Modelled case study: how a Perth family could cut energy bills

Illustrative scenario. The Morrison family is a composite drawn from typical Perth electrification journeys. Names and personal details are fabricated; the costs, savings, and timelines reflect realistic figures for a 4-bedroom Duncraig home using current WA tariff rates and rebate values. This article walks through what the journey looks like — not a profile of any specific household.

When the Morrison family — our illustrative Duncraig household — set out to electrify their 1990s-built home, they had one goal: cut their energy costs without sacrificing comfort. Across three modelled years, their bills fall substantially as solar, efficient appliances, and EV charging change the household load. Here's how that journey plays out, step by step.

The starting point

The House:

• 4-bedroom, 2-bathroom home built in 1992
• 220m² living area
• North-facing roof (ideal for solar)
• Ducted evaporative cooling, no heating
• Gas hot water, gas cooktop, gas bayonet heater

The Family:

• Parents (Michael, 42, and Sarah, 40)
• Two children (Emma, 14, and Jack, 11)
• Two cars (commuting 25,000km/year combined)

Annual Energy Costs (2022): | Item | Annual Cost | |------|-------------| | Electricity (8,500 kWh) | $2,640 | | Gas (supply + usage) | $760 | | Petrol | $4,200 | | Total | $7,600 |

Year 1: solar foundation

The decision

After a $950 quarterly electricity bill over summer — the evaporative cooling running constantly — the household started researching solar.

What they installed

• 10kW solar system (25 x 400W panels)
• 8.2kW Fronius inverter
• North-facing panels at 15-degree tilt
• Total cost: $9,200 after STCs

Why they chose this size

The roof could fit 10 kW, and the payback difference between 6.6 kW and 10 kW was minimal. With an EV and battery on the horizon, going bigger made sense.

First-year results

• Generated: 16,800 kWh
• Self-consumed: 5,200 kWh
• Exported: 11,600 kWh
• DEBS credits: $232 (at 2c/kWh standard rate — most midday exports)
• Electricity bill: $1,100 (down from $2,640)
• First year savings: $1,540
• Payback on track: 6 years

Year 2: heat pump hot water + induction

The catalyst

Their 18-year-old gas hot water system started leaking. Decision time: replace with gas ($1,800 installed) or switch to heat pump?

Heat pump installation

• iStore 270L heat pump hot water
• Installed in garage (quiet location)
• Cost: $3,400 installed ($2,600 after STCs)
• Runs during solar production (10am-2pm)

The induction switch

With the electrician already on site, indoor air quality was the next consideration. With two children with asthma in the house, induction made the shortlist.

• Fisher & Paykel 4-zone induction cooktop: $1,100
• New electrical circuit: $450
• Compatible cookware (kept most existing): $280
• Total: $1,830

Gas disconnection

With no gas appliances remaining, they disconnected:

• Disconnection fee: $180
• Annual supply charge eliminated: ~$180 (AGL standard plan)

Year 2 results

| Item | Before | After | |------|--------|-------| | Electricity | $1,100 | $950 | | Gas | $760 | $0 | | Total | $1,860 | $950 |

Year 2 savings: $910 Cumulative savings: $2,450

The unexpected benefits

In a switch like this, the cooking change tends to surprise people most. Induction is faster, and cleanup is easier — nothing bakes onto a cool surface, so a household often finds the kids help cook more because it feels safer.

The other commonly reported benefit is indoor air quality. Removing a gas cooktop ends indoor combustion in the kitchen, which families with asthmatic kids often notice — though it's an illustrative benefit here, not a measured medical result.

Year 3: battery and EV

Battery decision

With solar exports earning just 2c/kWh at the standard DEBS rate but evening electricity costing ~32c/kWh, a battery starts to make sense.

