Ideally, a south-facing roof would give you the most effective power generation for each solar panel. With an east or west-facing roof, efficiency will drop by around 15%. This is because the sun rises in the east and sets in the west, meaning roofs facing in these two directions will only be effective for half of the day. A north-facing roof is the least effective, but the beauty of a north-facing roof at the front of your property – means that it is a more effective south-facing roof at the rear of your property.