In recent years, the scientific community has given significant regard to studies on the use of nanofluids (NF) in thermal energy systems like solar collectors. In the present study, role of rGO-based NF in thermal performance enhancement of flat plat solar collector (FPSC) has been investigated. The thermal performance of FPSC has been tested by using DI water and rGO-based NF as working fluid. rGO-based NF has been prepared by suspending 0.05 vol. concentration of rGO in DI water. Thermal performance has been tested for three vol. flow rate from 0.5 lpm to 1.5 lpm and solar intensity from 600 to 1000 W/m2. It has been found that maximum thermal performance occurs at vol. flow rate 1 lpm and solar intensity of 800 W/m2 by using DI water and rGO-based NF. Thermal performance has been found to decline with an increase in the reduced temperature parameter. When employed as the working fluid in FPSC under the same flow circumstances, the maximum thermal performance was discovered to be 59.7% when utilising rGO-based NF, which is 21.5% higher than that of DI water. Therefore, using r-GO based NF as the working fluid in FPSC is an appropriate choice.