Hybrid Solar System Calculator

What this calculator does

It sizes a grid-connected hybrid PV-plus-battery system for an Australian home, based on your daily energy use, your zone’s Peak Sun Hours, and the share of your load you want to back up during a grid outage. Outputs:

• PV array (kW DC) — nameplate to offset your target percentage of annual import
• Battery (usable kWh and nameplate kWh) — sized for evening peak plus your chosen backup duration
• Hybrid inverter (kW continuous) — within the AS/NZS 4777.2 PV-to-inverter ratio and your backup surge requirement
• Annual PV yield (kWh), self-consumption (%) and annual export (kWh) at your retailer’s feed-in tariff

Defaults reflect a typical Australian household: 18 kWh/day, 4.8 Peak Sun Hours (Zone 3 — Sydney, Melbourne, Adelaide, Perth, Brisbane average per Bureau of Meteorology), 5 kW backed-up critical load (fridge, lights, internet, ceiling fans, one split-system AC), 6-hour backup, LFP battery at 90% DoD and 95% round-trip efficiency.

How hybrid sizing works (first principles)

1. PV array (kW DC)

PV_kW = (daily_kWh × offset) ÷ (PSH × performance_ratio)

Performance ratio bundles inverter conversion, soiling (Australian dust is more aggressive than Europe), panel temperature derate (rooftop modules in inland Australia hit 65–70 °C — a 14% temperature loss vs. 25 °C STC), wiring loss, and shading. CEC and Clean Energy Regulator guidance puts PR at 0.78–0.84 for compliant installs; this calculator defaults to 0.80 — slightly conservative for the high-PSH Australian context.

2. Battery

usable_kWh    = backup_hours × backed_up_load_kW
nameplate_kWh = usable_kWh ÷ (DoD × round_trip_efficiency)

LiFePO₄ (the universal chemistry across CEC-approved batteries in 2026) cycles to 90% DoD and returns 95% of energy in. NMC chemistry (older Tesla Powerwall 2, LG Chem RESU) returns similar round-trip but loses 0.5% capacity per year faster in the Australian heat. Don’t trust any battery datasheet claiming above 95% round-trip without IEC 61427-2 testing data.

3. Hybrid inverter

inverter_kW = max(PV_kW ÷ 1.33, backed_up_load_kW × 1.25)

AS/NZS 4777.2 allows up to 133% PV-to-inverter ratio. Two constraints: PV peak output (the 133% cap) and motor surge headroom on the backup loop (refrigerator compressors, pool pumps, split-system AC inrush). The greater of the two is binding.

Australian installed costs (2026)

Mid-2026 pricing per SunWiz market reports, Clean Energy Council installer averages, and hipages quotes:

STCs are deducted at point of sale and worth approximately A$36–A$40 per certificate in mid-2026 (the spot price tracks the STP target). The federal Cheaper Home Batteries Program from 1 July 2025 applies a 30% discount capped at A$372 per usable kWh, stackable with state schemes in NSW, VIC, ACT, and TAS. Feed-in tariffs from major retailers (AGL, Origin, EnergyAustralia) sit at 4–8 c/kWh per Australian Energy Regulator data — well below the 28–38 c/kWh import rate, which is precisely why self-consumption (and therefore batteries) now drives payback rather than export.

When a hybrid system pays off in Australia

1. Your evening peak is more than 5 kWh. Solar Citizens analysis shows the median Australian home now consumes 60% of its electricity between 17:00 and 22:00 — exactly when PV is producing nothing. A 10 kWh battery shifts that peak entirely under self-consumption.
2. You’re on a time-of-use retail tariff with a peak/shoulder spread above 18 c/kWh. EnergyAustralia Total Plan Home Saver, AGL Solar Savers, and Amber Electric all expose wholesale price signals that make battery arbitrage viable independent of solar.
3. You experience grid outages. Bushfire-prone areas (Blue Mountains, Adelaide Hills, Yarra Ranges), cyclone regions (FNQ, Pilbara) and storm-vulnerable rural networks (Essential Energy, Ergon, Western Power) routinely see outages above 12 hours/year. EPS-capable hybrids (Sungrow SH-RT, Goodwe ET, Fronius GEN24 Plus) maintain critical loads during the outage.

For full payback maths see the solar battery ROI calculator. For the FiT side specifically, run the feed-in tariff calculator.

