The tiers came in on 1 May 2026 as part of changes to keep the discount around 30% across battery sizes as prices fall. They are simple once you see them applied slice by slice.
The three tiers
| Tier | Usable capacity band | Share of the factor |
|---|---|---|
| Tier 1 | First 14 kWh | 100% |
| Tier 2 | 14 to 28 kWh | 60% |
| Tier 3 | 28 to 50 kWh | 15% |
The program recognises batteries from 5 to 100 kWh usable, but only 50 kWh is counted. Anything above 50 kWh adds no certificates.
How the percentages are applied
Each slice of capacity is multiplied by the factor and then by its tier percentage. At the 6.8 factor that applies from May to December 2026 at the time of writing:
- Tier 1, a full 14 kWh: 14 x 6.8 = 95.2 STCs.
- Tier 2, a full 14 kWh: 14 x 6.8 x 0.60 = 57.12 STCs.
- Tier 3, the last 22 kWh: 22 x 6.8 x 0.15 = 22.44 STCs.
Add them for a 50 kWh battery and you get 174.76, rounded down to 174 STCs. The same battery at a single flat rate would earn 340. That gap is the point of the tiers: they aim the discount at household-sized batteries.
What each size earns at 6.8
| Battery | STCs | Value at $38 to $40 |
|---|---|---|
| 14 kWh | 95 | about $3,600 to $3,800 |
| 20 kWh | 119 | about $4,500 to $4,800 |
| 28 kWh | 152 | about $5,800 to $6,100 |
| 50 kWh | 174 | about $6,600 to $7,000 |
Values use the spot range of roughly $38 to $40 and are indicative only. Going from 28 kWh to 50 kWh adds just 22 STCs, which is about $850 for 22 kWh of extra hardware.
Which factor applies
The tiers sit on top of the factor, which steps down every six months: 6.8 now, 5.7 on 1 January 2027 and 5.2 on 1 July 2027. The factor page lays out the schedule and what it does to common sizes.
What this means for you
If you are choosing between 14 kWh and 28 kWh, the second 14 kWh costs about as much hardware as the first but earns 60% of the certificates. Whether it is worth it depends on your load and any VPP offer, not just the rebate. Run both sizes through the battery STC calculator.
Installers should make sure each quote states usable kWh, since that is the number the calculation uses. The battery STC overview and the worked examples cover the rest, and pricing shows what certificates settle for.