Off-Grid Solar Calculators

Inverters and charge controllers

PWM vs MPPT Efficiency & Yield Comparison

A PWM controller roughly clamps the array to battery voltage, so you harvest about V_battery / Vmp of the panel’s rated power. An MPPT converter keeps the array near Vmp and typically delivers around 95% of that power to the battery.

Inputs

Units
W

Nominal voltage of the battery bank.

V

Must stay above battery voltage for the PWM model to apply.

h

Terms of Service

Results

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Engineering methodology

A PWM controller roughly holds the array near battery voltage, so harvest ≈ P_array × (V_battery / Vmp) × peak sun hours. An MPPT converter keeps the array near Vmp: harvest ≈ P_array × MPPT efficiency × peak sun hours. The model requires Vmp greater than battery voltage. It is a yield comparison, not a laboratory efficiency test.

Frequently asked questions

When is a cheap PWM controller good enough?

When module Vmp is already close to battery voltage (classic “12 V” panels on a 12 V bank). As Vmp rises well above V_battery, PWM leaves more energy unharvested and MPPT usually wins.

Why must array Vmp stay above battery voltage in this comparison?

The PWM ratio V_battery / Vmp is only meaningful if the array can still push current into the battery. If Vmp is below battery voltage, a PWM controller cannot charge usefully and the model is marked invalid.

Is MPPT always about 30% better than PWM?

No. The gap depends on Vmp versus battery voltage, temperature and sun hours. Matched 12 V modules on 12 V PWM can be close. High-voltage grid modules on a 12 V PWM controller waste a large fraction of nameplate power.

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