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, https://pitchgauge.com or https://www.ursupplier.com/tools/angle_measurement/

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

Page last updated: 22/11/19