How to Size Your Battery to Your Solar Panels

You've got solar panels on your roof. Now you want a battery.

The question is: what size batteries for your solar panel?

Too small, and your battery runs flat before midnight. Too large, and your panels can never reliably fill it, meaning you're paying for storage that sits idle.

The good news is that your existing PV system is the best starting point for working out your ideal solar battery size.

Your Solar System Size Is a Key Starting Point

The size of your solar panel system is one of the most useful numbers to start with, because it tells you how much surplus energy you'll typically have to store each day. But it isn't the only factor, and it doesn't set a hard ceiling.

A solar battery stores excess solar generation, but most batteries can also charge from the grid.

This is useful on time-of-use tariffs, where you can top up during cheap off-peak or solar-soak windows and use that energy during expensive peak periods. It also matters if you join a Virtual Power Plant (VPP).

That means the right battery size depends on several factors working together:

• Solar surplus: how much generation is left over after your daytime usage, across different seasons
• Your tariff: whether off-peak or free-power windows make grid charging worthwhile
• Your consumption: how much you use in the evening and overnight, and how that might change
• Inverter capability: how fast your inverter can charge and discharge the battery, and whether it supports grid charging

If your battery relies on solar alone, pairing a large battery with a small array means it will rarely fill up. That reduces its value and your return on investment. If your tariff and inverter allow cost-effective grid charging, a larger battery relative to your system size can still make financial sense.

How to calculate solar battery size based on your solar system?

There is no fixed ratio between solar panel size and battery capacity. The right size depends on two numbers: how much surplus solar you export on a typical day, and how much power you use overnight. Your inverter app or retailer portal will show both.

Check your numbers in winter as well as summer, and allow for backup needs or future changes like an EV or heat pump. An accredited installer can confirm the size using your actual data.

Then Factor In Your Nighttime Usage

The Quick Way: Estimate From Your Bill

Once you know your system size, nighttime usage is the next number to nail down.

Your panels cover the day.

Whatever you draw from the grid between sunset and the following morning is what the battery needs to replace.

Check your electricity bill for your daily kWh average, then estimate how much of that falls outside daylight hours.

18kWh/day household average estimates:

• 7-9kWh nighttime demand
• Battery with 8-10kWh range for basic coverage

For households where most people are out during the day, roughly 40-50% of daily consumption happens overnight.

On an 18 kWh/day average, that's around 7-9 kWh of nighttime demand, pointing to a battery in the 8-10 kWh range for basic overnight coverage. If you run high-draw appliances in the evening, including ducted air conditioning, an EV charger, or electric water heating, that figure climbs quickly.

For many people, this estimate is enough to start a useful conversation with an installer. If you'd rather nail the number down more precisely before that conversation, the next section shows you how.

The Detailed Way: Calculate Your Evening Load Appliance by Appliance

If you want a more accurate figure than a bill estimate can give you, it's worth going through your evening appliance use step by step. This is especially useful if your usage pattern is irregular, or if you run high-draw appliances that can skew a simple percentage estimate.

Step 1: Find the Wattage of Each Appliance

Every appliance you use after dark has a wattage. Many have it printed directly on the unit. If yours only shows volts and amps, the calculation is simple:

Watts = Volts x Amps

So an appliance rated at 240V and 5A draws 1,200 watts. Once you have the wattage for each device, you have everything you need.

Step 2: Multiply by Hours of Use

For each appliance, multiply its wattage by how many hours you run it in a typical evening.

A few examples:

• 10 LED downlights at 10W each = 100W total. Run for 4 hours = 400 Wh
• A 200W TV (60 inch LCD) running for 3 hours = 600 Wh
• A 2,400W split system air conditioner running 2 hours (but only cycling about 50% of that time) = 2,400 Wh

Add these up to get your total watt-hours (Wh) of evening demand.

Divide by 1,000 to convert to kilowatt-hours (kWh), which is how battery capacity is measured.

