Battery STCs are calculated from usable capacity, a per-kWh factor that changes by year, and a three-tier schedule that pays full value on the first 14 kWh and less on the rest. For a typical 13.5 kWh home battery installed in 2026 the answer is 91 STCs, around $3,500 at current spot. The mistakes that matter happen at two points: using nominal capacity instead of usable, and forgetting the tiers on larger units.
The rules here reflect the Cheaper Home Batteries Program as announced and amended, with the tiers in place since 1 May 2026. Always check the Clean Energy Regulator’s current calculator before you quote or lodge. For the program background, see our installer guide to the program.
The inputs
Usable capacity (kWh). The energy the battery can deliver in normal use, as specified by the manufacturer on the approved product listing. It is frequently lower than the nominal figure on marketing material. Eligible sizes are 5 to 100 kWh usable, with up to 50 kWh counted for certificates.
The factor. 6.8 STCs per kWh for installations in 2026. It falls to 5.7 on 1 January 2027 and to 5.2 on 1 July 2027, then steps down every six months to 2030.
The tiers.
| Usable capacity | Share of the factor |
|---|---|
| First 14 kWh | 100% |
| 14 to 28 kWh | 60% |
| 28 to 50 kWh | 15% |
Above 50 kWh nothing further is counted.
The calculation
- Split the usable capacity into the tiers.
- Multiply each slice by the factor and its share.
- Add the slices.
- Round down to a whole number.
Worked examples: 2026 installs (factor 6.8)
| Usable kWh | Working | STCs | At $38 |
|---|---|---|---|
| 10 | 10 x 6.8 | 68 | $2,584 |
| 13.5 | 13.5 x 6.8 = 91.8 | 91 | $3,458 |
| 16 | 14 x 6.8 + 2 x 0.6 x 6.8 = 95.2 + 8.16 = 103.36 | 103 | $3,914 |
| 20 | 95.2 + 6 x 0.6 x 6.8 = 95.2 + 24.48 = 119.68 | 119 | $4,522 |
| 28 | 95.2 + 14 x 0.6 x 6.8 = 95.2 + 57.12 = 152.32 | 152 | $5,776 |
| 40 | 152.32 + 12 x 0.15 x 6.8 = 152.32 + 12.24 = 164.56 | 164 | $6,232 |
| 50 | 152.32 + 22 x 0.15 x 6.8 = 152.32 + 22.44 = 174.76 | 174 | $6,612 |
The jump from 10 to 14 kWh is worth 27 STCs, about $1,000. The jump from 28 to 40 kWh is worth 12 STCs, about $450. The extra capacity still helps the customer, but the rebate barely follows it. See the answer on battery rebate tiers.
The same batteries in 2027 (factor 5.7)
| Usable kWh | STCs | Change vs 2026 |
|---|---|---|
| 10 | 57 | -11 |
| 13.5 | 76 | -15 |
| 20 | 100 | -19 |
| 28 | 127 | -25 |
| 50 | 146 | -28 |
A 13.5 kWh battery loses 15 STCs, about $570 at $38, on 1 January 2027, purely because of the date. See the factor change in 2027.
Common mistakes
- Nominal instead of usable. A battery sold as 15 kWh may have 13.5 kWh usable. The claim must reflect the usable figure with evidence behind it.
- Flat factor on everything. Applying 6.8 to all capacity overstates larger systems.
- Wrong year. The factor is set by installation date.
- Counting over 50 kWh. Anything above 50 kWh earns nothing.
- Rounding up. The result is rounded down.
The sums for stacked systems
If a customer installs solar and a battery together, the two are calculated separately: solar by kW, zone and deeming years; battery by usable kWh, factor and tiers. A 6.6 kW zone 3 solar system (45 STCs) with a 13.5 kWh battery (91 STCs) earns 136 STCs in 2026, around $5,170 at $38. The same pair installed in 2027 earns 36 + 76 = 112, around $4,256. State rebates and VPP incentives are on top of this and vary; see battery rebate stacking.
Put it in your quote
Show four lines: usable kWh, factor, STC count and the dollar value at the rate you can lock. A customer can follow it, and so can a reviewer. The same four lines should match the claim, the datasheet and the label photo. If you lodge a claim where those four disagree, a rejection is likely.
Spreadsheet version
For a tiered calculation, a formula such as =ROUNDDOWN((MIN(A2,14)+0.6*MAX(0,MIN(A2,28)-14)+0.15*MAX(0,MIN(A2,50)-28))*F2,0) with usable kWh in A2 and the factor in F2 does the job. Test it against the table above before you rely on it.
Is the bigger battery worth it for the rebate alone?
Compare the incremental STCs of each step against the incremental cost of hardware. Going from 13.5 kWh to 20 kWh adds 28 STCs (119 minus 91), about $1,060 at $38. If the extra 6.5 kWh costs the customer more than that, the rebate is not what justifies the upgrade. Going from 20 kWh to 28 kWh adds 33 STCs, about $1,250. Beyond 28 kWh, each additional kWh earns only 15 per cent of the factor, or roughly 1 STC at 2026 values, about $39.
This is not an argument against larger batteries. A household with high evening use, an electric vehicle or a backup requirement may need the capacity. It is an argument for honest quoting: show the customer the rebate by tier, so the purchase is made on the usage case rather than a belief that the discount scales.
Cash tied up per job
Batteries move more money per job than solar, so settlement terms matter more. A 13.5 kWh battery claim is worth about $3,450. Fifteen battery jobs a month is over $50,000 of certificates in flight, before any solar. On ten-day settlement you carry about half of that on average; on 24-hour settlement, almost none. If your business is shifting toward batteries, revisit the settlement terms with your buyer, because the working-capital effect is large. The answer on battery rebate installer cash flow covers the quoting side.
Keeping the calculation defensible
Keep three documents in the job file that tie to the count: the manufacturer’s datasheet showing usable capacity, the label photo showing model and serial, and the calculation itself. If the regulator ever asks how you arrived at 91 STCs, you can answer in a sentence and prove it in a minute.
What to do next
Check your quote template against the tiers, and read battery installation photo requirements so the evidence matches the number. The battery STC pillar and battery submission guide cover the claim, and today’s rate turns the count into dollars. The answer on how many STCs per kWh of battery is the one-line version.