MPPT
stands for Maximum Power Point Tracking. This is a simple explanation on how
MPPT works and why Starlight Solar recommends using this type of controller.
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
panels are rated in watts or the power a solar panel can produce under specific
conditions. To determine watts, multiply the voltage (Vmp) by the current
(Imp). The Voc and Isc refer to other measurements and are not used in
calculating power.
Here is
an example: Our Kyocera 130 watt solar panel is rated at 7.4 amps at 17.6
volts. By multiplying the amperage by the voltage you get the rated wattage.
Here's the math: 17.6 Vmp X 7.4 Imp = 130 watts.
A solar
panel is a constant current device. The voltage may vary but the current
remains relatively the same for a given amount of sunlight. Our example 130
watt panel will produce 7.4 amps in full sun but the voltage can change widely.
Non-MPPT charge
controllers will connect your solar panel directly to your batteries. This will
limit the power captured from the panel. The battery acts as a load and will pull down the solar panel voltage
lower. MPPT controllers do not connect
the solar panel to the battery directly. If your panel voltage is lower,
then your power will be lower as well.
Here is an example: If your battery is at 12.2 volts it will pull down the
Vmp voltage of the panel to just slightly more than the battery voltage.
Because the power delivered from your charge controller is the result of
voltage time’s amperage, you will get less power delivered to your battery.
Here's the math: 12.2 X 7.4 = 90 watts.
You will
only get about 90 watts of power out of your 130 watt panel. Here is the important part: The power is STILL
available at the panel 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 volts, the most you can
ever capture from the 130 watt panel is 104 watts! In order to capture the
full 130 watts, you must convert all the voltage into current. ONLY MPPT
controllers can do this.
The
higher a panels 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, Starlight Solar