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Bypass Diodes and Shading


Q:

Sean,
Why are all three bypass diodes affected by shading on the short edge of the module? What about the wiring/arrangement of the diodes causes them to be affected this way?
Also, what does MPPT stand for?
Thank you,

A:

MPPT stands for Maximum Power Point Tracking.
As we showed on the IV curve, there is a "sweet spot" where PV will work best with the optimal voltage and current combination for a given temperature and irradiance. With temperature and irradiance constantly changing, the MPPT will shift to optimize the PV production.
Before bypass diodes were used with PV, when there was shading, it would take out the entire string and heat up the shaded PV cell.
A normal PV module has 60 cells arranged in rows of 6 x 10 with 20 cells per bypass diode. When 1 or more cells in a group of 20 gets shaded, the current will go through the bypass diode rather than getting stuck at the shaded cell.
If the short row is shaded, then there will be cells from each group that are shaded, effectively bypassing the entire module.
Thanks,
Sean


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