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Solar PV Electrical Calculator

Design solar PV electrical systems with string sizing, inverter selection, and protection coordination.

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Solar PV cable sizing determines the minimum conductor area for photovoltaic string and array cables that carry DC current from panels to the inverter. IEC 62548 specifies requirements for voltage drop, current-carrying capacity under elevated roof temperatures, and short-circuit protection. PV cables must withstand continuous operation at maximum power point current multiplied by a 1.25 safety factor.

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How Solar PV & Energy Storage Works

The solar PV electrical calculator sizes the DC and AC cabling, protection, and inverter connections for photovoltaic array installations.

The calculation determines string current (Isc x 1.25 for NEC 690.8 or Isc x 1.2 for IEC 62548), string voltage range (Voc at minimum temperature to Vmpp at maximum temperature), and array configuration (series modules per string, parallel strings per MPPT). DC cable sizing accounts for the continuous current derating of 125% per NEC Article 690.8(A) and environmental correction factors.

IEC 62548 provides the international design requirements for PV arrays. NEC Article 690 covers solar PV system installations. AS/NZS 5033 defines PV array installation requirements for Australian conditions. Results include string configuration, DC and AC cable sizes, overcurrent protection ratings, inverter sizing ratio, and voltage window verification.

PV System Design Parameters

ParameterRequirementStandard
String cable sizing≥ 1.25 × IscIEC 62548 Clause 7
DC voltage limit≤ 1500V (utility) / 600V (residential)IEC 62548 / NEC 690.7
Voltage drop target≤ 1–2% (string), ≤ 1% (main DC)IEC 62548
Inverter AC cable≥ 1.25 × max output currentAS/NZS 4777.2
Earth fault detectionRequiredIEC 62548 Clause 8

Source: IEC 62548, AS/NZS 4777.2, NEC Article 690

Frequently Asked Questions

How do I calculate the maximum PV string voltage?
Maximum string voltage occurs at the lowest expected ambient temperature when module Voc increases. Per IEC 62548 Clause 7.2 and NEC 690.7, the maximum voltage is Vmax = Voc(STC) x number_of_modules x temperature_correction_factor. NEC Table 690.7(A) provides correction factors (e.g., 1.14 at -15 degrees C for crystalline modules). For a 20-module string with Voc = 45V at minimum temperature factor 1.12, Vmax = 45 x 20 x 1.12 = 1008V. This must not exceed the maximum system voltage rating of the inverter, cables, and isolators (typically 600V or 1000V for residential, 1500V for commercial).
How do I size DC cables for a solar PV array?
DC cable sizing per AS/NZS 5033:2021 Clause 4.4 and IEC 62548 Clause 7.4 must satisfy three criteria: current carrying capacity (cable rated for 1.25 x Isc of the string per NEC 690.8), voltage drop (typically limited to 1-3% on DC side for efficiency), and short circuit withstand. DC cables in PV systems must be double-insulated or equivalent per IEC 62548 Clause 7.4.1 (PV-designated cables such as H1Z2Z2-K or PV1-F). AS/NZS 5033 Table 4.1 provides installation methods, and cable sizing follows AS/NZS 3008.1.1 with continuous duty derating.
What overcurrent protection is required for PV arrays?
PV string overcurrent protection is required when three or more strings are connected in parallel, per NEC 690.9 and IEC 62548 Clause 7.5. The fuse rating must be between 1.25 x Isc and 2.4 x Isc (or the module's maximum series fuse rating, whichever is less) per NEC 690.9(B). AS/NZS 5033 Clause 4.3.3 similarly requires fuse protection rated between 1.25 x Isc and 2.0 x Isc per string. For two-string systems, overcurrent protection is not required per IEC 62548 because reverse current through a single faulted string from one other string cannot exceed module ratings.
How do I match a PV array to an inverter?
Inverter matching requires that the PV array's maximum voltage (at minimum temperature) does not exceed the inverter's maximum DC input voltage, the array's MPP voltage range (at minimum and maximum operating temperatures) falls within the inverter's MPPT range, and the array's maximum short circuit current (Isc x 1.25) does not exceed the inverter's maximum DC input current per IEC 62548 Clause 7.3. The array's peak power should be within 80-130% of the inverter's rated AC power (oversizing by 10-30% is common to maximise energy harvest at non-peak conditions).
What earthing requirements apply to PV systems?
PV system earthing depends on the inverter topology. For galvanically isolated (transformer-based) inverters, either positive or negative DC conductor may be earthed per IEC 62548 Clause 7.7. For transformerless inverters, the DC system must be floating (unearthed) and residual current monitoring is required per IEC 62109-2. NEC 690.41 requires functional grounding or ground-fault detection. AS/NZS 5033 Clause 4.6 specifies that all exposed conductive parts must be earthed and equipotential bonding must be provided for the array frame. Lightning protection for PV arrays follows IEC 62305 and should be coordinated with surge protection devices at the array and inverter.

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Standards Reference

  • IEC 62548 — PV array design
  • NEC Article 690 — Solar PV systems
  • AS/NZS 5033 — PV array installation