If you already have solar, our Battery-Only Calculator recommends the right battery capacity (in kWh) for your home based on your existing generation, your daytime-versus-evening usage split, your backup needs and any EV charging. Sizing a battery for an existing solar system is a different exercise to sizing a new solar-plus-battery system from scratch — this tool is built specifically for retrofit.
Updated August 2026 for NSW residents. Rebate figures reflect incentives current as of August 2026, which step down on a set schedule — confirm current values before quoting.
Quick answer (TL;DR)
- Built for retrofit — your solar array is already fixed, so the questions are narrower and more precise.
- Asks your day/night usage split, blackout-protection needs, critical appliances and EV charging.
- Returns a recommended kWh capacity and a shortlist from our confirmed retrofit range.
- Federal Cheaper Home Batteries Program (~30% off) plus NSW PDRS (~$1,100–$1,500) apply.
- From 1 July 2026 the NSW incentive no longer requires existing solar (you likely already have it).
Because your solar array is already fixed in size and orientation, this calculator focuses on a narrower and more precise set of questions than our full sizing tool — how much surplus solar you're currently exporting, how your household uses electricity across the day, and what level of backup protection you want during a blackout.
You'll tell us roughly how your household electricity use splits between daytime (when your solar is generating) and evening/overnight. A household largely empty during the day and busy from 5pm will benefit from a larger battery than one with someone home all day.
Blackout protection is one of the most under-considered factors in battery sizing. We ask how important guaranteed backup power is and for how long — a couple of hours to keep the fridge and Wi-Fi running is a very different specification to whole-home backup lasting through an extended storm outage, a real consideration across parts of the Blue Mountains, Southern Highlands and Central Coast.
If backup matters, we ask which specific circuits or appliances need to stay powered — fridge and freezer, medical equipment, a sump pump, home office equipment, or the whole house. This determines whether a partial "essential circuits" backup board is sufficient or whether whole-home backup is worth the additional cost.
If you own or plan to buy an EV, charging habits significantly change battery sizing. We ask about your current or planned EV charging pattern so the recommendation accounts for that extra load rather than being overwhelmed by it.
Finally, we ask how many hours (or days) of backup you'd ideally want during an outage, which — combined with your critical appliance list — lets us model realistic runtime rather than a theoretical maximum.
Your results include a recommended battery capacity in kWh, a shortlist of suitable products from our confirmed range configured for retrofit, and an estimate of your additional annual savings from increased self-consumption. Where an AC-coupled configuration is the better fit for an existing, healthy inverter, we'll specify that; if your existing inverter and system configuration would actually suit a DC-coupled hybrid option instead (sometimes worth considering during a broader upgrade), we'll flag that too rather than forcing a single pathway.
When you already have a working solar inverter, ripping it out to install a DC-coupled battery is usually unnecessary and adds cost without a proportional benefit. An AC-coupled retrofit connects independently to your switchboard, working alongside your existing solar inverter rather than replacing it. This keeps installation simpler, generally faster, and less disruptive — often completed in a single day. Our confirmed battery and hybrid range (Sigenergy, Goodwe, Fox ESS and Sungrow) gives us configurations to suit both retrofit and full-upgrade scenarios, and our consultants steer you to the right one honestly.
Retrofitting a battery in August 2026 is well-timed. The federal Cheaper Home Batteries Program discounts roughly 30% off the installed cost via STCs (around $272/kWh for the first 14kWh, tapering through 28kWh and beyond), and the NSW PDRS battery incentive adds a further $1,100–$1,500 upfront, stacking on top. From 1 July 2026 the PDRS battery incentive no longer requires existing solar to qualify — though since you're reading this page, you likely already have it.
(Figures current as of August 2026 — these incentives step down on a set schedule; confirm current values before quoting.)
Use the Battery-Only Calculator to find the right battery size for your existing solar system, or call 0421 458 217.
