Step 2 DC Cable Sizing - Min. Cross-Sectional Area

Concept

Amin dc cable Minimum CSA of cable (mm²)

Ldc cable Length of the longest string/array cable (m)

• Sometimes positive & negative wire length might not equal.

Idc Maximum possible operating current in cable (A)

ρ Resistivity of cable, assume copper if assumption not given (Ω mm² m⁻¹)

• Copper = 1/56

• Alumminium = 1/34

loss Maximum allowed voltgae drop / Maximum allowable voltage loss in string/array cable (decimal)

Vnom Nominal voltage (V)

Step 2.2 Calculate Vnom

This formula is for GCPV scenario, off-grid connection might be different.

Vnom = VPmax min string * Ns

 VPmax min string Minimum voltage of string at maximum power (V) or

• Minimum voltage at maximum power for each module

• Minimum module output voltage per MPPT

• Step 3 Voltage >> Voltage at maximum power, VPmax when Tmod is maximum

Ns Total PV modules in series per string (units)

Example Calculation for Step 3 Voltage >> Voltage at maximum power, VPmax

• fmm Vpmax = 1 (Assume since didn't provide)

• βVpmax = -0.423 % C⁻¹ 

• VPmax STC = 39.2V

• Tmod = 63.11 ℃ (Assume since didn't provide)

From assumption,  VPmax min string = 32.88 V

Vnom_string = 32.88 * 21= 690.48 V

Vnom_array = 32.88 * 21= 690.48 V

Step 2.4 Decide cable size

Cable size > Amin dc cable

• The typical DC cable cross sectional area for PV systems commercially available and popularity used are 1.5mm²; 2.5 mm²; 4 mm²; 6 mm²; 10 mm²; 16 mm²

• However, according to MS1837:2018, the minimum cross-sectional area is 2.5 mm².

2.5mm² cable size is selected for string and array cable.