You’ve already got solar, or you’re about to, and now you’re wondering if a battery makes sense.
You start Googling. Or worse, you talk to three different installers and get three different recommendations. It’s confusing. And honestly, kind of exhausting.
You’re not looking to become an energy expert. You want a clear, no-nonsense way to figure out: what size battery will work for my home?
Here’s the good news: it’s not complicated once you know what to look at. Fortunately, your friends at PSC Energy are here to help guide you through this choice. You don’t need to decode a dozen quotes or memorise technical specs.
In this article, you’ll learn about the following:
- Step 1: Check Your Nighttime Energy Use
- Step 2: Estimate Your Solar Energy Surplus
- Understanding Seasonal Variations in Solar Energy Surplus
- Step 3: Think About Future Use for Your Solar Battery
- Choosing Between Modular and Non-Modular Solar Battery Systems
- Step 4: Know Your Load Types
- Planning for Future Energy Needs
By the end of this guide, you’ll learn how to calculate the correct battery size for your home, based on your real-world energy habits.
Step 1: Check Your Nighttime Energy Use
Start here. This is the number that usually matters most when it comes to choosing your battery size.
Grab your latest electricity bill. You’re looking for your average daily usage. It’s listed in kilowatt-hours (kWh). If the bill gives you a total for the quarter, just divide it by the number of days in the billing period. That’s your baseline.
But here’s the part that most people miss: Not all your daily usage happens when the sun is down.
Think about your routine. If you’re out of the house during the day (work, school runs, errands), then a big chunk of your energy use is probably happening at night. That’s when you cook dinner, run the heating or aircon, turn on lights, and settle in to binge-watch something.
Here’s a quick example:
- Daily usage: 20 kWh
- You’re out during the day
- Nighttime usage estimate: 10–14 kWh
That’s the target range for your battery size: the amount you’ll want stored up to keep your home running from sunset to sunrise without relying on the grid.
This is the number to beat if you aim to reduce evening grid use or keep the lights on during an outage. We know it’s just a rough estimate, but you need estimates until you can precisely pinpoint your needs.
If you’re interested in learning more about solar systems, you might want to check out our introductory article titled, New to Solar: Start Here.
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Step 2: Estimate Your Solar Energy Surplus
Now that you’ve got an idea of how much energy you need at night, the next question is: do you have enough spare solar to charge your battery in the first place?
Here’s the thing most installers won’t tell you upfront: Your battery is only as useful as your solar surplus. This is the leftover energy your panels generate after your home has used what it needs during the day.
Let’s break it down with an example:
- Your solar system generates: 25 kWh per day
- Your use during the day: 10 kWh
- Solar surplus: 15 kWh
That 15kWh is what’s available to store in your battery.
But what if your solar doesn’t produce much? Say:
- Solar generation: 25 kWh
- Daytime usage: 22 kWh
- Surplus: just 3 kWh
That’s not enough to fill even a small battery, which means you’d be paying for capacity you can’t use.
This is where people over-invest. They get sold on a big battery without realising they don’t have enough solar to fill it.
Here’s the rule of thumb we recommend at PSC Energy: your battery’s kilowatt hours (kWh) should be about double the number of kilowatts (kW) coming from the solar panels on the roof.
Real-world example:
- Daily usage: 20 kWh
- Solar generation: 25 kWh
- Daytime usage: 10 kWh
- Surplus: 15 kWh
- Nighttime usage: 10 kWh
- Ideal battery size: 10 to 13.5 kWh
That’s the sweet spot. It’s big enough to cover your needs, but not so big that you’re wasting money on storage you’ll never fill.
If you’re interested in learning a bit more about the benefits of solar batteries, you might want to start with the following article titled, 7 Benefits of Adding a Battery to Your Solar System.
Let’s talk solar savings. click here.
Understanding Seasonal Variations in Solar Energy Surplus
The amount of solar energy your system produces will not stay the same all year. It changes with the seasons. In summer, the days are longer, and the sun is higher in the sky, so your panels can generate more electricity.
In winter, daylight hours are shorter, and the sun sits lower, so your solar production naturally drops. This is even more dramatic if your panels get shaded or if your roof doesn’t face the ideal direction.
Other factors can also play a role. Trees that lose their leaves in winter might not shade your panels then, but in summer, leaves could block part of your system.
To properly understand how much surplus energy you have, track your solar output across a full 12 months. Many inverter apps do this for you. With a full year of data, you can see when your system produces more than you use and falls short. This insight can help you size your battery more accurately. You’ll be able to plan for storage that covers your needs during low-production months, without overspending on capacity you won’t use in summer.
Understanding your seasonal ups and downs is one of the smartest ways to make sure your battery works well for you all year round, not just on the sunniest days.
If you’re interested in learning a bit more about which way to point your solar panels, you might want to check out the following article titled, Which Way Should Solar Panels Face in Australia?
Ready to go solar? click here.
Step 3: Think About Future Use for Your Solar Battery
Right now, your battery size might seem straightforward. But what about next year? Or five years from now?
Energy usage doesn’t stay the same forever, and if you’re already thinking long-term with solar and batteries, it makes sense to plan ahead.
Here’s what often changes:
- You buy an electric vehicle, and suddenly you’re charging at home.
- You start working remotely a few days a week.
- Your kids get older and start leaving the aircon running all afternoon.
- You install a pool pump or upgrade appliances.
