What size battery do I need? A quick guide

Sonnen solar battery system installed in residential house

What size solar panel array do you need for your home? And if you’re considering battery storage, what size battery bank would be most appropriate? This article includes tables that provide an at-a-glance guide, as well as links to more comprehensive calculators.

Solar system sizing table (no batteries)

If you’re considering solar panels for your home, you’ll get the most value from them by directly ‘self-consuming‘ the energy that they produce during daylight hours. The simple reason for this is that using the solar yourself allows you to avoid purchasing expensive energy from the grid instead of earning only a small credit for sending it into the grid. This is a crucial fact about going solar in Australia today.

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Your rate of self-consumption will depend on the amount of energy that you use daily, the pattern of your consumption throughout the day, and the size of the system that you install. You can increase your solar self-consumption ratio by running more of your devices during daylight hours – possibly manually, on timers or using a home energy management system.

The table below contains very rough solar self-consumption ratio estimates for a range of popular solar system sizes and energy consumption levels. Generally, we recommend keeping to a system size that means your self-consumption ratio remains above 30%.

 Your daily energy consumptionSelf-Consumption Ratio for Different Solar System Sizes
2kW Solar3kW Solar5kW Solar7kW Solar10kW Solar
5-10kWh30%25%17%13%9%
11-15kWh48%38%26%20%15%
16-20kWh57%46%34%26%20%
21-25kWh66%53%40%32%24%
26-30kWh73%59%44%37%28%
31-40kWh82%67%50%42%34%

Remember: The table above is a highly generalised, indicative guide; it does not take into account your location or the tilt & orientation of your roof – not to consider system prices or financial details like payback period. If you’d like to take a more detailed look, use our Solar PV System Payback Estimator or our Simple Solar System Sizing Estimator.

The below video gives a run-through on how to select the right solar system size

How to Choose the Right Solar System Size for your Home from Solar Choice on Vimeo.

Picking the Correct Solar and Battery System Size

Tesla Powerwall and SolarEdge comms box 1Using Sunwiz’s PVSell software, we’ve put together the below table to help shoppers choose the right system size for their needs. PVSell uses 365 days of weather data Please read the paragraphs below and remember that the table is a guide and a starting point only – we encourage you to do more research (and get more opinions) before deciding on a system size.

The battery bank sizing calculator

The battery bank sizing table

Your daily energy consumption
Largest recommended battery size for…
Solar system size
2kW3kW5kW7kW10kW
5-10kWh
Maximising returns:5kWh4kWh4kWh4kWh4kWh
Maximising energy independence:22kWh (3 days of energy autonomy)35kWh (5 days of energy autonomy)35kWh (5 days of energy autonomy)35kWh (5 days of energy autonomy)
11-15kWh
Maximising returns:4kWh7kWh9kWh8kWh8kWh
Maximising energy independence:40kWh (3 days of energy autonomy)65kWh (5 days of energy autonomy)65kWh (5 days of energy autonomy)
16-20kWh
Maximising returns:3kWh6kWh13kWh12kWh11kWh
Maximising energy independence:55kWh (3 days of energy autonomy)90kWh (5 days of energy autonomy)
21-25kWh
Maximising returns:2kWh5kWh12kWh16kWh15kWh
Maximising energy independence:23kWh (0.77 days of blackout protection)70kWh (3 days of energy autonomy)
26-30kWh
Maximising returns:1kWh4kWh11kWh18kWh18kWh
Maximising energy independence:40kWh (1.5 days of blackout protection)
31-40kWh
Maximising returns:3kWh10kWh17kWh23kWh
Maximising energy independence:27kWh (0.7 days of blackout protection)

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Since 2008 our knowledge and sophisticated software have allowed over 300,000 Australian households and businesses to make a well-informed choice on their solar & battery installer.

Comments

  1. Can you tell me when new back up batteries ( new technology) will be available and when the government will subside there batteries .
    I have 5 ks system Thank You

    1. Hi Sinikk. Backup power is already possible with the right battery setup. As for a government subsidy, a few small jurisdictions (ACT and City of Adelaide) offer battery incentives, but there is nothing on the federal level.

      Hope this helps!

  2. These tables are all well and good but when determining the economic criteria it falls apart because of the current huge disparity in costs between different battery storage makes. A Powerwall 2 with a stated capacity of 13.5 kWh and a cost of say $12000 installed compared to a Sonnen 6kwh with a installed cost of $12000 it’s a no brainer whatever else is variable i.e. Size of PV system home consumption or usage patterns. Even if you don’t use the full capacity of the PW2 battery it still represents better value and you don’t need a complicated chart to tell you that. Or am I missing something?

    1. Hi Patrick,

      Thanks always for your thoughtful input. You are well on point with this observation. We’ve written lots of articles on the financial case for solar & batteries and regularly point out (e.g. here) that – for now – solar makes more sense on its own. We’ve also pointed out that smaller battery banks tend to have faster payback periods than larger ones for the majority of homes. Our calculators yield the same results as well.

      The focus of this article is sizing, with the aim of educating people about how large a battery bank they can actually make use of – giving them a starting point for shopping around. This will help people to avoid being oversold on system size, especially in instances when the bigger battery bank does indeed cost significantly more than the smaller one. If the larger battery bank is more cost-effective and can operate at partial states of charge (so that it’s not a problem if it doesn’t reach ‘full’ most of the time – if ever), then by all means the larger one would be the smarter choice – and leaves room for expansion.

      As you’ve pointed out there are some significant price disparities at present, but we expect these to even out as time goes on and the market matures. At that point in time, these tables will become even more relevant.

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