The choice between string inverters and central inverters defines the cost structure, energy yield, and operational risk profile of every utility-scale and large C&I solar plant. Five years ago, central inverters were the default above 5 MW. Today, the boundary has shifted — Sungrow's SG320HX-20 1500 Vdc string inverter handles plants up to 100 MW with O&M economics that match or beat traditional central architectures. This article compares both approaches across CAPEX, OPEX, yield and failure modes — and gives you a clear framework for picking the right architecture.
What's the difference architecturally?
A string inverter is a compact, distributed unit typically rated 30–350 kW that converts DC from a small number of PV strings (5–30) into AC. A medium-sized project uses 10–100 string inverters distributed across the array. A central inverter is a large unit, typically 1–5 MW, that aggregates DC from combiner boxes serving hundreds of strings into a single conversion point. A 5 MW project uses 1–4 central inverters.
CAPEX comparison
Pure inverter cost per watt is similar — both architectures sit around $0.04–0.06/W in 2026 pricing. The CAPEX difference comes from Balance of System (BoS) components.
| Cost element | String inverter | Central inverter |
|---|---|---|
| Inverter | Higher unit count, lower per-unit cost | Lower unit count, higher per-unit cost |
| DC cabling | Shorter runs, smaller gauge — lower cost | Longer runs to central station — higher cost |
| DC combiners | Built-in, no separate combiners needed | Significant cost — typically $0.01–0.02/W |
| AC infrastructure | Distributed AC collection at lower voltage | Concentrated MV transformer near central inverter |
| Civil / station costs | None — wall or pole mounted | Concrete pad + skid + climate control |
| Net BoS savings | ~3–5% lower at 1500 Vdc | Reference |
O&M and reliability
String inverters have a fundamental reliability advantage: distributed failure. If a 150 kW string inverter fails on a 50 MW plant, you lose 0.3% of generation until repair. If a 2.5 MW central inverter fails, you lose 5%. For grid-tied plants with revenue per MWh contracts, this risk-weighted yield difference matters.
String inverters are also field-replaceable in hours — a technician with a forklift can swap a unit without specialized equipment. Central inverter swaps require cranes, factory technicians and 1–3 days of plant downtime.
Modern Sungrow string inverters like the SG320HX-20 have MTBF figures of 20+ years with smart forced-air cooling and self-cleaning air filters. Central inverters historically had air-conditioning systems that themselves became a primary failure mode in dusty or coastal environments.
Energy yield comparison
String inverters typically achieve 1–2% higher annual yield due to:
- Module-level MPPT optimization — each MPPT in a string inverter serves 2–5 strings, versus central inverters where hundreds of strings share one MPPT. Partial shading, soiling and string mismatch are handled more granularly.
- Higher conversion efficiency — modern string inverters hit 99%+ peak efficiency. The SG320HX-20 reaches 99.02%, on par with the best central inverters.
- Less DC loss — shorter cable runs from string to inverter reduce I²R losses on the DC side.
When to choose which
| Project profile | Recommended architecture |
|---|---|
| < 1 MW (small C&I, distributed) | String inverter (no question — central inverters don't make sense at this scale) |
| 1 – 10 MW (large C&I, mid-utility) | String inverter (e.g. SG150CX × N units) |
| 10 – 100 MW (utility) | String inverter 1500 Vdc (e.g. SG320HX-20) is now the default |
| 100+ MW (large utility) | Central inverters still competitive on pure CAPEX, but string inverters win on reliability-weighted IRR for most cases |
| Repowering / retrofit | String inverter — easier to retrofit into existing combiner-box infrastructure |
| Hot / coastal / dusty environments | String inverter — no central AC system to maintain, AFCI safety built-in |
Sungrow's lineup
For solar projects in the 1 MW to 100 MW range, our Sungrow inverter lineup covers every scenario:
- SG36CX-P2 / SG50CX-P2 — small C&I (36–50 kW)
- SG110CX-P2 / SG125CX-P2 — large C&I (110–125 kW)
- SG150CX — flagship 1000 Vdc C&I (150 kW, 98.8% peak)
- SG320HX-20 — 1500 Vdc utility-scale flagship (320 kVA, 99.02% peak)