Silicon is the second most abundant element in the Earth's crust... so we will never run out of silicon supplies. That is one of th ereasons I favor Silicon PV -- is that there is really no fundemental supply bottleneck limit on how much it can scale out to.
Having sadi that -- there may be transient supply problems for the supply of the high grade silicon feedstock. My guess is that we will likely see the type of cycle of supply shortages, followed by production rampup by the big suppliers such as Wacker and MEMC as well as new entrants into the market. This will lead to a supply glut and price drop, and a repeat of the cycle.
Currently the world produces 130,000 tons of polysilicon. I am not certain whether the 1366 Technologie's Direct Wafer Process can use metallurgical grade silicon (which is much easier to make and costs less, but has a lower purity than the Seimens process)
However there is no fundemental limit on the supply. Sand is everywhere. High grade silica ores are of course what manufacturers look for and which is the feedstock that is then reduced to metallic silicon needed by semiconductors including solar cells as well.
The world has many tens of billions of tons of high grade Silica sands that are easily recoverable -- so the raw feedstock is very abundant.
Does that help answer your question?