Maximum power point tracking is often called as MPPT. This is an electronic system which commands a solar panel or a set of solar panels to generate the maximum amount of power. The MPPT is not a physical system strapped with solar trackers that position the panels so that they remain under the sun at all times. Although they can be used along with solar trackers, you must know that both are different systems.
This fully electronic system varies the electrical operating point of the panels which enables them to deliver the maximum power. The Extra power generated by the panels is made available to the modules in the form of increased battery charging current.
MPPT is the automatic adjustment of Electrical Load(s) in order to obtain the utmost power out of the connected solar panels. The output from a solar panel varies every moment due to factors like weather conditions, cloud cover, cell temperature, air mass, module characteristics etc.
Solar Irradiance, temperature and total panel resistance have a complex relationship between them. This relationship is expressed by a "curve" called as the I-V Curve. Here "I" is Current and "V" is the Voltage. My Friend, don't mistake these "curves" for the curves.
Any particular PV cell has a single point of operation where the Maximum Power can be obtained but only when the Current(I) and Voltage(V) are the maximum. It can be said that Maximum power is transferred when the connected Load resistance is equivalent to the Series resistance, in our case the resistance of the solar cell. You can calculate this using the Maximum Power Transfer Theorem.
Now as the Current and Voltage have an exponential relationship the Maximum Power Point (MPP) occurs on the knee of the I-V Curve where (dP / dV) = 0. It can be said that the Characteristic Resistance of the solar cell is equal to the Load Resistance.
Maximum Power Point of a Solar Panel
In order to understand the MPPT, let’s first get to know how a conventional charge controller charges a discharged battery.
When a conventional charge controller starts charging the battery, it directly connects the solar panels to the battery. Because of this the solar panels are forced to operate at the battery voltage. This voltage is not the best voltage for generating the maximum power available from the modules.
My friend, now imagine that you have with you a single 75Watt solar panel along with a 12Volt Battery. And you have that solar panels’ power/voltage/current graph. This shows the voltage & current at Standard Test Conditions of 25°C and solar insolation of 1000W / Sq Mtr.
Battery Charging using MPPT
Now for our particular example the conventional charge controller simply connects the solar module directly to the battery. Thus the solar panel is forced to operate at 12Volts. Now by simply connecting the 75 Watt panel to the 12Volt battery, the conventional charger artificially reduces the power production in the range of 51 – 53 Watts.
Instead of directly connecting the batteries to the solar panel, a Maximum Power Point Tracking enabled charge controller computes the voltage at which the modules are able to produce the most amount of power.
Thus by taking a look at the graph the maximum voltage of the module is 17 Volts. The MPPT system thus operates the solar panels at 17 Volts to obtain the full 75 Watt of power despite the present battery voltage.
A highly efficient DC-DC Converter then converts the 17 Volt controller input to the necessary battery voltage at the output. If the whole system would have been 100% efficient then the battery charging current would have been calculated as per the formula below.
MPPT Calculation for Current Increase
You can now determine that the battery charge current increases by 1.85 Amperes i.e. 41.26%. This power would have been left behind by the conventional charge controller. But practically nothing is 100% efficient, so the actual charge current increase would be somewhat lower than the calculated value.
The charge controllers with the feature of Maximum power point tracking are most suitable for all in fact grid tie inverters give their best performance with Maximum Power Point Tracking.
They function especially well in cold climates. As lower module temperatures and discharged batteries increase the battery charging current, thereby extracting more power from the solar panels where it is required the most.
Thus buying an MPPT based inverter will always be beneficial for you, you'll earn & save more!!
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