15kW solar systems: A great size for large homes & businesses

building with the lights on at night

15kW solar systems are a great system size for homes with high levels of energy consumption or businesses with small to middling energy needs – provided that they have sufficient roof space to install one. This article takes you through (almost) everything you might want to know about 15kW solar systems, including how much space they take up, how much they cost, and how much energy you can expect them to produce. It also touches on whether a 15kW system is a good investment for your home or business.

How many panels & how much roof space for a 15kW solar system?

A modern-day 15kW solar system will be comprised of between about 37-45 panels and will require about 75-90 m2 of roof space, depending on the wattage of the panels (which are typically between 330-400W each). A typical residential solar panel is 1.7 metre by 1 metre. This means that for most homes, a 15kW solar system will not be an option unless it is ground-mounted.

15kW Solar Panel Systems – roof space and number of Panels
Solar panel watt rating330W400W
Approximate number of panels4537
The solar panel watt rating75m290m2

How much does a 15kW solar system cost?

Australia is home to some of the lowest solar installation prices in the world, and 15kW solar systems – because of their size – frequently offer some of the best value of any solar PV system size. You can view current indicative solar system prices on the Solar Choice Price Index (although 15kW is not yet a regular feature in our monthly Solar PV Price Index, 10kW has been included for a number of years now.)

As of July 2023 the average cost of a fully installed 15kW solar panel system in Australia is around $15,694 or $1.02 per watt after deducting the STC rebate and including GST.

The chart below gives a rough idea of what average prices for a 15kW solar system look like in (most of) Australia’s capital cities.

Average 15kW solar system costs based on Solar Choice Price Index

CityOut of pocket cost (incl GST and incentives)Cost per watt installed
Adelaide, SA$14,700$0.98
Brisbane, QLD$14,850$0.99
Canberra, ACT$14,850$0.99
Hobart, TAS$16,200$1.08
Melbourne, VIC$15,150$1.01
Sydney, NSW$15,450$1.03
Perth, WA$15,600$1.04

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How much energy does a 15kW solar system produce?

Depending on a number of factors, the actual power output of a 15kW solar panel system will vary. These variables include:

The table below gives indicative figures for how many kilowatt-hours of energy a north-facing 15kW solar system will generate per day (on average throughout the year) in Australia’s capital cities.

 Indicative daily 15kW solar panel output by capital city

CityAverage Daily ProductionEstimated Annual Production
Adelaide58 kWh per day21,079 kWh
Brisbane60 kWh per day21,900 kWh
Canberra58 kWh per day21,079 kWh
Darwin66 kWh per day24,090 kWh
Hobart47 kWh per day16,973 kWh
Melbourne50 kWh per day18,341 kWh
Perth63 kWh per day22,995 kWh
Sydney54 kWh per day19,710 kWh


  • Calculations completed via PVWatts using sunlight data from the Bureau of Meteorology
  • Conservatively assumes that the systems efficiency is 75%
  • Assumes the solar panels a mounted at a 30-degree angle to the north

Is a 15kW solar system right for your home or business?

As you can guess by the amount of roof space required, a 15kW is a serious amount of solar for the ordinary home – and in many cases, it will be too much. In most cases, it will only be appropriate if you’re using over 50kWh of energy on average per day – a number much more likely to apply to a business than a home. It may also be a good size choice for homes that have low electricity consumption and want to go off-grid (see: “Can I go off-grid with a 10kW solar system?“)

Because of the complexity involved (not to mention the cost), we recommend that you have the numbers crunched in detail before deciding to go ahead with a 15kW solar system. You can experiment with the numbers yourself with our Simple Solar System Sizing Estimator, check out our Solar Payback & ROI Estimator Tool or request a free, customised business case analysis from our engineering team based on your electricity bills.

Also, keep in mind that the Distributed Network Service Provider (DNSP) who is the company that owns the poles and wires in your area may have particular rules on what can be connected and what systems are permitted to export power. Often for single phase connections the limit is a 5kVA inverter which can accommodate 6.6kW of solar panels.

An additional consideration is that many of the electricity retailers feed-in tariff plans are capped at systems with a 10kW inverter. See a summary of the latest plans on this feed in tariff page.

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Is a 15kW solar system worth it?

These days solar feed-in tariff credits are a secondary benefit of having a solar system installed. Instead,  you’ll derive the most value out of your self-generated solar energy by ‘self-consuming‘ it – using as much energy as possible directly. Because solar feed-in tariff rates are generally lower than what you’ll pay for energy from the grid, the more solar energy you use yourself, the more you’ll save; meanwhile, the excess solar will flow into the grid and earn you credits which help to reduce your overall bill.

Payback Period & IRR for 15kW solar systems

The table below takes a look at payback times and internal rate of return (IRR) for those who install a 15kW solar system in select cities at two rates of self-consumption – 40% and 70%. Although these rates are high for most ordinary households with solar (typically more like 20-40%), we assume that anyone who goes ahead with a system in the 15kW range has done their research and ensured that a higher degree of their solar energy will go directly to their local energy demand (as opposed to into the grid). If you manage to achieve even higher self-consumption rates, the returns will look even more favourable.

Please note that we’ve assumed that the system is eligible for a solar feed-in tariff – which depends on the electricity retailer and the network rules.

Indicative payback periods for 15kW solar panel systems

 15kW System CostElectricity PriceFeed in RateSelf Consumption RateIRRAnnual SavingsPayback Period (Years)
Sydney$15,45029c7c30%17%$2,6315.7 years
60%27%$3,9953.8 years
Brisbane$14,85026c6c30%17%$2,4715.9 years
60%26%$3,7103.9 years
Melbourne$15,15022c5c30%12%$1,8847.8 years
60%20%$2,9365.0 years
Perth$15,60031c6c30%18%$2,8145.4 years
60%29%$4,3513.5 years
Adelaide$14,70035c8c30%22%$3,2134.5 years
60%35%$4,8843.0 years
Hobart$16,20033c8c30%19%$2,7725.2 years
60%31%$4,3233.3 years
Canberra$14,85029c7c30%17%$2,6975.4 years
60%29%$4,0623.6 years
Darwin$18,75027c9c30%17%$3,2615.7 years
60%24%$4,4004.2 years


  • Assumes the average daily energy usage is 50 kWh per day (very high for residential use)
  • The prices are based on the latest Solar Choice Price Index
  • Self-consumption rates of 30% (low) and 60% (very high) have been selected as examples only and as you can see are very important to the financial outcome

Calculate indicative ROI & payback periods for 15kW solar systems

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Jeff Sykes