A detailed model of a real solar thermal power plant has been built using a steady‐state power plant simulation software. The plant includes numerous parabolic trough collectors tracking the sun on a single axis. A heat transfer fluid flows in the focal line of the troughs collecting solar heat, which is transferred to high pressure water from the power block generating high pressure steam that is sent to a steam turbine to generate electricity via an attached generator. In addition, a spreadsheet has been formulated to work in tandem with the simulation software to model the daily operation of the plant. The spreadsheet is populated with 1 min increment time‐stamped operating data where computations are carried out to estimate the thermal energy contribution of the warm up and the cool down transient operations. Solar radiation offsets are calculated based on those transient heats and then incrementally added to the real‐solar radiation data to produce effective solar radiation records. Data columns of the effective solar radiation, ambient temperature, humidity, wind speed, time of day, day of year, and other geographical and optical constants are incrementally passed from the spreadsheet to the simulation program, which executes and outputs results back into the same spreadsheet. Simulation results matched well with plant data including data collected during warm up and cool down transient operations. © 2012 American Institute of Chemical Engineers Environ Prog, 32: 417‐424, 2013