How does solar work with 3-phase power? Short answer: it's the inverter that changes, not the panels. A 3-phase string inverter such as the Fronius Symo Advanced or SMA Sunny Tripower X converts DC from the array into three balanced AC outputs synchronised with the grid's phases at once. It isn't always mandatory. UK rules let each phase carry up to 3.68 kW through the simple G98 route, while Germany's VDE-AR-N 4105 caps the imbalance between phases at 4.6 kVA. This guide covers how 3-phase systems are designed, which inverters to use, how phase balancing works, and when a 3-phase architecture is required rather than just recommended.
Is your system specced correctly? The failure mode is rarely the panels. It's an inverter type that doesn't match the supply or the grid code, and that ends in a DNO rejection or a rewire after commissioning.
Having 3-phase power at the site doesn't mean you can skip a 3-phase inverter. The grid code decides.
What Is 3-Phase Power and Why Does It Matter for Solar?
Most residential properties in the UK are supplied with single-phase power, one live conductor at 230 V, plus neutral and earth. Larger homes, commercial properties, and most industrial sites receive three-phase power: three live conductors, each at 230 V to neutral (400 V between phases), offset by 120 degrees from each other. Three-phase supplies the higher current capacity needed for large HVAC, EV chargers, machinery, and large PV systems without overloading any single phase.
For solar, the supply type determines which inverter architecture you use:
| Supply Type | Typical Site | UK G98 ceiling | Recommended Approach |
|---|---|---|---|
| Single-phase 230V | Small residential UK/EU | 3.68 kW | Single-phase string inverter |
| Three-phase 400V | Larger homes, commercial | 3.68 kW per phase, 11.04 kW total | One 3-phase inverter, or one single-phase unit per phase with DNO agreement |
| Three-phase 208/480V (USA) | Commercial/industrial | Not applicable (UK rule) | 3-phase string or central inverter |
The 3.68 kW figure is 16 A at 230 V, the line the UK's Energy Networks Association draws between G98 (install, then notify the DNO) and G99 (get approval first). On a 3-phase supply the same line applies per phase, which makes 11.04 kW in total. A lone single-phase inverter on a 3-phase supply still uses one phase, so that phase carries the whole export while the other two sit idle.
How Does a 3-Phase Inverter Connect Solar to the Grid?
A 3-phase string inverter performs DC-to-AC conversion and outputs simultaneously on all three phases. Internally, it contains three separate inverter bridges sharing a common DC bus. The inverter measures voltage and frequency on each phase, synchronises its own output to match, and injects current equally across all three.
The DC side works identically to a single-phase inverter: strings of panels wire to one or more MPPT inputs, and the inverter independently tracks each string's maximum power point. Most 3-phase inverters from 10 kW upward have dual or triple MPPT inputs to handle different roof orientations.
| Inverter | Power Range | MPPT Inputs | Peak Efficiency | Notable Feature |
|---|---|---|---|---|
| Fronius Symo Advanced | 10-20 kW | 2 | 97.8% (10.0-3-M) | Arc Guard, SuperFlex design |
| SMA Sunny Tripower X | 12-25 kW | 3 | 98.2% | ShadeFix shade management, ArcFix |
| Huawei SUN2000-3-10KTL-M1 | 3-10 kW | 2 | 98.6% | Hybrid, AI arc detection |
| SolarEdge 3-phase + optimizers | 10-33.3 kW | Per-module (with optimizers) | 98.3% (SE33.3K-US) | Module-level optimization |
| GoodWe SMT series | 25-36 kW | 3 | 98.7-98.8% | Commercial rooftop |
| AUXSOL ASG-20TL-ZH | 20 kW | 2 (4 strings) | 97.34% | IP66, <10 ms backup, wide HV battery range |
For 10-20 kW sites, the Fronius Symo Advanced is a common 3-phase pick in the UK and Europe. The Fronius Primo is the single-phase equivalent, it shares the same monitoring platform but outputs on one phase only. US buyers have an extra check: on July 28, 2026, the FCC added foreign-produced connected inverters to its Covered List, which blocks new models from authorization while leaving models authorized earlier installable (pv magazine USA). Confirm the authorization date on the exact model, and read our FCC inverter rules explainer before specifying a Huawei, SMA, or any other imported unit.
What Is Phase Balancing and Why Does It Matter?
Why does phase imbalance cause real problems rather than just tripping a compliance checkbox? Phase balancing means distributing solar output evenly across all three phases. If one phase exports 5 kW and the other two export nothing, the supply transformer draws reactive current to compensate, which raises copper losses and heat, triggers protection relays, and accelerates transformer wear at commercial scale.
Grid codes put limits on it, and the numbers differ by country. Germany's VDE-AR-N 4105 says that when several single-phase generators share one connection point, the power difference between phases must not exceed 4.6 kVA, and any part of a system above 13.8 kVA has to use three-phase feed-in. The UK's G98 caps each phase at 3.68 kW (16 A), and above that G99 puts the arrangement in front of the DNO. IEC 61727 is the general utility-interface reference for PV.
