A solar thermal concentrator system is proposed comprising a free-form-trough (FFT) reflector and a cylindrical heat-pipe receiver. The profile of the reflector is designed using a free-form surface creation (FFSC) method such that each incident ray is directed to a certain user-specified point on the heat-pipe surface. The light ray paths within the concentrator system are analyzed using a skew-ray tracing approach. A method is then proposed for optimizing the geometry of the concentrator system in such a way as to achieve a uniform irradiance distribution on the heat-pipe surface. The validity of the proposed optimization approach is demonstrated by means of ZEMAX/SolidWorks-Flow simulations. The results show that the proposed FFT concentrator yields a significant improvement in both the irradiance uniformity and the heating efficiency compared to conventional cylindrical-trough and parabolic-trough concentrators. (C) 2015 Elsevier Ltd. All rights reserved.