Its not clear enough in the text, but what the author likely means is to place the panels flat, not standing, and not on the ground. Depending on what the material is, placing panels standing or at an angle can cause deforming or risk the panels falling and getting damaged.
... you should post it as a seperate question...
If you do that, please say whether the rest of the document appears to have been written by a native English-speaker.
peer agreement (net): +7