MPPT stands for Maximum Power Point Tracking

What Is MPPT

MPPT stands for Maximum Power Point Tracking. This is a simple explanation on how MPPT works and why Starlight Solar recommends using a solar charge controller that has MPPT technology. Simply put, MPPT is an electronic method of extracting the most power from your solar panels. The "tracking" has nothing to do with mechanically moving the panels to track the sun.

Solar Panel Basics

All solar modules are rated in watts. The wattage of a solar module is the amount of work that the module can do when it is illuminated with 1000 watts/m2 of sunlight. To determine wattage, multiply the operating voltage (Vmp) by the operating current (Imp). Voc and Isc refer to other measurements and are not used in calculating power.

Here is an example: Our Evergreen 205 watt solar panel is rated at 11.15 Imp at 18.4 Vmp. By multiplying the two numbers get the rated wattage of 205 watts.

Here's the math: 18.4 X 11.15 = 205.

A solar panel is a constant current device. The voltage may vary but the current remains the same for a given amount of sunlight.

Why MPPT Is Important

A Non-MPPT charge controller will connect your solar module directly to your batteries. By doing this, the battery acts as a load and will pull down the solar panel operating voltage. MPPT charge controllers do not connect the solar module to the battery directly. MPPT will convert the operating voltage into the battery voltage. This is because we can exchange current and voltage and yet have the same power. (study Ohms Law if you wish to verify this)

Here is an example of what happens with a non-MPPT controller: If your battery is at 12.2 volts, it will pull down the operating voltage of the module to just slightly more than the battery voltage.

Here's the math: 12.3 (module voltage) X 11.15 (constant current) = 137 watts.

You will only get about 137 watts of power out of the 205 watt module. Here is the important part: The power is still available but the controller can not capture it. As the battery voltage climbs, so will the power. If your charge controller is set to regulate at 14.4 volts, the most you can ever capture from the 205 watt module 160 watts! In order to capture the full 205 watts, you must convert all the voltage into current. ONLY MPPT controllers can do this.

The higher a modules operating voltage (Vmp) is the more current you will gain by using MPPT. All types of solar installations will benefit by using MPPT technology. RV’s have very limited space for solar panels. Most RV and motorhome systems have the panels mounted flat on the roof. Considerable power is lost in the winter months due to the low angle of the sun. Because of these limitations, it is very important to transfer all the power you can by using MPPT technology.