You are correct in a way but you have forgotten the energy (lots of oil, diesel and coal) required to;
-Mine and transport the sand
-Melt the sand to produce glass
-Mine and transport bauxite
-Smelter the bauxite into aluminium
-Transport glass, aluminium and other materials to china
-Construct panels
-Ship panels to Australia
-Truck panels to warehouse
-Truck panels to distributor
-Courier panels to your house
-Etc etc
