A Green Certificate (GC) is a “document” that proves that a unit of electricity has been produced from a Renewable Energy (RE) source. Generators receive a certificate for each pre-defined unit of electricity produced from their RE scheme that is delivered to the electricity network. Electricity from RE schemes is indistinguishable from other electricity, so the certificate is used to represent the “renewableness” or the “greenness” of a unit of the renewable energy generation. A GC becomes a Tradable Green Certificate (TGC) when the mechanism allows trading of GCs as a means of meeting an obligation. Note that for practical purposes Green Certificates are more likely to be electronic documents than paper documents.