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Tenergy requirements. Fossil fuel he world cannot continue to rely for long on fossil fuels for its 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 elec- trical power and lighting in isolated rural areas that are far away from the power grid. These systems are non- polluting, don’t deplete the natural re- sources and are cheap in the long run. The aim of this circuit is to demon- strate how we can utilise 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. 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 re- lay. 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 switch- _ ASHISH AHUJA SOLAR LIGHTING SYSTEM ing 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 ad- justed because the charging would practically stop in the early evening while we want the light to be ‘on’ dur- ing 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 re- chargeable battery. It requires a con- stant voltage of approx. 7.3 volts for its proper charging. Even though the output of the so- lar 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- ing and the battery is in the charging mode. At night, there will be no genera- tion 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 continu- ously 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 lim

SOLAR LIGHTING SYSTEM

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INTRODUCTION
With increasing concerns about fossil fuel deficit, skyrocketing oil prices, global warming, and damage to environment and ecosystem, the promising incentives to develop alternative energy resources with high efficiency and low emission are of great importance. Among the renewable energy resources, the energy through the photovoltaic (PV) effect can be considered the most essential and prerequisite sustainable resource because of the ubiquity, abundance, and sustainability of solar radiant energy. Regardless of the intermittency of sunlight, solar energy is widely available and completely free of cost. Recently, photovoltaic array system is likely recognized and widely utilized to the forefront in electric power applications. It can generate direct current electricity without environmental impact and contamination when is exposed to solar radiation. Being a semiconductor device, the PV system is static, quite, and free of moving parts, and these make it have little operation and maintenance costs. Even though the PV system is posed to its high capital fabrication cost and low conversion efficiency, the skyrocketing oil prices make solar energy naturally viable energy supply with potentially long-term benefits.Solar lighting system is the use of natural light to provide illumination.




B. PHOTOVOLTAIC SYSTEMS
1) Photovoltaic cell
The p-n junction diode conducts when it is forward biased similarly the photo voltaic cell is like p-n junction diode by the incidence of photons it will conducts and produce voltage.
PV cell are basically semiconductor diode. This semiconductor diode has got a p-n junction which is exposed to light. When illuminated by sunlight it generates electric power. PV cell are made up of various semiconductor materials. But mono-crystalline silicon and poly-crystalline silicon are mainly used for commercial use.



PROBLEM IDENTIFICATION

The aim of is to demonstrate how we can utilise 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. Urban and rural lighting can be done by using solar energy. The advantages of using solar energy are the cost reduction of installation in the case of non availability of electric grid, reduction of electricity bill and contribution to the protection of the environments (Clean and renewable energy source).



The regulator: An automatic voltage regulator circuit is designed to be powered by a 12 AC supply. The designed circuit will fail to operate at a voltage below 12V. However, if the entire circuit draws up to 0.5A and voltage passing through it is about 12V, then the power dissipated by the regulator will be I(Vm-Vr)=0.512 82w,Where 8v is the regulated voltage. The regulator requires a heat sink to avoid it shutting down when operated for a long time.

The power supply: The 6v, 4.5AH battery used here is charged by means of the power supply of 6V using one 2200 micro(35V) capacitor, one IC 7808 regulator, one 12V 2000 ohms relay, twelve diodes, one kilo ohm resistor, two 100 ohms resistors, three light emitting diodes, 12-16v solar panel.