If you’re adding a battery to an existing solar system, the two names that come up most often are the Tesla Powerwall 3 and the Sigenergy SigenStor. Both are excellent products. They are also built around very different design philosophies, and the right choice depends on your home, your electricity plan, and what you want the battery to do.
We install both. This is the comparison we walk our own customers through — including the fine print each manufacturer publishes that rarely makes it into the marketing.
The core design difference
Powerwall 3 is a single sealed unit: a 13.5 kWh battery with a solar inverter built in. One box, one size.
SigenStor is modular: an Energy Controller (the inverter) with separate battery modules stacked beneath it. You choose the controller size and the number of modules, so capacity can be tailored — commonly around 9 to 54 kWh.
That one difference drives almost everything below.
Retrofitting to existing solar
Most batteries in Victoria are being added to solar that’s already on the roof. Both systems handle this by “AC-coupling” — connecting alongside your existing inverter rather than replacing it. Two details matter:
- The Powerwall 3 can AC-couple up to 5 kW of existing inverter capacity. If your inverter is larger, the usual path is moving your panel strings onto the Powerwall’s own inverter and retiring the old one.
- The SigenStor’s limit is the rating of the Energy Controller you choose — a 6 kW controller pairs with inverters up to 6 kW, and larger controllers give more headroom.
A related point that surprises people who have read the Powerwall 3 datasheet: the headline figures of 20 kW solar input and 11 kW output describe it as the sole inverter on a new system. In a retrofit, the numbers that matter are 13.5 kWh of storage and a 5 kW charge rate. They’re good numbers — just different ones.
Capacity and physical fit
| Powerwall 3 | SigenStor (6 kW controller + 2 modules) | |
|---|---|---|
| Usable storage | 13.5 kWh | ~17.9 kWh |
| Width | 609 mm | ~850 mm with covers |
| Height | 1,105 mm | ~900 mm |
| Depth off the wall | 193 mm | 260 mm |
| Weight | 130 kg | ~160 kg |
Both can be floor- or wall-mounted, and both are outdoor-rated. The shapes differ: the Powerwall is tall and slim, sitting under 20 cm off the wall; the SigenStor stack is wider, shorter and deeper.
One limit worth knowing: Sigenergy supports up to six battery modules on a floor mount but a maximum of two modules on a wall mount. If you want a wall-mounted system larger than about 18 kWh, that changes the conversation. Both manufacturers also publish minimum clearances around their units, so the available wall width — not just the unit width — determines what fits. This is exactly the kind of thing a proper site assessment settles before you sign anything.
Charging from the grid — and the warranty fine print
Both systems can charge from cheap overnight electricity, either on a schedule or automatically when tomorrow’s solar forecast is poor. If you’re on a time-of-use or EV plan with a low overnight rate, this matters more than most people realise: on many of these plans the cheap window applies to everything your house draws, so filling the battery at off-peak rates and using it through the peak hours is genuine money on any cloudy day.
Here the warranty documents are worth reading closely:
- Tesla warrants the Powerwall 3 for 10 years and 70% capacity retention, with unlimited cycles for solar self-consumption, backup, and time-of-use grid charging.
- Sigenergy warrants the SigenStor for 10 years and 70% retention or a fixed energy throughput per module, whichever comes first — roughly equivalent to one full cycle per day for a little over eight years.
For a household cycling once a day, both warranties comfortably cover normal use. For a household aggressively cycling twice a day — a solar cycle plus a cheap-grid cycle — the Sigenergy throughput figure arrives years earlier. The battery keeps working; the capacity guarantee doesn’t. It’s not a reason to avoid the product, but it is a reason to have the grid-charging schedule configured deliberately, which is part of how we commission every system.
Efficiency claims
You’ll see “up to 98%” attached to the SigenStor and quieter figures from Tesla, whose datasheet states 89% round-trip solar-to-battery-to-home. The gap is smaller than it looks: the headline Sigenergy number is a DC-side conversion figure, while Tesla publishes a conservative whole-path number. Independent testing puts the SigenStor’s DC round-trip efficiency in the mid-90s. And in any retrofit, both systems are AC-coupled and both give up a few points converting through your existing inverter. Sigenergy holds a real efficiency edge — just not a nine-point one.
Electric vehicle owners
If you drive a Tesla, the Powerwall unlocks Charge on Solar in the Tesla app: the car charges only from surplus solar, and it works with any hard-wired home charger. It’s the smoothest solar-to-EV experience currently available, managed from the same app as the battery.
Sigenergy’s answer is its own EV charger range, including a DC module that slots into the SigenStor stack itself, with vehicle-to-home capability on compatible cars. It’s genuinely clever hardware — but there’s no direct integration with Tesla vehicles, and the DC module occupies a battery slot, which matters on a wall-mounted system limited to two.
One tip that applies to both: if your plan has a cheap overnight EV rate, keep charging the car directly from the grid in that window. Routing car charging through a home battery only adds conversion losses. The battery’s job is your house; the cheap window’s job is your car.
Backup power
Blackout backup is optional with both systems, and worth a deliberate decision rather than an assumption.
- The Powerwall 3 in Australia is installed with Tesla’s Backup Gateway, which acts as the system meter and controller. Because it’s already there, enabling backup is largely a wiring exercise.
- The SigenStor needs the Sigen Gateway for backup. Some supply channels now bundle it; if yours doesn’t, it’s an additional component.
Either way, the electrical work to wire essential circuits (or the whole home) is a separate line on any honest quote.
Track record and the app
Tesla is the incumbent, with the longest home-battery record in Australia and a famously simple app — car and home in one place. Sigenergy is the challenger: founded in 2022, growing fast, consistently well-rated by installers, with an app that offers far more data and control, down to detailed tariff-aware automation.
In the interests of full disclosure: Sigenergy’s 8, 10 and 12 kW single-phase Energy Controllers were subject to a voluntary recall in late 2025 over an AC connector design, since corrected. The 3–6 kW single-phase controllers — the size most Melbourne retrofits use — were never part of that recall. We verify connector revision on every unit we install regardless of brand.
What they cost
Prices depend on the site — switchboard condition, mounting location, safety requirements such as vehicle-impact bollards in garages — so treat any internet price as a starting point. As a guide, fully installed in metro Melbourne after the federal battery rebate:
- SigenStor 6 kW / ~18 kWh: typically from around $8,500
- Powerwall 3 (13.5 kWh): typically from around $10,900
The rebate is calculated on usable capacity, which is why the larger Sigenergy system attracts a bigger rebate despite the lower price. Note that the federal rebate value is now scheduled to step down every six months (this coming January and July) through 2030, so installing sooner rather than later locks in a higher rebate — see our rebate step-down article for the full schedule.
So which one?
Choose the SigenStor if you want the most storage per dollar, capacity tailored to your usage, and deep control over how the system behaves. For most self-consumption-focused homes it’s currently the sharper value.
Choose the Powerwall 3 if you drive a Tesla and want the one-app ecosystem with Charge on Solar, or you place a premium on the longest-established product and the cleanest warranty position for heavy grid charging.
Neither is a wrong answer. The wrong answer is buying either without a site assessment — wall clearances, inverter compatibility, switchboard capacity and safety requirements decide more of the outcome than the brand does.
Northwest Energy Solutions is a Victorian solar and battery retailer based in Mount Waverley. We install both systems and will tell you plainly which suits your home. Call 1300 255 663 or book a site assessment.
Specifications and warranty terms summarised from Tesla and Sigenergy published documentation, current at September 2026. Always confirm against the manufacturer’s latest datasheets.