A quick note on appliances that cycle on and off, like fridges, air conditioners, and pool pumps: they don't run at full draw continuously. As a rule of thumb, count them at roughly 50% of their rated wattage over the hours they're switched on. It's better to overestimate slightly than to run short.

Step 3: Add a Buffer

Once you have your evening total, add around 20% on top as a buffer because real-world usage is never perfectly predictable. For example, a cold night might mean the heater runs longer. A guest staying over adds load you didn't account for. Building in headroom also protects your battery from running to empty regularly, which extends its lifespan.

So if your evening calculation comes out at 8kWh, you're looking at a target solar battery size of around 9.5-10 kWh.

Battery Sizing by PV System Size

Here's how solar battery size recommendations land for the most common residential solar systems in Australia.

What Size Battery for a 5 kW Solar System?

A 5 kW system typically produces 17-22 kWh per day depending on location and orientation. Most households on this system size will find a battery in the 10-13.5 kWh range to be the right fit.

• If you self-consume around 50% of production during the day, ~10 kWh works well. Alpha T10 or Alpha G3 both offer great options in 10kWh capacity.
• If most of your output is being exported back to the grid, a 13.5 kWh battery captures more of that surplus. The Tesla Powerwall 3 (or Alpha ESS Smile 13.3 with 13.3kWh capacity) is a great match.

Compare All Batteries →

Our 10 - 13.5kWh battery range

• Alpha ESS T10 (10kWh)
• Sigenergy SigenStor 5.0 (10kWh with 2 modules)
• Anker Solix X1 (10kWh with 2 modules)
• Growatt ALP LV (10kWh with 2 modules)
• Alpha G3 (10.1kWh)
• Ambrion Raybox HS2 (10.24kWh)
• Alpha B3 Plus (10.08kWh with 2 modules)
• Alpha ESS Smile 13.3 (13.3kWh)
• Tesla Powerwall 3 (13.5kWh)

Learn more about being a 10kWh battery owner: 10kWh Battery Buying Guide

What Size Battery for a 6.6 kW Solar System?

The 6.6 kW system is one of the most common setups in Australia. It pairs well with batteries in the 10-15 kWh range for financial returns, or up to 16-20 kWh if energy independence is the priority.

For our range of 10 - 13.5kWh solar batteries, see above.

Compare All Batteries →

Our 14 - 20kWh battery range

• Fox ESS EQ4800 (13.98kWh in 3 modules)
• Sigenergy SigenStor 5.0 (15kWh in 3 modules, or 20kWh in 4 modules)
• Sigenergy SigenStor 8.0 (16kWh in 2 modules)
• Anker Solix X1 (15kWh in 3 modules, or 20kWh in 4 modules)
• Growatt ALP LV (15kWh in 3 modules, or 20kWh in 4 modules)
• Alpha ESS B3 Plus (15.12kWh in 3 modules, or 20.16kWh in 4 modules)
• Alpha ESS T10 (20.2kWh in 2 modules)
• Alpha G3 (20.2kWh in 2 modules)
• Ambrion Raybox HS2 (20.48kWh in 2 modules)
• Eveready Energy Vault (20.4kWh)

Learn more about what to expect with owning a bigger battery:

• 14kWh Battery Buying Guide
• 16kWh Battery Buying Guide
• The Federal Rebate's New Tiered System Come May 2026

What Size Battery for a 10 kW Solar System?

A 10 kW system suits higher-consumption households using 25-30+ kWh per day. Recommended battery sizes:

• For financial returns: 18-23 kWh
• For energy independence: 40 kWh+ (around 1.5 days of autonomy)

Compare All Batteries →

For our range of 18 - 20kWh solar batteries, see above.

Find 24 - 30kWh solar batteries listed below.

What Size Battery for a 13 kW Solar System?

