Definitions for "Green Tags"
Two products are created when a renewable energy facility, such as a wind farm, operates. First is the electricity that is delivered to the grid. Second are the environmental benefits, emissions offsets from creating the same amount of energy from non-renewable sources. These credits, called Green Tags, Renewable Energy Credits (RECs), or Tradable Renewable Certificates (TRCs), are sold to make up the difference between what it costs to build and run a renewable energy generator and what they can sell for the power for on the open market. A purchase of Green Tags replaces fossil-fuel-fired power with clean renewable energy. Every Green Tag increases the amount of green energy in the system. See also http://www.green-e.org/what_is/dictionary/trc.html
See RECs below
Created when a renewable energy facility generates electricity. Each unique certificate represents all of the environmental attributes or benefits of a specific quantity of renewable generation, namely the benefits that everyone receives when conventional fuels, such as coal, nuclear, oil, or gas, are displaced. You usually buy certificates from someone other then your electricity provider. What you pay for when you buy renewable energy certificates is the benefit of displacing other non-renewable sources from the regional or national electric grid.