Original scientific paper https://doi.org/10.2298/TSCI171231273TThe aim of this work is the redesign of the reflector geometry in hybrid concentrating collectors that are currently manufactured by SOLARUS Sunpower AB ** to improve the energy efficiency of their solar collectors. The analysis is first accomplished using a numerical model that uses geometrical optics to study the interaction between the sunlight and a concentrating collector along the year. More complex physical models based on open-source and advanced objectoriented Monte Carlo ray tracing programs (SolTrace, Tonatiuh) have been used to study the relation between the collector annual performance and its geometry. On an annual performance basis, a comparative analysis between several solar collector geometries was effectuated to search for higher efficiencies but with controlled costs. Results show that efficiency is deeply influenced by reflector geometry details, collector tilt and location (latitude, longitude) of the solar panel installation and, mostly, by costumer demands. Undoubtedly, the methodology presented in this paper for the design of the solar collector represents an important tool to optimize the binomial cost/effectiveness photovoltaic performance in the energy conversion process. The results also indicate that some modified concentrating solar collectors are promising when evaluating the yearly averaged energy produced per unit area, leading to evident improvements in the performance when compared to the current standard solar concentrating SOLARUS systems. Increases of about 50% (from 0.123 kW/m 2 to 0.1832 kW/m 2 ) were obtained for the yearly average collected power per reflector area when decreasing the collector height in 3.5% (from 143 mm to 138 mm). ability of future generations to meet their own needs * [1]. Apart from the social aspects, the two other pillars of sustainability currently referred to are environmental and economic features. The former has enhanced the RES, the economic aspects deal with the energy efficiency. Among the most used alternatives within renewable energies, solar energy plays a fundamental role.In the last few years, the costs of photovoltaic (PV) modules have dropped rapidly benefitting from technical improvements. Taking into account that the solar cells prices are still responsible for a great percentage of the overall costs related to conversion energy system, different techniques have been implemented to increase the solar energy production without the use of more solar cells. Example of this is the inclusion of reflector concentrators in the concentrating PV-thermal (C-PVT) collector to increase the solar irradiance in the solar cells [2,3]. This may have a higher importance in world regions where the average irradiation is low. However, concentrators present some drawbacks, namely a decrease in the conversion efficiency, related to a partial absorption of the incident radiation by the reflector, and a reduction in the reflectivity features, related to dirt or aging [4,5]. Additionally, the...