Is a 20kW solar system right for your home?
A 20kW system suits very large homes and small businesses, usually on three-phase power, usually using over 40 kWh a day. In Melbourne it averages about 74.8 kWh daily, so it covers most daytime use and exports the rest. Your last 12 months of bills are the best test: size for your daytime use first. A system larger than your need costs more to install and takes longer to repay.
Who a 20kW system suits
- 5+ or business people using over 40 kWh a day
- Homes with daytime use: pool pump, air conditioning, home office
- Homes planning a battery or EV
- Roofs with 93–109 m² of usable, mostly unshaded space
How a 20kW system works
Solar panels
43–52 panels · 93–109 m²
The panels turn sunlight into DC power. Facing north, east or west with little shade from 9am to 3pm gives the best yearly output.
Inverter
15 kW (panels up to 133% of inverter)
The inverter converts DC to the AC power your home uses and controls what goes back to the grid. It is the part most likely to need replacing in the system’s life.
Your switchboard
Solar first, grid second
Your home uses solar power first; anything left over is exported for a feed-in credit, and the grid tops you up at night or on cloudy days.
Monitoring
App or web portal
Monitoring shows production and use by the hour, so you can move dishwasher, washing and EV charging into sunny hours and spot faults early.
How much does a 20kW solar system cost in Victoria?
A 20kW system typically costs $13,240–$20,990 after the STC discount of about $4,484 that installers take off the invoice. Roof type, storeys, switchboard work and the panel and inverter brands decide where you land in that range. Quotes should itemise every component by model and warranty so you can compare like with like.
20kW system prices and output by city
| City | Output a day | Output a year | STC discount | Price | Payback |
|---|
| Sydney, NSW | 77.4 kWh | 28,260 kWh | $5,244 | $13,240–$20,990 | — |
| Brisbane, QLD | 83.3 kWh | 30,420 kWh | $5,244 | $13,240–$20,990 | 3.5–6.9 yrs |
| Adelaide, SA | 82.8 kWh | 30,220 kWh | $5,244 | $13,240–$20,990 | 2.5–5.2 yrs |
| Perth, WA | 90.4 kWh | 32,980 kWh | $5,244 | $13,240–$20,990 | 2.9–5.7 yrs |
| Melbourne, VIC | 74.8 kWh | 27,320 kWh | $4,484 | $13,240–$20,990 | — |
| Parramatta, NSW | 76.2 kWh | 27,820 kWh | $5,244 | $13,240–$20,990 | 3.3–6.6 yrs |
| Penrith, NSW | 78 kWh | 28,460 kWh | $5,244 | $13,240–$20,990 | 3.2–6.5 yrs |
| Newcastle, NSW | 80.3 kWh | 29,320 kWh | $5,244 | $13,240–$20,990 | — |
Output from NREL PVWatts per city. STC discount at each city’s zone and the current certificate price. Prices are market guidance (estimates), not quotes.
20kW compared with 13kW
Per kilowatt, bigger systems usually cost less because the fixed costs of a site visit, scaffolding, approvals and the inverter are shared across more panels.
| System | Typical price | Output a year | Price per kW |
|---|
| 13kW | $8,500–$13,500 | 17,758 kWh | $846 |
| 20kW | $13,240–$20,990 | 27,320 kWh | $856 |
What changes the price of your quote?
- Roof: tile, tin or flat, pitch and storeys (and whether scaffolding is needed)
- Panel and inverter brand and warranty length
- Switchboard upgrades and meter changes
- Single- or three-phase supply and your network’s export limit
- Shading fixes such as optimisers or microinverters
Why the cheapest 20kW quote can cost more
Very low prices usually mean unknown panel brands, a basic inverter or a short workmanship warranty. A system that fails in year six costs more than one that runs for 25 years, so compare warranties and named brands, not only the price. Ask for the inverter and panel warranty in writing before you sign.
How much power does a 20kW solar system produce?
In Melbourne a 20kW system makes about 27,320 kWh a year, or 74.8 kWh a day on average. Across major cities the daily average ranges from 74.8 kWh in Melbourne to 90.4 kWh in Perth. Output depends on cloud cover, dust, shading and the tilt of your roof, so your site is unique.
How output changes through the year
Summer days produce well above the average and winter days well below it, because of shorter days and a lower sun angle. Plan for winter bills to fall less than summer bills. A battery helps shift summer surplus to winter, but at a higher cost and longer payback.
