What Is MPPT
MPPT stands for Maximum Power Point Tracking. This is a simple explanation on how MPPT works and why we recommend using it for your off grid solar power system. Simply put, MPPT is an electronic method of capturing the most power from your PV solar modules.
MPPT controllers will convert the module operating voltage to battery voltage and raise the output current in the process. The word “tracking" has nothing to do get maximum power from PV modules.

PV Solar Basics

All PV solar modules are rated in Watts. This identifies the potential power that a PV module can produce. This power is the amount of work that the module can do when it is illuminated with sunlight. Multiply the operating voltage (Vmp) by the operating current (Imp) listed on the label and you will have the Wattage of the module. Voc and Isc refer to other measurements and are not used in calculating power.

For example, take 100 Watt solar module is rated at 5.5 amps at 18 volt V.
power of panel: 18 X 5.5 = 100 Watts.

The PV module MUST operate at 18 volts and 5.5 amps only give output 100Watt of power. It is important to understand that a solar module is a constant current device. That means for a given amount of sunlight, the current stays the same but the voltage can be pulled down by a load.

How Non-MPPT Charge Controllers Work
All non-MPPT charge controllers do the same basic thing: they connect the PV module directly to the battery. The battery acts as a load which will pull down the PV module operating voltage. In our example above, the V of 18 volts is pulled down to battery voltage.
Here's an example: If you had a battery at 12.7 volts and connected the 100 Watt PV module, you would still have the 5.5 amps of charge current. However, the operating voltage will be pulled down to the battery voltage so you will only be using 69.7 Watts.
Here's the math: 12.7 X 5.5 = 69.7 Watts.

The non-MPPT charge controller will keep pushing the battery voltage up until it reaches the set point of the charge controller. If your charge controller is set to regulate at 14.4 volts, the most you can ever use from the 100 watt module is 79.2 watts! (14.4 volts X 5.5amps = 79.2 Watts).

This is why MPPT charge controller were developed.

How MPPT Charge Controllers Work
The MPPT process will raise the current while lowering the voltage. This can be done through a process called DC to DC conversion. The reason this works is because we can exchange current and voltage and yet have the same amount of power (Watts). Example: 100 Volts at 1 amp = 100 Watts; 10 volts at 10 amps = 100 Watts; 1 volt at 100 amps = 100 Watts. Notice the voltage is lowered as the current is raised yet it produces the same power. (for more on this, study Ohms Law)
MPPT circuits use this process to lower the voltage close to the battery voltage while raising the current. As long as the voltage reaching the MPPT controller is higher than the battery voltage by about 5% or more, then the MPPT output current will be higher than the input.
With the PV module described above, we have the potential of 100 Watts of power. With the MPPT controller connected to this module, the DC converter can output over 6.9 amps while regulating the voltage to 14.4. (6.9 X 14.4 = 100 watts).
Why MPPT Is So Important
All types of solar installations will benefit by using MPPT technology. The higher the module operating voltage (Vmp) the more benefit you will gain by using MPPT. Recreational Vehicles (RV) have very limited roof space for solar modules. If you do not tilt the modules, 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.

DETAILED DESCRIPTION

What is MPPT?

It stands for Maximum Power Point tracking.

What is the difference between a MPPT and a non-MPPT controller?

A non-MPPT controller needs an array at the same nominal voltage as your battery bank. It then connects the array to the battery to charge and disconnects it when the batteries get full. This is pretty basic, but far cheaper than hiring someone with a meter and a switch.
An MPPT controller does a little more than that. Rather than connecting an array to the battery bank, this type of controller is a DC-DC converter. It can take a higher voltage than the battery as an input, and step it down to the battery voltage. Much like a step-down transformer in AC circuits, the voltage on the output drops and the amperage is increased, providing the same power out as is coming in (ignoring efficiency, of course).

If the power is the same, what is the benefit?

A better way to look at it is that an MPPT charger is more efficient at collecting the same amount of power from an array.

If the controller is just more efficient, how can it get more power from the array?

A common misconception is that a 12 volt module will operate at 12 volts. Even a car battery, at least with the car running, will be at a higher voltage. Go ahead. Start your car. We'll wait.
If you don't have a meter handy, it is common to see the battery charging (from the alternator) at about 14VDC. At rest, a full battery will be around 12.8VDC. PV modules are similar. Their actual voltage is higher than their nominal voltage, as long as they have enough light. PV modules also operate best at certain voltage and current levels. This voltage and current is located at the Max Power Point.

Where is this Power Point and how is it tracked?

An MPPT controller finds the voltage and current that produces the highest output; the Max Power Point. If we look at a graph showing the voltage and current drawn from a PV module, we will see that it does not follow a straight line.