For most Melbourne households, energy costs come in two separate bills: electricity for the home, and petrol for the car. Individually, each one is annoying. Together, they can easily add up to $5,000–$7,000 a year for a typical family. What fewer people realise is that a well-designed solar and battery system — combined with an electric vehicle and a smart charging strategy — can practically eliminate both bills at once.
This is not theoretical. It is already happening in Melbourne households right now, and the economics are getting better every quarter. Here is the strategy, the numbers, and what you need to set it up.
The Core Idea: One System, Two Bills Gone
The logic is straightforward. During the day, your rooftop solar panels generate more electricity than your home needs. That excess energy charges your home battery. In the middle of the day — when wholesale electricity prices in Victoria are often at their lowest or even negative — you use roughly three hours of ultra-cheap grid power to top the battery up completely. Then, in the evening and overnight, the battery powers your home and charges your electric vehicle while you sleep.
The result: your home runs almost entirely on solar and stored energy, your car runs on the same stored energy instead of petrol, and your grid import cost is minimal because the grid power you do buy is purchased at the cheapest possible time.
The Three-Hour Grid Charging Window
This is the part of the strategy that most people overlook. Victoria now has extended periods during the day — typically between 10am and 2pm — when the grid is flooded with rooftop solar from millions of homes and large-scale solar farms. During these hours, wholesale electricity prices on the National Electricity Market regularly drop below 5 cents per kWh, and on sunny days they can go negative. That means the grid is effectively paying retailers to take electricity off their hands.
If you are on a wholesale-linked retail plan — such as Amber Electric or Octopus Energy — you can access these rock-bottom or negative prices directly. Your hybrid inverter can be programmed to import grid power during a set window (say 10am to 1pm) to top up your battery. On a good day, that three-hour window fills or nearly fills a 15 kWh battery at a cost of a few cents total. On negative-price days, you are literally being paid to charge.
Even if you are on a standard time-of-use tariff rather than a wholesale plan, the off-peak or shoulder rate during these midday hours is typically 15–22 cents per kWh — still dramatically cheaper than the 35–45 cent peak rate you would otherwise pay in the evening.
How a Typical Day Looks
Here is a realistic daily energy flow for a Melbourne family running this strategy with a 10 kW solar system, a 15 kWh battery, and an EV doing 40 km of daily driving:
- 6am–9am: Battery powers the home (breakfast, hot water boost, getting ready). Solar is just starting to ramp up.
- 9am–3pm: Solar is generating 5–8 kW. Home loads (1–2 kW) are covered directly by solar. Excess solar charges the battery. During the cheapest 3-hour window (e.g., 10am–1pm), the inverter also imports grid power to fully top up the battery.
- 3pm–6pm: Solar generation is fading. Home loads are still running on the remaining solar and battery.
- 6pm–11pm: No solar. Battery powers the home through cooking, heating, TV, and evening routines. Typical draw: 6–8 kWh.
- 11pm–6am: Battery charges the EV. A typical 40 km daily commute needs roughly 8–10 kWh. The battery discharges into the car via a smart wall charger.
Total battery discharge overnight: roughly 14–18 kWh (home evening load plus EV charging). This is why a 15–20 kWh battery is the sweet spot for this strategy — a 10 kWh battery is not enough to cover both the home and the car.
The Numbers: What You Actually Save
Let us work through a realistic Melbourne scenario. These are conservative estimates based on typical Victorian tariffs and consumption patterns as of early 2026.
Without solar, battery, or EV
- Household electricity: 22 kWh/day average × 33c/kWh blended rate = $2,650/year
- Petrol: 15,000 km/year × 8L/100km × $1.95/litre = $2,340/year
- Total annual energy cost: roughly $4,990/year
With solar + battery + EV + smart grid charging
- Grid import: reduced to roughly 2–4 kWh/day (cloudy days, winter shortfalls), mostly at off-peak rates = $200–$450/year
- Daily supply charge: ~$1.10/day = $400/year
- Petrol: $0/year (car runs on battery-stored solar and cheap grid energy)
- Total annual energy cost: roughly $600–$850/year
What Hardware Do You Need?
To run this strategy properly, the system needs to be sized and configured correctly from the start. A generic 6.6 kW solar plus 10 kWh battery package will not cut it — the loads are too high. Here is what works:
- Solar array: 10–13.2 kW. Bigger is better here because you need to cover home loads, charge the battery, and have headroom for cloudy-day shortfalls. Melbourne averages 3.6–4.2 peak sun hours per day annually, so a 10 kW system generates roughly 36–42 kWh on a good day.
- Battery: 15–20 kWh usable capacity. This needs to handle 6–8 kWh of evening home load plus 8–10 kWh of EV charging. Modular battery systems (like stacked units) work well because you can start at 15 kWh and add capacity later if you get a second EV or add a heat pump.
