The alarming new global warming and increasing awareness related to climate change (mainly due to the high emissions of carbon dioxide) in recent decades linked all nations into a common cause, which requires ambitious efforts to combat climate change by adapting energy systems to its effects. The knowledge gain presented in this dissertation establishes the foundations for the development of a more efficient concentrating photovoltaic-thermal (PVT) solar collector. The presented work provides decision-makers with a broader, more detailed performance assessment of concentrating PVT solar collectors. A critical issue for concentrating PVT solar collectors lies in the respective reflector shape, which will determine, to some extent, the overall performance of the CPVT collector. Therefore, several symmetrical reflector design concepts were designed and optimized through Monte Carlo ray-tracing software. With the support of a MATLAB script, a simulation test methodology has been developed and optimized, allowing a more thorough analysis of the results regarding the viability of the different reflector shapes, which established the compound parabolic collector (CPC) to be the most appropriate reflector geometry for PVT solar collectors. Moreover, CPC-PVT solar collectors (based on the findings described above) were designed, built and outdoor tested (under steady-state method guidelines) for their thermal and electrical peak efficiencies, heat losses and incidence angle modifier (IAM) coefficients. The developments achieved in this dissertation significantly enhanced the annual performance of CPC-CPVT solar collectors, which closes the efficiency/performance gap between mature technologies such as PV modules or ST collectors.

Moreover, I would like to express my gratitude to the funding authorities that supported this project with funding, such as 1. Department of Building Engineering, Energy Systems and Sustainability Science of the University of Gävle. Papers I, II, III, IV and RES4BUILD project. 2. European Union's Horizon 2020 research and innovation program under grant agreement No. 814865. Paper II, IV and RES4BUILD project. Note: The output reflects only the author's view and the European Union cannot be held responsible for any use that may be made of the information contained therein. 3. Eureka Eurostars, under project number E10625. Paper II. 4. Swedish Foundation for International Cooperation in Research and Higher Education, under grant number ME 2018-7559. Paper III.