The meaning of Maximum Power Point Tracking

Maximum Power Point Tracking or MPPT is the algorithm that included in electronic control device use for extracting maximum available power from PV panels, which the maximum power change according to the variations in parameters such as solar radiation, ambient temperature and solar cell temperature.
The MPPT algorithm is implemented by using microprocessor to check the PV panels output at all time that there is no other higher output power from PV panels in form of current and voltage from the solar radiation at that time.
To get the higher power, the MPPT algorithm checks the PV panels output, and compares it to the battery voltage. If a trial shows what the best power is, it will move control point to use new PV panel's voltage and current output.

Figure 1	The I-V curves are shown maximum power from PV panels when exposed to irradiance 1000 W/m2
Source:	The parameters are measured by the IVTracer program by Sandia National Laboratories.

Figure 2	The I-V curves are shown maximum power from PV panels when exposed to irradiance 100 W/m2
Source:	The parameters are measured by the IVTracer program by Sandia National Laboratories.

As the graph in figure 1 and 2, we see that at the different solar radiations, PV panels deliver the variations in parameters as follows:

(1) Maximum power; Pm
(2) Maximum power voltage; Vpm
(3) Open circuit voltage; Voc
(4) Maximum power current; Ipm
(5) Short circuit current; Isc

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How Maximum Power Point Tracking works

The major principle of MPPT is to extract the maximum available power from PV panels by making them operate at the most efficient voltage. That is to say:
MPPT operates by checking the output of PV panels, compares it to the battery voltage, then fix the best power that PV panels can put out to charge the battery, and convert it to the best voltage to get maximum current into battery. Besides, it can also supply power to a DC load, which is connected directly to the battery.

MPPT is most effective under these conditions:

1. Cold weather or winter - Normally, PV panels work better at cold temperatures. Although, in winter the time of sun hours are low, if the device with MPPT is implemented, it allows producing more maximum power but lost less power.
2. Low battery charge - The lower the state of charge in the battery, the more current to a MPPT puts into the battery.

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