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.
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.
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.
Copyright 2007-2010, Starlight Solar