03-08-2011, 10:23 AM
[attachment=15037]
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