With a 3-phase inverter
Balancing is automatic. The inverter measures all three phases every few milliseconds and adjusts output to maintain equal current injection. There's no design action required beyond specifying a 3-phase unit.
With single-phase inverters or microinverters
Balancing requires design-stage allocation. For a 15-panel array on a 3-phase supply, you allocate 5 panels to each phase, connected to three separate single-phase inverters or via microinverters assigned to each phase at the consumer unit. The classic mistake is lumping 10 panels on Phase 1 and splitting the remaining 5 across Phases 2 and 3. That layout breaks the balance the DNO or inspector expects at commissioning, and the AC wiring then has to be redone.
The Enphase IQ8A microinverter is AC-output by nature, each unit is wired to whichever phase you designate at the AC connection point. This gives precise per-phase control at the cost of needing to manage phase allocation manually during design.
When Is a 3-Phase Inverter Required vs Optional?
Whether you need a 3-phase inverter depends on system size, supply type, and local grid code, it isn't simply about whether the site has 3-phase power.
Required in practice
- Germany: any part of a system above 13.8 kVA, and any layout whose phase imbalance would exceed 4.6 kVA (VDE-AR-N 4105)
- UK: systems above 3.68 kW per phase that need G99 approval, where the DNO won't accept single-phase units loading one phase
- Any commercial installation where DNO approval requires balanced generation
- Sites where single-phase export would cause sustained imbalance above the permitted threshold
Optional (single-phase permitted)
- Small residential systems up to 3.68 kW on one phase of a 3-phase supply in the UK, and small systems within the 4.6 kVA imbalance cap in Germany
- Off-grid and hybrid systems where grid export is not involved
- Battery storage systems that self-consume all generation before export
In the US, 3-phase solar is the norm for commercial and industrial sites and unusual for homes (most US homes are single-phase 120/240 V split-phase). Commercial US 3-phase operates at 208 V or 480 V between phases, and those voltage levels require US-certified inverter variants.
How Do Power Optimizers Work in 3-Phase Systems?
Power optimizers fit into 3-phase systems exactly as they do in single-phase, they're DC devices and don't interact directly with the AC phase configuration. A SolarEdge P370 optimizer or Tigo TS4-A-O sits between panel and string, performs per-panel MPPT, and passes DC to whatever inverter is downstream.
SolarEdge's three-phase inverters are designed to work with its P-series optimizers. The optimizer-to-inverter architecture scales to 3-phase commercial systems up to several hundred kilowatts by combining multiple inverter units on the same monitoring platform.
For shading on 3-phase commercial arrays, the optimizer case is stronger than in residential, larger arrays typically have more complex roof obstructions, and the yield recovery from per-panel MPPT is proportionally more valuable. See our power optimizer vs microinverter comparison for a full breakdown of MLPE architectures.
What Does a Typical 3-Phase Solar System Look Like?
A 10 kW commercial-edge 3-phase system on a UK business premises could look like this:
- 24 x 430 Wp TOPCon panels, 10.32 kWp array
- 1 x Fronius Symo Advanced 10.0-3-M, 3-phase string inverter, 2 MPPT inputs
- 2 strings of 12 panels, one per MPPT, both strings on the same roof face
- G98 notification, because 10 kW spread over three phases is 3.33 kW per phase, under the 3.68 kW line. Above 11.04 kW in total, or with other generation already on site, G99 approval comes first
- Export-capable smart meter, so a Smart Export Guarantee supplier can pay for exported kWh
Annual yield for this system in Southern England: approximately 9,800-10,500 kWh/year. That range comes from EC JRC PVGIS for London (10.36 kWp, south-facing, 35 degree pitch: 10,594 kWh/year at 14% system losses, about 9,900 at 20%). SEG rates in 2026 run from roughly 4p to 15p/kWh depending on tariff (comparison-site data), so every 1,000 kWh exported is worth about 40-150 GBP on top of self-consumption savings.
For larger commercial sites, warehouses, factories, schools, the same architecture scales to 100+ kW using multiple 3-phase string inverters or a central inverter, with DC combiner boxes aggregating multiple strings before inversion.
Central inverters are cheaper per kW than string inverters at very large scale, but string architecture holds up well below a few hundred kilowatts: one failed unit takes out a slice of the array instead of the whole site, and that redundancy usually justifies the small cost premium.
The financial case for a system this size is worked through in commercial solar ROI.
Summary
Solar works with 3-phase power through a 3-phase string inverter that exports balanced power across all three grid phases at once. In the UK, 3.68 kW per phase (11.04 kW total) is the G98 line, and in Germany the cap is 4.6 kVA of imbalance, so larger systems on a 3-phase supply should use a 3-phase inverter. The Fronius Symo Advanced (10-20 kW), SMA Sunny Tripower X (12-25 kW), and Huawei SUN2000 3-phase series cover much of what commercial and large residential installs need. Phase balancing is automatic with a dedicated 3-phase inverter; with microinverters, it takes careful phase allocation at design stage. Power optimizers are DC devices, so they integrate with 3-phase systems without any change to the AC side.