String inverter
An inverter that converts the DC output of one or more series strings of PV modules into grid-synchronised AC, typically with several independent MPPT inputs.
String inverters are the most common PV conversion architecture for residential, commercial and, increasingly, utility-scale systems. Each unit accepts one or more strings of modules, tracks their maximum power point and inverts the DC to single- or three-phase AC.
- Sizes: about 1.5–10 kW single-phase residential, 10–125 kW commercial, and 200–350 kW utility string inverters at 1,500 V DC.
- Efficiency: peak 98–99%; weighted European or CEC efficiency 97–98.5%.
- MPPT inputs: typically 2–12, allowing roof faces or rows with different orientation to operate independently.
- Design life: 10–15 years, so most residential financial models assume one replacement over a 25–30 year system life.
Compared with module-level electronics (microinverters, power optimisers), string inverters cost less per watt (often 0.05–0.15 USD/W for large units) and concentrate failures in one accessible box, but are more exposed to mismatch from partial shading. In utility plants they compete with central inverters of 1–5 MW; decentralised string designs simplify maintenance and reduce the energy lost when one unit fails.
Hybrid string inverters add a battery port for DC-coupled storage, which can capture energy that would otherwise be lost to clipping. Modern units also provide grid-support functions such as reactive power control and frequency-watt response required by grid codes like IEEE 1547-2018 and EN 50549.
Related terms
All terms →- String (PV)
A group of PV modules wired in series so that their voltages add up while the current stays that of a single module.
- Microinverter
A small inverter mounted behind one or a few PV modules that converts their DC output to AC at module level, with individual power point tracking.
- Power optimizer
A module-level DC-DC converter that tracks each panel maximum power point and conditions its output before it enters a string inverter.
- MPPT (Maximum Power Point Tracking)
Control algorithm in an inverter or charge controller that continuously adjusts operating voltage so a PV array delivers its maximum available power.
- DC/AC ratio
Ratio of a PV array DC nameplate capacity at STC to its inverter AC rating; also called inverter loading ratio (ILR).
- Inverter clipping
Energy lost when the DC power available from a PV array exceeds the inverter AC rating, so the inverter caps output at its maximum.