Hydrofoil based tidal arrays have emerged as a promising solution for large-scale power generation due to their high efficiency, cost effectiveness, and minimal interferences to the marine environment. In order to further maximize their power production and economic viability, an efficient tandem-hydrofoil based closely-interconnected tidal array is proposed, where the fore and hindfoils are closely spaced and interconnected to achieve constructive foil-foil interactions for energy capture. The power production, energy efficiency, capacity density, and levelized cost of electricity are obtained using a comprehensive approach that combines water tunnel experiments and computational fluid dynamics modeling. The results demonstrate that the capacity density of the proposed tandem configuration achieves at least 3 times higher than those of existing studies, while the hydrofoil deployment density is 4 times higher. Moreover, the energy efficiency and capacity density can be enhanced by enlarging the forefoil pitching amplitude or shortening the inter-foil spacing. Furthermore, the levelized cost of electricity is minimized to 50% that of existing studies, achieved by enhancing the energy capture and reducing the capital expenditures, thereby maximizing the commercial potential of the proposed hydrofoil based tidal array.