Step 4 of 6
Add a battery (optional)
A battery stores surplus generation during the day for use in the evening. It is not always the best financial decision — read below before you decide.
When a battery makes sense
A battery pays back fastest if you are home during the day (and would otherwise export surplus at a low SEG rate) and have significant evening usage. If you already have an EV and a time-of-use tariff, the tariff arbitrage alone often closes the gap on a battery's payback period.
How to size it
The rule of thumb is to match battery usable capacity to your typical evening electricity use — not your total daily usage. For a 3,500 kWh/year household, that is usually 4–6 kWh usable. Larger batteries improve resilience but extend payback proportionally. Our recommendation below is based on 60% of your daily usage stored at 90% depth of discharge.
DC coupling for DIY installs
If you are installing a string inverter (Step 3), you need an AC-coupled battery — one that has its own inverter built in and connects to the AC side of your system. DC-coupled batteries require a hybrid inverter. Make sure your chosen battery matches the coupling type of your inverter before ordering.
Skip this step?
If you want to add a battery later, or do not need one now, skip to Step 5 — you can always come back.