How many kVA of solar may you install, and what if you want more?

In Flanders you may connect up to 5 kVA of solar inverters on single-phase. On three-phase you can go up to 25 kVA before a grid study is needed. Want more panels than that? You can move to three-phase or go through the grid study. You can put more panels on the same inverter and accept that it caps the peak. Or you use and store the surplus yourself. The route that takes the limit away is a semi-off-grid system: the extra panels feed your own battery and consumers, not the street. So they do not count toward the grid limit.

Your warehouse, stable or roof has room for twice as many panels as the installer wants to put on it. The roof is not the problem. The connection is: 5 kVA on single-phase, or the step above 25 kVA where Fluvius first wants a grid study. Or you already have panels, and the room left is too small for the heat pump or electric van you plan.

Staying under the limit feels safe, but it has a cost. Every panel you leave off is cheap solar power you buy back from the grid in the evening and in winter. Going over it without the right procedure costs more: Fluvius charges administration fees and back-dated prosumer tariffs for late or missing registration. And more panels on a weak street cable can make your inverter trip on high grid voltage on the sunniest days.

A home in Heusden-Zolder ran into the single-phase limit of 5 kW, which was not enough to cover its use through the year. We built a semi-off-grid system in Heusden-Zolder: the panels run in the home's own off-grid system with its battery. The house only switches to the street when the battery is empty and there is no sun. In Aalst, the same approach made room for 20 kW of solar panels without registering them with Fluvius, because they only feed the house.

What does kVA mean for solar panels, and why does the inverter count?

Two numbers are easily mixed up. kWp is the peak power of your panels, measured on the direct current side. kVA is the power your inverter can deliver as alternating current to your installation and the grid. For a solar inverter, kVA and kW are in practice almost the same number.

The grid limit counts the inverters, not the panels. Fluvius adds up the power of all production inverters on your connection: solar, hybrid and wind. In Wallonia the maximum AC power of the inverters is also the reference. So a roof with 12 kWp of panels on a 10 kVA inverter counts as 10 kVA.

That is why installers can put a little more panel power on an inverter than its kVA. On the brightest hours the inverter then caps the output at its own limit. You lose a little at the peak. You gain in the morning, the evening and on grey days, when the panels never reach their peak anyway.

How much solar may you connect in Flanders?

Fluvius works with a few clear steps. They apply to the total power of all production inverters on one connection.

• Up to 5 kVA on single-phase. The 5 kVA covers all inverters together. A battery inverter that cannot handle solar power does not count toward it, following the Synergrid classification that Fluvius uses.
• From 5 to 25 kVA you need three-phase. The sum of all inverters stays at or below 25 kVA.
• Above 25 kVA, a grid study comes first. Fluvius checks whether the local grid can take the extra power before anything is installed and connected.
• From 30 kVA, a disconnection protection is compulsory. It separates your installation from the grid when the grid requires it.
• Above 10 kVA as a private person, you also register as self-employed, according to Fluvius.

Before you use the installation, it is inspected under the AREI by an accredited body. You register it in Mijn Fluvius, and a certified installer reports it too. Registering late or not at all costs administration fees and back-dated prosumer tariffs. The same applies when you add panels or replace an inverter later.

Is the grid operator limiting how much you may inject, even below these steps? That is a different problem, with its own fixes: read what to do with an injection limit or zero export.

What are the rules in Wallonia and Brussels?

In Wallonia, a "small production installation" goes up to 10 kVA. The maximum AC power of the inverters is the reference, as stated on the nameplate, and several units are added up. Going above 10 kVA is not forbidden, but it is no longer a small installation. The normal procedure with ORES or RESA then applies, with a grid study at your cost. The grid operator then decides how much you may inject.

What can you do when you want more panels than your connection allows?

There are six routes. Most sites combine two of them.

How does semi-off-grid let you install more panels?

In a semi-off-grid system, your panels, battery and consumers form your own island grid. A transfer switch keeps that island separate from the public grid. The grid is only the back-up: it steps in when the battery is empty and the sun is not shining.

Because those panels are not connected to the public grid, the grid limit does not apply to them. That is how a single-phase home in Heusden-Zolder went past 5 kW, and how a home in Aalst runs 20 kW of panels. It works the same for businesses. An SME or a farm on 3x400 V + N can extend its panels without paying taxes on them. Those panels are not connected to the grid.

Off the grid does not mean outside the rules. The installation is still inspected under the AREI before use. In Flanders an island installation with an inverter of 800 VA or more is also reported to the Vlaamse Nutsregulator. And if the public grid fails, you keep working on your own installation.

Does a battery help when you reach the limit?

A battery on its own does not raise the limit. A hybrid inverter that handles both solar and the battery counts toward the kVA like any solar inverter. A battery inverter without solar capability does not count toward the 5 kVA, according to Fluvius. What a battery does do: it keeps your midday surplus for the evening, so you buy less back.

The surplus can also go straight into useful work. A farm in Tielt runs semi-off-grid with smart control that sends extra solar power to its boilers. The Tielt farm expects to take only about 5% of its yearly use from the street. For peaks, self-consumption and back-up behind a normal connection, see our business batteries.

Which route fits your site?

It depends on three things: how many kVA you want to add, when you use your power, and what your connection is today.

Is a heavier connection refused altogether? Then read what to do when Fluvius refuses a heavier connection. Is there no grid at all, or would it cost a cabin? Then look at off-grid for businesses. Still weighing whether panels pay off at all? Read whether solar panels still pay off for a business in 2026.

What happens when you contact YouPower?

1. Step 1: You send what you have. Your connection (single or three-phase, and the amps), your current panels and inverters, and your yearly use in kWh.
2. Step 2: We measure where we can. Actual and peak consumption over a period show when you use power, and how much of the extra solar power you would really use.
3. Step 3: Our engineering office calculates the system. The type, number and position of the panels, the inverters and the battery, and which part stays on the grid.
4. Step 4: We build, test and commission it. We carry out the entire installation and have it inspected before it is put into use.
5. Step 5: We keep following it. You follow production, storage and consumption in real time in the app, with alerts on your phone.