This data packageincludes the modelling assumptions and input data to replicate the results of the case study included in the paper"Societal Effects of Large-Scale Energy Storage in the Current and Future Day-Ahead Market: A Belgian Case Study".Thispaper is part of the 18th International Conference on the European Energy Market (EEM22). The case study models the Belgian day-ahead electricity market, in which the existing storage is considered,in addition to large-scale battery energy storage systems of different sizes for varying renewable energy shares.A detailed description of the case study is provided in the readme file. This supplementary data package includes the following files: --Belgium Model Input Data.xlsx: Dataset used as input in the case study of the mentioned paper --Modelling Assumptions.pdf: Modelling assumptions considered in the case study --readme.txt (this file): Includes a detailed description of the data package The data included in this dataset was collected from public open sources [1]-[2]. Please notice that this dataset does not replace the original open access information. For accessing the data, please visit the following websites: [1] “ENTSO-E Transparency Platform.” [Online]. Available: https://transparency.entsoe.eu/dashboard/show. [Accessed: 06-Jul-2022]. [2] “Grid data.” [Online]. Available: https://www.elia.be/en/grid-data. [Accessed: 06-Jul-2022].