How does a battery connect to your existing solar system?

How does a battery connect to your existing solar system?

You can often add a battery without replacing your solar panels. The real question is how the battery joins your system. There are two main ways, and which one suits you depends mostly on the inverter you already have. [1] [2]

First, a quick bit of background. Solar panels make direct current (DC), but your home runs on alternating current (AC). An inverter converts one to the other. A battery stores power as DC, so somewhere in the system another conversion has to happen. The two ways of connecting a battery differ in where that happens. [1]

Option 1: AC coupling (keep your inverter, add a battery inverter)

Your existing solar inverter stays exactly as it is. The battery comes with its own inverter, either separate or built in, and connects to your home's AC wiring alongside the solar. That means two inverters working side by side. [1] [3]

• Why people choose it: it doesn't need to match your existing solar, which is why it's the usual way to add a battery to solar you already have. [1] [3] [4]
• The trade-off: power is converted more times on its way to and from the battery, so it's a little less efficient. [3] [5]

Option 2: DC coupling (one hybrid inverter does both jobs)

A hybrid inverter looks after both your panels and the battery, so solar can charge the battery directly before it's converted. [1]

• Why people choose it: it suits solar and a battery installed together. [1] [3] [4]
• The catch for existing solar: if you're adding a battery later, it can mean replacing your old inverter with a hybrid, which is a bigger job and cost. [1] [3] [4]

The same goal either way

Both options do the same job: they store your spare solar power so you can use it in the evening instead of buying it back from the grid. [1] [2]

What can change the answer

• Microinverters. If you have a small inverter under each panel, a hybrid inverter can't be connected to them, so the battery needs its own inverter. [1] [4] [6]
• "Battery-ready" hybrid inverters. Advice differs. Western Australia's government guide suggests a hybrid if you plan a battery later. Consumer group CHOICE and Solar Victoria warn that a hybrid bought well before the battery may not suit the battery you eventually pick, or may be out of date by then. [5] [4] [6]
• Blackout backup. Neither option keeps your power on in an outage by default. Backup only works if the system is installed for it. [1] [4]
• Your switchboard and network approval.

How to tell what you have

Your inverter's model number is on its label, usually underneath. Look it up, or ask an installer. [5]

What to do next

Don't guess, because the right choice depends on your inverter's age and type, your switchboard, and what you want the battery to do. Smarter Solar looks at your existing solar, your electricity use and your battery goals to create a free personalised plan you can discuss with vetted installers. Your installer confirms what suits your system.

Sources:

1. Batteries and Inverters, energy.gov.au
2. Batteries, Your Home (Australian Government)
3. Batteries, Your Home (Australian Government)
4. Solar battery systems explained, and Finding the right inverter, Solar Victoria
5. Customers with existing solar systems: installing a battery, Energy Policy WA
6. How to buy the best solar inverter, CHOICE
7. Energy Safe Victoria, SA Power Networks and Ausgrid guidance, from the repo's "Adding a battery to existing solar" article