Solar + battery + EV — the Perth savings triple stack

Each technology on its own saves money. Solar cuts your daytime bill. A battery shifts cheap solar to expensive evening hours. An EV replaces $2,500/year in petrol with $400-800 in electricity. But combine all three and something interesting happens — the savings compound.

Here's why, and what the real numbers look like for a Perth household.

The compound effect

Each addition doesn't just save independently — it improves the economics of the others:

Solar alone: You generate cheap electricity but export most of it at 2-7c/kWh because you're at work during the day. Self-consumption is typically 30-35%.

Solar + battery: Self-consumption jumps to 60-70%. The battery captures what you'd have exported at 7c and uses it in the evening when you'd have paid 32c (A1) or 54c (Midday Saver peak). The battery's value depends entirely on having solar to charge it.

Solar + battery + EV: Now your solar has three jobs — power the house, charge the battery, and charge the car. Self-consumption can hit 80-90%. The EV becomes a massive daytime load that absorbs solar generation you'd otherwise export for pennies.

This is the compound effect: each piece makes the others more valuable.

The numbers for a typical Perth household

Let's model a family of four in Joondalup with:

• 25 kWh/day electricity usage
• One car doing 15,000 km/year
• Currently spending $2,000/quarter on electricity (A1 tariff) and $3,000/year on petrol

Step 1: Solar only (6.6 kW)

| Metric | Value | |---|---| | Annual generation | ~9,500 kWh | | Self-consumption (30%) | 2,850 kWh saved @ 32c = $912 | | Export credits (70%) | 6,650 kWh @ 7c REBS = $466 | | Total annual benefit | $1,378 | | System cost (after STCs) | $5,500 | | Payback | 4.0 years |

Step 2: Add battery (10 kWh)

| Metric | Value | |---|---| | Additional self-consumption | 2,800 kWh shifted from export to evening | | Savings per kWh shifted | 25c (32c grid - 7c export) | | Battery annual savings | $700 | | VPP earnings | ~$80 | | Combined solar + battery | $2,158/year | | Battery net cost (after rebates) | $5,600 | | Combined payback | 5.2 years |

Step 3: Add EV + home charger

| Metric | Value | |---|---| | Petrol replaced | 15,000 km @ 9L/100km @ $1.85/L = $2,498/year | | EV charging cost (solar) | 2,700 kWh @ ~5c (marginal solar cost) = $135 | | EV charging cost (overnight) | 600 kWh @ 19c (EV tariff) = $114 | | Net fuel savings | $2,249/year | | Home charger install | $1,500-2,500 | | Combined solar + battery + EV | $4,407/year |

That's $4,407/year in combined savings — or roughly $367/month back in your pocket. The electricity bill drops from $2,000/quarter to under $800. The petrol bill drops from $3,000/year to $249.

Why the EV changes the solar maths

Without an EV, a 6.6 kW solar system exports 70% of its generation at low feed-in rates. With an EV charging at home during the day (timer set for 10am-2pm), you can absorb an extra 8-12 kWh of solar generation daily.

That's 8 kWh that was earning you 7c/kWh as export ($0.56/day) now offsetting 8 kWh you'd have bought at 32c ($2.56/day) — or displacing 8 kWh worth of petrol ($4.80 equivalent at $1.85/L).

The EV effectively converts your lowest-value solar output (daytime exports) into your highest-value use (fuel replacement). That's the triple stack.

The tariff play: Midday Saver + EV Add-On

This combination is specifically designed for solar + battery + EV households:

• Midday Saver base: 8.62c super off-peak (10am-3pm) for daytime loads
• EV Add-On: 19.38c overnight (11pm-6am) for EV charging when solar isn't available
• Peak avoidance: Battery covers the 53.84c peak window (3-9pm)

On this tariff stack, your effective electricity cost across 24 hours drops to roughly 12-15c/kWh blended — compared to 32c on A1. That's a 55-60% reduction in your per-unit cost before even counting solar generation.

System sizing for the triple stack

Don't size for today — size for the full stack:

| Component | Minimum | Recommended | |---|---|---| | Solar panels | 6.6 kW | 8-10 kW | | Battery | 10 kWh | 13.5 kWh | | EV charger | 7.4 kW (single phase) | 7.4 kW with solar integration | | Inverter | 5 kW hybrid | 8-10 kW hybrid (3-phase if available) |

The key insight: oversize the solar. A 10 kW system costs maybe $2,000 more than 6.6 kW but generates 50% more energy to split between house, battery, and car. The marginal cost per additional kW of solar is the cheapest energy investment you can make.

Upfront cost and combined payback

| Component | Cost (after rebates) | |---|---| | 10 kW solar | ~$6,500 | | 13.5 kWh battery | ~$6,500 | | 7.4 kW EV charger | ~$2,000 | | Total | ~$15,000 |

At $4,400/year savings, that's a 3.4-year combined payback. After that, you're saving $4,400 every year for the remaining 20+ years of the system's life.

Over 25 years (conservative estimate, ignoring electricity price increases): $110,000 in savings from a $15,000 investment. That's a 633% return.

The order matters

If you're building the triple stack over time:

1. Solar first. Always. It's the fastest payback, lowest risk, and enables everything else.
2. Battery second. Once solar is generating, the battery captures value you're currently losing to low export rates.
3. EV + charger third. The car decision is driven by vehicle costs and lifestyle, but once you have solar + battery, the running cost argument is overwhelming.

Installing a battery before solar, or an EV charger before solar, doesn't make financial sense. Solar is the foundation.

Related Reading

• Home Batteries in WA — the honest ROI picture — Battery-specific payback calculations and brand comparisons.
• EV Charging at Home in WA — tariffs and costs — Charging options and tariff strategies.
• WA Rebates Are Changing in 2026 — Federal and state rebate timelines.

Model your own triple stack: Our Savings Planner lets you toggle solar, battery, and EV simultaneously and see the combined savings for your specific usage and tariff. Or try the ROI Analyzer for a detailed 25-year projection.

Sources: SolarQuotes, Solar Choice