With over 4 MW of generating capacity installed worldwide, parabolic trough solar power plants are currently the lowest-cost concentrating solar power (CSP) option for electricity production. A parabolic trough plant uses a large field of solar collectors to capture solar radiation and transform it into sensible energy in a high- temperature heat transfer fluid; the thermal energy can be transported to a conventional power plant, or stored in a thermal energy storage system (TES) for later use. This seminar will present an example of the development and use of thermal systems models developed for commercial parabolic troughs plants, in which the effect of individual technical improvements on the overall plant performance were analyzed, and the least cost of energy option was identified. These thermal system models are fundamental for evaluating the overall benefit achieved by technical improvements on commercial applications as well as for guiding R&D decisions. Some of the alternatives studied included solar collectors, heat transfer fluids, thermal energy storage systems and power cycles.