Solar Battery ROI Calculator (Australia)

How the calculator works

The solar battery ROI calculator works out the four numbers an Australian household needs to commit to storage: annual savings uplift, net battery cost after the Federal Cheaper Home Batteries Program rebate and any state stacks, simple payback in years, and 10-year net present value at a 5% real discount rate.

Plug in nine inputs and the tool returns the investment case. The engine matches our solar self-consumption calculator but reframes the output around the purchase decision rather than the operational ratio.

1. PV system size (kW DC) — your existing or planned array. Clean Energy Regulator 2025 STC data places the residential SGU median at 8.2 kW; the historic 6.6 kW is still common for retrofits.
2. Peak sun hours/day — annual average from BoM solar exposure data. Darwin 5.6, Brisbane 4.9, Sydney 4.2, Perth 5.5, Adelaide 4.6, Melbourne 4.0, Hobart 3.7.
3. Annual usage (kWh) — pull 12 months from your retailer portal. AER 2026 Residential Energy Consumption Benchmarks for a 3-person home: NSW 6,400, VIC 5,000, QLD 7,200, WA 6,800, SA 5,600.
4. Retail rate (c/kWh) — your variable usage rate. AER Default Market Offer (DMO) 2026 single-rate: NSW 34c, SE QLD 32c, SA 39c. Victorian Default Offer 28c. WA Synergy A1 30c.
5. Feed-in tariff (c/kWh) — your retailer’s solar export rate. Post-2024 most retailers pay 4–7c flat or use time-of-day blocks. WA DEBS pays 10c peak (3pm–9pm) and 2.5c off-peak.
6. Battery capacity (kWh) — usable storage. Powerwall 2/3 13.5 kWh, Sungrow SBR 9.6 kWh per module, BYD HVM 2.76 kWh per module (stack to 11–22 kWh).
7. Battery installed cost (A$) — turnkey including Clean Energy Council–accredited installer labour, isolators, switchboard upgrades, and DNSP grid-connection approval.
8. Federal CHB rebate (%) — start at 30 for 2026 installs; the rebate steps down approximately 10% per year through 2030.
9. Daytime overlap (%) — your unaided self-consumption percentage. Default 30%; raise to 40–50% if you run ducted AC, pool pump, or EV charging through midday.

How the math works

annual_kWh_produced  = system_kW × peak_sun_hours × 365 × 0.77
no_battery_self      = min(annual_use, annual_prod × overlap_pct/100)
battery_capture      = battery_kWh × 365 × 0.92 × 0.85
with_battery_self    = min(annual_use, no_battery_self + battery_capture, annual_prod)
bill_no_batt         = max(0, imports × retail − exports × fit)
bill_w_batt          = max(0, imports × retail − exports × fit)
annual_uplift        = bill_no_batt − bill_w_batt
net_battery_cost     = battery_cost × (1 − chb_rebate_pct/100)
simple_payback_yr    = net_battery_cost / annual_uplift
10yr_NPV             = Σ uplift_t/(1+0.05)^t − net_battery_cost

The 0.77 multiplier is the IEC 61724-1:2017 performance ratio, slightly conservative for Australia given the strong irradiance offsetting the temperature derate. SunWiz 2025 fleet-aggregate field PR for AU residential is 0.78–0.81. The 0.92 × 0.85 = 0.782 effective battery utilisation matches CEC’s residential battery performance assumptions in the 2026 SGA Best Practice Guide.

Worked example: 6.6 kW PV in Sydney, 10 kWh Tesla Powerwall 2 on AGL

• 6.6 kW × 4.2 PSH × 365 × 0.77 = 7,791 kWh/yr generated
• Annual usage 6,400 kWh, baseline overlap 30%
• No battery: self = min(6400, 7791×0.30) = 2,337 kWh
  • Imports 4,063 × 34c = A$1,381 · Exports 5,454 × 6c = A$327 credit
  • Bill = max(0, A$1,381 − A$327) = A$1,054 · Bill without PV A$2,176 · Savings A$1,122/yr
• With Powerwall 2 (13.5 kWh): capture = 13.5 × 365 × 0.92 × 0.85 = 3,857 kWh
  • self = min(6400, 2337 + 3857, 7791) = 6,194 kWh
  • Imports 206 × 34c = A$70 · Exports 1,597 × 6c = A$96 credit
  • Bill = max(0, A$70 − A$96) = A$0 (floored) · Savings A$2,176/yr
• Battery uplift: A$1,054/yr · Net cost A$13,500 − 30% CHB = A$9,450
• Simple payback 9.0 yr · 10-yr NPV slightly negative without VPP, slightly positive with VPP

