How can I access historic data that was published on entsoe.net before January 2015?

All the data previously published on entsoe.net between 2011 and 5 January 2015 has been migrated and packaged for download in either XLXS or XML files.

You can access this data by year at: https://transparency.entsoe.eu/content/static_content/Static%20content/legacy%20data/year%20selection.html