RECS certificates were in place before Guarantees of Origin, and not all countries have yet joined the AIB in order to benefit from the European Energy Certificate System (EECS). For this reason, renewable energy is represented by both RECS certificates and renewable energy Guarantees of Origin.

Guarantees of Origin are obligatory in all countries within the European Union under EU Directive 2001/77/EC and its successor, 2009/28/EC (renewable energy); and EU Directive 2004/8/EC (high efficiency CHP).

There is no requirement for Guarantees of Origin for fossil and nuclear energy, or for lower efficiency CHP. 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 provides certificates for fossil and nuclear energy.

Further, not all countries have implemented the Directive(s) in the same way: for instance, code “x” may be “wind” in one country, and code “y” in another. Also, the information on certificates is not always collected in the same way. This hinders the international transfer of Guarantees of Origin, and leads to market participants in some countries using the voluntary RECS scheme instead.