- Hybrid inverter: must support both solar input and grid-to-battery charging with a programmable charge window. Not all inverters support scheduled grid charging — your installer needs to confirm this.
- Smart EV charger: a charger that can be scheduled to draw from the battery (via the house circuits) during off-peak hours. Most modern 7 kW wall chargers support scheduling natively.
- Electricity plan: a wholesale-linked tariff (Amber, Octopus) maximises savings by letting you buy grid power at the cheapest moments. A standard time-of-use plan still works, just with smaller savings on the grid-charging portion.
The Tariff Landscape That Makes This Work
This strategy was not viable five years ago. Two things have changed in Victoria that now make it work:
First, feed-in tariffs have collapsed. When feed-in rates were 11–12 cents per kWh, exporting solar to the grid made reasonable economic sense. Now that they are 3–5 cents, the opportunity cost of not self-consuming is negligible. You are better off storing every kWh you can and using it yourself.
Second, daytime wholesale prices now regularly go negative. The massive growth in rooftop solar across Victoria means the grid is oversupplied during the middle of the day. Wholesale-linked retail plans pass these prices through to consumers, creating a window where charging your battery from the grid costs next to nothing — or less than nothing.
Meanwhile, evening peak prices remain high (35–50 cents on time-of-use plans, sometimes spiking higher on wholesale plans). The spread between daytime buy price and evening avoid price is what drives the entire strategy.
What About Winter?
This is the honest part. Melbourne winters reduce solar generation significantly — a 10 kW system might produce only 15–20 kWh on a short, overcast June day, which is not enough to fully cover home loads plus EV charging. During these months, you will rely more heavily on grid charging during the cheap midday window, and your grid import costs will increase.
Realistically, a well-configured system will cover 85–95% of your combined home and EV energy needs across the full year. The shortfall in winter is partly offset by lower EV consumption (shorter days, potentially less driving) and by the fact that wholesale prices can still be low during winter midday hours when large-scale solar and wind generation is strong.
System Cost and Payback
Let us be upfront about what this system costs to install, before we talk about returns:
- 10 kW solar system: $8,000–$11,000 installed (after STC federal rebate)
- 15 kWh battery + hybrid inverter: $12,000–$16,000 installed
- Solar Victoria battery rebate: up to -$2,950
- Smart EV wall charger: $1,200–$2,000 installed
- Total system cost (net of rebates): roughly $18,000–$26,000
With annual savings of $4,100–$4,400, the simple payback period is approximately 4.5–6 years. After that, the system is generating free energy for the remaining life of the equipment — typically 15–25 years for panels and 10–15 years for batteries.
If you factor in rising grid electricity prices (which have increased roughly 8–12% per year in recent years) and rising petrol prices, the payback period shortens further because the value of what you are avoiding increases every year.
Common Mistakes That Break the Strategy
This approach works well when it is designed correctly, but a few common errors can undermine the economics:
- Undersizing the battery. A 10 kWh battery cannot reliably cover both evening home load and EV charging. You will end up importing expensive peak-rate grid power in the evening, which defeats the purpose.
- Choosing an inverter that does not support grid-to-battery charging. Not all hybrid inverters can be programmed to charge from the grid during a set window. If yours cannot, you miss the cheap midday charging opportunity entirely.
- Staying on a flat-rate electricity plan. The strategy relies on the price difference between cheap daytime imports and expensive evening rates. A flat rate (e.g., 30c/kWh all day) significantly reduces the arbitrage benefit.
- Ignoring switchboard and metering requirements. Homes with older switchboards may need an upgrade before a battery and EV charger can be safely connected. This adds cost and should be identified early.
- Not scheduling the EV charger. If the EV draws power from the grid directly (because it is set to charge immediately when plugged in), rather than from the battery via the house circuits at a scheduled time, you lose control of when and how the energy flows.
Is This Strategy Right for Your Household?
This approach works best for households that meet most of the following criteria:
- You already own or are planning to buy an electric vehicle
- Your roof can support a 10 kW or larger solar array (north-facing or split east-west with reasonable pitch)
- You have moderate to high evening electricity usage
- You are willing to switch to a time-of-use or wholesale-linked electricity plan
- You have a garage or dedicated parking space where an EV wall charger can be installed
- You drive at least 30–40 km on most days (lower daily driving means less fuel saving, which weakens the case)
If you are a low-mileage driver, retired at home during the day, or live in an apartment without roof access, the full strategy may not apply — but elements of it (particularly the solar plus battery portion) can still be worth modelling.
How to Get Started
The most useful first step is a design-backed proposal that models the complete energy flow: solar generation, battery charge and discharge cycles, grid import windows, and EV charging demand. This should be based on your actual electricity bill, your roof layout, and your driving pattern — not a generic package.