Worked Example

One household, multiple decisions. This dashboard shows how these choices change annual cost and emissions.

Baseline

Starting Point

These values match the default inputs on the dashboard.

Transport assumptions

  • Distance: 12,000 km/year
  • Petrol car: 7.4 L/100 km at $1.95/L
  • EV: 14.0 kWh/100 km at $0.20/kWh
  • Grid intensity: 0.58 kgCO2e/kWh

Heating assumptions

  • Heat demand: 12,600 MJ/year
  • Gas heater efficiency: 0.90
  • Gas price: $0.04/MJ
  • RCAC COP: 3.5, electricity tariff: $0.20/kWh

Result

Default Outcome

Comparison Annual cost change Annual emissions change Interpretation
Petrol -> EV -$1,395.60 -1,076.88 kgCO2e Strong win on both cost and emissions
Gas heater -> RCAC -$360.00 -138.20 kgCO2e Moderate savings; still positive
Combined total -$1,755.60 -1,215.08 kgCO2e Lower cost, lower emissions

Decisions

What Changes the Outcome Most?

These are typical household decisions that can move your result up or down.

Decision Example choice Effect on result Why it matters
When you charge EV Daytime solar or off-peak tariff Lowers EV running cost Electricity price is the EV's fuel price
Which EV model 12.6 vs 15.9 kWh/100 km Can change EV energy by ~25% Vehicle efficiency affects electricity use directly
Your annual km 8,000 vs 20,000 km/year Scales both savings and emissions impact More distance amplifies whichever option is cheaper/cleaner
Heating system quality RCAC COP 3.0 vs 5.0 Big effect on heating energy use Higher COP means more heat per kWh and less energy consumed
Gas price and electricity tariff Different retailers, different plans Affects the cost of either option Prices make a big difference to the money outcome
Grid emissions factor State-based intensity value Changes calculated electricity emissions Cleaner grids decrease emissions from EV and RCAC

Scope

What Is Not Included

    These calculations do not consider:

  • Vehicle maintenance costs;
  • Daily gas or electricity supply charges; or
  • The impact of installing solar panels on a house.