What is the best method to clean our panels?

Simple green or another environmentally friendly solution, scrub brush and garden hose. Do not use any corrosive solutions or power washer as it will compromise the outer surface of the part. Any corrosive solution is not only bad for the environment surrounding the structure being cleaned but also as with a pressure washer will damage  the outer shell of our part which provides the UV protection from early bearding, chalking and of coarse once this begins the strength in the physical properties of our parts become compromised.