A 13 kW system is typically found on larger homes or all-electric households. Solar battery bank sizes in the 24-50 kWh range are appropriate, with the upper end suited to households running EVs, ducted air con, and other high-draw loads.

Compare All Batteries →

Our 24 - 30kWh battery range

• Fox ESS EQ4800 (23.3kWh with 5 modules, or 27.96kWh with 6 modules)
• Alpha ESS B3 Plus (25.2kWh with 5 modules, or 30.24kWh with 6 modules)
• Anker Solix X1 (25kWh with 5 modules, or 30kWh with 6 modules)
• Sigenergy SigenStor 5.0 (25kWh with 5 modules, or 30kWh with 6 modules)
• Sigenergy SigenStor 8.0 (24kWh with 3 modules, or 32kWh with 4 modules)
• Tesla Powerwall 3 (27kWh with one expansion pack)
• Growatt ALP LV (30kWh with 6 modules)
• Alpha ESS T10 (30.3kWh with 3 modules)
• Alpha G3 (30.3kWh with 3 modules)

Our 35 - 50kWh battery range

• Alpha ESS Smile 13.3 (39.9kWh with 3 modules, or 53.2kWh with 4 modules)
• Fox ESS EQ4800 (41.93kWh with 9 modules)
• Alpha ESS T10 (40kWh with 4 modules, or 50kWh with 5 modules)
• Growatt ALP LV (40kWh with 8 modules)
• Sigenergy SigenStor 8.0 (40kWh with 5 modules, or 48kWh with 6 modules)
• Tesla Powerwall 3 (40.5kWh with 3 modules, or 54kWh with 4 modules)
• Alpha G3 (40.4kWh with 4 modules, or 50.5kWh with 5 modules)

Solar Battery Sizes Chart

So you can get an understanding of general solar battery sizing recommendations at a glance.

Daily Usage	PV System	Battery for Returns	Battery for Independence
10-12 kWh/day	5 kW	10 kWh	13.5 kWh
14-18 kWh/day	6.6 kW	10-13 kWh	16-20 kWh
20-25 kWh/day	10 kW	15-18 kWh	32-40 kWh
26-35 kWh/day	13 kW	20-23 kWh	40-50 kWh

These are indicative figures based on north-facing panels at a 30° tilt. Your installer should model your specific roof orientation, location, and usage profile.

Compare All Batteries →

Find My Fit

What You Want From the Battery Also Matters

Most people adding a battery to an existing solar system are after one of three things, and each shifts the sizing differently.

To maximise solar savings: Size to what the solar system can reliably fill at least 60% of days. Smaller batteries tend to deliver better payback periods. Expecting to buy some grid electricity at certain times of year is normal and financially sensible.

For greater energy independence: You'll size larger than what's optimal purely for returns, accepting a longer payback in exchange for more autonomy. This makes the most sense in areas with unreliable grid supply or expensive peak tariffs.

For backup power: If you want to cover multi-day outages, you'll need significantly more capacity. Three days of autonomy is a good baseline for genuine resilience; five days is considered strong off-grid readiness. Bear in mind that systems designed for this purpose will have considerably longer payback periods.

Learn more about blackout protection.

Otherwise? Get What You Can Afford Now, Then Scale Up

If your ideal battery size is out of budget right now, that's okay. Start with what you can afford and choose a modular battery system such as Alpha ESS, Sigenergy or Fox ESS, which allow you to add capacity over time. Even a smaller battery that covers part of your evening load is delivering real savings from day one.

What you want to avoid is buying a closed, fixed-capacity system that can't be expanded, and then finding yourself locked out of growth later.

One important caveat: the federal Cheaper Home Batteries Program rebate can only be claimed once per property or premises.

Important Note: This also applies to properties you buy, rent or inherit. If a solar battery has claimed STCs with an installation at a dwelling, you won't be able to use the rebate to add on another battery.

This means if you undersize significantly now, any future capacity upgrade won't attract the same discount. If your budget allows you to get close to your target size from the start, that's the better financial move.

