OVO has two plans that matter for batteries and EVs. The Free 4 Plan gives free power every day from 11am to 3pm. The EV Plan charges 4.5c/kWh from midnight to 6am. New customers pick one – the current EV Plan has no free midday hours.
OVO rates checked on OVO's plan pages on 6 November 2026. OVO doesn't publish Victorian rates for the other hours on those pages, so every saving below assumes 34c/kWh – the true figure depends on your address and network. Supply charges don't change and aren't counted.
Free 4: how much a battery can store in 4 free hours
A battery can only charge as fast as its inverter or charger allows. Four hours at that power is the most it can take from the grid for free. Stored power comes back with about 10% losses, and each kWh you use from it in the evening saves the 34c you'd otherwise pay.
| Charging power | Into the battery (4 hrs) | Usable later | Worth per day | Worth per year |
|---|---|---|---|---|
| 3.3 kW | 13.2 kWh | 11.9 kWh | $4.04 | $1,474 |
| 5 kW | 20 kWh | 18.0 kWh | $6.12 | $2,234 |
| 8 kW | 32 kWh | 28.8 kWh | $9.79 | $3,574 |
| 10 kW | 40 kWh | 36.0 kWh | $12.24 | $4,468 |
| 15 kW | 60 kWh | 54.0 kWh | $18.36 | $6,701 |
The yearly figure only counts if you actually use that much power outside 11am–3pm every day, and the battery is at least that big. A 5 kW battery charger fills about 20 kWh; a typical family uses 12–18 kWh in the evening and overnight, so 8–10 kW of charging only pays off with a big battery, electric heating or an EV. On single-phase power, keep long charging loads to about 50 A (11.6 kW) in total – the 15 kW row needs three-phase. Why.
Free 4: charging the car itself
| Charger | Type | Into the car (4 hrs) | Driving range | Saved vs 34c |
|---|---|---|---|---|
| 7 kW | Single-phase wall charger (most homes) | 28 kWh | about 175 km | $9.52 |
| 11 kW | Three-phase wall charger | 44 kWh | about 275 km | $14.96 |
| 22 kW | 22 kW charger – most cars only accept 11 kW AC | 44 kWh | about 275 km | $14.96 |
The car has to be home and plugged in between 11am and 3pm. A 7 kW charger adds about 28 kWh – roughly a week of normal Melbourne driving – in one session.
EV Plan: midnight to 6am at 4.5c
Six cheap hours a night. Charging the car directly saves the full difference (34c − 4.5c = 29.5c a kWh). Charging the battery to run the house the next evening saves a little less, because of battery losses.
| What's charging | kWh in 6 hrs | Cost | Saved per night | Saved per year |
|---|---|---|---|---|
| Battery, 5 kW charging | 30 kWh | $1.35 | $7.83 | $2,858 |
| Battery, 8 kW hybrid inverter | 48 kWh | $2.16 | $12.53 | $4,573 |
| Battery, 10 kW charging | 60 kWh | $2.70 | $15.66 | $5,716 |
| EV, 7 kW wall charger | 42 kWh | $1.89 | $12.39 | — (a car rarely needs a full window every night) |
| EV, 11 kW three-phase charger | 66 kWh | $2.97 | $19.47 | — (a car rarely needs a full window every night) |
Battery rows assume all stored power is used in the house at 34c. The EV Plan's rate outside midnight–6am may be higher than OVO's other plans – check the plan fact sheet.
Winter heating: 3-bedroom home, family of four
Example home: a 7 kW reverse cycle split in the living room running 5pm–11pm, and a 2.5 kW split in each of three bedrooms running 10pm–7am at 18–20°C. On a cold Melbourne night that draws about 18 kWh (7.2 kWh living room, 10.8 kWh bedrooms). We count 120 heating nights a year (June–August plus colder nights in May and September).
| How the heating is paid for | Per night | Per winter | Saved per winter |
|---|---|---|---|
| Normal rate, 34c all night | $6.12 | $734 | — |
| EV Plan, no battery (bedrooms 12am–6am at 4.5c) | $4.00 | $480 | $255 |
| EV Plan + battery charged at 4.5c for the evening | $0.86 | $104 | $631 |
| Free 4 + battery charged free 11am–3pm | $0.00 | $0 | $734 |
The most a family of four could save in a year
This is the theoretical ceiling: every kWh the home uses is bought at $0 (Free 4) or 4.5c (EV Plan) instead of 34c. Same family, same 3-bedroom home:
- Everyday use (lights, cooking, fridge, washing, hot water): 16 kWh a day – 5,840 kWh a year
- Winter heating as above: 2,160 kWh a year
- One EV doing 15,000 km a year: 2,400 kWh a year
- Total: 10,400 kWh a year, which costs about $3,536 at 34c plus supply charges
What stops you reaching the ceiling:
- Battery size and charging speed. On a cold night this home uses about 37 kWh outside 11am–3pm. To run it all from free power the battery needs about 40 kWh and a charger of about 11 kW. The EV Plan's 6-hour window makes 7 kW enough.
- The car. For Free 4 it must be home at midday, or charged from the battery (which needs a bigger battery).
- Fair use. Free 4 has no daily cap, but OVO can move very heavy users to its standard contract.
- Other-hours rates. Plans with free or cheap windows can charge more at other times. Any power you still buy outside the window costs more.
- Solar. If you have solar, Free 4 means you export more at a low feed-in tariff, so part of the saving overlaps with what solar already gives you.
The battery itself isn't counted here. For the payback on the battery, use the calculator.