make some with your panels, you help the environment by reducing greenhouse gases and emissions. These systems are so durable they have been known to last years. PV cells are supposed to stay good anywhere from twenty-five to forty years. Most suppliers of solar panels have a standard twenty-five year warranty. Finally, solar panels take minimal maintenance and they can be placed basically anywhere that gets a good amount of sunlight all year. There is no question that alternative energy IS the future and the future is right now.

You can generate you own energy for a lot less than you think! DIY Energy features reviews and news on popular Do it Yourself Alternative Energy Projects. Learn to build solar panels, and wind powered generators for a fraction of the cost of an installed system.