By Finn Peacock, Chartered Electrical Engineer, Fact Checked By Ronald Brakels

Last Updated: 3rd Jun 2024

How Many Batteries Do You Need?

three powerwall batteries in sydney

Installation credit: Teho

How many batteries you need depends on what you want your solar batteries to achieve. Most people set out with the aim of reducing their grid electricity imports to zero.

As you’ll soon see, this lofty energy storage aim will actually be very expensive for most households.

Let’s do a crash course on how much energy storage an ordinary Australian household will need.

The average Australian home uses roughly 16kWh of electricity per day (Please read this if you are not completely clear on the difference between a kW and a kWh –  it is super important).

Naturally, if you have a house that has a big air-conditioner and pool pump etc, you’ll use a lot more than that.

Assuming that most Australians work a 9-5 job and are not home during the daytime, they’ll probably only use only around 30% of their electricity during the day, when the sun is up and their solar panels are producing electricity.

That means that they need to buy the other 70% from the grid; so how many solar batteries do you need to need to cover that 70%?

Sizing your solar battery system

In terms of system sizing – battery sizes are expressed as kilowatt-hours, or kWh.

If the average home uses 16kWh, 30% of this during the day and 70% at night, that works out to about 5kWh of daytime usage, and 11kWh of night-time usage.

So, simple math would dictate that the average Aussie would need about 11kWh of solar battery storage to offset all their night usage.

The Tesla Powerwall 2 has 13.5kWh capacity and costs around $15,000 fully installed as of February 2024. That’s assuming a straightforward installation without additional costs.

Bear in mind there is no need to offset all your night-time electricity use with batteries. If you run the numbers, the best payback is from the first kWh of energy storage – because it works the hardest, as you add subsequent kWh their payback gets longer. So don’t bankrupt yourself looking to cover every last kWh of nighttime electricity with your batteries.

However, the most important thing to consider when sizing and comparing solar batteries is that it is impossible to do without a detailed understanding of your energy usage profile. This means you need a good energy monitor on your home with good data as a first step.

Then a good installer can use their software to show you exactly what the optimum number of batteries and solar panels is for your situation and what the payback will be. After this, you’ll be going into your solar battery investment with your eyes wide open, instead of it being a leap into the unknown.


>> Next: What brand of batteries should you buy (or is Tesla your only choice)? >>


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