HOW SOLAR PHOTOVOLTAIC SYSTEM WORKS
SOLAR PHOTOVOTAIC (SPV) ARRAY
The basic element converting sunlight into electricity are solar cells made out of sandy silicon material. A solar cell generates approximately 0.6 volts open circuit voltage and 30 mA/sq.cm short circuit current under Standard Test Condition (STC). Therefore, to create a module/panel capable of charging a 12volts battery, 36 numbers identical solar cells are connected in series as a building block of practical utility to make a module. Also, by arranging these modules in series or in parallel, a required voltage or current or power level can be generated.
Since the sunlight is only available during the day, SPV array provides DC electricity during the day. Power from the array varies with variation in the sunlight falling on the modules. So the power needed during a low sunshine hour and at night requires storage energy which is provided by the battery. Similarly, the solar isolation falling on the array varies from day to day, so the ratio of average isolation in the best month could be as high as 1.5 to 2 times of that received during lean month. Accordingly, there may be situation where the battery is getting overcharged which can damage the battery fast if not checked. To guard against such an undesirable occurrence, a charge controller is required for each solar photovoltaic system. The function of any solar system is to allow charging current into battery bank till it is charged enough to its capacity and prevent it from getting overcharged and finally released to appliances or machines for use.
A low voltage disconnect feature is provided to prevent battery from getting deep discharged through load. Therefore a two-stage charging process is essential;
First, a fast recharging of battery compared to on-off relay type chargers since faster recharging increases the performance of the system by storing more of the SPV array’s limited output.
Secondly, the charge controller allows the maximum current generated in the SPV array to the battery bank till it is charged to its capacity. Then it regulates further charging current to keep battery in float stage and protect the battery from getting overcharged. This final float setting reduces battery gassing and ensures battery remains in complete charging stage.
E-BOOK : Solar Technology- A Comprehensive Book on Solar Technology, Battery/Panel Configurations and Installations