The objective of this study was to compute the optimal depth increase of the embossed panels of a stainless water tank used for an energy storage system. The pressing used to emboss the panels of the stainless water tank decreases their thickness. By assuming that the panels had the same volume before (V o ) and after the change (V c ), we found an equation that computed how much the thickness of the panels decreased. According to the obtained thickness equation, the thickness of arch-embossed panels decreased by 50% relative to flat panels, and that of pyramid-embossed panels decreased by up to 30%. We also performed finite element method analyses of four flat panels, four arch-embossed panels, and four pyramid-embossed panels by applying the thickness equation for different depth increase. As a result, the optimal depth increase of the arch-embossed panels was 70-90 mm, and that of the pyramid-embossed panels was 150-200 mm. We concluded that these computed optimal depth increase could be useful in the economic design of a stainless water tank for an energy storage system.