Each of these adds a little more pressure to your energy system, and if your battery’s already at its limit, you might find yourself pulling from the grid again sooner than expected.
That’s why it’s smart to ask:
“Can this battery grow with me?”
Some battery systems are modular; you can add extra storage later if your needs change. Others aren’t. You’d have to replace the whole setup to upgrade, which can cost thousands.
So even if you’re starting small, look for a system that gives you room to grow.
Here’s a tip: When speaking with your installer, ask: “Can I add more storage later without replacing the whole system?”
If they can’t give you a straight answer, that’s a red flag.
Flexibility matters, especially if your lifestyle is in flux or you’re making this decision as a long-term investment.
If you’d like to learn a bit more about our aftercare, you might want to check out the following article titled, Penrith Solar Centre’s Service Department Safeguards the Future of Your System.
Choosing Between Modular and Non-Modular Solar Battery Systems
Not all solar batteries are built the same, and one of the biggest differences is whether the system is modular or non-modular.
A modular battery system is designed to grow with you. You can add more battery units over time as your energy needs increase. This gives you flexibility. If you get an electric vehicle in a few years or start using more energy at night, you can add more storage without changing the whole setup.
A non-modular battery, on the other hand, is a fixed-size system. If you want more storage down the line, you usually need to replace the entire system or add a second, separate one, and that can be expensive and complicated. For many households, this kind of setup works fine, especially if your energy usage is steady and not likely to change much.
But if you expect your energy needs to grow, it’s worth thinking ahead. Modular batteries give you options later. They also make it easier to start small if your budget is tight now. You can always expand when you’re ready.
If you’d like to learn a bit more about modular batteries, you might want to check out the following article titled, Sigenergy SigenStor Quietly Becomes Australia’s Top Solar Battery Brand.
Let’s go solar today. Click here.
Step 4: Know Your Load Types
So far, we’ve talked about how much energy you use. But another layer to this is how your appliances use that energy.
Not all devices draw power in the same way. And if you plan to use your battery for blackout protection or to run high-load appliances, it’s crucial to understand this.
Here’s a quick breakdown:
Appliance Power Draw Usage Pattern
Fridge: low, continuous, always on
Oven: high, short bursts, occasionally used
Ducted Aircon: high, sustained, seasonal, hours at a time
Pool Pump: medium, daily, fixed schedule
EV Charger: very high, variable, often overnight
Why does this matter?
Because your battery has two limits:
- Capacity – how much energy it can store
- Discharge rate – how quickly it can release that energy
So even if your battery can run your aircon for three hours, it might not be able to discharge fast enough to handle it in real time.
This is especially important if your main goal is blackout protection. You don’t want to assume your whole house will stay online, only to find that your oven and aircon are too much for the battery to handle.
Look at:
- Which appliances matter most to you during a blackout?
- What is their power draw?.
- How much battery would you need to keep those specific loads running?
This turns your battery plan from a rough estimate into a tailored setup that won’t let you down when you need it most.
If you’re interested in learning a bit more about the process of choosing components for your solar system, you might want to check out the following article titled, How to Shop for a Solar System.
Planning for Future Energy Needs
Your energy use today might not be the same as in two or three years. That’s why it’s important to consider your future plans before choosing a battery size.
- Are you thinking about buying an electric vehicle?
- Do you plan to install a pool, add ducted air conditioning, or switch to an electric hot water system?
- Maybe you’re planning to work from home more often.
These changes will increase the amount of electricity you use, especially in the evening, when a battery would help most.
Talk to your installer about where your energy use might go. Ask them how easy it would be to upgrade your battery system if your needs change. Find out if the system they recommend supports expansion or if you’d be locked into one size.
It also helps to make a rough plan. Think about the next three to five years. Are there any big purchases or life changes on the horizon that could impact your usage? Even if you’re not sure yet, it’s better to remember future needs rather than getting stuck with a system that falls short later.
Choosing a battery isn’t just about what works right now. It’s about making sure your system keeps working for you as your life evolves. When you plan for future growth, you give yourself more flexibility and fewer regrets.
If you’re interested in learning a bit more about the NSW solar battery rebate, you might want to check out the following article titled, Everything You Need to Know About the Home Battery Rebate for NSW.
Final Thoughts: Choose the Best Fit for Your Solar Battery
Here’s the truth most battery marketing glosses over:
A bigger battery isn’t always better. A battery that’s too big for your solar system won’t fill. One that’s too small for your nighttime needs won’t give you the savings or backup you’re hoping for.
The smart move is to size your battery based on fit, not just features.
To recap:
- Start with your nighttime usage. That’s the load your battery will likely need to cover.
- Then check your solar surplus. That’s how much charge you can realistically store each day.
- Size your battery to the smaller number. It’s the only way to make sure it performs the way you expect.
- Think about future usage. If life might change, choose a system that can scale with you.
- Understand your appliance loads. If backup power matters, make sure your battery can handle your essentials and is fast enough to be useful.
This isn’t about getting the “best” battery on paper. It’s about getting the right battery for your lifestyle, your home, and your energy habits.
And once you know your numbers, the rest gets a lot simpler.
When you’re ready to talk to an expert, PSC Energy is here to help. We’ve guided thousands of customers through this choice. It’s what we do.
If you’re interested in learning a bit more about the federal solar rebate, also known as the Federal Cheaper Home Batteries Program, you might want to check out the following article titled, What the 2025 Federal Election and the Government Rebate Means for Solar Batteries in Australia.
