What is the optimum size of wire for 5 kW system?

​The sizing of the wire is very important for any solar power system. The over-sizing can increase the overall cost while under sizing can lead to the burning of the wires. The heat generated in the wires is directly proportional to the square of the current flowing in them, meaning higher is the current more it will heat the wires and we need thick wires to keep the wires cool.

​Heat 𝞪 (Current)²

The 5 kW system specifications

Let me assume that I will be using 200 Watts panels to design my solar power system. So, for that purpose, I am going to use 5000/200 = 25 solar panels in total for designing the system.
The Electrical Characteristics of the 200-Watt/ 12-volt solar panel is as follows:

​The optimum system voltage for the 5 KW system is 60 Volts. Therefore, I need to connect 5 strings of solar panels in parallel and each string has 5 solar panels (200 Watts/12 volts) in series in order to make the system voltage of 60 volts. 

• The system’s maximum current will become Imp x 5 = 11.13 x 5= 55.65 Amperes.

Therefore, we need to design the wire which can tolerate the 55.65 amperes of the current.
Before going ahead, we should know the certain variables to know the diameter of the wire and these are as follows:

• Material of the wire
• Resistivity of the wire
• Length between the panels and the inverter
• Voltage-drop

The copper wires are generally used for connecting the equipment and the resistivity of the copper is \(1.72 * 10^{-8}\) Ohm-meter. The distance between the solar panels and the inverter is assumed 3 meters, as the 2 wires one negative and one positive are running parallel between the terminals, therefore the total length is 2 x 3 = 6 meters. The voltage drop across the wires is 5% of the system voltage that is 5% of 60 is 3 volts.
Putting all these values in the formula given below:

​Diameter of the wire is 1.56 mm or 13-gauge wire should be used for the connecting the solar panels with the inverter.

Conclusion

In the parallel combination, the current adds up while the voltage across the strings remains the same whereas in the series combination the voltage adds up and the current flowing in the series remains the same.