How Many Solar Batteries Do You Really Need?

By Twilight Energy

Max (left), a school-based apprentice helps Kaine (a fully qualified electrician) install a battery

Thinking about adding a battery to your solar system? You’re not alone. More South Australians are looking at storage to cut bills, protect against blackouts, and future‑proof their homes. But the big question is: how much battery storage do you actually need?

The Quick Answer

As a rule of thumb, aim for at least 25% of your daily energy use, plus a 2 kWh buffer for backup.

So if your household uses 20 kWh a day, don’t go smaller than a 7 kWh battery. It might not last all night, but it will usually cover the expensive evening peak when grid power costs the most.

What Do You Want Your Battery To Do?

Your ideal battery size depends on your goals:

• Lower bills: A smaller battery can soak up excess solar and offset peak rates.

• Blackout protection: You’ll want extra capacity to keep essentials running.

• Grid independence: Covering all your night‑time use requires a larger system — and a bigger budget.

How Much Energy Do Aussie Homes Use?

• The average household: ~16 kWh per day.

• Large homes with air‑con, pools, or electric hot water: 30 kWh or more.

• Busy family homes with EVs: 60 kWh+ daily.

If you’re out during the day, around 70% of your usage happens at night — when your panels aren’t generating. That’s where batteries step in.

John from Colonel Light Gardens, loves his 13.5kWh Tesla Powerwall "it suits my usage perfectly"

Battery Sizing Basics

Battery capacity is measured in kilowatt‑hours (kWh).

• If you use 16 kWh daily, about 11 kWh happens at night.

• Add a 2 kWh buffer for backup, and you’re looking at a 13–14 kWh battery to comfortably cover most evenings.

Why Smaller Batteries Can Be Smarter

Here’s the catch: batteries aren’t cheap. Installed costs are typically $800–$1000 per kWh before rebates.

The first few kilowatt‑hours of storage usually give the fastest payback because they’re used every single night. As you add more capacity, the payback period stretches out.

So if your priority is return on investment, don’t oversize. But if your goal is energy independence, a bigger battery may be worth it.

The Most Important Step: Know Your Usage

The best battery size isn’t based on averages — it’s based on your actual energy profile.

• Download your smart meter data (ideally 12 months).

• Work with a trusted installer (like Twilight Energy) to analyse it.

• Use that data to size your solar and battery system for the best financial and lifestyle outcome.

Twilight Energy’s Take

At Twilight Energy, we believe in right‑sizing your system. Bigger isn’t always better — but smarter always is. Whether you’re chasing lower bills, blackout protection, or full grid independence, we’ll help you design a solution that fits your home, your budget, and your future plans.

Ready to explore your options? Talk to the Twilight Energy team today and let’s design a solar + battery system that works for you.