I often heard that solar panels are best if they are facing south, others say any direction but north. But a study by pecan street research institute says west is the best side is west offering 2-11% improvement.
http://inhabitat.com/have-we-all-been-installing-solar-panels-the-wrong-way/
http://inhabitat.com/have-we-all-been-installing-solar-panels-the-wrong-way/