The principal data source used for this website is the European association for the cooperation of transmission system operators for electricity (entsoe). The entsoe database includes data from most European countries including many not members of the European Union, however, the current website mainly analyses data from EU countries.
For most countries the data available on the entsoe site, starts on 5 Jan 2015, however in a few cases the data for 2015 is missing or has extensive omissions. The yearly EXCEL files are downloaded from the site with times set to UTC. The entsoe files have 21 different fuel types: for simplicity coal, peat and "other" are combined and called "coal" in the plots. "Fossil" combines this "coal" plus oil and all classes of gas.
Occasionally, there are missing entries in the entsoe data, marked N/A. These N/A entries are edited out by hand. For short periods (hours, 1-2 days) the N/A is replaced with an interpolation from the nearby data. For long periods the N/A are set to zero. This is more often the case for the cross-border flow data, particularly for eastern borders. Rarely there are clear errors in the data with entries set anomalously to zero or very low for short periods. These omissions are usually 1-3 hours. These also are corrected by interpolation.
The entsoe database only contains data from 2015. and only for European countries The BP Statistical Review of World Energy has data for the whole world, starting from 1965 for a few countries and 1985 for most countries. Plots starting before 2015 in this website use this BP data.