Single-phase vs three-phase — what it means for your solar system

Short answer

In Romania, residential connections are either single-phase (one phase — 230 V) or three-phase (three phases — 400 V). For solar PV, this matters in two ways:

1. On single-phase, your PV system is limited to 6–9 kW, set by the home's main breaker (NOT "5 kW" as many sites repeat).
2. Above that limit you need a three-phase upgrade — separate request to the grid operator, RON 3,000–8,000 typical cost.

If you don't know what you have, start with How to identify your electrical service.

The real single-phase limit: 6–9 kW

The limit is NOT imposed by the grid; it's set by your home's main breaker (the master fuse in your switchboard). The math:

Main breaker	Practical PV limit
16 A	~3.7 kW
20 A	~4.6 kW
25 A	~5.7 kW
32 A	~7.3 kW
40 A	~9.2 kW

Most Romanian residential houses run 25 A or 32 A — meaning the real limit is 5.7–7.3 kW. It's not a flat 5 kW. If an installer tells you "max 5 kW on single-phase" and your main breaker is 32 A, ask why not 7 kW.

The grid operator (E-Distribuție, DEER, Distribuție Energie Oltenia, Delgaz Grid, etc.) issues your technical connection approval (ATR) with the approved capacity — your installer tells you how far you can go before filing.

When you need three-phase

Upgrade to three-phase if:

• you want a PV system >9 kW (large homes with several favourable roof faces),
• you have or plan a heat pump + EV charger combo — peak draw exceeds single-phase capacity,
• you run industrial loads at home (welder, three-phase workshop tools, machine tools),
• you plan to export heavily as a prosumer and want to avoid losses from phase imbalance.

If you're running a heat pump (~5,000 kWh/yr extra) plus an EV charger (~3,500 kWh/yr) plus summer AC (~1,500 kWh/yr), single-phase becomes tight fast. Three-phase is the right 15+ year investment.

How to check what your house has

Three quick methods:

1. Switchboard — one big single breaker = single-phase. Three breakers ganged together (3 levers locked by one common bar) = three-phase.
2. Electricity meter — the label says 230 V (single-phase) or 400 V / "3x400 V" (three-phase).
3. Wires from the pole to the house — 2 wires (live + neutral) = single-phase; 4 wires (3 phases + neutral) = three-phase.

Step-by-step in How to identify your electrical service.

How to upgrade to three-phase

Steps with the grid operator (slightly different per operator, same logic):

1. Connection-modification request — file on the operator's website (E-Distribuție, DEER, Distribuție Energie Oltenia, Delgaz Grid, etc.) or in person. Ask for a three-phase upgrade. Roughly RON 50 to issue the ATR.
2. Solution study — the operator evaluates the local network: is there a three-phase line on a nearby pole? If yes, costs are low. If not, three-phase cable has to be pulled — cost grows with distance.
3. ATR (technical connection approval) — tells you the approved capacity, the timeline, and the connection fee.
4. Connection contract — sign, pay the fee (typically RON 3,000–8,000; much more for long distances or new buried runs).
5. Physical work — the operator (or a certified contractor) pulls the cable, swaps the meter, reconnects. 1–3 months from ATR to live connection.
6. Switchboard rewire — an electrician (or your PV installer) rewires the indoor switchboard to three phases. Another RON 500–2,000.

Typical costs (order of magnitude)

Situation	Three-phase upgrade cost
Three-phase line already on the gate pole	RON 3,000–4,500
Three-phase cable at 30–80 m distance	RON 5,000–8,000
Three-phase cable at 100 m+ / new buried run	RON 10,000+ (rare; usually not worth it)

Plus switchboard rewire (RON 500–2,000) and possibly a new meter (free with a new connection contract).

How this affects PV sizing

If you're on single-phase and stay on single-phase:

• max 6–9 kW system (check your main breaker first),
• single-phase inverter mandatory (don't put a three-phase inverter on a single-phase house — won't work),
• watch phase balance — irrelevant when you only have one phase, but relevant for your neighbours on the same phase (the operator may require regulation).

If you upgrade to three-phase:

• you can go up to 27 kW (3 × 9 kW) as a residential prosumer,
• three-phase inverter mandatory (string or hybrid, three-phase),
• panels can be distributed more freely across the roof without hitting phase limits.

What capacity you actually need depends on consumption + future plans (EV, heat pump, AC) — see How much does a solar system cost? for ballpark figures.

---

Want quotes from installers who handle the three-phase upgrade too? Request quotes →

See also: How to identify your service · How to choose an installer