Follow these steps for guidance on how to use the calculator.

1. Gather the essential information

  • Details of your solar panel system, such as number of panels, number of kilowatts
  • Your energy bill
  • Details of the overshadowing building 
    • if assessing the impact of a proposed development, check your council website for the detailed plans and permit application or contact the council for more information.
    • if assessing the impact from an existing development, find an aerial image of your house and the neighbouring property. This can be sourced from Google Maps, Google Earth or other aerial image sources.


  • the calculator assumes both properties are on flat ground and the overshadowing building is box shaped
  • where the overshadowing property is at a higher elevation (slope) the overshadowing will be greater than the tool estimates.

2. Select the calculator that most closely matches the slope of your roof.

Select from the calculators on the main page above.

To work out what your roof angle is, there are apps available online that can calculate this via a smart phone or computer, for example, or

Alternatively, your installer may have noted this on your original quote. If not, you could also take a photo of the cross section of the roof and use a protractor to calculate the roof pitch.

Image of protractor

3. Fill out the information in the ‘Yellow’ coloured boxes of the calculator

Image of example numbers included in the calculator tool

  • Type over the pre-populated figures. These are just typical numbers included so the tool works in case you forget to add a figure.
  • For help, hover your mouse above the cells showing a red mark to get more information.
  • A grey triangle will appear when you click on some yellow cells. Click on this triangle and a list of options will be revealed. You’ll need to select the value that matches your situation most closely (these are pre-set options – the calculator won’t work if you try to input something else).

Image of example figures included in calculator tool under Solar System

4. Size or capacity of your solar panel system in kilowatts (kW)

For example, a 4 kW system is equivalent to about 16 modern panels, or about 22 older pre 2015 panels.

5. Number of panel rows – either 1 (single row) or 2 (two rows)

Image of single row and double rows of rooftop solar panels

6. Orientation – what compass direction do your panels face?

To check, look at your property on a map, refer to a mapping website such as Google Maps, or use a compass.

7. Solar panel technology type:  Select what matches your system

  • Standard rooftop solar system - the panels are connected to a wall-mounted appliance called an inverter.  
  • Micro inverter rooftop solar system – microinverters are located underneath each panel on the roof.

If you don’t know, and you cannot ask your supplier, select standard solar rooftop system.

8. Set back angle

Image of example setback angle included in calculator tool

Estimate the distance from the bottom of the roof to the bottom edge of the solar panels, as shown on the diagram below. If the panels extend to the bottom of the roof, please enter zero. You may be able to measure this or estimate it by looking at a map or using measuring tools in aerial photography such as Google Maps or Google Earth.

Image of where to measure for overshadowing by neighbour

Image of example of figure included in calculator tool for details of overshadowing building

9. Height above panels (a)

This is the height from the bottom edge of the solar panels to the top of the overshadowing building.

The height of a building storey is generally around 3.3 metres, but this varies from just under this figure to well over it.

For situations where the overshadowing house is on much higher ground, select the next highest 'height above panels' option.

Image of measuring horizontal distance between solar panel and neighbouring building

10. Horizontal distance from panels (standoff) [see (b) in diagram below]

This is the distance from the bottom edge of the solar panels to the overshadowing building. You may be able to measure this or estimate it by looking at a map or using measuring tools in aerial photography such as Google Maps or Google Earth.

Note that this distance may not correspond directly to a building 'setback' due to the solar panel position on the roof.

Image of measuring horizontal distance between solar panel and neighbouring building

11. Left distance from system edge and right distance from system edge

Estimate how far the overshadowing building extends beyond the left and right edges of the solar system. If the solar panels continue beyond the edge of the overshadowing building, this distance should be recorded as negative (see example below, where the solar panels extend 2 metres beyond the edge of the overshadowing building).

Note that the calculator assumes that the overshadowing building is 'box-shaped'.

Two images of building with rooftop solar panels and neigbouring building showing measurement and different placement of neighbouring building

Image of example figures in calculator tool under Economics

12. Usage on your bill

This number can be found on your electricity bill and is often referred to as the average daily usage (Use this figure).  

If the bill just shows a total amount of energy rather than a daily average, you need to divide this by the number of days in the billing period to get the daily average. In the example bill below we divide 893.52 kWh by 92 days = 9.7 kWh per day.  This input affects the assumption on how much solar generation is used onsite versus exported to the grid.

13. Import tariff

This is the rate that you pay for electrical energy from the grid, charged in cents per kWh. The calculator only works with a single number for this input, so if you have been charged different rates for different amounts of energy (e.g. on a time-of-use tariff), please enter a rough average tariff representing what you paid overall.

14. Supply charge

This is an amount you are charged every day, regardless of how much energy you import from the grid.  

In the example below the amount is 116.95 c/day, however this retailer granted a special discount of 8.71 c/day, so the effective supply charge is 108.24 c/day. Applying GST (multiply by 1.1) and the 7% pay-on-time discount (multiply by 0.93)1 as above we get 110.7 c/day.

15. Feed-in tariff

This is a rate at which your retailer pays you for energy you export (feed in) to the grid, defined in cents per kWh. The example below uses 12 c/kWh. GST is not payable on this rate.

Image of example figures included in calculator tool under Electricity Tariff Breakdown

For your assistance, a more detailed user guide is available here: 

Page last updated: 22/11/19