# PWM Solar Charge Controller Efficiency

Do you want to know the efficiency of a PWM charge controller?

It depends…

But generally, the efficiency of a PWM solar charge controller can be from 30% to 80%. This depends on several factors.

Let me show you how you can calculate the efficiency of your PWM charge controller.

There are many factors to consider to calculate the efficiency of your PWM charge controller.

These are:

• Solar panel voltage
• Battery voltage

## How does a PWM charge controller work

The working principle of a PWM charge controller is easy to understand.

It cuts the voltage to the same voltage as the battery.

In the following diagram, we have a 20V solar panel and a 12V battery.

The PWM charge controller ‘cuts’ the voltage down from 20V to 13V to charge the battery. The remaining 7V is lost.

The current stays the same. ### Solar Panel Voltage

If we use the same example of 20V and 13V charging voltage, then we need to calculate the following:

input voltage – output voltage = voltage loss

Current * voltage loss = power loss

Using the example:

20V-13V = 7V loss

5A* 7V = 35W power loss

As you can see, the power loss will be 35 Watts. That is equal to:

(power loss/solar panel power)*100 = total percentage power loss

(35W/100W)*100 = 35% power loss

### Battery Voltage

The input voltage of the PWM charge controller needs to be above the battery voltage.

For a 12V battery, we are going to use 18-22V solar panels

For a 24V battery, we are going to use 36-44V solar panels

Don’t use a PWM charge controller for a 48V battery. The losses will be too much. I don’t even think there are 48V PWM charge controllers.

An important aspect of the battery voltage and solar panel voltage:

Let’s explore this with an example: The efficiency of a PWM charge controller with high solar panel voltage

You have a 12V battery, a PWM controller, and a 300W solar panel with the following specifications:

• Power: 300W
• Current: 9A
• Voltage: 33V

Next, we apply the formulas:

33V-13V = 20V loss

9A* 20V = 180W power loss

As you can see, the power loss will be 180 Watts. That is equal to:

(180W/300W)*100 = 60% power loss

The efficiency of the PWM charge controller depends on the solar panel voltage and the battery voltage.

If we were to repeat the same calculations with a 24V battery, we would become the following:

33V-26V = 7V loss

9A* 7V = 63W power loss

As you can see, the power loss will be 63 Watts. That is equal to:

(63W/300W)*100 = 21% power loss

This is much better. If we have a high-voltage solar panel, we need to increase the battery voltage for the charge controller to be efficient.

If you would like to explore the best PWM solar charge controller, then read my article about it here.

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## FAQ

How can I calculate how many solar panels I can add to a charge controller?

I have written a whole article just about that. Read it here: How many watts can a PWM charge controller handle?

Can I use 24 volt solar panels to charge 12 volt batteries through PWM controller?

Yes, you can but you will have a lot of losses. It’s better to use a 12V solar panel for a 12V battery.

A 24 volt solar panel will have a voltage of 37V while a 12V solar panel will have a voltage of 18V.

Take a look at the previous example where I calculate the power loss of a 300W panel. The power loss can be as high as 60%.