How much silicon is there, in kg, in a 1kw panel? Thanks!
Fthenakis has published more on the subject than anyone, to my knowledge. His LCA lists a whole bunch of factors, but it's roughly 1.5kg of silicon in the PV itself.
But a module also has 16.1kg of tempered low-iron glass for a 210 Wp panel (p32). Glass is 60-80% silica, and silica is about half and half silicon and oxygen by weight. So there's 5kg - 6.5kg of silicon in the glass.
I'm not sure there is such a thing as a 1kW panel - it would be 5-7 square metres in size.
However, we can consider 1kW to be a useful unit - typically about five panels' worth - and that, very roughly speaking, would be roughly 40kg of silicon.
This isn't a sustainability issue though: not only are silicon cells recyclable, but the earth's crust is about 10% silica - it's one of the most abundant compounds on the planet.