in the article:
SolarReserve’s technology will use a tower with a holding tank of molten salt. An array of mirrors will reflect light onto the tank. The heated liquid is then pumped into a steam generator that will turn a turbine to make electricity.
Not sure why molten salt is a preferred heat store medium though.
The melting temp for NaCl is 800.8C (or 1473.4F), that’s a LOT of heat to store for using in a steam generator!
It's not corrosive and has a much higher boiling point than water, so the same volume can hold more heat. And as opposed to other possible exotic alternatives, it's not that toxic. Spills can be left to solidify, then picked up off the ground. Unless it's raining, then you get lye, but spraying a lot of a moderate acid around will take care of that.
Sorry, thinking sodium instead of salt, forget the lye part. I guess this is just like the old Solar Two project. If the tanks burst and it spilled all over, they’d just have to bring in front loaders to pick up the salts and recycle it.
But it will hold a LOT of heat per volume, more than most other substances, so it makes for an excellent heat sink.