Green tags are non-tangible energy commodities traded in the United States. A single green tag represents proof that 1-megawatt-hour (MWh) of electricity was generated from a renewable energy source recognized in the United States. A green tag can be sold and bartered and its owner can claim to have purchased renewable energy. Green tags are also known as Renewable Energy Certificates (RECs), Renewable Energy Credits, Renewable Electricity Certificates or Tradable Renewable Certificates.