Adding battery storage means picking a battery inverter, and for most Australian homes that comes down to 10kW or 15kW. The answer is set by your array size, your evening load, and whether you want the whole house running in a blackout or just the fridge.
If you are adding batteries to an existing system, our Complete Guide covers that side of it.
What is a Battery Inverter and Why is Size Important?
The battery inverter runs your Solar Battery system. Three jobs:
- Converts DC to AC: Solar panels and batteries produce DC. Your house runs on AC. The inverter does the conversion.
- Manages Battery Charging/Discharging: It decides when the battery takes charge from the solar panels and when it releases it.
- Grid Interaction: It moves power between the array, the battery, the grid and the house.
Size it too small and you cannot draw on stored energy fast enough to cover your evening peak. Size it too big and you have paid for capacity that never gets used.
Key Factors to Consider:
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Solar Panel Array Size:
Start here. What the array generates sets the ceiling on what the battery can absorb.
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Household Energy Consumption:
Your daily kWh and, more importantly, when you use it.
- Low Energy Consumption: A 10kW inverter covers a typical household comfortably.
- High Energy Consumption: Ducted air conditioning, a pool pump and a couple of large appliances running together will push past 10kW. That is where 15kW earns its price.
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Self-Consumption Goals:
Self-consumption means using your own generation rather than exporting it. In Australia the gap between what you are paid to export and what you pay to import is wide, which is the entire financial case for a battery.
- Higher Self-Consumption: A bigger bank and a 15kW inverter store more of the midday surplus for the evening. Only worth it if you actually generate that surplus.
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Backup Power Needs:
Decide how much of the house you want alive during an outage.
- Essential Loads Backup: 10kW runs lights, fridges and general power points.
- Whole-Home Backup: Air conditioning and an electric stove need 15kW. A 10kW unit will trip trying to start them.
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Future Energy Needs:
An EV charger, a pool or a heat pump added later all land on this inverter. Inverters are not cheap to swap, so size for the house you will have in five years.
How to Estimate Your Self-Consumption Ratio
Self-consumption ratio is the share of your generation you use yourself. Above 30% is a reasonable starting point, and a battery is what lifts it.
These are estimates. Your location and roof orientation will move them.
Financial Considerations
The 15kW unit costs more upfront and only pays back if you have the array to fill it and the evening load to draw on it. Buying capacity you cannot feed is the most common oversizing mistake.
The Importance of Professional Advice
Get an installer to look at your actual interval data rather than an estimate. Your retailer can supply it, and it settles the sizing question in a way no rule of thumb will.
Conclusion
Array size and backup expectations decide this. A 10kW array with essential-loads backup takes the 10kW inverter. A 13kW-plus array, heavy evening use, or whole-home backup takes the 15kW. Match the inverter to what your Solar Battery system actually has to move.