Optical and thermal simulation of a new solar tower steam generator is presented. The steam generator, placed on top of a solar tower, has two integrated receivers, external for boiling the steam and a cavity for its superheating. These two parts of the solar steam generator are facing different sections in a surrounding heliostat field and therefore can be operated independently. The evaporation part is shaped as an external cylindrical receiver which creates a cavity with an aperture for the superheating part. This novel arrangement allows high optical and thermal efficiencies. This concept of the integrated solar steam receiver is illustrated through a modeling of a large-scale plant producing superheated steam at 550 degrees C and pressure of 150 bars. The decoupling of the steam superheating part from the evaporation makes the system more economical, easy and safe to operate. (C) 2011 Elsevier Ltd. All rights reserved.