effects of shading on solar panels

even when shaded PV panels will produce voltages within their rating ,12-18 V, all they need is light to operate. The intensity of the light will vary the current output and thus the total watts coming from the panel...

>Hi!
>Im doing a research on solar panal
>effects of shading as well. To
>my knowledge, there must be bypass
>diodes for shading effects but the
>theory behind, Im still not very
>sure. Whether anot they shut off,
>is it possible if there is
>a circuit breaker behind so that
>as long as the panal did
>not get the full solar rays,
>it will shut down? Anyone out
>there would like to share the
>purpose of blocking diodes and bypass
>diodes as well?
>Cheers

If this is not too late ...

From what I know, blocking diodes are used to prevent current backflow at night, when the PV end up becoming a load. They are sometimes built-in for some higher wattage panels but not for lower wattage ones, though they can be installed by the user between the PV (+ve output cable) and the +ve end of the battery or charge controller input... though most if not all charge controllers would have a blocking diode built in at the PV input already.

Bypass diodes are most, if not always, built-in. They link the PV panels and allow the PV to output current even when it is partially shaded. When a PV is partially shaded, the shaded cells end up having higher impedence (resistance) and would pull down the overall voltage and current. It is called "bypass" diode by virtue that the diodes allow the shaded cells to be bypassed so that the remaining unshaded cells continue to work and produce the same voltage, albeit with slightly lower current than a full unshaded PV. Although the output current is slightly lower, it is still higher than if the shaded cell is added in the loop without a bypass.

Granted, it would also depend on how the PV is being shaded. If there are 24 cells in the PV, and 12 are fully shaded, then it is considered 50% shaded right? But if all 24 cells are half shaded ... the bypass would not work at all. Since all the cells are equally hampered. In such scenario, I am not sure how well a PV with built-in bypass would outperform one without.