Inverters by number of phases
Inverters by number of phases splits the range by how the unit connects to the AC side: 1-phase inverters feed a single line conductor, 3-phase inverters distribute their output evenly across L1, L2 and L3. The phase count has to match the building's grid connection, the feed-in limit the distribution operator applies to a single phase, and the way your smart meter nets consumption against export. It also decides whether a hybrid system can supply three-phase backup. Guide
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Phase count: matching the inverter to the grid connection
The number of phases is the one inverter property that is dictated by the building rather than by the array. A single-phase inverter injects all its power into one line conductor and neutral at roughly 230 V. A three-phase inverter splits its output across three conductors 120 degrees apart at roughly 400 V between lines. If the property has a three-phase supply, which is standard for most European houses with an electric hob, heat pump or wallbox, a three-phase inverter above a few kilowatts is nearly always the correct answer.
Two rules follow from the connection. First, most distribution operators cap how much generation may be fed into a single phase, commonly in the region of 3.6 kW to 5 kW, and a larger single-phase inverter simply will not be approved. Second, a single-phase inverter on a three-phase supply creates phase imbalance, which changes the economics of the whole installation depending on how your meter nets the three phases.
FROM THE FIELD
"The question I ask before anything else is how the meter nets. If the operator bills each phase separately, a single-phase inverter on a three-phase house can export on L1 while you pay for import on L2 and L3 at the same second. The array is working perfectly and the bill barely moves. On a summed meter the same hardware behaves completely differently, so the netting rule decides the design, not the price of the inverter."
Ladislav Proc · Photovoltaics specialist, ONSA Plus
How to choose between a single-phase and a three-phase inverter
Start at the main distribution board, not the roof. Count the line conductors on the incoming supply and read the main breaker rating. That tells you what is physically available, and the connection approval tells you what the operator will allow you to feed back.
Then check three things in order: the single-phase feed-in cap in your grid code, how the meter nets the phases, and whether you want backup on one circuit or on the whole board. Only after those does the choice between 1-phase and 3-phase become a shopping decision.
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Matching phases to the grid connection
The supply type is a fact about the property, and the inverter must fit it.
- Single-phase supply: only a single-phase inverter can be connected. Common in apartments, older terraced housing and small holiday properties.
- Three-phase supply: either type is technically connectable, but three-phase is the default above the single-phase feed-in cap and mandatory for three-phase backup.
- Balcony and plug-in systems: always single-phase, and limited by national plug-in rules rather than by the inverter itself.
- Large loads on site: a heat pump, a three-phase wallbox or workshop machinery all imply a three-phase board, and generation should be spread the same way.
The single-phase feed-in limit
Distribution operators limit generation on one phase because unbalanced injection raises the voltage on that conductor relative to the others. The exact figure is national and sometimes local, but a cap somewhere between 3.6 kW and 5 kW per phase is typical, which is why inverter power bands cluster at 3680 W and 4600 W. Exceeding the cap does not just risk a rejected application. It can trigger repeated shutdowns in service, because the inverter must disconnect when the voltage on its phase rises above the limit set by EN 50549 and the national grid code, and a single-phase injection at the end of a weak rural line reaches that threshold quickly.
Phase imbalance and why one inverter causes it
A three-phase inverter puts one third of its output on each conductor, so the network sees a balanced source. A single-phase inverter on a three-phase board puts everything on one conductor while the house continues to draw on all three. The result is a voltage rise on the generating phase, higher losses in the supply transformer, and a meter that records simultaneous export and import. On sites with a three-phase heat pump or wallbox the imbalance also means the generated power cannot fully serve those loads, because two of the three phases never see it.
Tip from practice
Before choosing a single-phase inverter for a three-phase house, ask the operator in writing whether the meter nets per phase or summed across all three. On a summed meter the imbalance costs you little financially. On per-phase billing the same installation can pay for imported energy at the very moment it exports, and no inverter setting will fix that.
Per-phase versus summed netting and the economics
The netting rule decides how much of your generation actually offsets consumption.
- Summed netting: the meter adds the three phases algebraically, so 3 kW exported on L1 cancels 3 kW imported on L2 and L3. A single-phase inverter behaves almost like a three-phase one on the bill.
- Per-phase netting: each phase is billed on its own. Export on the generating phase is sold or spilled while the other two are bought at retail price, which can cut self-consumption value dramatically.
- Export limiting: zero feed-in or capped feed-in regulation is measured at the connection point, so the control accuracy depends on a compatible smart meter installed on all live conductors.
- Load shifting: where netting is per phase, moving large loads onto the generating phase is a partial fix, but it is fragile compared with balanced generation.
