What Battery Size Do I Need in Perth?
What battery size do I need? For many Perth homes, useful comparison points are around 9 kWh, 18 kWh and 27 kWh, but the right capacity depends on how much electricity you use after solar production falls, how much surplus solar is available to recharge the battery, your backup reserve and any future loads such as EV charging.
Australis Solar designs home battery systems around your Synergy bill, available usage data, existing solar, roof and shading, inverter, switchboard, battery location, blackout requirements and future energy plans rather than automatically quoting a standard battery package.
Modular battery storage allows capacity to be selected around the property rather than a single fixed package size. Final equipment is confirmed after the system assessment.
What Battery Size Do I Need? Compare the Main Starting Points
These capacities are comparison points, not fixed packages. Two Perth homes with the same annual electricity use can need very different battery sizes because the timing of consumption, solar exports, backup requirements and future loads are different.
Lower evening use
A useful starting point where grid imports after sunset are relatively modest and the household does not need a large energy reserve.
- Lower evening and overnight consumption
- Limited large loads after sunset
- Good daytime solar utilisation
- Modest backup-energy requirement
Regular family-home consumption
Often worth modelling where a home has consistent evening demand and enough solar production to recharge a larger usable storage capacity.
- Regular afternoon and evening usage
- Air conditioning or pool loads
- Greater overnight operating buffer
- More room for a backup reserve
Larger or more electrified homes
Worth considering where overnight imports are higher, an EV is likely to charge after sunset, or additional stored-energy reserve is important.
- Higher evening demand
- Future or existing EV charging
- Larger solar generation
- Greater desired battery reserve
High-consumption or backup-focused homes
Larger modular storage can make sense where the property's energy model genuinely supports it, particularly with large solar arrays, major loads or extended backup objectives.
- High household electricity use
- Large PV systems
- Substantial EV energy requirements
- Longer backup-runtime objectives
How We Calculate the Right Home Battery Size
Total daily electricity consumption is not automatically the battery size you need. Solar can supply daytime loads directly, while the battery is generally most useful when it covers electricity that would otherwise be imported after solar production falls.
Measure when you import power
We review your Synergy bill and available usage or monitoring data to understand afternoon, evening and overnight electricity imports rather than relying on the bill total alone.
Check available solar surplus
Panel capacity, roof orientation, shading, exports and seasonal production help establish how much energy is realistically available to recharge the battery.
Allow for reserve and winter
Energy intentionally reserved for a blackout is not normally available for everyday household consumption. Perth winter production also needs to be considered separately from summer.
Add future electrical loads
EV charging, electric hot water, induction cooking, pool equipment and additional air conditioning can materially change the appropriate storage capacity.
Backup, EV Charging and Winter Can Change the Battery Size
The battery must be assessed as part of the complete home energy system. Stored energy, inverter output, charging strategy and the loads you expect to operate all matter.
Battery capacity affects runtime
Kilowatt-hours describe how much usable energy is stored. More capacity can provide a larger overnight or blackout buffer, but only if that energy can be charged and productively used.
Inverter power affects what can run
A large battery does not automatically allow every appliance to operate at once. Air conditioners, ovens, pumps and EV chargers must remain within the power limits of the inverter and backup system.
Vehicle charging changes demand
Where practical, charging an EV directly from surplus daytime solar can reduce the stationary battery capacity required. Regular evening EV charging can create a reason to model larger storage.
Battery Capacity Is Not Limited to One Module Format
Australis Solar does not size every Perth home around a single battery brand. The appropriate platform depends on the existing inverter, required capacity, backup objective, available installation space, phase configuration and future EV or expansion plans.
Sigenergy SigenStor
A modular pathway that can combine solar, battery storage, energy management, compatible backup hardware and EV charging within the wider Sigenergy ecosystem.
- 9 kWh-class battery module available
- Modular storage architecture
- Gateway-based backup pathways
- EV charging integration options
Fronius Reserva
Fronius provides multiple Reserva battery capacities for compatible Fronius hybrid inverter systems, with parallel battery configurations available where the system design supports them.
- Approximately 6.3–15.8 kWh per tower
- Expandable architecture
- Compatible hybrid inverter required
- Backup depends on the complete design
BYD Battery-Box
BYD provides another modular battery pathway for compatible inverter systems, including configurations suited to higher-capacity residential storage.
- Multiple stack sizes
- Parallel configurations available
- Compatible inverter required
- System-specific backup capability
How WA Rebates and 2026 Requirements Affect Battery Size
Incentives can improve the economics of battery storage, but they should not determine the battery capacity by themselves. Start with the property's energy requirements, then confirm current eligibility for the proposed system.
