Solar Panels, Bypass Diodes.

[Slowboat35]

Do I understand the purpose of these things correctly?
That they are there to isolate shaded PV cells that would otherwise block the passage of current from the rest of the array and allow it to find another path around the 'blockage' - this reducing power losses caused by local shading?

If so - so most solar panels have them? How do you tell when buying because they seldom seem to mention them?

 

[lustyd]

Pretty much yes. And yes most modern panels have two, wih the cells split into two strings of half the voltage, normally split vertically in half (the diodes live at the "top" next to the wiring. A "12V" panel is usually 18V with 2 x 9V strings each with a diode so two panels with one in partial shade will give 27V rather than 0V with no diodes or 18V with one per panel.