Find out how many solar panels and what size battery your home needs. Tweak options to hit your payback target
How much sunshine do you get?
Your nearest large city gives us a good estimate of the average sun hours your roof gets per day — cities closer to the equator or with clearer skies generally get more, which means fewer panels are needed to produce the same amount of power.
How much shade does your roof get?-
0%80%
In Australia the sun sits in the northern sky, so north-facing panels produce the most. East or west roofs lose around 10%, and south-facing roofs lose more. If your roof faces a few ways, pick the side the panels would go on.
Panels tilted towards the sun catch more of it. Most Australian roofs are pitched around 15–25°. Flat roofs produce a little less unless the panels go on tilt frames.
Do you already have solar?
Existing solar size-
1 kW20 kW
Feed-in tariff-
This is what your electricity retailer pays you for solar power you export to the grid — usually well below the retail rate you pay to buy power back, which is exactly why a battery can be worth adding.
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Does your utility offer a feed-in tariff?
Feed-in tariff rate-
A feed-in tariff means your utility credits you for solar you export to the grid, usually at a rate well below what you pay for electricity. That credit can offset your evening usage bill, though it's often modest enough that a battery still pays for itself by using your own solar instead of exporting it.
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How much electricity do you need?
Annual electricity usage-
2,000 kWh/year15,000 kWh/year
Pool usage
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1 kWh/day8 kWh/day
EV charging usage
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2 kWh/day30 kWh/day
Other usage
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1 kWh/day6 kWh/day
How much does grid power cost you?
$ per kWh-
kWh (kilowatt-hour) is a unit of energy — how much electricity you use over time. This is the rate you pay for each kWh you use from the grid.
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Peak $ per kWh-
kWh (kilowatt-hour) is a unit of energy — how much electricity you use over time. This is the rate you pay for each kWh used during peak (typically evening/night) hours.
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Off-peak $ per kWh-
kWh (kilowatt-hour) is a unit of energy — how much electricity you use over time. This is the rate you pay for each kWh used during off-peak (typically daytime) hours.
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$ per day-
A fixed daily supply charge, separate from usage — solar and battery can't reduce this part of your bill.
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My monthly power bill-
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Your bill without solar-
Solar & battery options
Solar panel size-
This is the output rating of a single solar panel — most residential panels sold today are rated somewhere between 400W and 500W. A higher-rated panel produces more power per panel, so you need fewer of them for the same array size.
300W800W
Solar array size-
kW (kilowatt) measures the size of your solar system — how much power it can produce at any moment. It's your panel count × your panel size above. A bigger kW system produces more power.
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Solar price (installed)-
This is priced per kW (kilowatt) of solar — the installed cost of panels, inverter, mounting and labor for each kilowatt of system size, after any rebate. Not sure what to enter? Installed solar in Australia typically runs about $1,000–$1,400 per kW, cheaper per kW for bigger systems. That already includes the federal STC rebate, but not necessarily any state-based rebate you might also qualify for. See current Australian solar prices →
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Battery size-
kWh (kilowatt-hour) measures energy over time — how much your battery can store, or how much electricity you use over a day.
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Battery price (installed)-
This is priced per kWh (kilowatt-hour) of battery capacity — the installed cost for each kilowatt-hour your battery can store, after any rebate. Not sure what to enter? Installed batteries in Australia typically run about $1,000–$1,400 per kWh, cheaper per kWh for bigger batteries. That already includes the federal battery rebate (delivered via STCs and usually applied upfront, same as solar), but not necessarily any state-based battery rebate you might also qualify for. See current Australian battery prices →
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Payback, solar size, battery size, solar price and battery price are all linked — move any slider above and these results follow.
Payback period is how long it takes for the money you save on your electricity bill to cover what you spent on the system. After that point, everything you save is money in your pocket.
Use the slider below to see what a shorter or longer payback period would mean for the options above.
Most homes need somewhere between 10 and 25 standard 400W panels (fewer if you use higher-wattage panels), depending on household size, appliance usage and local sun hours. A 3-bedroom home with average air conditioning and heating usually lands in the middle of that range — use the calculator above for a number based on your own home, city and panel size.
Most homes need just one battery — modern home batteries typically range from 5 kWh to 15 kWh each, and a single unit covers most evening and overnight usage. Larger homes, or homes with a pool, EV or workshop, sometimes add a second battery instead of buying an oversized single unit.
Battery size is measured in kWh and should roughly match your evening and overnight electricity use — most homes need somewhere between 8 kWh and 15 kWh. The calculator above works this out for you from your air conditioning, heating, hot water and any extras like a pool or EV.
