The easiest way to see the tiers is to run two real sizes. Both examples use the 6.8 factor that applies from 1 May to 31 December 2026, and an STC price of $38 to $40 (spot has been roughly that, against a $40 clearing house ceiling). Usable capacity is assumed.
Example 1: 13.5 kWh battery
13.5 kWh sits entirely inside the first 14 kWh tier, which counts at 100 per cent.
- 13.5 x 6.8 = 91.8
- Rounded down: 91 STCs
- At $38 to $40: about $3,458 to $3,640
This is the size of a common home battery, and it is the sweet spot of the current structure because every kWh is in the full-value tier.
Example 2: 28 kWh battery
28 kWh fills the first two tiers.
| Band | kWh | Calculation | STCs |
|---|---|---|---|
| First 14 kWh at 100% | 14 | 14 x 6.8 | 95.2 |
| 14 to 28 kWh at 60% | 14 | 14 x 6.8 x 0.6 | 57.12 |
| Total | 28 | 152.32 |
Rounded down: 152 STCs, or about $5,776 to $6,080. Doubling the battery size added around 67 per cent more certificates, not 100 per cent.
The same batteries on other dates
| Install window | Factor | 13.5 kWh | 28 kWh |
|---|---|---|---|
| Jan to Apr 2026 (before tiers) | 8.4 | 113 | 235 |
| May to Dec 2026 | 6.8 | 91 | 152 |
| Jan to Jun 2027 | 5.7 | 76 | 127 |
| Jul to Dec 2027 | 5.2 | 70 | 116 |
The 2027 columns assume the tier percentages stay as they are today. The January to April 2026 row had no size tiers, which is why a large battery then earned so much more.
What this means for installers
Put the usable kWh, the factor and the STC count on the quote, and use the same figures when you lodge. A mismatch between the quote, the assignment form and the claim is an avoidable reason for a query. The battery STC calculator does the tier maths, and the battery submission guide covers the paperwork. When the claim is complete, the rate we publish on /pricing/ is locked at lodgement, so the dollar side of your quote is settled on the day you lodge.
What this means for homeowners
The first 14 kWh is the best value per dollar of battery. Whether the next 14 kWh is worth buying depends on how much of it you will use, because it earns 60 per cent of the factor. Our answer on which battery size gets the biggest rebate works through that trade-off, and the battery STC pillar page sets out the rest of the program.