Simple Solar Power System. Design Note 18

Solar based power system is now becoming popular to save energy and money. It is easy to install a simple 100 Watts Solar lighting system for outdoor lighting. No need for constructing the circuits and all necessary units are readily available and anybody can install this. It runs on a 12 volt Car battery and no switching is needed. It turns on the outdoor lamps around 6 p.m and turns off at 6.a.m. The car battery can power the system for minimum 3 years so it is very cost effective. Another advantage is that, the outdoor lights will automatically turns on / off even if the inmates are not in home giving some security. Cost of the system is around Rs.5000 including battery.
The system requires the following:

1. Solar panel – 12 volt 10 Watts. It gives an open circuit voltage around 16-20 volts in good sunlight. 10 watts panel gives around 1 Ampere current depending on the voltage. So this well charges the battery during day time. Its cost is around Rs.1200
2. Solar charge controller – It regulates the voltage and current for battery charging. Buy a good quality one with Automatic output by sensing light, Over and Under charge cut off etc. It stops charging when the battery is full and turns off the output when the battery voltage drops below 11 volts. So this always keeps the battery in healthy condition. It also has an LDR switch which turns on the output in the evening and turns off in the morning. 12 volt DC LED lights can be directly connected to its output. If CFL is used, a simple inverter is needed. The Solar charger controller costs around Rs.1200
3. 12 volt 100 Watt Car Inverter – It is also readily available and gives 230 volt AC based on MOSFET inverter. It is generally used to power video player in Car. Maximum 80 Watts AC load can be connected to it. So seven 11 watts CFL can be safely connected. But to minimize the current consumption, it is better to limit the load to 25 watts ( one 11 W+ one 8W+one 5W CFL).Keep the rule, less load more time for lighting . The 12 volt 100 watt Car inverter costs around Rs.350
4. 12 volt 35 Amps Car Battery– It costs around Rs.2500 and works well for 3 years minimum if properly charged and discharged.

If 12 Volt DC LED lights are used, the inverter is not required.LED lights can be directly connected to the output of Solar charge controller. Fig 1 shows the Layout of Solar power system and Fig.2 is the Solar charger controller with light sensing on/off switch and other facilities.

Fig.1 Layout of Solar power system


Fig.2 Solar Charge Controller


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