No. It’s a common myth. Whilst south facing is the most optimum facing position, as a rule of thumb – an identical East or West facing roof would generate 85% as much energy as the south-facing roof. You may prefer to have an east and west facing roof than the south and north-facing roof as you could fit twice as many electric residential solar panels on the east/west roof than just south facing. Even a North facing roof will generate approx 55% as much energy as a south-facing roof. For example, a 20 year old 10% efficient south-facing solar panel would generate approximately the same amount of energy as a modern north-facing solar panel.   How do solar panels generate electricity