SMA System Architecture¶

String Inverter Fundamentals¶

A string inverter connects a series string of solar panels directly to the inverter. The inverter performs a single MPPT for the entire string.

Panel 1 ─┐
Panel 2 ─┤
Panel 3 ─┤ → String (series circuit) → SMA Inverter (MPPT) → AC Grid
Panel 4 ─┤
Panel N ─┘

Series circuit behavior: - Voltage adds: 10 × 40V panels = 400V string - Current is limited by the weakest panel (shade, failure, soiling)

Multi-String Architecture¶

Commercial SMA systems often have multiple strings feeding one or more inverters. Sunny Tripower and similar commercial models have dual MPPT inputs — two independent MPP trackers, each handling one string or string group.

String A (N panels) → MPPT 1 ─┐
                                ├→ SMA Inverter → AC
String B (N panels) → MPPT 2 ─┘

Dual MPPT allows different string orientations or lengths to be optimized independently — a significant advantage over single-MPPT designs.

Commercial String System Typical Layout¶

Array (multiple strings)
   ↓ per string
String Combiner Box (combines DC from multiple strings)
   ↓
SMA Inverter(s)
   ↓
AC Combiner / MDP
   ↓
Utility Meter / Grid

For large commercial (100kW+): Multiple inverters in parallel, each handling a segment of the array. Monitoring aggregates across all inverters.

Grounding and Isolation¶

SMA residential Sunny Boy inverters are transformerless (HF or LF isolation): - Higher efficiency - Lighter weight - Requires grounded array per local code

Some older SMA inverters have galvanic isolation (transformer) — heavier, lower efficiency, but historically allowed ungrounded (floating) arrays.

In the field: check whether the system requires a grounded or floating array. Grounding fault detection behavior differs.

Related¶

• MPPT Fundamentals
• SMA Sunny Boy
• SMA Field Failures