Series- or Parallel Interconnection

We recommend using an MPP solar controller in the medium voltage range (parallel connection of 12V solar modules). Power components like those of a solar regulator can work more efficiently with medium voltages. Using MPP solar regulators in the upper voltage range (series connection of 12V solar modules / parallel connection of 24V solar modules / voltage input close to the maximum PV voltage limit) has some disadvantages.

The popular opinion that a series connection of several solar modules with a resulting high PV voltage provides an increased control range for the MPP tracking and thus switches the device on earlier in the morning and off later in the evening is correct. But on the one hand the output of the solar modules due to the low standing sun is so low that this cannot result in any significant added value in the charging behavior (regardless of whether 12V or 24V modules are in use). On the other hand, the permanent operation of the solar controller in the upper voltage range during a sunny day, as already described, causes a reduced efficiency of the power level (reduced charging current at high component temperatures)

 Reihenschaltung   Parallelschaltung 
 Series Interconnection    Parallel Interconnection

In the case of partial shading, the system performance of the series connection of modules is severely impaired (example: a defective bulb in a chain of lights). In the parallel connection, partial shading only causes the loss of the PV power of the respective shaded module. The other module can continue to deliver its full PV power because it is directly connected to the solar controller. The same applies to a denser cloud cover or high fog as to the situation already described in the morning or in the evening. A sufficiently high PV voltage is reached quickly, but the available PV current is so low in poor lighting conditions that the resulting PV power (power = voltage x current) does not add any added value to the charging behavior. Only an increase in the number of solar modules can compensate for supply deficits in poor lighting conditions, as this is the only way to increase the sum of the PV currents and thus the total PV output.

The possible efficiency of a 12V solar module is not inferior to the possible efficiency of a 24V solar module, as the specified maximum power (Wp) is calculated in the same way by multiplying the PV voltage with the PV current. With 24V modules, the voltage is higher, but the current is lower (compared to 12V modules).

We are often asked why our MPP solar controllers have a maximum PV input voltage limit of 50V and why this is not significantly higher. For devices and systems that are not provided with special touch protection, only safety voltages may be used (SELV Safe Extra Low Voltage). How high these may be in different applications is specified in DIN VDE 0100. As manufacturer, we want to guarantee safe handling at all times in every application, during installation, operation and in any service case.

With the maximum PV input voltage of 50V DC, the maximum system voltage is limited SELV-conform.

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