What is a green certificate? A green certificate is a tradable asset which proves that electricity has been generated by a renewable (green) energy source. It is also referred to as Renewable Energy Certificate (REC) or Renewable Obligation Certificate (ROC). A green certificate is typically issued per 1 MWh of renewable power. Alternatively, the number of green certificates may depend on the source, whereby greener or more innovative technologies may obtain more certificates than other technologies per MWh of power produced.