Home › Lessons › Solar PV physics › Shading and bypass diodes: a shadow costs more than its size

Shading and bypass diodes: a shadow costs more than its size

Solar PV physics · Intermediate · about 15 minutes · part of Solar PV Systems

A module is three substrings in series, each behind a bypass diode. Shade one third and it cannot carry the string current, so its diode takes over: the module loses that third’s voltage, the IV curve gets a step and the PV curve a second peak, and the shaded cells run hot. A hand-sized shadow on one cell can cost a third of the module.

Shading and bypass diodes: a shadow costs more than its size: the circuit on the simulator's bench

Open this lesson in the labFree, in your browser, no account needed.

How it works

No shade. Possible power now 0 W of 100 W; running at 0 W.

Open the IV / PV curve card and drag a shade slider in the panel’s inspector: the step appears in the current curve and the power curve grows a second hump. An MPPT can land on the wrong hump.

Try it on the bench

  1. Shade third 1 to 80 %: the possible power falls by about a third, not by 27 % (80 % of a third).
  2. Shade all three lightly (20 % each): no bypass, power falls only 20 %. Even shade is cheap; a dense shadow on one cell is expensive.
  3. Raise the load to 10 Ω with one third shaded: the panel sits on the lower hump of the PV curve.

Parts on the bench

In the course

Solar PV Systems, module “5 · Shading, bypass and blocking diodes”.

More on solar pv physics