How much of it will you use?
Most homes use about 25–35% of their solar output as it is made and export the rest for a feed-in credit. Moving washing, dishwashing, pool pumps and EV charging into the middle of the day raises that share and the saving. Smart schedulers can automate this and boost your return.
How much will a 20kW system save, and when does it pay back?
At Parramatta power prices a 20kW system saves about $3,181–$4,008 a year, so it pays back in roughly 3.3–6.6 years. After that, the power it makes is close to free for the rest of its 25-year panel life. Payback varies by city and your current electricity rate, so check your own postcode.
Work out the saving for your bill
Enter your recent bill and daily usage to see your own saving, payback time and the best system size for your home. Most homes find a 20kW system either oversizes their roof or exceeds their daytime use, so the calculator helps you right-size.
Open the solar size & savings calculator →
How many panels does a 20kW system need?
A 20kW system needs 43–52 panels, depending on the panel rating: higher-wattage panels mean fewer panels and slightly less roof space. A 475 W panel is 2.2 m² and needs 43 panels; a 390 W panel is 1.8 m² and needs 52. Modern panels are efficient enough that the difference in roof footprint is small.
Panels and roof space by panel size
| Panel rating | Panels needed | Area per panel | Panel area in total |
|---|
| 390 W | 52 | 1.8 m² | 94 m² |
| 420 W | 48 | 2.0 m² | 94 m² |
| 445 W | 45 | 2.1 m² | 93 m² |
| 475 W | 43 | 2.2 m² | 95 m² |
Area from a typical 21.5% efficient panel; allow extra for edge clearances and walkways.
How much roof space does a 20kW system need?
Plan for about 93 m² of panels, or 93–109 m² once you allow for edge clearances and gaps between rows. A 390 W panel is 1.8 m² each; a 475 W panel is 2.2 m² each. Split arrays across two roof faces work well; east–west layouts make a little less in total but spread production across the day.
What size inverter suits a 20kW system?
Usually a 15 kW inverter. Rules allow panel capacity up to 133% of the inverter rating, which is why 20kW of panels is often paired with a 15 kW inverter; your network operator may also cap exports. Check with Solar Advice and your local distributor before ordering to confirm the maximum.
What’s included in a 20kW solar package?
A complete quote should list every item below by brand and model, with the warranty for each: solar panels (count and wattage), inverter (type and size), AC and DC cabling, mounting hardware, switchboard work, monitoring, labour and the STC rebate. Itemisation lets you compare quotes fairly and spot what each installer includes.
43–52 solar panels
Check: brand, model, 25-year performance warranty
15 kW inverter
Check: brand, 5–10-year warranty, battery-ready option
Mounting and cabling
Check: rails rated for your wind region, isolators
Monitoring
Check: app access, consumption monitoring
Installation
Check: accredited installer, workmanship warranty in years
Approvals and paperwork
Check: STC discount shown on the quote, network approval
Which brands are used in 20kW systems?
Solar Advice installs panels, inverters and batteries from leading brands with 10–25 year warranties. Each brand page shows specific models, their ratings, warranty terms and typical costs so you can see what you are paying for.
Solar panels
AikoCanadian SolarJinkoLONGiRECSunPower (Maxeon)Trina
Inverters
EnphaseSolarEdgeSungrowFroniusGoodWeHuawei
Batteries
BYDEnphaseSigenergySolarEdgeSungrowAlpha ESSEnphase IQ BatteryFranklinWH
20kW solar with a battery
Adding a battery stores daytime surplus for the evening. A 20kW system makes about 74.8 kWh a day in Melbourne, so roughly 37 kWh is spare on an average day for a battery to store. A battery lets you use more of your own power and improves backup during a grid outage.
How much does a 20kW system with a battery cost?
| Battery | Battery installed | Incentives | 20kW solar + battery |
|---|
| 10 kWh | $9,000–$13,000 | − $2,520 | $19,720–$31,470 |
| 13.5 kWh | $12,150–$17,550 | − $3,402 | $21,988–$35,138 |
| 20 kWh | $18,000–$26,000 | − $4,434 | $26,806–$42,556 |
Incentives: Cheaper Home Batteries. Market guidance, not quotes; incentive amounts change on set dates.
What size battery suits a 20kW system?
