This thesis is a part of an ongoing applied research project at the Solar Energy Laboratory at UC Merced, with the objective of developing a solar thermal system able to increase the temperature of a heat transfer fluid to output temperatures around 200°C(∼400°F). The goal of this project is to design and implement a modular, low profile, scalable and solar-powered system to offer an on-site heat source. Operating temperatures on the target range of this project create the possibility of providing a renewable source of heat to a number of thermally activated technologies such as refrigeration, air-conditioning, power generation, desalination, water treatment and others. This thesis presents three heat transfer models that were built to conduct a preliminary performance assessment of three concentrating solar thermal units. Each solar thermal unit is comprised of an optical concentrator and a thermal element. The optical element is a non-imaging, reflective concentrator in the family of the compound parabolic concentrators (CPC). The thermal element includes a solar radiation absorber that transfers heat to a fluid, and an evacuated glass tube that encloses the absorber. The three concentrating solar thermal units discussed in this work are: • Type I: All Glass Dewar: Direct Flow. • Type II: All Glass Dewar: Indirect Flow. • Type III: Metal Absorber with Glass-to-Metal Seal. The solar thermal system would be integrated by thermal units connected in series to gradually increase the temperature of the fluid. The optical analysis was carried out by other authors but some relevant results to the thermal analysis are presented in this work.