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Solar Charge Controller Calculator

Size an MPPT or PWM charge controller for a solar array and battery bank.

About Solar Charge Controller Calculator

MPPT controllers convert excess array voltage into charging current and typically deliver 20 to 30 per cent more energy than PWM when array voltage substantially exceeds battery voltage. PWM is only sensible when array and battery voltages are closely matched; otherwise the wasted voltage difference is pure loss.

Formula

Solar Charge Controller

Controller amps = array watts × efficiency ÷ battery voltage × 1.25

MPPT
Tracks the maximum power point, recovering excess array voltage as current
PWM
Clamps array voltage to battery voltage, discarding the difference

Worked example

With the default values below, Solar Charge Controller Calculator returns Controller Current Rating Required of 60.63. Change any input above and every figure here is recalculated in your browser.

Inputs used

Array powerminimum 0 W
1,200 W
Battery bank voltageminimum 1 V
24 V
Controller typeone of MPPT, PWM
MPPT
Array voltage at maximum powerminimum 1 V
72 V

Results

Controller Current Rating Required
60.63 A
Nearest Standard Rating
80 A
Charging Power Delivered
1,164.00 W
Controller Efficiency
97.0%
Verdict
Controller type suits this array and battery combination

Step by step

  1. 1Values used
  2. 2Solar Charge Controller
  3. 3Controller Current Rating Required= 60.63 A
  4. 4Nearest Standard Rating= 80 A
  5. 5Charging Power Delivered= 1,164.00 W
  6. 6Controller Efficiency= 97.0
  7. 7Verdict= Controller type suits this array and battery combination

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 2 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 Charge Controller calculated?

Controller amps = array watts × efficiency ÷ battery voltage × 1.25 MPPT controllers convert excess array voltage into charging current and typically deliver 20 to 30 per cent more energy than PWM when array voltage substantially exceeds battery voltage.

Why does Solar Charge Controller matter?

PWM is only sensible when array and battery voltages are closely matched; otherwise the wasted voltage difference is pure loss.

What values do I need to enter?

This calculator takes 4 inputs: Array power, Battery bank voltage, Controller type, Array voltage at maximum power. 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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