Adding a Battery to Your Existing Solar? Don't Make the Two-Kitchen Mistake

Here's the easiest way to think about it.

Imagine your home has two separate kitchens. Kitchen 1 has its own chef, its own fridge, its own oven. Kitchen 2 has the same. They're both making meals for your family, but they can't see what the other one is doing. Chef 1 might be cooking a roast while Chef 2 is also cooking a roast. Nobody's coordinating. Nobody's sharing ingredients.

That's essentially what happens when you run two inverters from different brands side by side.

Your existing inverter keeps doing its thing, converting solar from the original panels and sending power into your home or back to the grid. It has no idea there's a battery in the house. It can't send power to it directly. It doesn't even know it exists.

The new hybrid inverter runs the new panels and manages the battery. It decides when to store power, when to use it, when to export. It's the smart one. But it can only work with the panels connected to it.

Now, there is a workaround. The new system's gateway (a CT clamp on your meter board) monitors your whole home's energy use. So it can see when the old system is producing excess and divert that into the battery. But it's doing this the long way around. The power has to be converted from DC to AC by the old inverter, flow through your switchboard, get measured by the gateway, then get converted back to DC to charge the battery. Every conversion step loses energy.

And you're running two apps. Two monitoring systems. Two things to troubleshoot when something goes wrong.

Instead of bolting a second system alongside the first, the better move in most cases is to ditch the old inverter entirely and rewire the existing panels directly into the new hybrid inverter via DC coupling.

Think of it like knocking down the wall between those two kitchens and putting one head chef in charge of everything.

DC coupling means the solar from your existing panels goes straight to the new inverter and battery in its raw DC form. No unnecessary conversions. No energy lost in translation. One system sees all the panels, controls the battery, manages your export limits, and gives you everything in a single app.

It's cleaner. It's more efficient. And it's significantly easier to live with day to day.

A lot of installers will default to the "add alongside" approach because it's simpler for them. Less rewiring. Fewer changes to the existing setup. Faster install. They're not necessarily being dodgy, it's just the path of least resistance.

But as the homeowner, you're the one who has to live with the system for the next 15-20 years. And running two disconnected systems for two decades because it saved the installer half a day on the install.... that's not a great trade-off.

It's worth asking the question. Even if the answer is "we can't do it because of X" (roof layout, panel compatibility, wiring distances), at least you've had the conversation.

This is where it gets important.

When you consolidate everything into one inverter, that inverter needs to be big enough to handle all your panels. Not just the new ones.

In Australia, the CEC allows a DC/AC ratio of up to about 1.33. So if you've got 26kW of total panels across old and new, you'd need a minimum 20kW inverter. At that ratio you're right at the limit with no headroom.

If your household is a big energy user (ducted air conditioning, pool pump, EV charger, large home), you want that inverter doing more than just handling the panels. It also needs enough throughput to charge the battery quickly during peak sun hours while simultaneously running the house. A 10kW inverter trying to manage 26kW of panels and a 48kWh battery while your ducted system pulls 5-6kW is going to be a bottleneck.

Taking Sigenergy as an example (since they're popular in the Australian market right now), their 3-phase range runs from 5kW all the way up to 29.9kW. For a setup with 26kW of panels and a large battery, the 25kW 3-phase model would be the sweet spot. Handles all the panels comfortably, charges the battery fast, and has room to breathe.

Yes, a bigger inverter costs more upfront. But if your power bills are $400-500 a month, the efficiency gains from running one properly sized system versus two undersized ones will pay for the difference pretty quickly. If you're unsure what size system you need, our solar and battery calculators can help you figure out the right fit.

If you're getting quotes to add panels and a battery to an existing system, here are the questions worth asking before you sign anything.

The two-inverter approach isn't always wrong. There are genuine situations where it's the best option, like when panel types are wildly incompatible or when the existing inverter is under warranty and removing it doesn't make financial sense.

But more often than not, consolidating into one properly sized hybrid inverter with DC coupling is the cleaner, more efficient, and more liveable solution.

One system. One app. One brain running your whole home's energy.

That's the kitchen you want to be cooking in.