May 15, 2026

Battery Retrofit Installations: How to Add Battery Storage to an Existing Solar System in Australia

Millions of Australian homes have had solar panels on their roofs for three to eight years. They were early adopters, they’ve seen the benefits, and now — with electricity prices higher than ever and battery costs significantly lower than when they installed solar — they’re asking: “Can I add a battery to my existing system?”

The answer is almost always yes. But how you add the battery depends on what solar system they already have, and the options range from straightforward to complex.

This is a growing market for solar installation businesses — and because these are existing solar customers or referrals from them, the conversion rate is high. They already understand the value of solar. They already trust the technology. The battery is a natural next step.

This guide covers the technical options for battery retrofits, the compatibility considerations, the compliance requirements, and how to build battery retrofits into your business model.

Why Battery Retrofit Is a Growing Opportunity

The timing is right. The cohort of homes that installed solar in 2015–2020 is now in the “solar is paid off, battery makes sense” window. Their solar system has reached or passed payback, electricity prices have risen substantially since they installed, and battery prices have fallen substantially.

Feed-in tariffs are at historical lows. In most states, the feed-in tariff for solar export is now 3–10 cents/kWh. In contrast, grid electricity costs 25–40 cents/kWh in most areas. The economics of self-consumption vs. grid export have shifted dramatically — a battery that stores daytime solar for evening use is now much more financially compelling than it was when feed-in tariffs were 20+ cents.

State incentives are available. Several states (particularly VIC and ACT) have battery incentive schemes that apply to battery retrofits, not just new solar + battery installs. This reduces the customer’s upfront cost and improves payback.

Understanding Battery Retrofit Options

There are two primary technical approaches for adding battery storage to an existing solar system: AC coupling and DC coupling (hybrid inverter replacement).

Option 1: AC Coupling — The Universal Retrofit

AC coupling adds a battery system that connects to the AC side of the existing solar inverter — after the inverter, not between the panels and the inverter.

How it works: The existing solar system operates as it always did. The battery system (e.g., Tesla Powerwall, sonnen, ALPHA ESS SMILE, Selectronic SP PRO with AC-coupled battery) sits alongside it, connected to the household’s AC electrical system. The battery charges from excess solar generation (via the house metering or a CT clamp) and discharges to supply the home during low-solar or evening periods.

Advantages:

Works with almost any existing grid-connect inverter — compatibility is rarely an issue
The existing inverter stays in place — no waste, no cost to replace a functioning inverter
Simpler installation in most cases

Disadvantages:

AC coupling introduces a conversion step (DC from panels → AC from inverter → DC to battery → AC to house), reducing round-trip efficiency slightly compared to DC coupling
The battery charger is a separate unit (within the battery system), adding some cost
Not all battery systems support AC coupling gracefully at all scales

Best AC-coupled battery products for retrofits:

Tesla Powerwall 3 (has its own inverter and CT metering for AC coupling)
sonnen ecoLinx and eco series (designed for AC coupling)
ALPHA ESS SMILE (popular mid-range AC-coupled option)

Option 2: DC Coupling (Hybrid Inverter Retrofit)

DC coupling replaces the existing solar inverter with a hybrid inverter that manages both the solar panels (DC) and the battery (DC) directly.

How it works: The existing solar inverter is removed. A new hybrid inverter (e.g., Fronius GEN24, SolarEdge with battery, Sungrow SH series, Goodwe ES series) is installed in its place. The solar panels connect directly to the hybrid inverter’s solar input. The battery connects to the hybrid inverter’s DC battery port. The hybrid inverter manages all energy flows: solar to battery, solar to house, battery to house, grid charging (if configured).

