Nowadays, attention is directed towards the possibilities of harnessing the potential of tornado by creating an artificial convective vortices for green electricity generation. In view of this research trending, a novel new solar vortex power generator, designed, fabricated and experimented at University Technology Petronas, Malaysia. In this paper, ANSYS - FLUENT 15 software was used to simulate the influence of inflow slot size on the vortex updraft velocity. Two cases hav been investigated. Case 1 with new dimension of 0.1 m width and guide vane height of 0.6 m. Whereas, case 2 with slot dimension of 0.3 m height and 0.15 m width. From the attained results, it could be deduced that the slot size is an important parameter which impacts on the vortex strength. The vortex exit velocity increased by 50 a nd by 2.6 for the case 1 and case 2, respectively. This indicates that the slot height is highly influencing the vortex strength. Thus far, the indexes from the numerical simulation can be used in re-designing of the inflow slot size for optimal performance. © 2018 The Authors, published by EDP Sciences.