For a 10 kWh Sungrow SBR (A$9,800 gross, A$6,860 after CHB) on the same setup: uplift ≈ A$890/yr (less capture than 13.5 kWh), payback 7.7 yr — the better deal at this site.

Worked example: same 6.6 kW + 10 kWh battery on Amber Electric VPP

• Amber wholesale pass-through retail rate averages 28c (with peaks to A$2/kWh on summer demand events)
• VPP dispatch revenue averages A$400/yr for a 10 kWh unit cycling once daily
• Wholesale arbitrage adds A$150/yr from overnight charging at 8c and self-using at 28c equivalent
• Combined uplift roughly A$1,300–A$1,500/yr · Payback drops to 4.6–5.3 yr (net cost A$6,860)

The VPP and wholesale-tariff combination is the highest-value play in Australia in 2026. Outside Amber, Tesla Energy Plan and OVO Loop deliver similar economics.

State-by-state quick reference

• NSW (Ausgrid/Endeavour) — 34c retail, 6c FiT, PDRS pass-through ~A$1,400 discount. Strong battery case.
• VIC (Powercor/AusNet) — 28c retail, 5c FiT, Solar Homes battery loan A$8,800 interest-free. Strongest stack in Australia.
• QLD (Energex) — 32c retail, 5c FiT, no state battery rebate but VPP programs active (Energy Queensland VPP). Marginal-positive case.
• WA (Western Power, Synergy DEBS) — 30c retail, 10c peak FiT / 2.5c off-peak FiT. Time-of-day FiT changes the equation; batteries time-shift exports into the peak window. Strong case.
• SA (SAPN/AGL) — 39c retail, 5c FiT, no SA rebate currently. Federal CHB alone delivers payback ~6 yr.
• TAS (TasNetworks/Aurora) — 30c retail, 9c FiT (highest standard FiT in AU). Battery case weaker because FiT is closer to retail.

When the Australian battery maths doesn’t work

Three conditions delay or kill the case:

1. Annual usage below 3,500 kWh. Pensioners, single-occupant homes, and holiday properties self-consume most production unaided and capture little incremental from storage.
2. No CHB eligibility. Pre-2025 installs that did not retrofit a battery, or DIY installs without CEC accreditation, forfeit the 30% rebate. Without it, payback typically stretches past 12 years.
3. High FiT legacy contract (NSW 60c, ACT 45c, VIC 60c). Pre-2017 premium FiT contracts still in effect make exports more valuable than self-consumption — adding a battery cannibalises the FiT income. Roughly 12,000 NSW households still hold these contracts (expire 2024–2027 depending on scheme).

Model the bill-arithmetic baseline first with our solar feed-in tariff calculator and the underlying self-consumption physics with our solar self-consumption calculator.

Sources

• Clean Energy Council, “Battery storage market report 2026”; CEC Approved Solar Retailer code.
• Clean Energy Regulator, Small-scale Renewable Energy Scheme (SRES) and Cheaper Home Batteries Program guidance, July 2025.
• Australian Energy Regulator, “Default Market Offer 2025–26 Final Decision.”
• Australian Bureau of Meteorology, Daily Solar Exposure climatology 1990–2024.
• SunWiz, “Australian Battery Market 2025 Insights”; AEMO ESOO 2025 demand assumptions.
• Solar Choice and SolarQuotes 2026 quote aggregator data (median state-by-state installed cost).
• Victorian Government, Solar Homes Program battery loan terms (current 2026).

For a wider Australia-specific cost picture, also see our cost of solar panels calculator and our deep-dive how-much-does-a-solar-system-cost-2026 guide.