In this paper, the design and analysis of a shell and tube heat exchanger used to combine parabolic trough solar collectors (PTSCs) and an organic Rankine cycle (ORC) based geothermal power plant is presented. A thermal model for the PTSC was first used to find the temperature of the thermal oil entering the heat exchanger under different solar irradiation intensity. Then, a detailed thermal model for the shell and tube heat exchanger based on logarithmic mean temperature difference method was formed. A computer code was developed using Engineering Equation Solver to study the effect of some key design parameters on the heat transfer surface area of the heat exchanger and the pumping power. Furthermore, a two-stage Taguchi method was applied to find the design parameters that give the minimum heat transfer surface area and pumping power. In addition, the effect of the solar irradiation intensity on the optimum design parameters was assessed. The results show that the baffle spacing is the most dominant design parameter; and Therminol VP1 or Dowtherm A as the PTSC side fluid and R245fa or R600 as the ORC side fluid should be selected. In addition, it was found that when the solar irradiation intensity increases from 450 W/m(2) to 1000 W/m(2), the minimum heat transfer surface area increases from 2.644 m(2) to 8.681 m(2). (C) 2017 Elsevier Ltd. All rights reserved.