Single-phase vs three-phase inverter — which to choose for solar

1. The key difference — in 30 seconds

Single-phase = 1 phase + neutral, 230V, max 6-9 kW continuous (depending on the main breaker). Typical for small/medium residential houses.

Three-phase = 3 phases + neutral, 400V between phases, capacity 15-22 kW and above, balanced load distribution across 3 cables. Typical for larger houses, halls, heavy loads.

For residential solar in RO 2026: if you stay under 6 kWp and don't have heavy loads (EV, heat pump), single-phase is fine. Above that threshold or with heavy loads, three-phase is mandatory — the DSO refuses the ATR for over-spec single-phase.

2. How to find out which connection you have

3 methods:

1. Check the breaker panel — if the main breaker has 1 phase wire + 1 neutral entering it, you're single-phase. If you see 3 phase wires (L1, L2, L3) + neutral, you're three-phase.
2. Supply contract — it states the connection type and the maximum approved installed power (PIA).
3. Call the DSO (Distribuție Energie Oltenia, Electrica Distribuție Muntenia, DEER, etc.) with your consumption point code — they tell you in 5 minutes.

If you have a smart meter, you can also check on the DSO portal directly.

3. Technical threshold — when three-phase becomes mandatory

The limits in Romania 2026:

• Single-phase max: 6-9 kW continuous — depends on the main breaker (32A → ~7.4 kW, 40A → ~9.2 kW). Solar above this → DSO forces a three-phase connection.
• Heavy loads requiring three-phase:
  • EV charging ≥7.4 kW (a 22 kW Wallbox = three-phase mandatory)
  • Heat pump ≥12 kW thermal
  • Three-phase electric oven / range
  • Large electric tankless water heater
• OUG 163/2022 prosumer limit: 27 kWp residential — in practice, above ~6-9 kWp solar, you're three-phase regardless.

If the DSO refuses your ATR for under-spec capacity, you have 2 options: lower the solar power below 6 kWp or switch to three-phase (DSO work order).

4. Cost: inverter + new connection

5 kW inverter prices 2026:

Type	Typical price	Models
Single-phase 5 kW	4,000-6,000 RON	Huawei SUN2000-5KTL-M1, Sungrow SH5RS, Goodwe GW5000-EH
Three-phase 5 kW	5,500-7,500 RON	Huawei SUN2000-5KTL-M0, Sungrow SH5.0RT, Goodwe GW5000-ET

Difference: ~25-30% more expensive three-phase, for the same nameplate power.

New three-phase connection (if you don't have one): DSO cost 3,000-8,000 RON for the work (cable, meter, pole intervention). The cost is on you, per Energy Law 123/2012. If you're at the 6 kWp limit, the math: more expensive inverter 1,500 RON + new connection 5,000 RON = 6,500 RON extra over single-phase. Worth it only if you're scaling later (EV, more solar).

Sweet spot: if you already have three-phase → take three-phase even at 4-5 kWp (more scalable). If you have single-phase and stay under 6 kWp → single-phase, keep what you have.

5. Inverter compatibility on the Romanian market 2026

The most common brands offer both variants:

Brand	Single-phase	Three-phase
Huawei	SUN2000-3/4/5/6KTL-M1	SUN2000-3/4/5/6/8/10KTL-M0
Sungrow	SH3/4/5/6RS	SH5/8/10/15/20RT
Goodwe	GW-EH series	GW-ET series
Deye	SUN-3/4/5/6/7K-SG03LP1-EU	SUN-5/6/8/10/12K-SG04LP3-EU
Solis	S6 single	S6 three

Three-phase only (premium subset): Fronius Symo, SolarEdge HD-Wave (with DC optimizers), SMA Sunny Tripower.

All have LFP battery compatibility — see Dyness vs Pylontech for specific battery+inverter pairings.

6. Who fits what + decision

Single-phase if:

• Small/medium house with existing single-phase connection
• Solar 3-6 kWp for self-consumption
• No EV ≥7.4 kW, no large heat pump
• You want minimum upfront investment

Three-phase if:

• You already have a three-phase connection (free)
• Solar above 6 kWp
• You're planning a three-phase Wallbox EV, large heat pump, or future scaling
• You want balanced distribution across 3 phases (more electrically stable)

Quick decision tree:

1. What connection do you have today? → existing three-phase: take a three-phase inverter (even at 4 kWp) → existing single-phase: continue to step 2
2. How many kWp of solar do you want? → under 6 kWp + no heavy loads: take single-phase → above 6 kWp or you have/want EV/heat pump: three-phase + DSO upgrade required
3. Budget for new connection? → yes, I have 5-8K RON for the DSO work: three-phase + future scaling → no: stay on single-phase, max 6 kWp solar

For full project context, see how to start with solar. For the ATR contract, see prosumer contract. For precise system sizing, the calculator. For a quote from verified firms, request a quote.