Can you add a battery and back-up to existing solar panels with SMA or SolarEdge?

Yes. You can add a battery to existing solar panels with SMA or SolarEdge, and with the right design get back-up for the whole house. The simplest route keeps your solar inverter and adds a battery inverter next to it, as in our home battery with an SMA inverter. Phases, back-up and certificates decide.

Your panels are years old, and a heat pump or two cars now use much power. Since the digital meter, surplus earns little. And at the last power cut, the sun was shining and the house went dark.

In Bornem, a 15.4 kWh battery with its own Color Control now works with the existing SMA inverter.

Can you add a battery to existing solar panels without replacing the inverter?

Yes. AC coupling keeps the solar inverter and adds a battery with its own inverter; a hybrid inverter replaces the old one.

As the Flemish government explains, AC-coupled solar power is converted twice, while a hybrid inverter sends direct current straight into the battery, with lower losses.

Our systems take the first route: a Victron MultiPlus-II works with almost all grid-tied solar inverters. Below are home batteries we installed, next to an existing inverter or cabinet or with full three-phase back-up. Tap a town for details.

How do you add a battery to an existing SMA or SolarEdge inverter?

An SMA inverter is one of the easiest to combine with a battery. SMA Benelux says an AC-coupled system can sit anywhere in the house, independent of the solar inverter. SMA sells self-consumption battery inverters with manual or automatic back-up, the off-grid Sunny Island, and a switch box for automatic whole-house back-up.

SMA hybrids, such as the three-phase Sunny Tripower Smart Energy, replace your old inverter. Next to Victron, a Sunny Boy throttles through frequency shifting when the battery is full. Data-link power control does not exist, so export limits are set another way.

With SolarEdge, the inverter model decides, because the optimisers work with it. Its own batteries are DC-coupled, and Dutch overviews note that older or non-hybrid models, often three-phase, must go. A Belgian installer describes back-up as Home Hub plus Backup Interface: a SolarEdge battery retrofit often becomes an inverter project.

Since 2019, its "Alternative Power Source" mode lets the inverter run next to Victron, also in an outage. Victron lists only single- and three-phase HD-Wave models with minimum firmware; SolarEdge support must enable frequency shifting.

Will your solar panels keep working in a power cut, even in winter?

Only if the battery system forms its own grid and cuts your house off from the street. Per Victron, a grid-tied solar inverter alone fails in a blackout. The takeover takes under 20 milliseconds, so computers keep running.

A surplus-only battery is quick to add; three-phase back-up is a different project. All three phases need back-up, or a heat pump stops anyway. Which circuits move behind the battery? Our guide to a home battery with back-up power explains three levels. Buy the wrong battery first, and you pay twice.

In winter, a flat battery cannot restart AC-coupled panels, because they need a grid to start. If the heat pump empties it before sunrise, the sun shines and the house stays dark. Victron calls DC solar chargers (MPPT) necessary here, so plan that restart in the design.

In Roosdaal, extra panels on a new MPPT added energy without the cost of a grid study. In Maaseik, an existing generator joined the home battery in off-grid mode; see a generator with a battery.

How big must the battery be next to existing solar panels?

Victron's factor 1.0 rule: solar power may not exceed the battery inverters' continuous power at 25 °C. Count the solar inverter where panels exceed it. A MultiPlus-II 48/5000 delivers 4,000 W, so three, one per phase (12,000 W), carry a 10 kW solar inverter.

For lithium, Victron asks at least 4.8 kWh per 1.5 kWp of AC-coupled solar; bigger lasts longer on back-up.

Hence 30.8 kWh on 9 kVA in Kortenberg. Size on your solar inverter and must-run loads, not only on evening use. We measure first.

Which rules apply, and do you keep your green certificates?

A Belgian owner with two old SMA inverters writes that he "may not change anything". In Flanders you keep your certificates if you follow Fluvius:

• No extra panels on the certified installation; they go on a separate inverter, as a new installation.
• A hybrid inverter only with a battery, or when the old one is broken.
• Inverter power up to a limit: 5 kVA on single-phase, 10 kVA on three-phase (Synergrid C10/26).

An AC-coupled battery changes nothing on the certified installation. Fluvius still advises asking your installer first, because a wrong change costs the certificates. A home battery is also AREI-inspected and registered:

• Registration with Fluvius within 30 days of inspection, via Mijn Fluvius below 25 kVA; bigger systems need a grid study.
• Limits: up to 25 kW an AREI declaration and Synergrid rules; 5 kVA single-phase, 25 kVA multi-phase, 5 kVA imbalance per phase.
• A new inverter must be on the C10/26 list and reported to Fluvius. Changing inverter and breaker means a new AREI inspection, and the new power sets any prosumer tariff.
• Back-up wiring changes the installation, so it is inspected before use.

In Wallonia and Brussels, declare it to ORES, RESA or Sibelga. On an older network, first read what a 3 x 230 V connection allows.

When is adding a battery not worth it?

Inverter tripping on high grid voltage at noon? Read why a solar inverter switches off when the voltage is too high.