How does output of a solar power system varies if the solar panels do not face True North?
Solar panels will produce the most output in kW/h if they face True North on a standard 23-30 degree pitched roof. (For example solar power systems produce solid output in Sydney if they are tilted 25 degrees). Nevertheless, sometimes it is not possible to face the panel True North as the best available roof space faces North West, West or East.
Australia and NZ have very good sun irradiation, said simply – solid sunshine hours - and therefore when analyzing the loss of output electricity due to non ideal positioning of the panels one finds that the loss is not that huge. For example while in Sydney a True North pointed panel on a typical 23 degree roof will give you maximum output (100%) an North West pointed panel on a 15 degree roof will still give you 97.1 % of available output. Even a panel pointing completely West on the same roof will still give you 91.7% of available output. So in summary in our sunny climate pointing the panel in a not 100% perfect alignment with the most ideal scenario will still give the customer still solid solar irradiation output.
So in summary: On a standard pitched roof across Australia, you will on average loose approximately 15 to 17% of total generation in kW/h by facing the panels due West or East rather than North. However this may allow the household to take better advantage of the power generated. For example, for a household where more power is used in the afternoon as members of the family are home then, it would be more beneficial to have the panels on a North West facing roof. This will allow the panels to generate more power in the afternoon and enable the household to more effectively use the power when it is generated. This is because more power is produced by the panels when the sun is perpendicular to the panels.
The table below is relevant for Sydney, NSW, Australia and shows how much out of an ideal possible 100% solar power system output, a solar electric system can lose due to varying roof angles and due the fact that the panels do not face True North.
Output ratio in Sydney, NSW at different angles
Tilt angle is the angle from the flat towards the sun