PWM vs. MPPT A concrete example will explain this clearly:
The basic physical formula:
Power (watts) = V (Volts) x I (Amps)
If we use a nominal 12V, 100W solar panel to charge a 12V battery system, the actual Vmp is 17V, and we can calculate its current output:
I = Power / V
I = 100 / 17 = 5.88 amps
Now we know the panel output is 17V and 5.88A.
Scenario 1: The photovoltaic system is with PWM solar charge controller.
PWM will drag the voltage down to battery charging voltage – approximate 14V. After going through the PWM, the solar energy only remains 14V and 5.88A.
That is:
P = V x I = 14 x 5.88 = 82.32 W
Scenario 2: The photovoltaic system is with the MPPT solar charge controller.
The MPPT not only drags the voltage down to 14V, but also increases the current, so that the power almost equals to power out.
So, if the voltage decreases by 17/14 = 1.21
Then the current to battery increases by 1.21, we get
5.88 x 1.21 = 7.11A
Total power out
P = 14 x 7.11 = 99.54 W
In this example, the power wasted by PWM is
99.54 – 82.32 = 17.22W
Almost 20% energy was not converted to battery chemical energy. If we consider the scenario in a large solar array, the loss could be tremendous.
So, it’s better to use MPPT for large solar array.
