Abstract Carbon nanotubes (CNTs) are known to be capable of enhancing optical and thermal properties of fluids prominently. Due to the modified features of the nanofluids with dispersed CNTs, they are used in various solar systems including PV/thermal (PV/T), collectors and water heating technologies. In this review article, firstly, the findings of the research performed on the thermal conductivity of nanofluids with CNTs are represented. In the next step of the study, the research conducted on the utilization of the mentioned nanofluids in solar systems are reviewed. On the basis of the reviewed literature, it is concluded that nanofluids with CNTs improve the performance of solar systems from both energy and exergy points of view. The performance of these nanofluids in the solar system is under the influence of various factors including the type of CNTs, operating conditions, concentration and the system they are applied in. Finally, according to the results of our literature review, suggestions are provided for future studies in this field which can lead to further enhancement in the efficiency of solar systems incorporating the investigated nanofluids.