Where possible, also size slightly ahead of your current needs.

For instance, many people are considering electric vehicles to reduce their fuel and maintenance costs. However, an EV can also increase a household's energy use (and therefore bill) by around 30-50%.

A pool pump, additional air conditioning, or a growing household will also push demand up over time. That little headroom now can help save money in the long term, over retrofitting new equipment onto your existing system later.

Should You Add More Solar Panels at the Same Time?

Of course, if your existing system is undersized relative to your consumption, you might also want to add panels to improve your whole setup.

More generation means more energy available for your home and to fill up the battery each day.

Consider adding panels if:

• Your system regularly generates less than you consume during the day
• Your roof has available space and suitable orientation
• You're adding an EV or other high-draw appliance

What Does a Solar Battery Cost in Australia per kWh?

With the federal Cheaper Home Batteries Program in effect from 1 July 2025, upfront battery costs have dropped considerably.

• Pre-rebate pricing for lithium-ion systems (including inverter, software, and installation) has historically been around $850-$1,000+ per kWh
• The rebate is capped at approximately $244 per kWh of usable capacity up to 14 kWh from May 1 2026 with a reduced rate for every kWh after that, before admin fees (or around $335 per kWh and $300 after admin fees, before the May deadline)
• This represents an estimated 30% reduction in upfront installation cost
• A typical 10 kWh battery added to an existing system will come in around $7,000-$13,500; a 13.5 kWh battery sits around $9,500-$15,500 (after the rebate)
• Adding to an existing system costs a little more than buying new panels and a battery together

Key rebate eligibility requirements:

• Minimum 5 kWh usable capacity
• CEC-approved battery and inverter, installed by an accredited installer
• Must have VPP (Virtual Power Plant) capability, though joining a VPP is optional
• Can only be claimed once per property, so size carefully from the start

The Clean Energy Regulator now lets you get an estimate on the STCs (small-scale technology certificates) your installation may produce, which influences how much of the rebate you get to tap into. It's based on your location, how much usable battery capacity you are installing, and the date you have it installed.

STCs are what installers apply for, create, and sell on a marketplace to liable electricity retailers and wholesale electricity purchasers, who are obligated to buy and surrender a volume proportional to what they sell to customers.

This way, installers handle the paperwork, and you get an upfront discount when you install.

STCs Are for Both Solar Panels and Batteries

Solar PV systems (panels and inverter) and solar batteries are both listed as eligible small-scale renewable energy systems under the Small-scale Renewable Energy Scheme, part of the national Renewable Energy Target.

That means a new solar and battery install can create small-scale technology certificates (STCs) for both parts of the system. Your installer creates and sells those certificates, and you get the value as an upfront discount. No paperwork on your end.

• Solar panels: the number of STCs depends on system size, your postcode's sunshine zone and how many years are left until the scheme ends in 2030. A 6.6 kW system typically earns around $1,500 - $2,000 in STC value.
• Batteries: under the Cheaper Home Batteries Program, eligible batteries earn STCs per kWh of usable capacity, worth roughly 30% off the upfront cost.

Solar + Battery Costs by System Size

Buying panels and a battery together is generally cheaper than adding a battery to an existing system later, because the inverter, design work and labour are shared across one job.

System	Indicative installed price (after federal rebates)	Best suited to
6.6 kW solar + 6 kWh battery	$10,900 - $14,900	Smaller households, lighter evening use
6.6 kW solar + 10 kWh battery	$12,000 - $19,000 (mid-range: ~$15,000 - $18,000)	Typical 3-4 bedroom family home
8 kW solar + 13.5 kWh battery	$14,000 - $20,000	Larger families, higher evening use
10 kW solar + 13.5 kWh battery	$18,000 - $25,000	High-use homes, pools, home EV charging
10 kW solar + 14 kWh battery	$18,500 - $25,500	As above, maximising the full-rate rebate
10 kW solar + 15 kWh battery	$19,500 - $27,000	High-use homes wanting more overnight coverage
10 kW solar + 20 kWh battery	$23,000 - $30,000	All-electric homes, energy independence

Why 14 kWh Is Worth a Look on a 10 kW System

Since 1 May 2026, the federal battery rebate pays its full rate only on the first 14 kWh of usable capacity. Every kWh above that earns 60% of the full rate, up to 28 kWh.

