Solar savings, payback and output calculator for Melbourne

How the solar calculator works

This solar panel calculator has three modes, at the top of the page:

• Savings: what a system makes, how much of it your home uses, what that saves you a year and, with a price, the payback.
• Payback on a quote: enter the price on your quote to see its price a watt against Melbourne market averages for that size, and how long it takes to pay back.
• Monthly output: the kWh a system makes in each month, for any roof direction and panel tilt.

The savings and payback modes work month by month, in six steps:

1. Output. PVGIS models your system’s yearly output: about 1,419 kWh per kW of panels, before any inverter limit, for a north-facing roof tilted 20° in Mount Waverley, Melbourne, with 14% system losses and weather data from PVGIS-ERA5, 2005 to 2023. Each month gets its share of the year from the same model.
2. Your use. Daily use × the share you use while the sun is up is your daytime use. The rest is your evening and night use.
3. Self-use. On an average day each month, solar covers your daytime use first.
4. Battery. Spare solar charges the battery, up to its usable size and your evening use, and the battery runs the house after dark. This is before charging and discharging losses, so a real battery delivers a little less.
5. Export. Whatever is left goes to the grid and earns your feed-in tariff.
6. Saving and payback. Yearly saving = solar used × your usage rate + exports × your feed-in tariff. Payback = your price after rebates ÷ the yearly saving.

For daily use, divide the kWh on your bill by the days in the billing period. The example uses 20 kWh a day. For comparison, the Essential Services Commission’s Victorian Default Offer rules use 4,000 kWh a year, about 11 kWh a day, as the reference amount for a home.

Where the numbers come from

• Solar output: PVGIS (European Commission Joint Research Centre), run for a roof in Mount Waverley, Melbourne, facing north, east or west. Model inputs: north, east and west.
• Usage rates: the Victorian Default Offer flat rates for 1 July 2026 to 30 June 2027, 25.96c to 31.98c per kWh depending on your network, set by the Essential Services Commission. The same determination gives the daily supply charges and the 4,000 kWh reference amount. The 2026–27 price determination
• Feed-in tariffs: no Victorian minimum since 1 July 2025, so the calculator takes your retailer’s rate. Essential Services Commission
• Prices: the Solar Choice Price Index, October 2026, Melbourne, used only where you leave the price blank, and labelled as market data, not our price. See the index
• Self-use benchmarks: Solar Victoria’s figures for how much of their solar homes use, with and without a battery. Is a solar battery right for your home?

Assumptions

• One average day for each month, not hour by hour.
• Solar covers daytime use first, then charges the battery, then is exported. All daytime use counts as covered whenever the day’s solar adds up to more than it.
• Your usage rate and feed-in tariff stay as you enter them for the whole year.
• Year-one output, with no shade and no export limit. A 6.6 kW system is modelled on a 5 kW inverter, as on our 6.6kW system page; other sizes and roofs are before any inverter limit.

Worked example by season

This is the calculator’s starting example: a 6.6 kW system on a north-facing roof with a 5 kW inverter, a home using 20 kWh a day with 40% (8 kWh) while the sun is up, the Victorian Default Offer flat rate in the United Energy area (27.35c per kWh) and a 3c feed-in tariff. Over a year it makes about 9,319 kWh, uses 2,920 kWh as it is made and exports 6,400 kWh.

Winter makes about 49% of summer’s solar, and the saving falls from $2.97 to $2.44 a day. It falls by less than the output because the 8 kWh this home uses in daylight is covered in every season: what winter loses is mostly export, worth 3c a kWh. A smaller system, or a home that uses more power in the day, feels winter more, because its solar no longer covers the daytime use.

Using your solar vs exporting it

Every kWh of solar you use saves your usage rate. Every kWh you export earns your feed-in tariff, which is far lower. Victoria has had no minimum feed-in tariff since 1 July 2025, so retailers set their own, and it can’t go below zero. At the example’s 27.35c and 3c, a kWh you use is worth about 9 times a kWh you export.

That is why the calculator splits your solar into what you use and what you export. In the example, the home uses 31% of its solar and exports the rest, yet the $800 a year it saves on the solar it uses is worth far more than the $190 its exports earn. Solar Victoria says most homes with solar panels only use around 25% of the energy they generate. The calculator leans high on this share: see what the estimate leaves out.

• Shift daytime loads: run the dishwasher, washing machine and hot water on a timer while the sun is up. In the example, moving 2 kWh a day into daylight (40% to 50%) saves about $180 more a year.
• Store it for the evening: a battery moves spare solar into the evening. See adding a battery.
• Compare the whole plan: a higher feed-in tariff is worth little if the plan charges more for the power you buy. Victorian Energy Compare lists the plans on offer.

Feed-in tariffs in Victoria

Adding a battery to the estimate

Enter a battery’s usable kWh and the calculator moves spare solar into the evening. Each day the battery stores whichever is smallest: the spare solar, its usable size, or your evening use. Every kWh it moves saves your usage rate instead of earning the feed-in tariff.

In the example, a 10 kWh battery fills on an average day in summer and spring, but stores only about 8 kWh a day in winter, when there is less spare solar. It adds about $830 a year to the saving and lifts the share of solar the home uses from 31% to 68%. Those figures are before charging and discharging losses, so a real battery saves a little less.

The calculator has no battery price, so enter your quoted price for the whole system to see its payback.

Battery size calculator

Does a battery pay for itself?

The battery rebate

Checking a solar quote: price and payback

The payback mode is a solar cost calculator that starts from the price on your quote. Enter the total after rebates and the system size, then your own use and tariffs, and it shows the price a watt, the Melbourne market averages for that size, the STCs that should already be off the price, the yearly saving and the simple payback.

