A common belief about solar is that panels must be on a north facing roof to generate a good amount of energy and make them worthwhile. However, is this really true? How much do we really lose on roof areas that face east, south and west? Is it a deal-breaker if we only have a south-facing roof?
To answer these questions, we first modelled a house in sunny Brisbane. On a house with a roof face that tilts 20 degrees facing north, a standard 6.66 kW array of solar panels will produce around 10,500 kWh per year of energy. This should save the customer about $420 per quarter. On the same house, if the panels faced south, the amount of energy produced drops to around 8,050 kWh per year, saving the customer about $325 per quarter. East and west facing roofs both produce about 9,300 kWh per year with about $370 per quarter in savings. So, there is certainly a reasonable difference in outputs and savings, but are all still good investments?
If the system cost, say, $4,200, the north facing system would pay itself off in 2.5 years. Pretty good. The east and west facing systems pay themselves off in about 2.8 years, and even the south facing system can pay for itself in 3.3 years. So yes, there is a difference with panels facing different directions, but given estimated system lifetimes of 25 years they are all still incredibly good investments.
Next let’s go down to Melbourne to see if moving further away from the equator makes any difference to the situation.
Using the same 6.66 kW array, a north facing roof will generate about 9,300 kWh per year. As expected, a good bit less than for Brisbane. This still creates savings of about $370 per quarter and the system will pay itself off in 2.8 years, a bit longer than the 2.5 years in Brisbane. For east and west facing panels, 8,270 kWh will be generated, saving the customer about $330 per quarter with a 3.2-year payback. This compares with a 2.8-year payback in Brisbane. And for the worst case, the south-facing roof in Melbourne, 6,730 kWh are generated per year with savings of about $269 per quarter. This worst-case scenario is still a good investment, with a 3.9-year payback on a system that should last 25 years!
The good thing about a flat roof is that panels should be tilted in order to let them self-clean with rain, even if it costs a bit more. They can be tilted in any direction. So of course, we’d choose north!
The direction your solar panels face certainly does affect the energy output and the payback periods for investment. However, even for a house in Melbourne, panels on faces that do not face north still make for incredibly good investments. The worst-case scenario of a south facing roof in Melbourne still pays itself off in 3.9 years meaning there’s about 21 years to make money from the system. So, no matter which way your roof faces, solar is a great investment!
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