Case Study 16.9kW Residential

Real life solar example with before and after bill

This case study is a prime example of why first and foremost you should consider utilising all of your suitable roof-space before even contemplating batteries. Customer was a fairly average to low user but has decided to take full advantage of solar as an investment and oversized the system.

The customers average daily usage is 12.2kWh.

Some solar companies would recommend a 3.5kW system for this amount of usage or potentially up to a 6.5kW to try and cover the power bill. Whilst these would represent a great investment there was the roof space to allow a much more prosperous investment for the future.

As the customer was looking to stay in the property long term they opted for some of the highest quality products available on the market and requested the largest possible solar system to be installed.

The customer decided against batteries due to the high cost (if you are considering batteries read this post first – Click Here)

Upgrading to three phase

The customers existing power supply was single phase which is standard for domestic properties. On single phase the maximum inverter capacity is 10kW with a 5kW export limit so in order to maximise the potential benefit the customer decided to upgrade to three phase power.

The three phase upgrade costs $3000 but allowed the customer to install a 15kW three phase inverter with full export functionality.

The best roof space allowed for a 52 panel 16.9kW system
The systems average daily production: 70.98kWh
That’s 581% of the customer usage!

Why oversize the system?

You may be thinking why would you install a system that is going to produce 5.8 times what they actually use? This is because your energy retailer will buy excess power off you at surprisingly reasonable rates even without Government schemes. Feed in tariffs are available from around 10-20c/kWh depending on location and energy Retailer.

So for the electricity that can be used during the day the customer is offsetting their rate of power which prior to getting solar was 32c/kWh. This means that for people considering solar that are able to use more power during the day will save even more but this case study proves even with low daytime usage the investment is still very attractive.

For this particular example the customer switched energy retailers to Energy Australia who at the time of writing are offering a 16.1c/kWh solar buy back rate (feed in tariff). 

The System Installed

  • 16.9kW
  • 52 x 325w Q Cells Q Peak DUO German Engineered Solar Modules
  • 1 x Fronius Symo 15.0-3 Austrian made 15kW three phase solar inverter
  • 1 x 3 Phase Fronius Smart Meter
  • Total System Cost: $26,944.00
  • STC Solar Rebate $10,044.00
  • Customer Price after rebate: $16,900
  • 3 phase upgrade cost: $3000.00
  • Total Investment: $19,900.00
Client had the option to finance for $363.44 per month over 5 years

Full monitoring included with system

Customer has full access to online monitoring and receives email alerts if there are ever any errors

Click here to view live system data

Best production day 28th December 2018:



  • Before Solar power bill $353.62 DUE
  • After Solar power bill $948.70 CREDIT
  • Energy Offset: $232.96
  • Total Solar Benefit for quarter: $1,181.66
  • Estimated annual savings: $4500
  • 4.42 year payback period / 22.62% per annum


Adapt Energy (03/04/2019)

If the client opted for a 6.6kW system their annual savings would have been more like $1800 per annum with a payback period of 3.8 years. Although the shorter ROI is on offer on the smaller system, the customer wouldn’t have an annual profit of $3000+ on top of having no power bill.