The market prices below are installed prices with the federal STC discount already taken off and GST included, as the Solar Choice Price Index reports them; check that your quote is on the same basis. A 6.6 kW system installed in 2026 earns 39 STCs in most of Melbourne, up to about $1,500, at $38 per STC, the top of the $33–$38 the Clean Energy Regulator says agents usually pay.

For this home, payback grows with the size of the system: about 5 years for 3 kW and about 8 years for 10 kW. A bigger system makes more, but this home uses only 8 kWh in daylight, so the extra is mostly exported at 3c. A home that uses more power in the day, adds a battery or gets a higher feed-in tariff gets more from a bigger system.

These paybacks lean short: see what the estimate leaves out.

What a fair price looks like

• Compare the price a watt. Bigger systems cost less a watt: in October 2026 the Melbourne standard averages ran from $1.33 a watt for 3 kW down to $0.89 a watt for 10 kW. So compare quotes of the same size, or compare the price a watt.
• Standard or premium. The index’s Melbourne premium offers, with dearer panels and inverters, averaged 15–17% more than its standard offers for the same size. The payback mode shows both averages for the sizes the index lists.
• Same basis. Check that the STC discount is taken off, GST is included, and the price is for solar only. A quote with a battery needs the battery payback calculator.
• Like with like. The exact panel and inverter models, and the extras a roof or switchboard can need, change the price. Our solar panel cost guide lists them.

Is solar worth it in Melbourne?

Solar panel cost in Melbourne

Rebate calculator

STC calculator

Solar output by month, roof direction and tilt

The monthly output mode answers a narrower question: how many kWh a system makes in each month on your roof. Pick the system size, the direction the roof faces (eight directions, or half east and half west) and the panel tilt, from flat to 40°. It draws on 65 PVGIS runs for Mount Waverley, Melbourne, one for each direction and tilt, with the same 14% system losses and weather years as the rest of this page.

North-facing panels make the most. PVGIS puts the best tilt for a north-facing roof here at 35°, at 1,455 kWh per kW of panels a year, but the top of the curve is flat: at the 20° the rest of this page uses, a north roof makes 98% of that, and at 10° still 93%. Flat panels make 86%. Direction matters more than tilt: at 20°, east and west roofs make 85% and 84% of the best, and a south-facing roof 67%.

Tilt changes the shape of the year as well as the total. Steeper panels catch more of the low winter sun and less of the high summer sun: facing north, panels at 40° make 24% more than at 20° in June and 11% less in December. The month-by-month figures below are for 1 kW of panels, so multiply them by your system’s size: a 6.6 kW system facing north at 20° makes 9,319 kWh a year on its 5 kW inverter.

A west or east-west roof makes more of its solar in the afternoon, which can suit a home that uses more power then. Our guide to roof direction covers that, and shade, which the model leaves out.

Roof direction, tilt and shade

From system size to panel count

This calculator works in kW of panels, not panel counts. To turn one into the other, divide the system’s watts by the panel’s: with the 435 to 475 W panels in our solar panel guide, a 6.6 kW system takes 14 to 16 panels.

To size a system from your power bill, use the sizing calculator in our guide to how many solar panels you need, then bring that size back here.

Size your system from your bill

What the estimate leaves out

• Supply charges. The daily supply charge stays the same with solar, so it isn’t in the saving.
• Your roof. The model is a roof in Mount Waverley, Melbourne with no shade. The savings and payback modes use panels tilted 20°; the output mode covers 8 directions and tilts from flat to 40°. Shade from trees or a second storey, and your exact location, also change the output. The design for your roof comes with its own estimate.
• The inverter. PVGIS doesn’t model the inverter. Where the panels exceed the inverter’s rating, it trims output in the brightest hours, mostly in summer: about 0.5% a year for 6.6 kW of panels on a 5 kW inverter, about 2.5% a year for 15 kW of panels on a 10 kW inverter and about 11.3% a year for 19.8 kW of panels on a 10 kW inverter, worked out from PVGIS’s hourly output. The calculator takes this off for 6.6 kW, modelled on a 5 kW inverter as on our 6.6kW system page. Every other size is before any inverter limit.
• Export limits. Each network caps how much a home can export per phase, and some, including CitiPower, Powercor and United Energy, plan to lower the fixed limit to 1.5 kW per phase during 2026–31. The estimate doesn’t cap exports, so on a low limit the export credit is lower than shown. See the export limits by network.
• When you use power. The model counts all your daytime use as covered whenever the day’s solar adds up to more than it. Real panels make little early and late in the day, so power used at breakfast or late in the afternoon often still comes from the grid. So the estimate leans high on self-use, battery use and saving, and short on payback. In the example the home uses 31% of its solar; Solar Victoria says most homes with solar only use around 25%.
• Real days. The model uses an average day for each month. Cloudy days leave less solar to use and store, which also makes it lean high on self-use and battery use.
• Time-of-use prices. On a time-of-use plan, solar used in the 11 am to 4 pm “solar soak” window saves less (the Victorian Default Offer solar soak rate in the United Energy area is 17.26c), and a battery that runs the house in the 4 pm to 9 pm peak saves more (40.32c).
• Price changes. The Victorian Default Offer resets every 1 July, and retailers often change their rates and feed-in tariffs then too. The estimate keeps today’s inputs for every year.
• Panel ageing. Panels make a little less each year. Going by the performance warranties of the panels in our solar panel guide, they can lose 1% to 2% of their power in the first year and 0.25% to 0.4% a year after that. The estimate uses year-one output.

Our solar packages

The 6.6kW system in detail

The 5kW solar system

Solar calculator: your questions