Solar panels cover your daytime and evening electricity use, based on your city's average sunshine. Battery covers only your evening and night usage — the only portion that needs to be stored rather than used straight from the panels.
Panels and battery solve different problems in reality — panels supply daytime power, battery covers evening and night power — and their prices move independently in the market. Locking them together would misrepresent how real quotes actually work.
It's meant to represent an all-in installed cost per kilowatt — panels, inverter, mounting and labor — not just equipment. When you compare it to a real quote, check the installer's number covers the same things.
Leave the sliders at their defaults, or use these as a starting point: installed solar in Australia typically runs about $1,000–$1,400 per kW, and installed batteries about $1,000–$1,400 per kWh — both after typical rebates, and cheaper per unit for bigger systems. These guide prices include the federal STC rebate for both solar and batteries, but may not include every state-based rebate — so your real price after all the incentives you qualify for could be lower still. Actual quotes vary by state, brand and installer, so use these figures to sanity-check quotes, not replace them. See current Australian solar prices and battery prices from Solar Choice.
Yes — the $/kW and $/kWh prices above assume any rebate or incentive is already applied, since that's what a real installer quote reflects. If you're pricing from your own quote, just enter what you were actually charged. If you're using our typical-price guide instead, keep in mind it factors in the federal STC rebate for both solar and batteries, but may not capture every state-based rebate — so a real quote after all your available incentives could come in lower.
It's a reasonable planning estimate, not survey-grade data — actual output also depends on your roof's angle, shading and orientation. Treat the payback number as a solid starting point for shopping, not a guarantee.
Extra loads add to your evening usage, which increases the battery size needed to cover them — and battery is the more expensive component per unit of capacity. More usage generally means more cost before it means more savings.
Solar and battery only save you money up to what you actually use. Oversizing either one past what you need still helps a little, but with fast diminishing returns, since there's nowhere useful for the surplus to go.
That's the goal — the number is a target to shop and negotiate toward, not a guaranteed price. If every quote comes back higher, that's useful information too: it tells you your target payback period needs to stretch out a little.
Because battery only saves you money up to the size of your evening and night usage — once it covers that, adding more capacity adds cost without adding savings. Panels work the same way for daytime use, which is why sizing them independently shows you which lever actually moves your payback.
Assumptions
This calculator makes simplifying assumptions to give you a fast estimate. Here's what's baked in:
Solar panels default to 400W, adjustable via the Solar panel size slider — system size is panel count × panel wattage.
The $ per kilowatt figure is meant to be an all-in installed cost — panels, inverter, mounting and labor — not just equipment.
Sunshine figures are city-level averages, not survey-grade, and assume a north-facing roof at about 15°. Other directions and angles are adjusted by a simple factor (east/west about 10% less, south 15–25% less, flat about 7% less). If you pick "Don't know", we assume north-facing at 15°.
Your electricity cost uses the rate(s) you set in "How much does grid power cost you?", defaulting to 0.25 per kWh (shown in your local currency symbol, not adjusted by a real exchange rate). On "Flat rate" pricing, your evening/night usage — the part battery can offset — is charged at the same rate as your daytime usage; on "Peak/off-peak rate", evening/night usage is charged at your peak rate and daytime usage at your off-peak rate. The daily supply charge is added to your bill total but can't be reduced by solar or battery, so it isn't counted in your savings. If you don't have a bill handy, we derive an equivalent per-kWh rate from the monthly amount you enter instead.
Battery is sized at roughly 1.1× your evening and overnight usage, to leave a small buffer.
Savings assume the system offsets up to about 85% of the relevant load — real-world self-consumption varies with timing, weather and appliance habits.
If you enter your annual kWh directly rather than answering the usage questions, we split it roughly 60% daytime / 40% evening & overnight to estimate solar vs battery sizing.
Prices exclude taxes and financing costs, and don't account for panel or battery performance degradation over time. They're assumed to already include any rebate or incentive, since that's what a real installer quote reflects — though our own typical-price guide only accounts for the federal STC rebate, not state-based rebates, so a real quote could come in lower.
Currency and pricing are localized for Australia, based on real market data.
If you already have solar, we assume it fully covers your daytime usage first, with anything left over available to export or charge a battery. Battery savings are then just the difference between what you'd pay to buy that evening electricity from the grid and what you'd have earned exporting it instead — not a full solar payback, since you already own the panels.
If a feed-in tariff is switched on, any solar you generate beyond your daytime usage is treated as exported to the grid, first captured by a battery if you're sizing one, then credited at your feed-in tariff rate to offset your evening usage bill. Total savings are still capped at your full bill without solar — we don't model a net cash payment for excess beyond that.
