Solar Modules Power Characteristics:
The current and power output of photovoltaic modules (aka Solar Panels) are approximately proportional to sunlight intensity. At a given intensity, a module's output current and operating voltage are determined by the characteristics of the load. If that load is a battery, the battery's internal resistance will dictate the module's operating voltage.
A module which is rated at 17 volts will put out less than its rated power when used in a battery system. This is because the working voltage will be between 12 and 15 volts. As wattage (power) is the product of volts times amps, the module output will be reduced. For example: a 50 watt module working at 13.0 volts will produce 39.0 watts (13.0 volts X 3.0 amps = 39.0 watts). This is important to remember when sizing a PV system.
It is also important to know when sizing your PV system that increases in the temperatures of the cells in the modules increases the current slightly, but a drastic increase in temperature will decrease the voltage.
Maximum power is derived at the knee of the curve. Check the amperage generated by the solar array at your battery's present operating voltage to better calculate the actual power developed at your voltages and temperatures.
For additional information or questions relating to PV Module String Sizing, give us a try by sending us an email or giving us a call. Solar Sales Inc is here to help you.