The 20% efficiency is, as stated in the other comment, about correct for a plant without thermal storage. See far example [1]. What happens with the higher effi

The 20% efficiency is, as stated in the other comment, about correct for a plant without thermal storage. See far example [1]. What happens with the higher efficiency ratings is that they put more mirrors on the tower, or have a smaller turbine. That is, the ratio between thermal input and electric output increases. They can do this because any heat that isn't used by the turbine right at that moment can be stored temporarily and then used later on when the incoming heat isn't enough to power the turbine at 100%. Which means that with an efficiency rating of 73%, you still need many more mirrors than with the capacity factor of 25%, but you just don't upgrade your turbine, and instead rely on thermal storage. Which one is preferred (bigger turbine or thermal storage) depends on the cost of turbines and thermal storage, and on whether you want to have baseload power or higher output during the day. As a note, the 72.9% and 56.2% you quoted were estimates made in 2003 for the year 2020, so I wouldn't put to much trust into them. As for Ivanpah itself, it appears to not have any thermal storage planned (which would have to be the biggest thermal storage ever created to be useful), according to [2], so it would be limited to about a 25% capacity factor. [1] http://www.nrel.gov/docs/fy11osti/49303.pdf http://www.nrel.gov/docs/fy11osti/49303.pdf [2] http://www.basinandrangewatch.org/IvanpahFSA-reliability.html http://www.basinandrangewatch.org/IvanpahFSA-reliability.htm...