This paper describes the results of a simulation study, validated by experimental results of a solar process heat system and represents the unsteady performance analysis of the system. The study focuses on the effect that the collector flow rates, temperature distribution and stratification have on the overall thermal and exergetic performance of the particular systems. The simulation is performed for the process heat system established in İzmir, Turkey. The analysis considers the unsteady-state thermal and exergetic analysis of the collector and the storage tank individually. The variation of the storage tank temperature is evaluated along the height of the storage tank at every hour during a day. The values obtained from the measurements at the İzmir Organize Sanayi Bölgesi-Industrial Process Heat System are compared with the predicted simulation results. The effects of the mass flow rates and temperature distribution of the load and collector on the performance of the system are discussed. The simulation results indicate that the exergetic efficiency is highly dependent on the ratio of mass flow rates and the use of an auxiliary heater in the system.