String Inverter
A string inverter is a type of solar inverter where multiple solar panels are connected in series to form a "string," and the combined DC output of the entire string is fed into a single centralized inverter for AC conversion.
String inverters are the most widely deployed inverter technology for residential and commercial solar due to their low cost, high reliability, and simple installation. A typical residential system uses one or two string inverters; large commercial systems may use several.
How String Inverters Work
Solar panels in a string are wired in series, which adds their voltages together while keeping the current constant. For example, twelve 40V panels wired in series produce 480V DC at the inverter input (within the typical 300–600V MPPT range for residential string inverters).
The inverter continuously tracks the maximum power point (MPP) of the combined string using MPPT algorithms, ensuring maximum energy extraction as irradiance and temperature vary.
String Inverter Limitations
The primary limitation is the "Christmas tree light" effect: the weakest panel in a string limits the output of the entire string. If one panel is shaded, dirty, or degraded, the entire string output is reduced proportionally.
This makes string inverters less suitable for:
- Sites with partial shading from trees or obstructions
- Rooftops with multiple orientations or tilts
- Systems where module mismatch is likely
DC/AC Ratio
String inverters are designed to handle a specific DC input range. The DC/AC ratio — the ratio of solar array DC capacity to inverter AC capacity — is typically 1.1–1.3 for optimal performance. A 10 kW inverter might be paired with a 12–13 kW DC array, allowing the inverter to operate near its rated capacity during most daylight hours.