AS/NZS standards and CEC compliance

• AS/NZS 3000:2018 Wiring Rules — covers AC installation, RCD protection (Type AC or Type B for inverters), and earthing. Every hybrid install requires the AC isolator on the meter panel and a roof-top DC isolator on the PV string.
• AS/NZS 4777.2:2020 (Amdt 2:2024) — inverter grid-connection standard. Sets export limits, voltage and frequency ride-through, anti-islanding (2 s disconnect, 60 s reconnect), and Demand Response Mode (DRM 0–8) which retailers and DNSPs now use for emergency curtailment.
• AS/NZS 5139:2019 — battery installation standard. Mandates location rules (no bedrooms, no roof cavity, no under-stairs), fire separation distances, and signage. Lithium installs above 20 kWh trigger additional separation requirements.
• CEC accreditation — Required for installer (signing off the system) and designer (sizing it). Installs without CEC sign-off cannot claim STCs and most state rebates.

DNSP approval is a separate step. In NSW (Ausgrid, Endeavour, Essential), VIC (CitiPower, Powercor, Jemena, AusNet, United), QLD (Energex, Ergon), SA (SAPN), WA (Western Power), and TAS (TasNetworks), pre-approval is required for any inverter above 5 kW single-phase or 10 kW three-phase. Lead times in mid-2026 range from 5 business days (SAPN) to 12 weeks (Western Power in constrained suburbs).

Common Australian sizing mistakes

• Sizing battery for whole-home backup by default. A standard Australian house uses 18 kWh/day; whole-home backup needs around 20 kWh usable — about A$20,000 even after the federal battery rebate. Most installers should size for critical-load circuits only (fridge, fans, lights, internet, one AC) at 4–7 kWh usable.
• Ignoring zone-based STC deeming. A system in Zone 1 (Darwin, FNQ) earns about 22% more STCs than the same system in Zone 4 (Tasmania). Plug your postcode into the STC calculator before signing a contract.
• Buying NMC battery chemistry for an outdoor wall mount. NMC loses cycle life rapidly above 35 °C ambient — Brisbane and Perth garages routinely hit 45 °C in summer. LFP is the only safe outdoor wall-mount chemistry in Australia.
• Forgetting export-limit firmware. Most metropolitan DNSP approvals now require either a 5 kW or 10 kW export cap. The installer must commission the inverter with the correct firmware lock — otherwise the system risks being switched off remotely under AS/NZS 4777.2 DRM commands.
• Skipping the smart meter swap. Solar export and TOU billing both require a Type 4 or Type 5 smart meter. In Victoria this is universal; in NSW, QLD, SA, and WA your retailer must arrange the swap before activation. Typical lead time mid-2026 is 4–8 weeks, sometimes blocking commissioning entirely.

Worked example: family home in suburban Sydney

A four-person Sydney household consumes 22 kWh/day, wants 70% self-consumption, and needs to back up a critical loop of 4 kW (fridge, freezer, kitchen lights, ceiling fans, internet, one reverse-cycle split AC) for 6 hours during summer outages.

PV array: 22 × 0.70 ÷ (4.5 × 0.80) = 4.3 kW for bare offset. With a 10 kW DNSP allowance and STC support, sizing to 10 kW PV is the right call — extra summer generation feeds the battery and lifts annual self-consumption to 75–85%.

Battery: usable = 6 × 4 = 24 kWh usable, nameplate = 24 ÷ (0.90 × 0.95) = 28 kWh nameplate. Two Tesla Powerwall 3s (27 kWh combined) or three Sungrow SBR 9.6 (28.8 kWh combined) fit.

Hybrid inverter: max(10 ÷ 1.33, 4 × 1.25) = max(7.5, 5.0) = 7.5 kW continuous. A Sungrow SH10RT (10 kW) gives margin for AC compressor surge; a Fronius GEN24 Plus 10.0 with backup interface is the alternative.

Investment: approximately A$32,000 after STCs and before the federal Cheaper Home Batteries rebate. After the 30% federal battery rebate (A$372/kWh cap × 27 kWh = A$10,044 cap, but limited to 30% of installed battery cost), net out-of-pocket is around A$26,000. Annual electricity bill savings approximately A$3,200, payback 8–10 years depending on retail price escalation and feed-in tariff trajectory.

Sources

• Clean Energy Council — Approved Installers and Retailers — accreditation and product lists
• Clean Energy Regulator — STC scheme — STC entitlement rules
• Australian Energy Regulator feed-in tariff data — quarterly FiT and retail price reporting
• SunWiz market reports — installer pricing and battery shipments
• Solar Citizens — household consumption pattern data
• hipages solar pricing guide — Australian quote benchmarks
• DCCEEW Cheaper Home Batteries Program — federal battery rebate