In concentrating solar power plants, the heat capacity of thermal storage media is a key factor that affects the cost of electricity generation. This work investigated the effective specific heat capacity of binary nitrate eutectic salts seeded with silica nanoparticles, using both experimental measurements and molecular dynamics simulations. The effects of the mass concentration (0-2.0 wt%) and average size (10, 20, and 30 nm) of the nanoparticles on the specific heat capacity value of nanofluids were analyzed. The results show that specific heat capacity increases when adding 10 nm silica nanoparticles up to 1.0 wt%, and then it decreases at higher concentrations. At this optimal mass concentration, the 20 nm nanoparticles displayed a maximum enhancement in the average specific heat capacity (by similar to 26.7%). The simulation results provided information about the different energy components in the system. The rate of potential energy change versus nanoparticle mass concentration was found to be maximized at 1.0 wt% concentration, which agrees with the experimental measurements. The potential energy components in the simulation system indicate that the change of Coulombic energy contributes the most to the variation of specific heat capacity.