This upload contains the Supplementary Information file and the underlying data as Excel-file for the referenced Journal article ("Hourly marginal electricity mixes and their relevance for assessing the environmental performance of installations with variable load or power") More specifically, it provides time series of the Spanish electricity generation mix for the year 2021 for energy system analysis (as used as basis for the underlying publication), including imports and environmental impacts of the hourly generation mix for all EF3.0 impact categories (Marginal_Electricity_Results_Analysis_2021_V17.xls) a spreadshhet calculator for determining the average and marginal hourly benefits of a generator with variable load (a PV installation, but the generation profile can be substituted by any other) Load-Gen_Balancing__V15.xlsm life cycle inventory data for import into openLCA and re-use in combination with the ecoinvent databse (Version 3.7.1). Further details are available on request to the main author.