The present numerical study using ANSYS FLUENT 18.1 is based on improving the thermohydraulic performance of a solar air heater by embedding truncated half conical vortex generators (THC-VGs) on the absorber plate. Grey relational analysis (GRA) optimization technique is employed to achieve the best configuration for the applicable range of Reynolds number (Re = 3500-16000). The THC-VGs are fixed on the absorber plate at a relative pitch ratio, P/e range of 2.67-6.67 and placed such that the angle of attack, alpha lies in between 0 degrees and 90 degrees. RNG k-epsilon turbulent model is employed to solve the complex governing equations of CFD. Results are analysed by computing different performance parameters like, Nusselt number, Nu, thermal enhancement factor, TEF, friction factor, f, friction factor enhancement factor, FEF and thermohydraulic performance parameter, THPP. A maximum percentage enhancement of 187% in Nu is noted for alpha = 60 degrees, P/e = 2.67 and Re = 16000. Results are supported with proper justifications by using different contours derived from the post processing unit of the CFD code. Proper flow dynamics along with thermal behaviour due to the introduction of THC-VGs are explored. Correlations for Nu and f are developed as a function of Re, P/e and alpha.