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Can I add a battery to my old solar system, or do I need a new inverter?

Sometimes yes, sometimes no. Some batteries connect alongside your existing inverter (AC-coupled). Others bring their own hybrid inverter, which usually replaces your old one. Which is better depends on your inverter’s age, your solar size and what you want in a blackout. We check before you buy.

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The two ways to add a battery

  • AC-coupled (alongside your inverter): the battery has its own inverter and sits next to the one you have. Tesla says Powerwall 2 is designed to be added to an existing solar system and works with all major inverter brands, and that Powerwall 3 can also be added to existing solar. SolaX lists AC coupling for retrofits with its X1-VAST and HS51.
  • Hybrid or all-in-one (replaces your inverter): one inverter handles solar and battery together. Sigenergy’s SigenStor, the GoodWe ESA and Sungrow’s hybrid inverters work this way, and so does Powerwall 3, which has its own solar inverter built in.

What decides it

  • Age and condition of your inverter. If it is near the end of its life, replacing it with an all-in-one avoids paying twice.
  • Size of your solar. Some batteries limit how much AC-coupled solar can sit in the backup circuit. Tesla, for example, lists a limit of 7.6 kW AC per Powerwall for systems with AC-coupled solar only in the backup circuit, because high fault current in an outage can damage the equipment.
  • Blackout backup. The design decides whether your panels can keep recharging the battery in an outage. We tell you exactly how your set-up will behave.
  • Export limit and phase. See solar export limits and single-phase vs three-phase.

What we check

The inverter model and age, the panels and wiring, the switchboard (batteries often need RCBO upgrades to meet current standards) and a compliant battery position, on a face-to-face site visit. If your panels cannot cover the day and charge a battery, we design the extra solar needed so the battery fills. Read more: adding a battery to existing solar.

Why locals choose us

  • Our own in-house team designs every system and does every install. 25 years in solar and large commercial electrical work. No subcontractors.
  • A face-to-face site visit before every install: compliant battery position, switchboard and RCBO check, no surprises on the day.
  • SAA-accredited installer and Sigenergy-approved, with a 25-year workmanship warranty on our installation work.

Questions we get asked

Can any battery be added to any solar system?

No. Some connect alongside your inverter, others need their own. We check your system first.

Will I need to replace my solar inverter?

Not always. If it is in good condition an AC-coupled battery may suit; if it is old, an all-in-one may be the better long-term design.

Will my old panels charge the battery in a blackout?

It depends on the design. We explain exactly how your system will behave before install day.

Does the rebate still apply?

The federal battery rebate applies to a battery added to existing solar, and we take it off at point of sale. It steps down on 1 January 2027.

Sources

Last checked 7 October 2026. Only the manufacturer’s, the network’s or the government’s own documents are used; app menus and defaults change between models and versions, so if your screen looks different, call us rather than guess.

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