Last month I sat at a kitchen table in Blackburn with a couple who’d just been quoted $4,200 for a 6.6kW solar system and, separately, $11,500 for a 10kWh battery to go with it. They wanted one number: which one pays for itself first. That’s the wrong question, but it’s the one everyone asks, so let’s actually answer it properly rather than wave it away.
On the numbers, a well-sized rooftop solar system on an average east-coast home pays itself back in roughly three to five years. A home battery bolted onto that same system, in most cases, is still sitting somewhere between seven and eleven years, and that’s before you account for the fact that the battery’s usable capacity degrades the whole time it’s working. The gap isn’t close. It isn’t even really a fair fight. But the reasons why matter more than the headline, because they tell you what each piece of kit is actually for.
Why solar panels pay back faster, on the numbers #
A solar panel converts sunlight into power you’d otherwise be buying from the grid at retail rates, which on most standard plans still sits somewhere around 28-35c/kWh depending on your state and retailer. Every kilowatt-hour your roof makes and your house actually uses in daylight hours is a kilowatt-hour you didn’t pay for. That’s the whole mechanism. There’s no second conversion step, no round-trip loss, no degrading chemistry sitting in a box in the garage.
The economics are blunt. A 6.6kW system in Melbourne or Sydney, installed for somewhere in the $4,000-$6,000 range after the federal small-scale technology certificate rebate, will generate something like 8,000-9,500kWh a year depending on orientation and shading. If a household is home during the day, or runs the pool pump, hot water and dishwasher on a timer through the middle of the day, self-consumption rates of 40-60% aren’t unusual. That’s what gets payback down into the three-to-five-year bracket. A household that’s out at work all day and exports most of it instead gets paid the feed-in tariff, which on most retailer plans now sits well under 10c/kWh and in some cases under 5c – I’ve written before about how thin those feed-in numbers have become, and it changes the maths more than people expect.
Why the battery case is weaker than the brochure says #
A battery doesn’t generate anything. It just moves energy you’ve already made from one time of day to another, and every one of those shifts costs you something. Round-trip efficiency on a typical lithium home battery sits around 85-90%, so you lose a slice of every kilowatt-hour just by storing and releasing it. Think of it like decanting wine between bottles. You don’t lose much each time, but you do lose some, and if you do it every single day for a decade it adds up.
The bigger problem is what the battery is competing against. It’s not competing against the grid price, it’s competing against your own feed-in tariff. If your retailer is still paying you 8-10c/kWh for exported solar, the battery only has to beat that gap to the retail import price to be worth cycling. Once export tariffs were higher a few years back, batteries looked better on paper. Now that feed-in rates have fallen in most states, the arbitrage a battery captures each cycle is often worth 20-25c/kWh rather than the 30c+ people assume, and that’s before accounting for the capital cost sitting idle for years.
Run the actual figures: an 10kWh battery doing one full useful cycle a day, saving 20c/kWh after losses, saves around $2 a day, call it $700 a year. Against an $11,500 outlay, even with state battery rebates knocking a few thousand off the sticker price in places like Victoria’s Solar Victoria scheme or the federal Cheaper Home Batteries Program that started paying rebates this year, you’re still looking at seven-plus years before the thing has earned its keep. And that’s assuming you’re cycling it fully every single day, which most households don’t – plenty of batteries sit half-charged through winter when solar generation drops and there’s nothing left to store by 3pm.
The export limit most people don’t know they’re hitting #
Here’s something installers deal with that homeowners rarely hear about until the paperwork lands: most distribution networks now cap how much a household can export back to the grid, often somewhere around 5kW for a single-phase connection, sometimes less in constrained parts of the network. If you’re on a tight export limit and you’ve oversized your solar system, the inverter has to throttle itself in the middle of the day rather than push power the local feeder can’t absorb. That’s energy you paid to generate and then had to throw away.
