String

A string is a group of solar panels connected in series to create a higher-voltage circuit. The term comes from the visual metaphor of panels linked in a chain — each panel's positive terminal connects to the next panel's negative terminal, like beads on a string.

String sizing — choosing how many panels to wire in each string — is one of the most important decisions in solar system design. The string length must be calculated so that the combined voltage stays within the input voltage window of your charge controller or inverter under all temperature conditions.

The minimum string voltage must be high enough to exceed the equipment's startup voltage (MPPT start voltage), while the maximum string voltage (Voc at the coldest expected temperature) must not exceed the equipment's maximum input voltage. Getting this wrong can prevent the system from starting or, worse, damage the inverter or charge controller.

In a typical residential grid-tied system, strings contain 8 to 14 panels each, depending on panel voltage specs and inverter input requirements. Off-grid systems with MPPT controllers often use shorter strings of 2 to 4 panels.

Larger systems use multiple strings connected in parallel at a combiner box, which feeds the combined output to a central string inverter. Microinverter systems eliminate string design entirely by converting each panel's output individually.