15kW solar systems: A great size for homes & businesses (if you can fit one on your roof)

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.

A 15kW solar system for Kennards Hire in Rutherford, NSW.

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

A modern-day 15kW solar system will be comprised of between about 45-55 panels and will require about 75-95 m2 of roof space, depending on the wattage of the panels (which are typically between 250-330W each). This means that for most homes, a 15kW solar system will not be an option unless it is ground-mounted.

You can explore your own roof’s solar potential here.

15kW solar systems:

Number of panels & area required

Wattage of panels330W275W
Approx no panels:4555
Approx area required:77m294m2

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. According to Solar Choice’s own data, as of May 2019 the average price of a fully installed 15kW solar system in Australia is around $1.14 per watt – or about $17,000 for the whole system. You can view current indicative solar system prices here (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.)

For anyone looking to install a 15kW solar system, this price point can act as a reference point – some installers will offer a lower price, while others will offer a higher price. The thing to look for is the comparative value of the system – a balance between quality products and price.

The chart below give a rough idea of what average prices for 15kW solar system look like in (most of) Australia’s capital cities, as of May 2019.

Average 15kW solar system prices
(by capital city, as of May 2019)
CityOut of pocket cost
(incl GST and incentives)
Cost per watt, installed
Adelaide$16,950$1.13
Brisbane$17,100$1.14
Canberra$16,200$1.08
Hobart$19,350$1.29
Melbourne$16,800$1.12
Sydney$17,250$1.15
Perth$15,300$1.02
Average:$17,100$1.14

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15kW solar system energy output

Depending a number of factors, the actual power output of a 15kW solar power 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. (If your location is not listed, check out NREL’s PVWatts calculator.)

 Indicative daily 15kW solar system output by capital city

(Data ranges via PVWatts & Bureau of Meteorology, assuming 75% system efficiency for a north-facing array tilted at 30 degrees)

Adelaide54 – 61kWh
Brisbane 58 – 61kWh
Canberra54 – 62kWh
Darwin~67kWh
Hobart43 – 49kWh
Melbourne47 – 54kWh
Perth60 – 65kWh
Sydney51 – 56kWh

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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 40kWh 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 who 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 your network company may have a default limit on solar system size – they may not allow you to connect a system larger than 5kW to the grid without extra paperwork and inspections. Check with your solar installer or local network company for more details.

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15kW solar system financial returns

These days solar feed-in tariff credits are a secondary benefit from 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.

The table below gives a rough overview of the difference between retail electricity rates and solar feed-in rates by city, based on some of the most competitive offers available.

We note, however, that eligibility for feed-in tariffs depends in part on the system size – some retailers in some locations may not pay out feed-in tariffs on systems over 10kW in capacity. Make sure you incorporate this into your analysis before making a decision about your system size.

Payback & 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 may not be the case in reality, depending on the retailer and the network.

Indicative returns for 15kW solar systems @ average prices (as of May 2019)

(Assuming 40kWh electricity consumption/day, system efficiency of 75%)

 Sydney* Brisbane**
$17,250 $17,100
 @ 40% self-consumption @ 70% self-consumption@ 40% self-consumption@ 70% self-consumption
 ~5.4 year payback ~4.4 year payback ~5.3 year payback ~4.6 year payback
 ~19% IRR~23% IRR ~19% IRR ~22% IRR
 ~$3,105 annual savings ~$3,786 annual savings ~$3,149 annual savings ~$3,639 annual savings
Melbourne** Perth**
$16,800$15,300
@ 40% self-consumption@ 70% self-consumption@ 40% self-consumption70% self-consumption
~6.1 year payback~5.1 year payback~4.6 year payback~4.0 year payback
~16% IRR~20% IRR~22% IRR~25% IRR
~$2,675 annual savings~$3,165 annual savings~$3,236 annual savings~$3,726 annual savings

*Assumes 12c/kWh feed-in tariff, 25c/kWh flat electricity purchase rate

**Assumes 12c/kWh feed-in tariff, 21c/kWh flat electricity purchase rate

**Assumes 7c/kWh feed-in tariff, 27c/kWh flat electricity rate

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