• Tesla Powerwall 2 (13.5 kWh)
• Installed with Storm Watch feature
• Cost: $13,500
• Part-funded by the WA Battery Scheme — a $130/kWh rebate (capped at $1,300) plus an interest-free loan up to $10,000 for Synergy customers
• Repayments on the financed portion: about $112.50/month over 10 years

How they use it

The battery:

1. Charges from solar during the day
2. Powers the home from 5pm-10pm
3. Provides backup during blackouts
4. Participates in Tesla Energy Plan VPP

The EV leap

With the older of the two cars due for replacement, the natural pick was an EV:

• BYD Atto 3 Extended Range
• 60.48 kWh battery, 420km range
• Cost: $47,990 (no stamp duty in WA for EVs under $50k)
• Home charging: Dedicated 7kW charger ($1,200 installed)

EV charging strategy

Charging is mostly from solar: plug in mid-afternoon and the car grabs the last few hours of generation, while the battery still fills enough to run the house overnight. In a setup like this, grid power for charging is needed only a few times a month.

Year 3 results

| Item | Cost | |------|------| | Electricity (minimal grid use) | $380 | | Battery loan payment | $1,350 | | Public charging (occasional) | $150 | | Petrol (second car only) | $1,800 | | Total | $3,680 |

But wait - the second car still uses petrol. Once that's replaced with an EV, their annual energy cost will drop below $1,000.

The complete picture

Total investment over 3 years

| Item | Cost | |------|------| | 10kW solar | $9,200 | | Heat pump hot water | $2,600 | | Induction + circuit | $1,830 | | Gas disconnection | $180 | | Battery | $13,500* | | EV charger | $1,200 | | Total | $28,510 |

*Part-funded by the WA Battery Scheme (rebate + interest-free loan up to $10,000)

Annual savings

| Comparison | Annual Cost | |------------|-------------| | Before electrification (2022) | $7,600 | | After electrification (2025) | $3,680 | | Annual savings | $3,920 |

When the second car is replaced with an EV:

• Projected annual cost: $1,100
• Projected annual savings: $6,500

Payback analysis

| Investment | Payback Period | |------------|---------------| | Solar | 6 years | | Heat pump + induction | 5 years | | Battery | ~23 years on price alone (financing can offset the upfront cost — see below) | | EV vs new petrol car | 8 years |

Lessons from this scenario

What works well

1. Oversizing the solar. Extra capacity costs little upfront but enables every later step — the heat pump, the battery, the EV.

2. Timing the heat pump to the gas system's failure. Replacing a unit that has already failed means no wasted equipment, and the decision is easier to make.

3. The WA Battery Scheme rebate and interest-free loan. A $130/kWh rebate (capped at $1,300) plus an interest-free loan up to $10,000 cover most of the battery cost, so there's no need to find $13,500 upfront.

4. VPP participation. A compatible VPP can add event income when the battery helps during grid-stress events, but the annual value depends on event count, exported kWh, and the program rate.

What's worth doing sooner

1. A bigger battery. 13.5 kWh is enough, but 20 kWh would cover most days without drawing from the grid.

2. Switching to induction earlier. The indoor air-quality benefit alone makes it worth doing before the hot water system forces the issue.

3. Planning for the EV from the start. Installing the 7 kW charger circuit during other electrical work saves a second electrician visit later.

Tips for others

Start with solar

It makes the economics of everything else work. Go a little bigger than you think you need — electricity use only climbs as you electrify.

Don't overthink the cooktop switch

Induction can feel like a big change, but most people settle into it within a week. The air-quality benefit for a household with kids is the part worth not delaying.

Do the maths on financing

In this scenario, repayments and modelled battery savings need to be compared using the same household inputs and loan terms. Your figures depend on your bill, system size, finance rate, tariff, export profile, install price, and household load shape, so model your own before relying on it. The same logic applies to the EV, where avoided fuel cost depends on kilometres, charging timing, and vehicle choice.

What's next?

From here, the natural next steps are:

1. Replacing the second car with an EV
2. Adding more battery capacity if prices drop
3. Smart-home automation to optimise energy use
4. A V2H (vehicle-to-home) setup for emergency backup

Want to see what electrification could mean for your household? Try our Electrification Calculator for a personalised analysis based on your specific situation, usage, and location.