“Guarantees of Origin are obligatory in all countries within the European Union under EU Directive 2009/28/EC (renewable energy); and EU Directive 2012/2/EC (high efficiency CHP).
There is no requirement at EU level for Guarantees of Origin for lower efficiency CHP. Nor is there a requirement at EU level for Guarantees of Origin for fossil and nuclear energy – although these are issued in Austria, Sweden and Switzerland.
However, it is useful to have certificates for all types of energy, as it enables anyone selling energy to consumers to let them know where all of the supplied the energy comes from, rather than having to use a statistically-based “residual mix”. For this reason, EECS supports certificates for fossil and nuclear energy.
Without EECS, each country might implement the Directive(s) in different ways: for instance, code “x” may be “wind” in one country, and code “y” in another. Also, the information on certificates would not always be defined in the same way. This would hinder the international transfer of Guarantees of Origin.” Source: https://www.aib-net.org/faq/types-certificate