The rebate rises in a straight line with usable capacity: 6.8 certificates per kWh for 2026 installs, falling to 5.7 from 1 January 2027 and to 5.2 on 1 July 2027, with eligible capacity capped at 50 kWh. So yes, the largest eligible battery earns the biggest rebate in dollars. That is not the same as the best choice.
The numbers
| Usable capacity | 2026 STCs | Approx. value at $38 |
|---|---|---|
| 5 kWh | 34 | about $1,290 |
| 10 kWh | 68 | about $2,580 |
| 13.5 kWh | 91 | about $3,450 |
| 50 kWh | 340 | about $12,900 |
The figures are market values at the time of writing, and the discount on your invoice will reflect the price your installer assumes. The key point is that every extra kWh earns the same rebate. A bigger battery does not get a better rate, only a bigger total.
Why bigger is not always better
You pay for every kWh, and the rebate covers only part of the price. A battery much larger than your overnight use will not fill up often enough to repay its cost. The right size usually depends on how much power you use after sunset, how big your solar system is and whether you want backup.
Questions to ask
- How many kWh do I use between sunset and sunrise?
- How much surplus solar will I actually have to store?
- Is the stated capacity usable capacity or the total?
- What is the price per usable kWh after the rebate?
That last figure is the best way to compare quotes of different sizes.
What this means for you
Make sure the battery is on the approved list and can join a virtual power plant, because those are conditions of the program. See eligible battery list and the battery STC overview. For the formula, read the battery STC calculator guide.
Finally, think about the future. If you expect to add an electric vehicle, switch from gas or grow your household, a slightly larger battery today may be worth it, particularly while the 2026 factor is higher. But be honest about likelihood: plan for the life you have, and let the rebate be a welcome bonus rather than the reason for the size.