Lumenx

Calculator

What size system does your house actually need?

Oversize it and you export power for a few cents. Undersize it and you keep buying at full price. This works backwards from the usage on your bill.

  • Sized from your usage
  • Panel count and roof area
  • Two honest answers

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.

Working from home, a pool pump or ducted cooling pushes this up. Out all day pushes it down.

m²

Optional. Leave blank if you do not know. Rough guess is fine.

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. 01Panel count assumes 440W modules and roughly 2 m² of roof per panel, including spacing.
  2. 02Generation uses your state capital's approximate peak sun hours and a performance ratio of 0.80.
  3. 03It assumes unshaded, reasonably north-facing roof space. Complex or shaded roofs fit less and produce less.
  4. 04Quarterly usage is multiplied by four. If your summer and winter quarters differ a lot, use an average quarter rather than your worst one.

FAQ

System size, answered.

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

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Look again on the charges breakdown page, where the kWh for the period is almost always printed. If it genuinely is not there, divide your usage charge by your usage rate in cents and multiply by 100.

It depends on your feed-in tariff and whether you plan to add a battery. A low feed-in tariff and no battery plans argues for the smaller number. A battery, an electric car or a pool argues for the larger one.

No. Beyond the point where you consume it or store it, extra generation earns only your feed-in rate, which is usually a fraction of what you pay. That is the whole reason sizing matters.

The other tools

SavingsSolar Savings CalculatorMost savings calculators pick their own electricity price and hand you a big number.Battery sizeSolar Battery CalculatorA battery is not sized from your roof, it is sized from what you use after dark.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
  • Solar Victoria Authorised Retailer
  • Clean Energy Council Member
  • NETCC Approved Seller