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Calculator

How much battery do your evenings actually need?

A battery is not sized from your roof, it is sized from what you use after dark. This checks both halves: what you need to store, and whether your solar can fill it.

  • Sized from evening usage
  • Checks your solar can fill it
  • No price guesswork

Your numbers

  • Victoria (VIC)3.6 hrs
  • New South Wales (NSW)4.2 hrs
  • Queensland (QLD)4.8 hrs
  • South Australia (SA)4.6 hrs
  • Western Australia (WA)5.2 hrs
  • Tasmania (TAS)3.3 hrs
  • Australian Capital Territory (ACT)4.4 hrs
  • Northern Territory (NT)5.8 hrs

Sets the peak sun hours used in the generation estimate, based on the state capital.

kWh

On your bill, the total kWh for the billing period. Use kWh, not dollars, if it is printed.

For most households this is the bigger share. Evening cooking, heating, TV and hot water all land here.

kW

Existing or planned. This is what has to charge the battery.

Most lithium batteries publish a usable figure around 90 percent of nameplate.

Fill in your quarterly usage and your answer appears here.

Nothing here is sent to us. The maths runs in your browser, and there is no email gate.

Still needed

  • Your quarterly usage

These come off your electricity bill. We ask for them rather than guessing, which is the entire point of this tool, and the reason the answer will be about your house rather than an average one.

What this assumes, in full.

Every calculator makes assumptions. Most sites hide theirs, because naming them makes the headline number look less impressive.

  1. 01Daily usage is your quarterly kWh divided evenly across the year. Real usage swings with the season, and winter is when storage is tightest.
  2. 02Generation uses your state capital's approximate peak sun hours and a performance ratio of 0.80.
  3. 03It assumes the battery cycles once a day. Round-trip efficiency losses of a few percent are not modelled.
  4. 04It does not size for blackout backup. Backup changes the wiring and the equipment, not just the capacity, so tell us if it matters to you.

FAQ

Battery size, answered.

If the numbers here do not match what a salesperson told you, ask them which assumption they used.

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Not on its own, because that needs a price. It tells you what size you would need and whether your solar can actually fill it, which are the two questions people get wrong before price even comes up.

Because a battery's nameplate capacity is not all usable. Most manufacturers publish a usable figure, and it is the usable figure that has to cover your evening.

Realistically, no. Going off grid needs several days of storage and a much larger array, and for a grid-connected home it is rarely the sensible spend. A battery shifts your solar into the evening, which is a different and much better value proposition.

The other tools

SavingsSolar Savings CalculatorMost savings calculators pick their own electricity price and hand you a big number.System sizeSolar System Size CalculatorOversize it and you export power for a few cents.PaybackSolar Payback CalculatorWe will not invent a price to make this look good.Feed-in tariffFeed-in Tariff CalculatorFeed-in tariffs have fallen a long way.Rebate eligibilityRebate Eligibility CheckThis tells you which programs are worth pursuing and what each one needs.

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Ready for a lower power bill?

Send us your address and a recent bill. Here is exactly what comes back.

  • A fixed, itemised price, not a range
  • Every rebate you qualify for, applied for you
  • A design built on your roof and your real usage
  • No pushy sales visit, ever
Get a Free Quote1800 577 319
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  • Clean Energy Council Member
  • NETCC Approved Seller