Sizing, Worked Examples and Quote Checklists
New solar and battery package worked example: both sets of STCs, net price and payback
A worked example pricing a new rooftop solar and home battery package in Australia with both solar and battery STCs, compared with solar alone, using illustrative numbers.
If you have no solar yet, a combined solar and battery package earns two discounts: solar STCs, based on system size, your postcode zone and a 5-year deeming period in 2026; and battery STCs at 6.8 per usable kWh for the first 14 kWh for installations from 1 May to 31 December 2026. In our illustrative example, a 6.6 kW solar system plus a 13.5 kWh battery in a zone 3 postcode creates about 136 certificates, worth roughly $4,896 at $36 each. The more important question is whether the battery improves the package's payback compared with solar alone — often it does not shorten payback, because solar on its own pays back faster. A battery makes sense in the package when your evening use and tariff gap are large enough to justify it, or when you value backup.
All prices, rates and savings below are illustrative. For the rules, see solar STCs and the 2030 end and the battery STC factor. For sizing, start with the sizing guide.
The example household
| Input | Illustrative value |
|---|---|
| Location | Zone 3 postcode (for example, much of Sydney or Brisbane) |
| Daily use | 20 kWh: 7 kWh daytime, 13 kWh evening and overnight |
| Solar system | 6.6 kW, about 26 kWh a day in summer and 14 kWh in winter, averaging 20 kWh |
| Battery | 13.5 kWh usable |
| Import rate | 35 c/kWh flat (to keep the example simple) |
| Feed-in tariff | 5 c/kWh |
| Installation | November 2026 |
Step 1: the discounts
Solar STCs: 6.6 kW × 1.382 (zone 3 rating) × 5 years = 45.6 → 45 STCs Battery STCs: 13.5 kWh × 6.8 = 91.8 → 91 STCs Total: 136 STCs × $36 = $4,896
The CER's postcode zone table and STC calculator give the exact figures for your address.
Step 2: prices
| Package | Gross price (illustrative) | Discount | Net price |
|---|---|---|---|
| Solar only, 6.6 kW | $6,600 | 45 × $36 = $1,620 | $4,980 |
| Solar + 13.5 kWh battery with hybrid inverter | $19,600 | $4,896 | $14,704 |
| Battery's share of the package | $13,000 | $3,276 | $9,724 |
Step 3: savings from solar alone
On average, the system produces 20 kWh a day. The household uses about 7 kWh of it directly during the day and exports the rest.
- Self-consumed: 7 kWh × $0.35 = $2.45 a day
- Exported: 13 kWh × $0.05 = $0.65 a day
- Daily benefit: $3.10; yearly ≈ $1,132
- Simple payback for solar only: $4,980 ÷ $1,132 ≈ 4.4 years
Step 4: extra savings from the battery
The battery can shift up to the smaller of its capacity, the exports and the evening use. Exports average 13 kWh a day in this example, but are higher in summer and lower in winter:
| Season | Exports | Evening use | Shifted |
|---|---|---|---|
| Summer | 19 kWh | 13 kWh | 13 kWh (limited by use, under 13.5) |
| Winter | 7 kWh | 13 kWh | 7 kWh (limited by solar) |
| Average | 10 kWh |
- Value per shifted kWh: (0.35 − 0.05) × 0.9 = 27 c
- Extra yearly saving: 10 × $0.27 × 365 ≈ $986
- Battery's own payback: $9,724 ÷ $986 ≈ 9.9 years
Step 5: the combined picture
| Option | Net price | Yearly saving | Simple payback |
|---|---|---|---|
| Solar only | $4,980 | $1,132 | 4.4 years |
| Solar + battery | $14,704 | $2,118 | 6.9 years |
The package pays back more slowly than solar alone, because the battery's own payback (about 10 years) is longer than the solar's. But over 10 years the package saves about $21,180 against $11,320 for solar alone, so after subtracting the net prices the package is only slightly ahead at 10 years ($6,476 against $6,340), and pulls further ahead only if the battery keeps working well beyond that. The choice depends on whether you weigh speed of payback or total savings, and how confident you are in the battery's life.
What can change the answer
- A time-of-use tariff with a high evening peak rate raises the battery's value; a flat rate as used here understates it for many households.
- A bigger solar system fills the battery in winter, raising the average kWh shifted, if your roof and export limit allow.
- State incentives, such as the WA Residential Battery Scheme, lower the battery's share.
- Installation timing: a January 2027 installation loses one year of solar deeming (4 years) and drops the battery factor to 5.7. In this example that cuts the discount to 36 + 76 = 112 STCs, about $4,032 — roughly $864 less.
Questions to ask when getting package quotes
- Quote the solar alone and the solar with battery, so you can see the battery's real price.
- Show the number of solar STCs and battery STCs separately, and the price per STC.
- State the panel, inverter and battery models and confirm all are CEC-listed.
- State the expected installation date.
- Explain the sizing, using your usage data.
Then follow the quote comparison guide.
FAQ
Should I install solar now and a battery later?
That is a common approach. Choose a hybrid or battery-ready inverter so a battery can be added later without replacing it, and remember both discounts fall over time.
Is the battery discount larger than the solar discount?
In 2026, for a typical-sized system, yes: in this example the battery creates about twice as many certificates as the solar. Both fall each period until 2030.
Do both parts need the same installer?
Not necessarily, but a single job is simpler for warranties and certification. Each part must be installed by an SAA-accredited installer; the battery installer needs a battery endorsement.
Sources
- Clean Energy Regulator — rooftop solar and battery STC rules, postcode zones, calculators
- Clean Energy Council — approved products
- Energy Made Easy — tariffs and feed-in rates for your address
