Definition
A string inverter converts DC power from multiple PV strings (wired in series, then paralleled) into AC power for grid connection. Typical capacity ranges from 3 kW (residential) to 250 kW (commercial), with 2–12 MPPT channels and UL 1741-SB listing for US installations.
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 16170 — 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.
Frequently Asked Questions
10 commonly searched questions about String Inverter.
What is a string inverter?
An inverter that converts DC from one or more PV strings (modules wired in series) to AC. Typical capacity 3–250 kW. Modern string inverters have 2–12 MPPT channels for independent sub-array control.
Major string inverter brands?
Sungrow, Huawei (commercial/utility); SMA, Fronius, SolarEdge (residential/commercial); Sol-Ark, Tesla (hybrid); Solis, Growatt (budget); Enphase IQ8M and microinverter equivalents.
What MPPT count do I need?
Match to electrically distinct sub-arrays. Residential single-roof: 1–2 MPPTs. East-west residential: 2+ MPPTs. Commercial mixed orientation: 4–8+ MPPTs. Utility-scale: 1–2 MPPTs (uniform site).
What's the efficiency?
Modern string inverters: 97–99% European weighted efficiency. Transformerless inverters slightly higher than isolated-transformer designs.
What is the warranty?
Standard: 5–10 years. Extended warranties to 20 years available from most manufacturers ($500–$2,000 per inverter).
Can string inverters be repaired?
Limited field repair. Most failures = replace entire inverter. Some module-level repair possible (fan, capacitor) for industrial central inverters.
Where should the inverter be mounted?
Wall mount (residential), pad mount (commercial), or rack mount (utility-scale). Outdoor-rated (NEMA 4 / IP65); avoid direct sunlight to reduce thermal cycling.
How does string inverter compare to microinverter?
String inverter: lower cost per W, longer string length, central failure point. Microinverter: per-module MPPT, higher cost per W, distributed reliability. Choose based on shading, roof complexity, and budget.
What if my inverter fails?
System goes offline until replacement (typically 1–3 weeks shipping). Some manufacturers offer 'inverter swap' service for fast field replacement.
What's the lifetime?
Design life 10–15 years. Many modules outlive their first inverter. Plan for 1–2 inverter replacements over a 25-year PV system lifecycle.
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