Charging Solar Battery in Free Electricity Periods
A three-hour free-power window can be worth far more than a few loads of washing. For households with a compatible battery, charging solar battery free electricity periods can store low-cost grid energy for the expensive hours that follow. Used properly, it can reduce evening grid purchases, protect your battery reserve and make a sharp time-of-use plan work harder for your home.
The catch is that “free” is not automatically “profitable”. Your battery, inverter settings, tariff rules, solar forecast and household demand all matter. A poorly configured system may fill the battery just before a sunny day, leave no room for solar generation, or cycle the battery for savings too small to justify it. The winning approach is simple: charge strategically, not blindly.
How free electricity periods work with a home battery
Some electricity retailers offer nominated windows where usage is free, heavily discounted or rewarded through credits. The timing may be overnight, in the middle of the day, or set around periods when the grid has plenty of renewable generation. These plans are usually paired with higher rates at other times, so the headline offer is only one part of the maths.
A hybrid inverter can be programmed to charge the battery from the grid during the eligible period. Later, when peak electricity rates arrive, the home draws from the battery first. This is often called tariff arbitrage: buying energy when its cost is lowest and using it when its value is highest.
For an Adelaide household paying a high evening peak rate, storing several kilowatt-hours during a genuine free window can make a noticeable dent in the bill. It can also be useful in winter, when solar production is lower and evening heating demand rises. But the actual benefit depends on whether you would otherwise have enough solar stored for the night.
Charging a solar battery during free electricity periods
The best settings start with the battery’s job. Is it primarily there to soak up excess solar? Cover the expensive 4 pm to 9 pm period? Keep backup power available for a blackout? Or all three? A battery cannot always do every job at maximum level on the same day.
If your system is mainly built to reduce evening imports, set grid charging only for the retailer’s free or lowest-cost period, then set discharge windows around the expensive tariff period. A sensible minimum state of charge should remain in the battery after evening use. That reserve is especially valuable for homes relying on backup power for refrigeration, internet, lighting, medical equipment or a garage door during an outage.
Avoid setting the battery to charge to 100 per cent every day simply because electricity is free. If tomorrow is forecast to be clear, leaving capacity for your own solar can be the smarter move. Solar energy that goes straight into the battery is still highly valuable, particularly where feed-in tariffs are low. The ideal schedule changes with the season, weather and how much power the household uses after sunset.
Check the charge rate, not just the battery size
A 10 kWh battery cannot necessarily absorb 10 kWh in a two-hour free window. The limiting factor may be the inverter’s grid-charge output, the battery’s allowed charge rate or household loads running at the same time.
For example, a battery capable of charging at 5 kW could theoretically take in around 10 kWh over two hours. In reality, charging losses and power used by the home reduce the amount stored. If the oven, ducted air conditioning or EV charger is running, much of the free power may bypass the battery and go directly into those loads.
This is not always a bad result. Running flexible loads during the free period can be excellent value. The point is to understand your total site demand and avoid assuming every free kilowatt-hour will end up stored for later.
Account for round-trip losses
Batteries are efficient, but not perfect. Energy is lost when electricity is converted, stored and delivered back to the home. A plan offering truly free energy can still be attractive despite those losses. A merely discounted window needs more careful comparison against the rate you avoid later.
A practical rule is to compare the full cost of one stored kilowatt-hour with the peak rate you expect to avoid. Include charging losses, any daily plan fee difference and the possibility that solar would have charged the battery anyway. If the gap is small, simpler solar-first operation may deliver almost the same outcome with fewer battery cycles.
The tariff fine print can make or break the deal
Before changing battery settings, read the plan’s tariff schedule rather than relying on an advertisement or app banner. Free periods can have usage caps, specific meter requirements, exclusions, changing times or a requirement to opt in. The retailer may also charge higher shoulder and peak rates that outweigh the free period for a high-use household.
Look at a recent bill and identify when your home genuinely uses energy. Families with cooking, cooling and EV charging in the evening may gain more from stored free energy than a household that is usually empty after 5 pm. Conversely, a home with strong daytime solar and low evening demand may not need much grid charging at all.
South Australian households should also check whether controlled loads, hot water tariffs and solar feed-in arrangements are affected by a plan change. One attractive free window does not automatically make the whole offer the cheapest option across a year.
Make solar, EV charging and hot water work together
The battery is only one part of the home energy picture. A well-timed free period can also power an EV charger, heat-pump hot water system, dishwasher, pool pump or pre-cooling cycle for the house. These loads can deliver direct savings without putting extra cycles through the battery.
There is a priority decision to make. If the free window is short and your evening peak rates are steep, charging the battery first may be the right call. If an EV needs a meaningful overnight top-up for tomorrow’s commute, the EV may deserve priority. If solar is expected to be strong the next day, using the free window for hot water or EV charging while leaving battery capacity available can be the better arrangement.
Smart controls make this easier, but they still need clear instructions. Set a maximum EV charging rate where necessary, schedule high-load appliances outside the battery charge window, and review the results in the inverter and retailer apps after the first few weeks.
When grid charging is not the right move
Grid charging is not a universal setting. It may be a poor fit when a household has abundant solar, a decent feed-in tariff, limited evening usage and no compelling free or off-peak window. In that case, cycling the battery from the grid can add wear without delivering meaningful bill savings.
It is also worth being cautious if backup resilience is the priority. A battery fully discharged each evening may reduce what is available during a blackout. Some systems can reserve a fixed percentage, while others offer more detailed schedules and backup circuits. The capability depends on the battery, hybrid inverter and how the switchboard has been designed.
Three-phase homes need another layer of checking. Battery output, phase balancing and backup coverage vary between systems. A large battery capacity is valuable, but it does not automatically mean every three-phase appliance will run during an outage or that the battery can charge at the rate you expect.
A practical setup process
Start by confirming that your battery and inverter support scheduled grid charging. Then verify the free-period timing and any retailer conditions. Set the grid-charge window, nominate a realistic target state of charge, and set discharge periods that avoid the most expensive imports.
For the first fortnight, watch four numbers: battery state of charge at the start and end of the free period, grid imports during peak time, solar export in the middle of the day, and total daily usage. These figures show whether the schedule is working or simply moving consumption around.
A system may need seasonal adjustments. Winter can justify more grid charging because solar harvest is lower and heating loads are higher. In a bright Adelaide summer, a solar-first strategy may take the lead, with the free period reserved for an EV, heat-pump hot water or occasional top-up before a forecast hot evening.
OG Trade can help match battery capacity, hybrid inverter output, backup requirements and tariff strategy before installation, so the system is built for the way your household actually uses energy. The goal is not to chase a clever setting for one week. It is to build a home energy setup that keeps buying expensive grid power to an absolute minimum, even as seasons and electricity plans change.