Payback equals the installed cost after the federal battery rebate, divided by your yearly saving. The yearly saving is roughly the kWh the battery supplies each day, times the gap between your grid rate and your feed-in tariff, times 365, plus any VPP payments. High evening use and a well-sized battery shorten payback; low night use and small solar stretch it.
- Payback = cost after rebate ÷ yearly saving.
- Yearly saving is roughly kWh used from the battery × (grid rate minus feed-in tariff) × 365.
- High evening use and spare solar shorten payback; low night use and small solar stretch it.
- Count winter, when Adelaide solar makes about 40% of summer output.
- Be wary of any payback number given without seeing your bills.
What payback actually means
Payback is the number of years it takes for a battery's savings to add up to what you paid for it. After that, the savings are yours.
We don't publish a standard payback figure, and you should be wary of anyone who does without seeing your bills. Two homes in the same street with the same battery can get very different results. What we can do is show you exactly how to work it out, and then run it properly on your own numbers.
The payback formula
There are only two parts to it.
1. Your yearly saving = kWh the battery supplies per day × (your grid rate minus your feed-in tariff) × 365, plus any VPP payments.
2. Your payback = installed cost after the rebate ÷ yearly saving.
Why the gap between the two rates? Every kWh in the battery is solar you would otherwise have exported for the feed-in credit. Using it at night instead saves you buying a kWh from the grid. The difference between those two rates is what each stored kWh is worth to you.
Send us a recent bill. We'll size the battery, apply the rebate and show you every input so you can check the maths. Free and itemised.
Fill in your own numbers
Grab your latest bill and the quote, and fill in this table:
| Input | Where to find it | Your number |
|---|---|---|
| A. Grid rate (c per kWh) | Your bill, usage charges | |
| B. Feed-in tariff (c per kWh) | Your bill, solar credits | |
| C. kWh from the battery per day | Your overnight use, capped at the battery's usable size and what your solar can fill | |
| D. VPP payments per year | Retailer's VPP offer, if you join | |
| E. Cost after rebate | Your itemised quote |
Yearly saving = C × (A minus B) ÷ 100 × 365, plus D. Payback in years = E ÷ yearly saving.
Be honest with C. Use a figure your solar can fill on an average day across the year, not just in January. In winter, Adelaide solar makes about 40% of its summer output.
Need a starting point for E? On typical NG Elec jobs in 2026, after rebates, incl GST, a battery added to existing solar starts from about $9,000 and most land between $10,000 and $14,500, roughly $350 to $600 per usable kWh. Solar and battery together mostly lands between $14,000 and $25,000. Your itemised quote is the real number. See our price guide.
What shortens payback
- High evening and overnight use. Air con, cooking, a pool pump or an EV charged at night all give the battery more to do.
- Plenty of spare solar. If you export a lot now, the battery fills most days, summer and winter.
- The right size. A battery that empties most nights earns more per dollar than one that's half used.
- The rebate. The federal program cuts the upfront cost. It's strongest on the first 14 kWh and steps down every January and July, so the install date matters. See our battery rebate guide.
- A good VPP deal, if the retailer's terms suit you. Joining is optional.
- Rising grid prices. Each kWh you don't buy is worth more.
What stretches it out
- Low night use. If you're out most evenings, there's less for the battery to cover.
- Small or ageing solar. If there's not much spare, the battery won't fill, especially in winter.
- An oversized battery. Capacity you don't use still costs money.
- Extra site work. Switchboard upgrades, backup wiring or an inverter swap add to the cost. They may be worth it, but count them.
- Higher supply and peak charges on some retail plans, including free-power plans. Count the whole bill, not just the cheap hours.
Where Solar Sharer fits
Since 1 July 2026, SA retailers must offer at least one plan with free grid power from midday to 3pm, capped at 24 kWh a day. It's the federal government's Solar Sharer offer, and it's opt-in. With a battery, it can add to C: on cloudy winter days, or if your solar is small, the battery can top up free between 12 and 3 and cover the evening peak, so it does more work than your solar alone could give it.
The catch is that these plans usually have higher daily supply charges and peak rates. Run the sums on the plan's full rates before you count on it. We can set the battery's charge schedule for the free window when we commission it, if you're on one of these plans. More in Solar Sharer free power.
Common mistakes when working out payback
- Using the battery's full size every day. On a lot of days it won't fully empty or fully fill. Use what you'd realistically draw from it.
- Using the summer bill only. Winter has less spare solar, so the battery does less.
- Forgetting the feed-in tariff. A stored kWh isn't worth your full grid rate, because you give up the export credit.
- Leaving out extra work. Count switchboard upgrades or backup wiring in the cost if they're needed.
- Ignoring the rebate timing. The install date sets the rebate, and it steps down every January and July.
Get these right and your own estimate will be close to ours.
Battery life and the bigger picture
A battery's capacity drops slowly over time, and every brand has its own warranty terms. Check the payback sits comfortably inside the warranty period, and use a slightly lower average capacity over the battery's life rather than day-one capacity.
Payback isn't the only reason people buy a battery. Blackout backup, using more of your own solar and relying less on the grid matter to a lot of our customers. Just keep the money side and the comfort side separate so you know what you're paying for.
The quickest way to get a real answer is to send us your bills. We'll size the battery to your overnight use using our battery sizing method, apply the rebate, and give you the inputs so you can check the maths yourself.