The data presented were collected and published as part of the iDesignRES project, specifically under Task 1.1 and Task 1.3 of WP1. These tasks involved gathering detailed energy system data for Spain, covering electricity and gas, to be used as test data for the models employed within the iDesignRES project. The data which is presented here focuses on Spain’s electric power system, comprised of the transmission grid at voltage levels of 220 kV and above, provided in its actual form without aggregation or loss of spatial resolution. Additionally, it contains comprehensive generation data for all conventional units with capacities exceeding 1 MW, along with the most accurate possible estimation of renewable generation distribution across the network. While electricity demand time series for the entire country were sourced from the ENTSO-E Transparency Platform, the spatial distribution of consumption across the grid was estimated using population distribution data.