Sizing residential solar & battery systems: A quick guide

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.

rooftop solarSolar 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 the 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 the amount of energy that you use on a daily basis, 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. If the cell is red, the system is probably too large (or better suited for having batteries). If the cell is green, the system size is likely have a favourable payback period (keeping in mind that the higher the percentage is, the better).

 Your daily energy consumptionSolar system size
2kW3kW5kW7kW10kW
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.

Watch the video to understand how to size your solar system

Tesla Powerwall and SolarEdge comms box 1Solar & battery system sizing table

Using 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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James Martin II

Contributor at Solar Choice
James was Solar Choice's primary writer & researcher between 2010 and 2018.

He is now the communications manager for energy technology startup SwitchDin, but remains an occasional contributor to the Solar Choice blog.

James lives in Newcastle in a house with a weird solar system.
James Martin II

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.

Comments are closed.