Methodology

Solar PV

Solar generation is estimated using your STC zone rating, which represents average daily peak sun hours for your area, as published by the Clean Energy Regulator.

System sizing:We recommend 5kW for smaller bills (<$1,800/yr), 6.6kW as the standard recommendation, or 10kW for larger households (>$2,500/yr).

STC rebate: system_kW × zone_rating × 10 (deemed years) × $39/certificate.

Home Battery

Battery savings come from shifting solar energy from low-value export to high-value peak usage periods (tariff arbitrage).

Pricing: $900–1,200 per kWh of storage capacity, including installation. Warranty: typically 10 years.

Ceiling Insulation

Insulation savings are calculated as a percentage reduction of your heating and cooling costs, based on your current insulation status and climate zone.

R-value recommendations follow NatHERS guidelines. Pricing: $8–15/m² for ceiling batts including installation.

Heat Pump Hot Water

Savings are calculated as the difference between your current hot water system's annual running cost and a heat pump's estimated running cost.

Heat pumps qualify for both federal STCs (approximately 25 certificates) and various state rebates (up to $1,000 in VIC).

Draught Sealing

Based on government data (energy.gov.au) showing draught sealing can reduce heating costs by ~20% and cooling costs by ~15%.

Cost: $200–800 for professional draught sealing. Often the fastest payback of all upgrades.

Double Glazing

Window upgrades reduce heat transfer, with savings estimated at 12–15% of heating/cooling costs based on government efficiency data.

Double glazing has a longer payback but a 30+ year lifespan. Strongest case in cool/alpine climates (zones 7–8).

Efficient Air Conditioning

Savings are based on the COP (Coefficient of Performance) difference between your current system and a modern reverse-cycle unit.

For gas heater replacement, additional savings from gas supply charge elimination are included.

General Assumptions

• Electricity rates: State averages for 2025–26 from retailer pricing data
• Heating/cooling share: 30–50% of total bill depending on climate zone (higher in alpine, lower in tropical)
• Hot water share: 25% of total bill (15% if gas-connected)
• Floor area: Estimated from bedroom count (90–250 m²)
• Payback: Average cost after rebates ÷ annual savings
• 10-year benefit: (Annual savings × 10) − average cost after rebates
• Confidence:"High" when based on your specific inputs; "Medium" when we've used defaults or estimates

Data Sources

• Clean Energy Regulator — STC zone ratings and certificate values
• NatHERS — Climate zones and insulation R-value recommendations
• energy.gov.au — Draught sealing and efficiency improvement percentages
• Solar Choice Price Index — Solar system pricing by state
• State government rebate program documentation (VIC, NSW, QLD, SA, WA, TAS, NT, ACT)