That means a 14 kWh battery captures the most rebate per kWh. Going from 13.5 to 14 kWh adds full-rate rebate, while going from 14 to 15 kWh adds capacity at a reduced discount. It's still worth it if your nighttime usage needs it, but it's a sizing decision worth making deliberately.

Cost of Solar Battery Storage Only, by Size

A 10 kWh battery added to an existing solar system typically comes in around $8,000 to $10,000 after the federal rebate, with the wider market ranging from about $7,500 to $13,500.

Usable capacity	Indicative installed price (after federal rebate)	Typical fit
5 kWh	$4,500 - $7,500	Light evening use, entry-level storage
10 kWh	$7,500 - $13,500	Most 5-6.6 kW systems
13.5 kWh	$9,500 - $15,500	6.6 kW systems with higher evening use
15 kWh	$11,000 - $17,000	6.6-10 kW systems
20 kWh	$14,000 - $22,000	10 kW+ systems, all-electric homes

Bigger batteries usually cost less per kWh. Installation labour is roughly the same whether it's a 5 kWh or 15 kWh unit, so the fixed costs are spread across more storage.

How your existing solar is set up also matters:

• Hybrid inverter already installed: the battery can often connect directly (DC-coupled), which is usually $1,000 - $2,000 cheaper.
• Standard string inverter: the battery will need its own inverter (AC-coupled), which typically adds around $3,000 to the job.

Sizing a smaller system? Our 5kWh Solar Battery Buying Guide covers the entry point into storage in detail.

Cost of Solar Panels Only (After Federal Rebates)

A 6.6 kW solar-only system, the most popular size in Australia, typically costs $4,000 to $8,500 installed after STCs.

System size	Approx. panels	Indicative price (after STCs)	Best suited to
5 kW	12-17	$3,500 - $7,000	Small households, low daytime use
6.6 kW	16-20	$4,000 - $8,500	Standard 3-4 bedroom family home
8 kW	19-24	$6,000 - $10,500	Larger families, higher use
10 kW	24-30	$6,500 - $12,000	Pools, EV chargers, heavy daytime loads

Prices vary by state. Perth, for example, tends to sit at the lower end, while regional and remote areas can pay 5-15% more for the same install.

If you're planning a battery, keep in mind that a solar-only system with a standard string inverter will usually need a separate battery inverter later. Choosing a hybrid inverter now can make adding a battery cheaper down the track.

What Your Quote Is Actually Paying For

Two quotes for what looks like the same system can be thousands of dollars apart. Here's where the money goes.

Equipment. Panels, the battery and the inverter make up the bulk of the cost. Premium brands can cost 20-40% more than mainstream alternatives, usually for better warranties, software or efficiency. On a combined install, solar tends to account for roughly half to 60% of the total, with the battery making up the rest.

Your roof. A single-storey home with a simple, north-facing tin roof is the cheapest to work on. Tiled roofs, steep pitches and multi-storey access all add time and safety equipment.

Installation complexity. Long cable runs from the switchboard, three-phase power, split arrays across different roof faces and export-limit hardware can each add hundreds to thousands of dollars.

Inverter requirements. A hybrid inverter manages both panels and battery in one unit. If your existing system uses a standard inverter, you'll need a separate battery inverter, which adds to the bill.

Rebates. Federal STCs for both solar and batteries come off the price upfront. The value depends on your location, system size, battery capacity and the date of installation, so two otherwise identical systems installed months apart can end up with different prices.

