As part of the energy sector transformation, a substantial deployment of large-scale energy storage systems (ESS) is expected to support the integration of variable renewable energy sources (VRES). Understanding the value of this technology is of high relevance for investors and policy markets to assess their potential role in future energy systems. The present paper develops a model aiming to assess how large-scale ESSs participating in the day-ahead electricity market affect the market social economic welfare (SEW). This model considers two alternative bidding strategies by the ESSs owners participating in the market (i.e., a price-taker and a price-maker approach). The presented analysis considers a large case study representing the Belgian wholesale day-ahead electricity market, in which, in addition to existing ESSs, additional storage capacity is simulated for varying shares of VRES. Results suggest there is an added societal value driven by the participation of large-scale ESS in the electricity market in Belgium.