Nimesh Katariya A string inverter is an inverter that converts DC power from one or more series-connected PV strings into grid-synchronised AC power through built-in MPPT inputs. In the US it is listed to UL 1741 with IEEE 1547-2018 grid support; in India, safety follows IS 16221 (IEC 62109) and anti-islanding follows IS 16169.
Quick Facts
| Field | Detail |
|---|---|
| Term | String Inverter |
| Category | Solar Components |
| Capacity Range | 3 kW - 250 kW (single unit) |
| MPPT Channels | 2-12 typical |
| Standards | UL 1741-SB, IEC 62109, IEEE 1547 |
| Difficulty Level | Beginner to Intermediate |
String Inverter Architecture
A string inverter takes one or more parallel PV strings (each string = multiple modules in series), runs MPPT per channel, performs DC-to-AC conversion, and outputs grid-compliant AC.
Internal stages
- DC input filter + per-channel MPPT controller.
- Boost stage (DC-DC), optional, raises voltage to inverter bus.
- Inverter stage (DC-AC), typically IGBT-based 3-phase.
- AC output filter: LC filter for THD compliance.
- Grid-support controller: IEEE 1547 functions.
MPPT count vs. capacity
- 3-6 kW residential: 1-2 MPPTs.
- 7-11 kW residential: 2-3 MPPTs.
- 30-100 kW commercial: 4-8 MPPTs.
- 100-250 kW commercial/utility: 6-12 MPPTs.
Sizing Considerations
- DC/AC ratio (ILR): 1.15-1.40 typical.
- MPPT count: one per electrically distinct sub-array.
- Per-MPPT current limit: critical for high-current bifacial modules.
- Voltage window: must accommodate cold Voc and hot Vmp.
Major Manufacturers (2024)
| Manufacturer | Market | Capacity range |
|---|---|---|
| Sungrow | Global utility | 30 kW - 350 kW |
| Huawei | Global commercial/utility | 30 kW - 330 kW |
| SMA | Global residential/commercial | 3 kW - 110 kW |
| Fronius | Europe residential/commercial | 3 kW - 100 kW |
| SolarEdge | Residential with optimizers | 3 kW - 100 kW |
| Sungrow EMEA | Europe/India | 10 kW - 350 kW |
| Sol-Ark | US residential hybrid | 5 kW - 30 kW |
| Tesla | US residential hybrid | 5 kW - 11.5 kW |
| Growatt | Global budget | 1 kW - 110 kW |
| Solis | India/Asia | 2 kW - 110 kW |
Standards & Certifications
- UL 1741 / UL 1741-SB, US listing.
- IEC 62109-1/2, Safety.
- IEEE 1547-2018, DER interconnection.
- IS 16221 / IS 16169, India.
Key Takeaways
- String inverters convert DC from PV strings to AC, with 2-12 MPPT channels for sub-array optimization.
- Capacity 3 kW (residential) to 250 kW (commercial/utility).
- Choose MPPT count to match electrically distinct sub-arrays.
- Plan for 1-2 inverter replacements over a 25-year PV system lifetime.
- Specify UL 1741-SB for US compliance; IS 16221 for India.
Related Reading
String inverter selection rarely happens in isolation, it shapes the single-line diagram, the DC/AC ratio used in the yield model, and the MPPT strategy for every sub-array on site. Our guide to NEC-compliant SLD generation covers how modern SLD tools represent multi-inverter, multi-MPPT layouts for permitting, while bankable yield simulation software walks through how DC/AC ratio and inverter clipping actually get modeled for lender due diligence.
Since each MPPT channel’s job is to hunt for the sub-array’s maximum power point in real time, readers who want the control-theory side of that behavior can go deeper with Qbits Energy’s MPPT glossary entry and its related piece on choosing inverters by MPPT specification.
String inverters replaced the older PCU units in many Indian tenders. Each MPPT input must accept the string current and string voltage of its strings.
Disclosure: Qbits Energy is a Heaven Designs group company.
Frequently Asked Questions
3 commonly searched questions about String Inverter.
What is the difference between a string inverter and a microinverter?
How many strings can connect to a string inverter?
Do string inverters need rapid shutdown in the US?
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