What Size Solar Inverter Do I Need?
The inverter is sized to your panel array, not the other way round. Most Irish homes pair a panel array of a given kWp with an inverter rated slightly lower in kW, a deliberate choice that costs less and barely affects yearly output. This guide covers the DC:AC ratio, a quick sizing table, and the grid limits that decide what you can fit. For the technology choice, see the inverter comparison and string vs micro vs optimiser guides.
Quick Answer
Size the inverter to your panel array using a DC:AC ratio of around 1.1 to 1.25, meaning the inverter is rated slightly below the array kWp. A 5 kWp array typically pairs with a 4 to 5 kW inverter. Ireland's diffuse light means peak output is rare, so mild clipping is acceptable and economical. ESB Networks allows up to 6 kW single-phase or 11 kW three-phase under the simpler inform-and-fit process. Most homes now choose a hybrid inverter so a battery can be added later.
The DC:AC ratio: why the inverter is smaller than the array
Panels produce direct current (DC). The inverter converts that to alternating current (AC) for your home and the grid. The DC:AC ratio compares the array size in kWp (the DC side) with the inverter rating in kW (the AC side). A ratio of 1.0 would match them exactly. In practice installers aim for around 1.1 to 1.25, so the array is modestly larger than the inverter.
The reason is that panels almost never hit their full rated output. The kWp figure is measured under standard test conditions: bright, direct, perpendicular sun at a set temperature. Irish light is diffuse and the sun is low for much of the year, so a 5 kWp array might only briefly touch 4 to 4.5 kW on the best summer days. Pairing it with a 4 to 5 kW inverter captures nearly all of that energy for less money than an oversized unit.
What "clipping" means
If the array ever produces more than the inverter can pass through, the inverter caps the output. That capped energy is lost, an effect called clipping. With a sensible ratio the amount clipped over a full year in Ireland is typically tiny, often well under 1% of total generation, because those rare peak moments are short and few.
A small, deliberate amount of clipping is normal and economical. It lets you fit more panels (more energy across cloudy days and winter) without paying for inverter headroom you would almost never use.
Solar inverter sizing table for Irish homes
As a starting point, here is the inverter size that typically suits each array size at a DC:AC ratio of roughly 1.1 to 1.25. These are common pairings, not hard rules. Your installer will fine-tune based on roof orientation, shading, and whether a battery is planned.
| Array size (kWp) | Typical inverter (kW) | Approx panels | Notes |
|---|---|---|---|
| 2.5 to 3 kWp | 2.5 to 3 kW | 6 to 7 | Small home or apartment, single-phase |
| 3.5 to 4 kWp | 3 to 3.6 kW | 8 to 10 | Common starter size, fits inform-and-fit easily |
| 4.5 to 5 kWp | 4 to 5 kW | 11 to 13 | Popular family-home size, single-phase |
| 6 kWp | 5 to 6 kW | 14 to 16 | At or near the 6 kW single-phase limit |
| 7 to 8 kWp | 6 kW (single) or higher (three-phase) | 17 to 20 | Three-phase preferred above 6 kW inverter output |
| 10 to 12 kWp | 8 to 11 kW (three-phase) | 24 to 30 | Large home, requires three-phase supply |
Indicative pairings for Irish installs at a DC:AC ratio of around 1.1 to 1.25. Panel counts assume roughly 400 to 440W panels. Final sizing depends on your roof, shading, and grid connection.
Single-phase vs three-phase: the grid limit that caps your size
The biggest practical limit on inverter size is your home's electricity supply. Most Irish houses have a single-phase supply. Larger or rural properties sometimes have three-phase. ESB Networks sets the export thresholds, and these often decide the inverter size before the roof does.
| Supply type | Inform-and-fit limit (NC6) | Above the limit |
|---|---|---|
| Single-phase | Up to 6 kW inverter output | Needs a full NC7 connection application |
| Three-phase | Up to 11 kW inverter output | Needs a full NC7 connection application |
Under the NC6 process (the simpler inform-and-fit route) you can install up to these limits and notify ESB Networks, rather than waiting for a formal approval. Go above them and you move to the NC7 process, which involves a connection application, possible network studies, and a longer timeline. For most homes, staying within 6 kW single-phase keeps the project simple.
