What Size Solar Battery Do I Need?

So, what size solar battery do you actually need?

Let’s be honest, choosing the right home solar battery size can feel a bit overwhelming. Between kilowatts, kilowatt-hours, DoD, backup modes, and everyone recommending something different, it’s easy to fall into the trap of either going too small and missing out… or going too big and overspending.

At SolarEze, we install solar battery systems all across Brisbane, the Gold Coast, and South East Queensland, and this is a question we get almost every day.

So let’s break it down in real-world terms.

Why Battery Size Matters

If your battery’s too small, it’ll run out before you really need it, like when the air-con’s on, dinner’s cooking, and the sun’s gone down. Too big? You’re spending extra on storage you may not use fully.

The goal isn’t the biggest battery you can buy. It’s the right-sized battery for your home’s energy habits, now and in the future.

Start Here: Your Power Bill

The first thing we look at is your average daily electricity usage. You’ll usually find this on your energy bill as your annual usage. Just divide that number by 365 to get your daily average in kilowatt-hours (kWh).

For example, if your household uses around 20kWh per day, then that’s your ballpark figure when thinking about battery capacity.

Not All Battery Capacity is Usable

This is something many homeowners don’t realise… the number on the box isn’t always what you can actually use, and here’s why:

• Depth of Discharge (DoD): Most batteries don’t let you drain them all the way to zero every day. Some have built-in limits to protect battery life, so a “10kWh” battery might only offer 8.5kWh of usable storage.
• State of Charge Limits: Some systems stop discharging when they hit a minimum reserve, usually 5–20%. It’s a safeguard, but it reduces usable energy.
• Battery Degradation: All batteries lose capacity over time. A battery that stores 10kWh today might only hold 7–8kWh in 8–10 years.

So when we talk battery sizing, we’re really talking usable storage, not just what’s printed on the spec sheet.

A Simple Rule of Thumb (That Actually Works)

Here’s the golden rule we follow:

Choose a battery with enough usable capacity to cover your average daily electricity use.

But don’t stop there. It’s worth thinking ahead. Energy needs change, especially as we electrify more of our homes.

Future-Proofing Your System

Many of our customers are either already driving EVs or planning to in the next few years. Others are replacing gas appliances with electric ones, or adding reverse-cycle air-conditioning. All of these changes increase your daily usage, so why not size your battery to meet tomorrow’s needs, not just today’s?

This is one reason we like modular systems, like the Sungrow SBH range. You can start with what you need now, and easily add more storage later.

Thinking About Blackouts?

If backup power is important to you, and in storm season across SEQ, it’s a smart idea, battery size matters even more.

You’ll want enough storage to keep your essentials running, even if the battery’s already been partly drained during the day. We also recommend checking that the system you’re considering includes proper blackout protection or EPS (Emergency Power Supply), not all of them do.

Good news: Sungrow’s hybrid battery systems do, and they support three-phase backup. That means your whole home, not just one or two circuits, can stay powered during an outage.

Can a Battery Help You Make Money?

Yep — under the right conditions, your battery can do more than just save you money.

With solar feed-in tariffs changing and smarter export models on the rise, there’s a growing opportunity to store energy and sell it back to the grid when demand (and payouts) are high, often in the evenings, not the middle of the day.

We’re also seeing the early stages of virtual power plant (VPP) programs here in Australia, where your battery becomes part of a larger network that supports the grid, and pays you for participating. While it’s still early days, having a battery with the flexibility to take part is a bonus.

On a Budget? Here’s How to Keep It Smart

We get it — not everyone wants (or needs) a massive battery from day one.

If you’re trying to keep costs sensible, here’s how to avoid overspending:

• Oversize your solar array slightly, so even on cloudy days you’re still generating enough energy to cover your needs.
• Model your system performance, we help our customers simulate how different battery sizes will perform across seasons.
• Choose a modular battery that you can expand down the track. (Again, Sungrow’s range is great for this.)

So, What Size Battery Should You Get?

Here’s a recap of how to figure it out:

✅ Check your daily electricity usage (in kWh)
✅ Look at usable battery capacity — not just total capacity
✅ Allow room for future electrification (EVs, heating, cooking)
✅ Plan for battery degradation over time
✅ Consider blackout protection and export opportunities
✅ Go modular if you’re unsure — it’s easier to grow later than to replace

Visit www.solareze.com.au to request a quote for your next solar installation and one of our friendly team members will contact you shortly. If you would like to talk to us immediately, call 0410 658 790 today and we will offer you a free solar consultation for your home.