|A frequently used analogy of the way electricity flows through cables is to compare it to water. The effects of shading on a solar panel can be compared to treading on a hose pipe. It doesn't matter where you put your foot because the flow is reduced through the whole length of the pipe.
Quite a small object or a shadow from a waste pipe vent on the roof can dramatically reduce the flow of electrons in all of the panels. Avoid shadows where installing solar panels or your system will be loosing a lot of potential solar power.