What Size Solar System Should You Have When Adding a Battery

If you are thinking about adding a battery to your home, you might wonder: Do I need to make my solar system bigger?

For many Australian homes — especially those with a standard 6.6kW system — the answer is yes. To get the most from your battery investment, make sure your solar system meets your current needs. This will also help you qualify for the new 30% battery rebate. It should also consider how you want to live in the future.

Here’s how to get it right.

Why Solar Size Matters When You Add a Battery

Solar panels generate the most energy in the middle of the day — often when nobody’s home. If you don’t have a battery, the extra energy goes to the grid. You get a small payment for this, usually about 5 to 7 cents per kWh.

With a battery, that surplus power gets stored for when you need it most: after dark, during price peaks, or when the grid goes down.

But here’s the catch: if your solar system isn’t big enough, you may not produce enough surplus energy to:

• Fully charge your battery

• Run large appliances like EV chargers

• Maximise your return on investment
  

How Big Should Your Solar Be to Support a Battery?

Here’s a general guide based on battery size:

💡 If you're planning to charge an EV, heat water with solar, or electrify your heating, a larger system will give you more flexibility and faster returns.

Why the Old 6.6kW Standard May Not Be Enough

A 6.6kW system is still common — and in many cases, fine for smaller households. But with feed-in tariffs dropping and electrification rising, many homes are upgrading to 10kW+ systems to:

• Cover battery charging

• Support EV charging

• Run appliances like air conditioning, hot water, and pool pumps

• Maintain performance during winter and cloudy days

Batteries work best when you have excess solar to store — not just enough to cover your daytime use.

Can You Still Use a Battery With a 6.6kW System?

Yes, but the results depend on your usage.

If you are not home during the day, your solar system may export most of its power. This could still be enough to charge a small to medium battery (5–10kWh).

But if you are using most of your solar energy or want blackout protection, you may need to upgrade the system. This will help deliver more energy to the battery.

Good News: You Can Add More Solar Too

If you’re retrofitting a battery to an existing solar system, Shoalhaven Solar can:

• Add a second solar array connected directly to your new battery (using hybrid inverters like Sigenergy)

• Replace your inverter to support more solar (e.g. upgrade from 5kW to 10–15kW)

• Design a modular system that grows as your needs change

Adding solar when you install a battery is often the best way to save money. It also helps you get the full 30% federal battery rebate. This ensures the system works as expected.

Do Export Limits Matter?

You may have heard of the 5kW export limit on single-phase homes. Here’s what that means:

• It only limits how much you can send to the grid, not how much you can generate and use yourself

• So installing 10–15kW of panels on a single-phase home is still worthwhile — especially with a battery to soak up the extra power

With larger systems, you can:

• Charge batteries faster

• Run your home directly from solar

• Export only what’s left (even if it’s limited)

And in many cases, Shoalhaven Solar can help you apply for an export increase if your network allows it.

Thinking About EVs or Going Electric? Go Bigger

Planning to buy an electric vehicle or swap gas appliances for electric ones? Future-proof your home by upsizing now.

• EV chargers alone can draw 7–22kW

• Electric hot water, heating and cooking all add to your usage

• A bigger system now avoids future upgrade costs later

We’ll size your system based on current and future energy needs — so you don’t outgrow it too soon.

How the Rebate Fits In

The new Cheaper Home Batteries rebate (30% off) is even more compelling if your system is well-matched:

• More solar = faster payback

• More solar = more stored energy

• Larger battery = more rebate value

For example:

• A 13.5kWh battery at $10,000 → $3,000 federal rebate

• Add NSW rebate → another $2,400 off

• Go bigger? A 27kWh system could earn over $9,000 in federal rebate alone

Proper system sizing ensures you can use that energy — and benefit from the savings.

Let’s Size It Right, From the Start

At Shoalhaven Solar, we’ll design a system that’s:

• Matched to your home and lifestyle

• Built to maximise rebates and savings

• Ready for future upgrades like EVs or all-electric appliances

Bigger Solar. Smarter Storage. Better Outcomes.

Don’t let an undersized solar system hold your battery back. Whether you're starting from scratch or retrofitting an older system, we’ll help you size it right — so you get every dollar’s worth.

Call Shoalhaven Solar on (02) 4464 1597 or request a quote. We’ll tailor a solar and battery system that works for you — today and into the future.