Usually 13.5–20 kWh. A battery larger than your daily surplus rarely fills, so size it to your evening use and the spare solar. A 20kW system with a 13.5 kWh battery costs $21,988–$35,138 after rebates; a 20 kWh battery costs $26,806–$42,556.
Does a battery pay back?
A battery pays back more slowly than panels alone, because you are only saving the gap between the grid price and the feed-in credit. Incentives and virtual power plant payments shorten the payback. In many cases, adding a battery extends total payback to 8–12 years, so size it to your evening use, not just for return.
Rebates and finance for a 20kW system
Several incentives apply in Victoria right now; most are taken off the installer's invoice. The Solar Homes rebate, the STC discount, interest-free loans and community rebate schemes vary by postcode and eligibility. Ask your installer which apply to your address and confirm current amounts before you sign.
Cheaper Home Batteries
About $252/kWh for the first 14 kWh, $151/kWh to 28 kWh and $38/kWh to 50 kWh (2026 rate)
Source: DCCEEW Cheaper Home Batteries, from 1 May 2026, checked 2026-10-16
Small-scale Technology Certificates (STCs)
Upfront discount: kW × zone multiplier × deeming years × STC price
Source: SRES: zone multiplier × 5-year deeming × $38 per STC, checked 2026-10-16
Solar Victoria hot water rebate
up to $1,400 locally made, $1,000 other
Source: Solar Victoria, from 1 July 2026, checked 2026-10-16
Solar Victoria panel rebate
up to $1,400
Source: Solar Victoria, from 1 July 2026, checked 2026-10-16
How a 20kW installation works
From first call to switch-on usually takes 4–8 weeks, most of it approvals and the network connection queue; the install itself is usually one day. You will need to obtain network approval and arrange a meter change with your distributor.
- 01
Assessment
A look at your bills, roof and switchboard, in person or from satellite images. The installer checks for shading, roof condition, age and direction, and whether your switchboard has space for a new circuit.
- 02
Design & quote
A panel layout, the inverter size and expected output, with an itemised written quote. The design takes into account roof space, shade patterns and your usage to find the best orientation.
- 03
Approvals
Network connection approval and the STC paperwork, handled by the installer. Your network operator must approve the export capacity and any export limit before installation.
- 04
Installation day
Panels, inverter and monitoring fitted, usually in a single day. The crew will run wiring, fit the inverter, set up monitoring and carry out safety tests.
- 05
Switch-on & monitoring
Meter change, switch-on and a walk-through of your monitoring app. Your distributor will replace the meter; you will then see real-time production and savings in the app.
20kW solar system questions
How much does a 20kW solar system cost?
Usually $13,240–$20,990 after the STC discount. The roof, brands and switchboard work set the final price.
How many kWh does a 20kW system produce per day?
About 74.8 kWh a day on average in Melbourne (27,320 kWh a year), more in summer and less in winter.
How many panels are in a 20kW system?
43–52 panels: 43 with 475 W panels or 52 with 390 W panels.
How much roof space does a 20kW system need?
About 93 m² of panels, or 93–109 m² of roof once clearances are allowed for.
What size inverter is used with a 20kW system?
Usually 15 kW, because panels can be up to 133% of the inverter rating.
What is the payback on a 20kW system?
About 3.3–6.6 years at Parramatta power prices, saving $3,181–$4,008 a year.
What battery suits a 20kW system?
Usually a 10–13.5 kWh battery; about 37 kWh is spare on an average day.
Is 20kW enough for my home?
It suits very large homes and small businesses, usually on three-phase power. Check your last 12 months of bills against the output above.
Can I add a battery to a 20kW system later?
Yes. A 20kW system is designed to accept a battery retrofit. You can add 10–20 kWh of storage later without changing the panels or inverter, though a hybrid inverter must be installed at the start if you plan to add a battery within a few years.
Will a 20kW system work on single-phase power?
Most networks allow up to 10 kW on single-phase. A 20kW system usually needs three-phase supply. Ask your distributor to confirm your supply and any export limits before you order.
How long do 20kW solar panels last?
Most modern panels carry a 25-year performance warranty and are designed to operate for 30+ years.
What's the difference between a string inverter and a hybrid inverter for 20kW?
A string inverter (15 kW typical) converts DC to AC only. A hybrid inverter does that and manages a battery. If you think you might add storage, a hybrid is better, though it costs more upfront.
Helpful links