WA Residential Battery Scheme
Eligible Synergy customers can currently receive a WA Government battery rebate of up to $1,300. VPP participation, supported equipment and other scheme requirements apply.
Read the Australis Solar WA rebate guide →Federal battery support
Under the current federal structure, the applicable STC factor is reduced for additional usable capacity above 14 kWh and again above 28 kWh. STCs can only be claimed on the first 50 kWh of usable capacity.
Federal Cheaper Home Batteries Program →Updated WA technical requirements
New and upgraded rooftop solar and household battery systems in the SWIS are subject to updated technical and commissioning requirements. The final network and export pathway depends on the proposed system and property.
Read the WA Solar Rules guide →Official information: WA Residential Battery Scheme  · Australian Government Cheaper Home Batteries Program
How Australis Solar Determines What Battery Size You Need
Australis Solar is a Perth-based, WA-owned solar company operating since 2008. We design, install and maintain custom solar, battery storage, blackout backup and EV charging systems around the property rather than forcing every customer into the same package.
Send your property information
Provide your address, recent Synergy bill, existing solar details and what you want the battery to achieve.
We review your energy profile
Usage, available interval data, solar production, exports and known future loads are assessed to establish the likely storage requirement.
We assess the property
The inverter, switchboard, supply, battery location, roof and solar system, backup requirements and practical installation constraints are reviewed.
We compare appropriate options
We compare capacity, inverter architecture, backup scope and expansion requirements before preparing the recommended system pathway.
Why Choose Australis Solar for Battery Sizing in Perth?
Designed around usage
Recommendations consider your Synergy information, solar production, exports, evening demand and future electrical loads.
In-house installation
Accredited in-house installers and licensed electricians support the installation, commissioning and handover process.
Integrated energy design
Solar panels, battery storage, inverter capacity, backup, switchboards and EV charging are considered as one home energy system.
Future planning
The design can account for future battery expansion, electrification and EV charging without automatically selling unnecessary capacity today.
Home Battery Size FAQs
These answers are useful starting points. The final battery capacity still depends on the property's energy use, solar production, inverter, backup requirements and charging strategy.
What battery size do I need for a Perth home?
For many Perth homes, 9 kWh, 18 kWh and 27 kWh are useful starting points, while higher-use or backup-focused properties may justify 36 kWh or more. The appropriate size depends on evening and overnight electricity use, available solar surplus, winter production, inverter capability, desired backup reserve and future loads such as EV charging.
Is a 9 kWh battery enough?
A battery around 9 kWh may be sufficient where evening and overnight grid imports are relatively low. It provides less operating buffer for homes with regular air conditioning, electric cooking, pool equipment, EV charging or a significant blackout reserve.
Is an 18 kWh battery enough for a Perth home?
An 18 kWh-class system is a useful capacity to model for homes with regular evening and overnight consumption and sufficient solar generation to recharge it. Whether it is too small or too large depends on the property's actual usage, solar surplus, backup reserve and future electrical loads.
What battery size do I need for whole-home backup?
There is no universal battery size for whole-home backup. Required capacity depends on the appliances that need to operate, their combined power demand, desired outage runtime, available solar during the outage and the battery reserve. Inverter output, phase configuration and backup hardware must also support those loads.
What battery size do I need if I have an EV?
It depends on how far the EV travels and when it is charged. Direct daytime charging from surplus solar can reduce the stationary battery capacity required. Homes that regularly charge an EV after sunset while also covering household evening use and backup reserve may benefit from larger storage.
Can I add a battery to my existing solar system?
Often, yes. The existing solar panels, inverter, meter, switchboard, phase configuration and network connection should be assessed first. Depending on the equipment, the solution may involve a compatible battery, an AC-coupled system, inverter replacement or a broader solar upgrade.
Does a larger battery receive a larger rebate?
Not indefinitely. The WA Residential Battery Scheme currently provides eligible Synergy customers with up to $1,300, subject to scheme requirements. Federal STC support also tapers for additional usable capacity above 14 kWh and 28 kWh, and STCs are limited to the first 50 kWh of usable battery capacity. Current eligibility should be confirmed when the system is quoted.
Find the Right Battery Size for Your Perth Home
Send Australis Solar your recent Synergy bill, existing solar details and information about your blackout and future EV requirements. We can assess the likely storage capacity, inverter compatibility, switchboard, charging strategy and installation requirements before recommending suitable options.
Final battery capacity, equipment compatibility, rebate eligibility, backup performance, network requirements and pricing are confirmed against the proposed installation.