A cylindrical-parabolic solar collector was thermally optimized for a winter season using a weather model and an extension of the present state-of-the-art collector theory. An accurate model for the cover transmittance and a seasonal performance model was developed. The optimum collector dimensions and materials were found to be a strong function of the design operating temperatures. The optical and thermal losses of a cylindrical-parabolic collector were compared and the results showed that the major loss for process heating temperatures was heat lost by natural convection. Reflection and cover losses were the next largest losses. Comparison of a flat-plate collector with a cylindrical-parabolic collector showed that a cylindrical-parabolic collector appears better suited for process heating than domestic hot water or space heating. Glass and plastic covers were analyzed and the optimum collector slope was obtained. The investigation resulted in a better understanding of how different collector dimensions and materials affect collector performance.