What Size Home Battery Do I Need in Australia?

Choosing the right home battery is not simply a matter of buying the largest capacity you can afford. The right battery size depends on how much electricity your household uses when your solar panels are not producing, how much excess solar you have available to recharge the battery, your inverter capacity, whether you want blackout backup, and how your electricity use may change in the future.

For most households, the best starting point is therefore not the battery catalogue. It is your own electricity usage data.

The Australian Government makes the same point in its guidance for the Cheaper Home Batteries Program: bigger is not always better, and an oversized battery can deliver less benefit if your solar system or inverter cannot make effective use of it.

The Short Answer: Size the Battery Around the Energy You Want to Shift

A home battery stores excess electricity—usually rooftop solar during the day—so you can use it later when your solar generation falls.

That means the most useful question is not: “How much electricity does my house use in a day?”

It is: “How much electricity do I want the battery to supply when solar is unavailable?”

For many households, that means electricity used from late afternoon through the night and into the following morning.

Australia’s Solar Consumer Guide notes that average household electricity consumption can vary significantly, with Australian homes commonly using around 11–23kWh per day. But daily consumption alone is not enough to size a battery because when that energy is used matters just as much. Smart meter interval data gives a much clearer picture.

First, Understand kWh vs kW

Battery capacity — kWh

Kilowatt-hours tell you how much energy the battery can store.

Think of this as the size of a water tank.

A 10kWh battery can store roughly twice as much energy as a 5kWh battery.

Battery power — kW

Kilowatts tell you how quickly the battery can deliver electricity at any one time.

Think of this as the size of the pipe coming out of the tank.

This matters because a large-capacity battery does not necessarily mean it can run every appliance simultaneously.

For example, an induction cooktop, air conditioner, oven and EV charger running together may require much more instantaneous power than a battery inverter can supply, even if the battery still has plenty of stored energy.

The Australian Government therefore recommends considering both battery capacity and rated power output when choosing a system.

Step 1: Find Out How Much Electricity You Use After Solar Production Falls

Start with your electricity data.

Your electricity bill normally shows average daily consumption, but the best information comes from smart meter or interval data, which records when you actually use electricity throughout the day.

Energy.gov.au recommends using around 12 months of interval data where available because electricity consumption can change considerably between summer and winter.

Look particularly at electricity used:

• from late afternoon onwards
• overnight
• before solar production starts in the morning

Illustrative example

If a household uses 20kWh per day, but 9kWh occurs during daylight hours and 11kWh occurs after solar production falls, a battery sized around the evening and overnight load may be more relevant than matching the full 20kWh daily figure.

You should also allow for operating reserve and conversion losses rather than assuming every labelled kilowatt-hour will arrive at your appliances.

Energy.gov.au notes that usable battery capacity is normally lower than total rated capacity, and lithium-ion battery systems also lose some energy during charging and discharging.

Step 2: Check Whether Your Solar System Can Actually Recharge the Battery

This is one of the most commonly overlooked parts of battery sizing.

A large battery is not especially useful if there is rarely enough excess solar to charge it.

The Australian Government explicitly warns that a battery only makes sense when there is surplus electricity available to store and that a battery may provide limited value alongside a solar system that generates little excess electricity.

Example: solar surplus matters

If your home exports only 5kWh of excess solar on a typical day but you install 20kWh of battery capacity, much of that capacity may remain unused unless the battery is deliberately charged from the grid. A home exporting 15–20kWh during the middle of the day has much more energy available to refill a larger battery.

Before choosing a battery, check:

• solar system size
• daily solar generation
• household daytime consumption
• daily solar exports
• seasonal variation
• roof orientation and shading

The aim is to size solar generation, battery storage and household demand as one system, not as three unrelated products.

Step 3: Decide What You Actually Want the Battery to Do

Goal 1: Use more of your own solar

If your main goal is simply to store afternoon solar and use it during the evening, focus on your normal evening and overnight consumption. You may not need enough battery capacity to operate the entire home independently.

Goal 2: Reduce peak electricity purchases

If you are on a time-of-use tariff, a battery can potentially store cheaper solar electricity and supply your home during higher-priced periods. In this case, analyse how much electricity you normally consume during the expensive tariff window.

Goal 3: Blackout backup

If backup power is important, capacity alone is not enough.

Not every battery system automatically powers a house during an outage.

A system must be specifically designed and configured for backup, and it may provide power to the whole home, essential circuits only, selected appliances, or only one phase of a three-phase property, depending on system design.

A homeowner who only wants lights, fridge, internet and a few power outlets during an outage may require a very different system from someone expecting to operate large air conditioning, electric hot water, cooking, pumps and an EV charger for hours.

So, Do You Need a 10kWh or 20kWh Battery?

There is no universal answer, but the following examples show how the decision can be approached. These are illustrative scenarios, not system recommendations.

An EV Can Completely Change the Calculation

If you are planning to buy an EV, tell your battery designer before the system is sized.

An EV can add substantial electricity consumption to a household, but that does not automatically mean you need a much larger home battery.

If the vehicle is parked at home during the day, it may be more efficient to charge the EV directly from excess solar instead of sending energy from solar to the home battery and then to the EV. Every additional conversion involves some energy loss.

Likewise, smart charging may allow the EV to charge during lower-cost tariff periods.

The better question is therefore: When will the EV charge? rather than: How much electricity does the EV use?

Future electrification should also be considered when sizing solar and batteries. Energy.gov.au specifically highlights EVs, electric hot water, cooking, heating, pools and increased air-conditioning as factors that can materially increase future household electricity demand.

