Choosing a solar battery by capacity alone can leave you paying for storage you rarely use. The right size depends on how much excess solar your system produces, how much electricity you use after sunset and what you expect the battery to do during a blackout.
A battery should match your household, not simply be the largest model that fits the budget.
Your evening and overnight usage set the starting point
Battery capacity is measured in kilowatt-hours, written as kWh. This indicates how much electricity the battery can store, although the usable amount may be lower than the advertised total capacity.
We use your smart-meter data to see how much electricity you normally use from late afternoon until solar generation resumes the next morning. That gives us a more useful starting point than household size alone.
A home that runs air conditioning, cooking appliances and pool equipment after sunset may need more stored energy than one with low evening demand.
Your solar system needs enough surplus to charge it
A battery stores electricity that would otherwise be exported, so the solar system needs to produce enough surplus after covering daytime household use.
If the battery is large compared with the available excess solar, it may not charge fully on a typical day. Grid charging may be possible under some electricity plans, but that changes the financial calculation and should be included in the recommendation.
Existing panel and inverter capacity, roof conditions and seasonal generation all affect how consistently the battery can charge.
Backup needs affect both capacity and power
Battery capacity determines how much energy is stored. Battery power, measured in kilowatts, affects how much equipment can run at once. Both matter during a blackout.
Keeping lights, refrigeration and communications running requires a different design from backing up air conditioning or most of the home. Your installer should identify the circuits included, their likely demand and how long the stored energy may last under stated assumptions.
The system should also explain whether solar can recharge the battery while the grid is unavailable.
Bigger is not always better value
An oversized battery may hold energy that the household rarely uses, increasing the cost without providing the same increase in savings. An undersized battery may regularly empty before the evening is over or provide less backup than expected.
The right balance depends on usable capacity, expected cycles, tariffs, warranty conditions and the value you place on backup. Any savings estimate should show the assumptions for solar generation, stored energy, grid imports and export rates.
Your quote should explain the sizing decision
Before choosing a battery, check:
- usable rather than total capacity;
- expected evening and overnight demand;
- typical excess solar available for charging;
- maximum battery power;
- essential or whole-home backup scope;
- compatibility with the solar system and inverter; and
- warranty terms, throughput and support.
At Forever Solar, we size storage around your usage and priorities so the battery has a clear job to perform.
Want to know what battery size could suit your home? Talk to us about a tailored battery plan.