Quick Answer
In a long series string, anticipate a 1-3% voltage drop per kilometer of cable and 2-5% per 100 meters, depending on cable gauge and solar panel voltage.
Understanding Voltage Drop in Series Strings
Voltage drop occurs when current flows through a wire, converting some of the electrical energy into heat. This is a crucial consideration in series strings, where the total system voltage is the sum of individual module voltages. When dealing with long series strings, it’s essential to calculate the expected voltage drop to ensure it doesn’t compromise the system’s performance.
Calculating Voltage Drop
To calculate voltage drop, use the following formula: Vd = (I x R) / 1000, where Vd is the voltage drop in volts, I is the current flowing through the wire in amperes, and R is the resistance of the wire in ohms per kilometer. For example, if you have a 20-kilometer cable with a resistance of 1.5 ohms per kilometer and a current of 5 amperes, the voltage drop would be 0.075 volts per kilometer, or 1.5 volts for the entire string.
Designing Series Strings with Voltage Drop in Mind
To minimize voltage drop, use larger gauge cables, which have lower resistance, or design series strings in parallel to reduce the total current flowing through the cables. For instance, if you have two 100-meter cables in parallel, the voltage drop would be halved compared to a single cable. When designing your series string, calculate the expected voltage drop using the above formula and adjust your cable size or string configuration accordingly to ensure the system operates within its specified voltage range.
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