Start with the actual tariff windows
Time-of-use tariffs can have peak, shoulder, off-peak and sometimes seasonal or event-based rates. Import and export prices may also differ. Record the exact times, days and charges rather than using a generic peak/off-peak assumption. Fixed daily charges and demand charges may remain unchanged by a residential battery, so include only costs the operating strategy can influence.
Prioritise solar before arbitrage claims
A battery charged from midday solar can shift locally generated energy into an expensive evening window. Grid charging during cheap periods may add another use case where rules and equipment support it. The best schedule depends on solar forecast, expected household load and backup reserve. Filling the battery from the grid too early can leave no room for free midday solar.
Reserve settings have an opportunity cost
Keeping 20% or 30% of usable energy for outages improves backup readiness but leaves less capacity for tariff shifting. The correct reserve is a risk choice, not a universal percentage. Homes with frequent outages, medical loads or well pumps may value reserve more highly than homes with reliable grids and flexible evening loads.
Efficiency narrows the tariff spread
A stored kilowatt-hour is not returned at 100% efficiency. Conversion and standby losses mean the cheap-to-expensive price spread must be large enough to cover round-trip losses before pure arbitrage saves money. Battery ageing and warranty throughput may also matter for very aggressive cycling, so compare tariff savings with the warranty terms for the exact model.
Use interval data to test the schedule
Thirty-minute or hourly smart-meter data reveals how much load actually occurs in expensive periods and how often solar can recharge the battery. Simulate representative summer and winter weeks. A battery sized for one perfect sunny day can underperform in winter, while a system sized only for winter may carry unused capacity through much of the year.
Use the checks together
Battery sizing guide Battery warranty-throughput guide should be used alongside the equipment manuals and local electrical requirements.