String design: Effect of shadow on string voltage and current

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Partial or complete shading of a module in string of a solar PV system can lead to significant reduction in the generation. It is important to ensure that the modules are provided with bypass diode so that in case of shading of the PV module, the current can by pass the PV module through the bypass diode. Following diagram shows the effect of the shading on a PV module string.

Shading on string

It is important to have an individual MPPT with the inverter string so that the effect of shadow on individual string is minimum. As can be seen in the above case the shadow on one string is leading the reduction in the overall power output of the whole PV system.

Shading on string

If we use the two MPPTs the power output of the strings is as follows:

Shading on string

 

Shading on string

Shading on string

Selection of an inverter with separate MPPTs leads to increased power output under the shadow conditions. In the above the net power output is increased by 11%.

 

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