This is genuinely where a battery earns its spot, and it’s not really about bill savings at all. It’s about not wasting generation capacity you’ve already paid for. A battery soaks up the exports your network won’t take, then lets you use that stored energy in the evening instead of buying it back at retail rates. I’ve covered the wider version of this problem before, because curtailment from export limits is becoming one of the bigger quiet headaches on rooftop solar and the midday minimum demand problem, and a battery is one of the only tools a household actually has to work around it rather than wait for the network to fix it.
Switchboard and string sizing realities that change the maths #
None of this happens in a vacuum. Before you even get to payback, there’s a physical reality in the meter box. Older homes, especially anything built before the early 2000s around inner suburban streets like Hartington Street in Thornbury or similar vintage housing stock, often have switchboards that need upgrading before a battery, or even a bigger solar inverter, can go in safely under AS/NZS 3000 wiring rules. That’s an extra $1,500-$3,000 that rarely shows up in the glossy quote comparison, and it hits the battery side of the ledger harder because batteries typically need a dedicated circuit and sometimes a separate meter.
String sizing matters too. A system that’s been designed around the household’s current circuit, with panels split correctly across strings to match shading patterns and roof orientation, will produce meaningfully more usable energy than one jammed onto a single string because it was cheaper to install. I’ve seen quotes that look identical on the panel brand and inverter model but produce noticeably different real-world output over a year, purely because nobody bothered to model the shading from next door’s gum tree properly.
What AEMO and the regulators are actually watching #
This isn’t just a household budgeting question. It feeds into how the grid itself is being managed. AEMO’s operational planning has flagged minimum demand periods in spring and autumn as an increasing risk precisely because so much rooftop solar now pushes power onto the grid at once, and distributed batteries are one of the few levers that can soak some of that up locally rather than needing a network solution. The Australian Energy Regulator’s work on export tariffs and two-way pricing is a direct response to that: some networks are moving towards charging for exports during the sunniest hours of the day and paying more for exports in the evening peak, which if it spreads will quietly improve the battery business case over time without changing a single thing in the garage.
That’s the trend worth watching rather than the current snapshot. If two-way tariffs become standard, the arbitrage a battery captures widens, because you’ll be paying to export at midday and getting properly rewarded for holding that energy back until 6pm. I’d argue most of the battery rebate schemes currently running are really a bridge to that future market structure rather than a standalone subsidy, and the households buying batteries now are partly front-running where tariffs are headed, not just chasing today’s bill savings.
So which actually pays back first #
Solar, no contest, for nearly every household doing this as a standalone decision. A battery bought purely to shave the electricity bill, on its own, with no export constraint problem to solve, is still a slow earner in 2026 – seven to eleven years is the honest range, and that’s before considering that most warranties sit around 10 years with degraded capacity by then.
Where I’d push back on the “solar wins, don’t bother” framing some installers push is the export-limited home. If your network connection throttles your exports and you’re generating more than the grid will take, a battery isn’t really competing with solar on payback at all. It’s rescuing generation you’ve already sunk capital into. In that specific case, sequence matters less than fit. Get the solar right first, always, but don’t assume the battery conversation is purely about bill arithmetic. Sometimes it’s about not wasting your own roof.
My own back deck faces north and should be perfect for a small veggie patch, except I’ve managed to turn three different basil plants into compost through sheer inattention, so take my scepticism about glossy payback projections as the scepticism of someone who also overestimates how disciplined they’ll be with maintenance. Batteries need the same honesty. Model your actual usage pattern, check your export limit with your distributor before you buy anything, and treat the headline payback figure on any quote as the optimistic case, not the expected one.
For a household weighing both at once, the better frame isn’t “which pays back first” but “what job is each one doing.” Solar generates. A battery times. Buy the generator first, and only buy the timer once you know you’ve got power going spare that the grid won’t take.
– Priya Nair, Solar & Distributed Energy Correspondent
Photo by Markus Winkler on Unsplash