Advantages:

Higher round-trip efficiency (one DC-DC conversion step rather than DC-AC-DC)
Better integration between solar and battery management
Usually better monitoring and data (single system view)
Often enables more sophisticated grid services (VPP, time-of-use optimisation, grid charging)

Disadvantages:

The existing inverter is replaced (creating an e-waste issue and losing any remaining inverter warranty)
More complex installation — requires panel string rewiring to the new inverter
Compatibility between existing panels and the new hybrid inverter must be confirmed (voltage, current characteristics)
Higher upfront cost (new hybrid inverter + battery vs. just battery in AC coupling)

When to recommend DC coupling:

The existing inverter is old, faulty, or at end-of-life — a compelling reason to replace anyway
The customer wants the most efficient system and better monitoring
The existing inverter’s warranty has expired and they’re not concerned about losing it

Option 3: Adding a DC-Coupled Battery to an Existing Hybrid Inverter

If the existing solar system already has a hybrid inverter (increasingly common in installs from 2020 onwards), adding battery storage can be a relatively simple process:

Confirm the battery is compatible with the existing hybrid inverter (most hybrid inverters from major brands support a specific range of compatible batteries)
Add the battery to the existing battery port on the hybrid inverter
Update the inverter configuration
Commission and test

This is the simplest retrofit scenario and often the most profitable — minimal labour, no inverter replacement, just battery hardware and commissioning.

Compatibility Assessment: What to Check Before Quoting

A thorough site visit and compatibility assessment before quoting is essential for battery retrofits. Key items to assess:

Existing inverter details:

Brand, model, age, current condition
Does it support battery integration directly (hybrid), or is it a standard string inverter?
What is the DC voltage range from the existing panels (relevant if considering DC coupling)?
Is the inverter still under warranty? (If yes, replacing it to DC-couple is a harder sell)

Switchboard assessment:

Is there space for the battery system’s electrical connections?
Is the metering suitable for the battery system’s requirements? (Some battery systems require an upgraded smart meter)
Is there space for any additional protection devices required?

Physical installation location:

Where will the battery be installed? (Refer to AS/NZS 5139 clearance requirements)
What is the installation environment temperature? (Extreme heat or cold affects battery performance and can affect compliance)
Is external (outdoor) or internal installation preferred/required?

Grid metering:

Does the property have interval metering (required for most modern battery systems with grid integration)?
If not, will a meter upgrade be needed? (This involves the DNSP and may affect timeline)

AS/NZS 5139 Compliance for Battery Retrofits

Battery retrofit installations are subject to the same AS/NZS 5139:2019 compliance requirements as new battery installations. The battery is new even if the solar system isn’t.

Key compliance requirements:

Location and clearances (see our AS/NZS 5139 guide)
Required signage and labelling
Ventilation assessment
Commissioning documentation
Notification of new battery installation to the DNSP (in most states)
Certificate of Electrical Safety (VIC) or Certificate of Compliance — Electrical Work (NSW) or equivalent

Don’t shortcut the compliance on a retrofit job because the solar system has been there for years. The battery is new work and needs to be certified as new work.

Pricing Battery Retrofit Jobs

Battery retrofit pricing varies based on the installation approach:

Approach	Battery Cost (trade)	Labour	Materials & Compliance	Total Installed
AC-coupled battery (e.g., Powerwall 3)	$9,500–$12,000	$1,200–$2,000	$400–$800	$11,100–$14,800
AC-coupled battery (BYD/ALPHA mid-range)	$4,500–$7,000	$1,000–$1,800	$400–$800	$5,900–$9,600
DC-coupling (hybrid inverter replacement + battery)	$6,500–$10,000	$1,800–$3,000	$600–$1,200	$8,900–$14,200
Add battery to existing hybrid inverter	$4,500–$8,000	$600–$1,000	$300–$600	$5,400–$9,600

Note: These are indicative ranges for residential jobs. Commercial and complex installations will vary.

Marketing Battery Retrofits to Existing Customers

Your existing solar customer base is your most valuable source of battery retrofit leads. Filter your customer database for installs 2+ years old and run a targeted campaign:

Subject: “Is it time to add a battery to your solar system?”

The message:

Remind them of their installation date
Share that battery prices have fallen significantly since their install
Share that feed-in tariffs have dropped — they’re now exporting solar at 4c and importing at 28c
Offer a no-obligation battery assessment (site visit + proposal)
Include a customer testimonial from a recent battery retrofit

This campaign costs almost nothing to run and can generate strong lead flow during a slow installation period.

You can automate this follow-up in ServiceM8 by tagging past solar jobs and creating follow-up tasks timed from the installation date. Set a 3-year follow-up task on every new solar install job — when that task fires, it’s your prompt to reach out with a battery offer.