What About a Heat Pump Hot Water System?

The same principle applies.

Moving from gas or resistive electric hot water to a heat pump may change your household electricity profile.

But if the heat pump can run primarily during solar-producing hours, much of its consumption may be supplied directly by rooftop solar. That can be more efficient than using valuable battery capacity overnight.

Good battery sizing therefore includes load scheduling, not just capacity.

Appliances that can often be shifted towards daytime solar may include:

• heat pump hot water
• pool pumps
• dishwashers
• washing machines
• EV charging

Reducing evening demand can sometimes make a smaller battery more effective.

Don’t Ignore Your Inverter

Your battery must also work with your inverter and electrical connection.

If you are adding a battery to an existing solar system, an AC-coupled system is commonly used, allowing the existing solar inverter to remain while a separate battery inverter is added.

If solar and battery are being installed together, a hybrid inverter may be suitable.

Your installer should check:

• inverter compatibility
• charge/discharge power
• single-phase or three-phase supply
• network connection requirements
• backup capability
• future expansion

A larger battery cannot overcome an inverter that cannot charge or discharge it at the required rate.

How the 2026 Federal Battery Discount Affects Sizing

As of 9 September 2026, Australia’s Cheaper Home Batteries Program provides an upfront discount of around 30% on eligible small-scale battery installations.

Eligible systems can have nominal capacities from 5kWh to 100kWh, while STCs apply only to the first 50kWh of usable capacity.

Importantly, the support structure changed on 1 May 2026.

The STC factor now tapers by capacity:

• first 14kWh: 100% of the applicable STC factor
• capacity above 14kWh and up to 28kWh: 60%
• capacity above 28kWh and up to 50kWh: 15%

The Government says these changes are designed to keep support broadly around 30% across a range of battery sizes while reducing incentives for unnecessarily large systems.

Key takeaway

Do not size your battery around the maximum rebate. Size it around your energy needs. A larger subsidy-eligible system is not automatically a better investment.

Bigger Is Not Always Better

Oversizing a battery can create several problems. You may:

• pay for capacity that is rarely used
• struggle to fully recharge it from solar
• reduce the proportion of the battery cycled each day
• increase upfront cost without proportionate savings
• discover that inverter or network constraints limit its usefulness

The Australian Government specifically advises consumers to consider daily electricity use, solar output and inverter output when choosing capacity, noting that bigger is not always better.

But Undersizing Can Be a Problem Too

Choosing too little capacity can also be frustrating.

You may regularly empty the battery early in the evening and start importing expensive grid electricity again before the night is over.

This is particularly relevant for homes with:

• high evening air-conditioning demand
• all-electric cooking
• large families
• regular overnight EV charging
• frequent blackouts
• future electrification plans

The goal is not to buy the smallest battery possible. It is to buy the amount of storage you can regularly and usefully cycle.

The Best Number Comes From Your Own Data

There is no single “Australian household battery size”.

A household using 15kWh per day can sometimes benefit from a larger battery than one using 30kWh per day if the first household has heavy evening demand and plenty of daytime solar surplus.

Conversely, a high-use household may need less battery capacity than expected if major loads such as EV charging and hot water can be shifted into solar-producing hours.

The most reliable approach is:

1. obtain your interval electricity data;

2. identify evening and overnight consumption;

3. measure available solar surplus;

4. decide how much backup you actually need;

5. account for future electricity demand;

6. check inverter and electrical compatibility;

7. compare several system sizes on expected annual usage—not just advertised capacity.

Choosing a PowerBay Battery

Once you know roughly how much usable storage you need, the next step is comparing systems that fit your home’s electrical configuration, inverter and backup requirements.

PowerBay’s current residential range includes modular Solplanet low-voltage battery configurations such as 5.12kWh, 10.24kWh and 20.48kWh. Product availability, system compatibility and final usable capacity should always be confirmed against the current product page and datasheet before purchase.

A PowerBay installer or system designer should size the complete system against your actual electricity profile rather than recommending capacity based solely on household size.

Final Takeaway

The right home battery is the one that matches your real electricity pattern, not the largest battery your budget or rebate allows.

If you remember only five things, make them these:

1. Size around evening and overnight demand—not total daily consumption alone.

2. Make sure your solar system produces enough surplus energy to recharge the battery.

3. Check both kWh capacity and kW power output.

4. Decide what blackout backup you actually need.

5. Allow for future EVs and electrification, but do not oversize simply “just in case”.

A properly sized system should work regularly, charge reliably and solve a clearly defined energy problem.

Frequently Asked Questions

1.Is a 10kWh battery enough for a home?

It can be, but household size alone does not determine the answer. A 10kWh battery may suit a home that uses roughly that amount of electricity during evening and overnight periods and has enough solar surplus to recharge it regularly.

2.Is a 20kWh battery too big?

Not necessarily. Homes with high evening consumption, larger solar systems, electrification or greater backup requirements may make good use of 20kWh. The key question is whether the capacity will be regularly charged and discharged.

3.Should my battery equal my daily electricity use?

Usually not automatically. Your battery primarily needs to cover the electricity you want to shift from solar-producing hours to periods when solar is unavailable.

4.Does a bigger battery give me better blackout protection?

More capacity can provide longer runtime, but backup also depends on battery power output, inverter design, backup circuits and which appliances are connected.

5.Can I charge a home battery from the grid?

Many systems can technically do so depending on configuration, tariffs and retailer settings, but whether this makes financial sense depends on your electricity plan and battery operating strategy.

Not sure what battery size suits your home?Contact PowerBay for a solution!