Should solar panels be wired in series or in parallel?

Series raises voltage and keeps current low, which suits long cable runs and maximum power point controllers; parallel keeps voltage low and copes better with partial shading. The controller’s input window decides which arrangements are possible at all.

The two arrangements move the same energy in different shapes, and the controller between panels and battery is what decides which shape is acceptable.

What series does

Adding panels in series adds their voltages while the current stays the same. Higher voltage means lower current for the same power, which means thinner cable and less loss over a long run. Tracking controllers generally work better with a comfortable voltage above the battery.

What parallel does

Adding panels in parallel adds their currents at the same voltage. That keeps everything inside a low-voltage window, and it limits the damage a shadow does, because each panel feeds the controller independently rather than throttling a string.

The shading question

Cells within a panel are in series, so shading is already destructive inside a single module — bypass diodes exist to limit that. Across modules, the arrangement decides whether one shaded panel drags its neighbours down with it. On a van roof under trees, that is the whole argument.

The limit that is not negotiable

The controller’s maximum input voltage, checked against the panels’ open-circuit voltage at the coldest temperature the installation will see. That is a calculation using the maker’s temperature coefficient, and exceeding the limit is one of the few mistakes on this shelf with no warning stage.

Where this page and the manufacturer’s documentation differ, the documentation is the one to follow. Every capacity, output, input window, current limit, cycle count and temperature threshold on this page comes from the maker’s own published figures, with the unit as printed and the source named. None of it is measured here, and no figure is converted into another convention, because a converted number is a different number. And for any panel rating: peak watts are measured under standard test conditions — a defined irradiance, a defined cell temperature and a defined spectrum. Those conditions exist so that two panels can be compared, not so that a yield can be predicted. This page reports the maker’s figure as a test result and derives no daily energy from it.