Factual error: In the first scene at the Pentagon, the sergeant tells the other officer that all satellites are being put into geosynchronous orbit to "hide them behind the planet." But objects in geosynchronous orbit don't remain hidden behind the Earth relative to the sun; they orbit once a day, remaining over a particular longitude on earth. Therefore, they would be subjected to the magnetic storms every day, during daylight at that longitude.
Factual error: The title and the whole plot of the movie is all wrong. The sun doesn't have enough mass to ever become a supernova. It will expand to become a red giant, throwing off its outer layers and then forming a planetary nebula. The core will eventually collapse into a white dwarf. This whole phase will take billions of years anyway.