Three-phase backup during an outage
Backup capability follows the phase count. A single-phase hybrid inverter can supply a protected single-phase sub-circuit, typically lighting, sockets, a boiler and networking equipment. Only a three-phase hybrid unit, or several single-phase units configured as a coordinated three-phase group, can energise a three-phase board. That matters if the property has a three-phase heat pump, a borehole pump, a lift or workshop machinery, none of which will run from a single-phase emergency output. Check also the backup output rating, which is often lower than the inverter's grid-tie rating, and whether the changeover is automatic or manual.
Extending an existing single-phase system
If a single-phase inverter is already installed and you want more capacity, there are three practical routes. Add a second single-phase inverter on a different phase, which improves balance and is often the cheapest step, provided the operator approves both units and the total. Replace the unit with a three-phase inverter and reuse the existing strings, which is the cleanest outcome when a battery or backup is also planned. Or keep the existing AC-coupled system and add a three-phase hybrid unit alongside it, which suits sites where the original inverter is still healthy. In all three cases the connection approval has to be updated before commissioning, because the registered generation capacity changes.
Single-phase and three-phase compared
| Aspect | Single-phase inverter | Three-phase inverter |
|---|---|---|
| Typical power | Up to about 5 kW, limited by the feed-in cap | From about 3 kW to 350 kW |
| Grid connection | One line conductor and neutral, roughly 230 V | L1, L2 and L3, roughly 400 V between lines |
| Phase balance | All output on one phase, voltage rise on that conductor | Output split evenly, balanced injection |
| Netting behaviour | Sensitive to per-phase billing rules | Serves loads on all three phases directly |
| Backup capability | Single-phase protected sub-circuit only | Whole three-phase board, including heat pump and pumps |
| Best suited to | Apartments, small roofs, single-phase supplies, balconies | Family houses with heat pump or wallbox, commercial roofs |
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Frequently asked questions about inverter phases
How do I know if I have a single-phase or three-phase supply?
Look at the main breaker in the distribution board. Three line conductors and a three-pole main breaker mean a three-phase supply. A single-phase supply has one line conductor and neutral. The connection contract with the operator states it as well.
Can I connect a single-phase inverter to a three-phase house?
Yes, technically, and it is common for small systems. It creates phase imbalance and its value depends on whether your meter nets per phase or across all three. Above the operator's single-phase feed-in cap it will not be approved at all.
What is the single-phase feed-in limit?
A cap on how much generation may be injected into one phase, set by the distribution operator to keep voltage rise and imbalance within limits. Typical figures fall between 3.6 kW and 5 kW, which is why inverters are built at 3680 W and 4600 W.
What does phase imbalance actually cause?
Voltage rises on the generating phase while the other two stay loaded, which increases losses, stresses the supply transformer and can push the inverter into protective disconnection. On weak rural lines this causes repeated shutdowns on sunny days with little consumption.
Does a three-phase inverter make my system produce more?
Not directly, since the array size sets production. It usually makes more of that production usable, because the output reaches loads on all three phases, avoids per-phase billing penalties and is less likely to trip on overvoltage. On a summed-netting meter the difference is smaller.
Can I run a heat pump or a three-phase wallbox from a single-phase inverter?
Only partially in grid-tie operation, and not at all in backup. A three-phase load draws on all three conductors, while a single-phase inverter supplies one. During an outage a single-phase backup output cannot energise a three-phase appliance at all.
Do I need a smart meter with either type of inverter?
You need one for export limiting, self-consumption control and accurate monitoring. On a three-phase board the meter or its current transformers must sit on all three live conductors, otherwise the inverter regulates on incomplete data. Use a meter from the manufacturer's approved list.
Can I get three-phase backup during a power cut?
Yes, with a three-phase hybrid inverter that has a backup output, or with coordinated single-phase units configured as a three-phase group. Check the backup power rating, which is usually below the grid-tie rating, and whether changeover is automatic.
I already have a single-phase system. How do I extend it?
Three options: add a second single-phase inverter on a different phase to improve balance, replace the unit with a three-phase inverter and reuse the strings, or add a three-phase hybrid alongside the existing one. Each requires an updated connection approval.
Can two single-phase inverters be used instead of one three-phase unit?
Yes, and on some platforms two or three units can be linked to act as a balanced group with three-phase backup. Without that coordination they are simply separate generators on separate phases, so total approved capacity and the per-phase cap both still apply.
Phase allocation and feed in limits are set by your grid operator and by the national connection rules.
About ONSA Plus
Why installers across Europe source inverters from us
ONSA Plus is a European B2B distributor of photovoltaics, battery storage, heat pumps and EV charging stations. In our own EU warehouses we keep over 1,500 products from 25+ brands, including Huawei, Solis, SolaX and Dyness.
We are not just a trading company. We design and service energy systems ourselves, so we answer questions on phase matching, feed in limits and netting from engineering practice, not from a catalogue. You handle a warranty claim directly with us and you buy per job.
