A battery may make sense if you export useful solar during the day and then buy significant electricity from the grid later. The right answer depends on actual exports, later usage, electricity rates, the existing solar system and what you want the battery to achieve.
The first two numbers I want to understand
If you already have solar, I want to know how much energy is being exported and how much electricity is being bought from the grid later in the day. Those two numbers tell us much more than starting with a battery capacity.
Why exports matter
A battery needs energy to charge. If your solar system produces a regular daytime surplus, that energy may be stored instead of exported. If there is very little surplus, a large battery may not have enough solar available to fill it consistently.
Why later grid use matters
The stored energy is most useful when it can replace grid electricity you would otherwise buy later. Homes with meaningful afternoon, evening or overnight use can therefore have a different battery opportunity from homes that use very little power after sunset.
What else I check
- Existing solar size and age
- Inverter brand, model and compatibility
- Electricity tariff and feed-in tariff
- Seasonal solar production and usage
- EV plans and other future loads
- Backup-power expectations
- Battery cost and any current incentives
More solar may come first
If the home still imports a lot of grid electricity during the day, the existing solar system may simply be too small. In that case I may compare adding solar before, or at the same time as, adding storage.
Do you need a hybrid inverter?
Not always. Some batteries can be AC-coupled to an existing system. In other situations an inverter replacement or system redesign can make more sense. The existing equipment should be checked before assuming the upgrade path.
Backup changes the design
A battery bought mainly to reduce bills can be operated differently from one that must keep essential circuits running during outages. If backup matters, I want to know which loads are important and whether reserve capacity is required.
A common pattern
A home exports solar through the middle of the day, then imports heavily from 5pm onward. That is a pattern worth modelling for storage. But if the same home has only a small solar system and little surplus generation, more solar may need to be considered first.
What I would do next
Start with a recent electricity bill and, where available, solar/export information. I then compare the existing system against the customer's later energy use before recommending a battery size or even deciding that a battery is the best next step.
Solar and battery performance and savings are estimates that depend on the individual site, electricity use, tariffs, equipment, installation and assumptions used. Current incentives and network requirements should be checked for the specific project before a proposal is finalised.
Want to look at your actual situation?
You do not need to know the system size first. Start with your electricity use, existing system and what you want to achieve.