Limits reflect ESB Networks micro-generation rules and are based on inverter output rating, not array kWp. Always confirm the current thresholds with your installer before ordering.
Size for a battery: why a hybrid inverter is the default
A hybrid inverter handles both your panels and a battery from a single unit. Even if you are not adding storage on day one, sizing the system around a hybrid leaves the door open. Adding a battery later to a system built with a basic string inverter often means a second AC-coupled battery inverter, or replacing the original unit entirely.
Plan ahead with a hybrid
- Battery-ready from the start. Add storage later without a second inverter. See solar battery storage.
- Match the inverter battery rating to the storage you might add, typically 5 to 10 kWh for a home.
- Check MPPT inputs. Two or more lets you run panels on different roof faces (east and west) on separate strings.
Mixed roof orientations
If your panels sit on two roof slopes facing different directions, a single MPPT input forces them to behave as one string, dragging the better roof down to the worse. An inverter with multiple MPPT inputs tracks each slope independently, recovering that lost yield.
For the trade-offs between string, microinverter, and optimiser setups on tricky roofs, read the string vs micro vs optimiser guide.
Common inverter sizing mistakes
Getting the size wrong in either direction costs you. Here are the two failure modes and how to avoid them.
Oversizing the inverter
Fitting a 6 kW inverter to a 4 kWp array wastes money. The extra capacity sits unused because the panels can never feed it. You pay more upfront for headroom that delivers no extra energy. A ratio below about 1.0 is usually a sign of oversizing.
Undersizing the inverter
Pairing a tiny inverter with a large array (a ratio well above 1.3) clips too much. On bright days the inverter caps output and you lose real generation. Mild clipping is fine, but push the ratio too far and the savings on the inverter no longer cover the energy you give up.
To compare specific units once your size is set, see the solar inverter brands overview and the inverter comparison.
Frequently Asked Questions About Inverter Sizing
What size solar inverter do I need for a 5 kWp array?
A 5 kWp array typically pairs with a 4 to 5 kW inverter, giving a DC:AC ratio of around 1.0 to 1.25. In Ireland's diffuse light the array rarely reaches full output, so a slightly smaller inverter captures nearly all the energy for less cost, with only a tiny amount of clipping over a year.
What is a good DC:AC ratio for solar in Ireland?
Most Irish installs use a DC:AC ratio of around 1.1 to 1.25, meaning the panel array kWp is modestly larger than the inverter kW rating. This is economical because peak output is rare in Irish conditions, so the small amount of clipping is far cheaper than paying for an oversized inverter.
Should the inverter be the same size as the panels?
Not usually. The inverter is normally rated slightly below the array kWp. Panels almost never hit their full rated output in Irish light, so an inverter sized at around 80 to 90% of the array captures nearly all the generation while costing less. An exactly matched or oversized inverter wastes money.
What is the largest solar inverter I can install in Ireland?
Under the ESB Networks inform-and-fit (NC6) process you can install up to 6 kW inverter output on a single-phase supply or 11 kW on three-phase. Above those limits you need a full NC7 connection application, which takes longer and may require network studies.
Do I need a hybrid inverter if I am not getting a battery yet?
It is the safer default. A hybrid inverter lets you add a battery later from the same unit. If you fit a basic string inverter now, adding storage later often means a separate battery inverter or replacing the original, so many homes choose a hybrid even before buying a battery.
Related Guides
Inverter Guide
Comparing string, micro, and hybrid inverters.
String vs Micro vs Optimiser
Inverter architectures compared: cost, shading, monitoring.
Solar Inverter Brands
Best solar inverter brands in Ireland ranked by efficiency, warranty, and value.
Equipment Guide
Panels, inverters, batteries, and what to choose.
Sources
- ESB Networks: Connecting micro-generation (NC6 / NC7), esbnetworks.ie
- NREL: System design and the inverter loading ratio, nrel.gov
- SEAI: Solar Electricity Grant, seai.ie
Last updated: September 2026
Fact-checked by John Rooney, Solar Energy Editor. Editorial policy
John Rooney is the editor of Solar Info and has been covering the Irish solar energy market since 2023. He fact-checks all content against official SEAI data and maintains relationships with SEAI-registered installers across Ireland.
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