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Solar Cable Size Calculator

Size DC solar cable for current capacity and acceptable voltage drop.

About Solar Cable Size Calculator

Solar DC circuits are held to a tighter voltage drop budget than AC because every lost volt is lost generation for the system’s whole life. Two per cent is the usual design target. Cable is a one-time cost while the energy loss recurs for 25 years, which is why solar DC cable is usually sized generously.

Formula

Solar Cable Size

Area = 2 I ρ L ÷ permitted volt drop, using the loop length

2 factor
DC circuits carry current out and back through two conductors
2% limit
Typical DC-side voltage drop budget for solar

Worked example

With the default values below, Solar Cable Size Calculator returns Minimum Cable Area of 2.478. Change any input above and every figure here is recalculated in your browser.

Inputs used

Array currentminimum 0 A
20 A
One-way cable lengthminimum 0 m
25 m
System voltageminimum 1 V
400 V
Permitted voltage dropaccepts 0–100 %
2 %

Results

Minimum Cable Area
2.478 mm2
Nearest Standard Size
4.0 mm2
Voltage Drop at That Size
4.957 V
Voltage Drop
1.239%
Power Lost in the Cable
99.130 W

Step by step

  1. 1Values used
  2. 2Solar Cable Size
  3. 3Minimum Cable Area= 2.478 mm2
  4. 4Nearest Standard Size= 4.0 mm2
  5. 5Voltage Drop at That Size= 4.957 V
  6. 6Voltage Drop= 1.239
  7. 7Power Lost in the Cable= 99.130 W

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Solar Cable Size calculated?

Area = 2 I ρ L ÷ permitted volt drop, using the loop length Solar DC circuits are held to a tighter voltage drop budget than AC because every lost volt is lost generation for the system’s whole life. Two per cent is the usual design target.

Why does Solar Cable Size matter?

Cable is a one-time cost while the energy loss recurs for 25 years, which is why solar DC cable is usually sized generously.

What values do I need to enter?

This calculator takes 4 inputs: Array current, One-way cable length, System voltage, Permitted voltage drop. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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Solar Cable Size Calculator – Calculate Minimum Cable Area