Each PV module has a so-called Maximum Power Point (MPP), the operating point at which the voltage used achieves the maximum power. The data of the modules can be taken from their data sheet.

Typical values of a data sheet could look something like this:

Where exactly is the MPP of a PV module?

The listed open-circuit voltage is available even under weak light conditions. If the module is loaded with a resistor by the inverter, the voltage decreases accordingly and the current increases. Under ideal conditions, the load corresponds to the MPP value of the module, according to the data sheet: Vmpp, in the example: 40V and the current: Impp, here 10A. If the inverter would load the module more than up to the Vmpp value, its power would decrease again. So, according to the fictitious data sheet, at maximum solar irradiation and optimal ambient temperature, the module delivers at 40V: 10A, which is P = U * I: 40*10 = 400 watts Pmax. Outside the optimal conditions, the voltage and current values deviate from the MPP values (Vmpp and Impp) given in the data sheet. So the task of a MPP tracker is to determine the ideal operating point, the ideal voltage for maximum power and to operate the module in the best possible range.

So far so simple, but what if several modules are connected in series and the MPP of the individual modules is different due to shading or other influences?

Partial shading: power optimizer vs. dynamic peak manager vs. bypass diodes vs. microinverter?

In order to better deal with partial shading, hew PV panels have 3 bypass diodes which can deactivate parts of the module. By adjusting the string voltage, the diodes switch through and bypass the shaded portion.

After the inverter optimizes the MPP based on the total voltage of all modules connected in series, a panel with a different MPP could potentially affect the entire string.

When optimizing strings, especially for shading, I have come across different optimization approaches in my research. Certain manufacturers, including Solar Edge, use so-called power optimizers for optimization: small additional devices under the respective panel, which determine the ideal MPP (Maximum Power Point) per panel and adjust the output voltage. In addition to the additional cost of the optimizers, the optimizers themselves also require some power, although not much.

As an alternative, Fronius advertises that their "Dynamic Peak Manager" does not require power optimizers. Described is the integrated shading management with an MPP tracking algorithm, which optimizes the yield at string level. The setting can be found under Device configuration, Inverter PV:

See: https://www.fronius.com/en-gb/uk/solar-energy/installers-partners/products-solutions/features/dynamic-peak-manager.

Another alternative is the use of so-called microinverters, similar to that of a balcony power plant. For example, even in larger systems, a microinverter could be hung under each PV panel, resulting in each panel having its own MPP tracker. A central inverter would thus be unnecessary. In addition to the well-known manufacturers of inverters for balcony power plants, the manufacturer Enphase has focused on this concept specifically for the use of larger plants.

can different PV modules be used in one string?

Finally, one more consideration about the use of different modules in a string. Should the modules used in a string have different current: Impp, the modules with lower current values would out-brake the modules with a potentially higher current value. Different voltages on the other hand could be compensated by the MPP tracker.

Conclusion

Contrary to what is often claimed, a little shade usually does not immediately lead to the complete failure of the entire string. Regardless of whether the inverter is capable of correcting the MPP, for complex setups there is the option of power optimizers or alternatively the use of microinverters for each individual PV panel. See also: PV - Considerations - Planning - Implementation