State Programs That May Also Help

On top of federal rebates, some states offer extra support, such as interest-free loans, state battery incentives or upfront payments for joining a Virtual Power Plant (VPP). Availability changes often and some programs run in limited rounds, so check your state's current offer:

• NSW
• VIC
• QLD
• SA
• WA
• TAS

Our state-by-state guide to home battery rebates in Australia sets out what is currently on offer in each state and territory.

Things That Can Push the Price Up

A few site-specific extras can add anywhere from a few hundred dollars to a couple of thousand on top of the package price.

Switchboard upgrades. Older homes often have switchboards that aren't up to current standards for solar and battery systems. Bringing one up to scratch typically costs around $800 to $2,000.

Roof complexity. Steep tiled roofs, multi-storey homes and roofs with limited flat space make installation harder. Split-array designs, where panels are spread across more than one roof face, also add labour and cabling.

Blackout protection. Most modern solar batteries are capable of backup power, but using that feature takes extra electrical work and components, such as setting up dedicated backup circuits. If you want your battery to keep the lights on during an outage, expect an additional cost. Learn more about blackout protection.

Feed-in Tariffs vs Using Your Own Solar

A battery earns its keep by letting you use more of your own solar instead of selling it cheaply to the grid.

Feed-in tariffs across Australia have dropped to around 4-7 cents per kWh in many areas, while buying power back from the grid at night can cost 35 to 48 cents per kWh or more. Every kWh you store and use yourself is worth several times more than one you export.

That gap is the main reason a solar and battery package can pay for itself, and why sizing the battery to your actual evening usage matters so much.

Takeaways for Your Ideal Battery Fit

By now, you should know how to work out what size solar battery you need.

Your PV system size, your evening usage, and your goals are the three things that determine your ideal battery size. Get those right, and the rest follows.

• Start with your solar system size to set the upper limit on battery capacity
• Estimate from your bill for a quick starting figure, or calculate appliance by appliance for precision
• Add a 20% buffer either way, then cross-check against your system size
• Let your goals (savings, independence, or backup) determine where in that range you land
• Think ahead so you don't need a costly upgrade outside the rebate window
• Start with what you can afford if budget is tight, but choose a system you can expand

Want a Personalised Recommendation?

Get a recommendation for a battery sized to your existing solar system, with an estimate on how much you can be saving based on your actual usage.

Find My Fit

FAQ

Would it be better to install solar panels and battery together, or add a battery later?

Installing solar and a battery at the same time is usually the cheaper option overall. You pay for one site visit, one design, and a single hybrid inverter instead of two separate pieces of equipment.

Retrofitting a battery later will cost a bit more. That said, waiting can still make sense if the budget isn't there yet, especially as battery prices keep falling. Just remember two catches:

• The federal battery rebate steps down every six months, so a cheaper battery later may come with a smaller discount.
• The rebate can only be claimed once per property, so a small battery now could mean a future expansion misses out on the full discount.

If you're likely to want more storage later, a modular battery that you can expand over time is a good middle ground.

How does the federal battery rebate work in 2026?

From 1 May to 31 December 2026, batteries earn 6.8 STCs per usable kWh. At typical certificate prices, that's roughly $245 - $270 per kWh, or about $2,500 off a 10 kWh battery.

The rebate is tiered by battery size:

• First 14 kWh: full rate
• 14 to 28 kWh: 60% of the full rate
• 28 to 50 kWh: 15% of the full rate

The rebate also steps down every six months as battery prices fall:

Installation period	STCs per usable kWh (first 14 kWh)
May - Dec 2026	6.8
Jan - Jun 2027	5.7
Jul - Dec 2027	5.2

The solar STC discount also shrinks each January, as there's one less year left in the scheme. In short, a system installed in December 2026 attracts more rebate than the same system installed in January 2027.

To see how rebates affect your break-even point, try our solar payback period calculator guide.