The most interesting thing to me is the picture of they guy on the deck of the boat (from the article). What is the material used to cover the solar cells? It m

The most interesting thing to me is the picture of they guy on the deck of the boat (from the article). What is the material used to cover the solar cells? It must be tough enough to survive salt water and people walking on it. And yet it must allow most of the light thru. Maybe it's a very newbie question to materials people. But it's interesting to me. My mental image of solar cells is they're more fragile than that.