Battery sizing is not one size fits all. The right capacity depends on daily consumption, solar generation, off-peak tariff opportunities, outage requirements and how the household may change.
Use more of the solar energy you generate
Solar arrays often generate more than a home can use during daylight hours, particularly from May to September. Export has value, but storing suitable surplus for evening use can reduce the amount bought back from the grid when everybody is home.
Use off-peak electricity intelligently
During the lower-generation months, batteries can charge on an appropriate off-peak tariff and supply that lower-cost energy during the day. The useful capacity depends on household consumption, tariff window and the level of grid independence being targeted.
Capacity and output are different
Battery capacity is measured in kilowatt-hours (kWh) and describes the energy available. Inverter output is measured in kilowatts (kW) and describes the power that can be delivered at one time. A large battery connected through an undersized inverter may still leave the property importing during high-demand periods.
Plan for future electrical demand
Electric vehicles, heat pumps, air conditioning, hot tubs, extensions and home working can materially change consumption. Future-proofing means discussing those plans and selecting equipment that can expand where appropriate—not automatically installing the largest battery.
Backup needs a deliberate design
Owning a battery does not automatically keep a home powered during an outage. Backup circuits, changeover equipment and suitable system capability must be included in the design. The site survey establishes what is practical and which loads should be prioritised.