String Inverter
A solar inverter that converts DC electricity from a series-wired group of panels (a string) into AC electricity, typically sited at the edge of the array, delivering the lowest cost per watt for unshaded rooftop and ground-mount installations.
The string inverter is the default topology for the majority of global solar installations. It takes the DC output of a string of series-connected panels, finds a single operating point that works for the whole string, and converts the power to AC for the utility grid or the customer's main panel. Because one inverter handles many modules, the hardware cost per watt is the lowest of any mainstream inverter architecture, which is the reason string inverters still dominate utility, ground-mount, and unshaded residential designs.
Stringing is the design step that makes or breaks a system. The inverter has a minimum and maximum DC voltage window, and the string voltage varies with ambient temperature (higher in winter cold, lower in summer heat). The designer has to pick a string length that stays inside the window across the entire operating temperature range at the site. Too few modules in a string and the voltage drops below the inverter's MPPT range on hot days. Too many and the voltage exceeds the maximum on cold winter mornings, which can damage the inverter.
Topology decisions
Modern string inverters run multiple independent MPPTs, usually 2 to 4 per unit, which lets a designer group panels of different orientations on separate strings without mismatch loss. For a residential job with a south-east and a south-west roof face, two MPPTs typically solve the orientation problem cleanly. For roofs with heavy shading or multiple small facets, the design may still call for microinverters or DC optimizers to avoid unacceptable yield loss.
Commercial and utility projects often favor large string inverters (50 to 350 kW) distributed across the array, because a failed unit only takes a fraction of the plant offline, and field replacement is simpler than swapping a central inverter.
Why it matters for solar installers
Stringing errors are among the most expensive post-install problems. A string sized for a mild climate that sees one cold morning below design temperature can brick an inverter in the first year. SolarVis' design engine applies manufacturer voltage windows and site temperature extremes automatically, so the stringing a rep proposes is the stringing that actually runs for 20 years.
Common questions
- How many panels connect to one string inverter?
- A residential string inverter typically handles 8 to 25 panels per input, with two or three inputs per unit, for systems up to roughly 15 kW. Commercial string inverters scale up to 100 kW or more per unit, with multiple strings of 20 to 30 modules each. The exact count depends on module voltage, inverter voltage window, and temperature extremes at the site.
- What is the biggest limitation of a string inverter?
- Shading and mismatch. Every module in a string operates at the current of the weakest module, so a single shaded or soiled panel can drop the whole string's output. DC optimizers and module-level electronics mitigate this, but in their absence a string inverter is best for uniform, unshaded arrays.
- How long does a string inverter last?
- Modern string inverters typically carry 10 to 12 year warranties, with optional extensions to 20. Field life is commonly 15 years, after which replacement is planned maintenance. Unlike modules (which degrade slowly), inverters tend to fail outright, which is why monitoring and fast replacement are part of the total cost of ownership.
