There is one fundamental difference between a fixed quota for renewables with tradable green certificates and other systems of support. The fixed quota results in different renewable technologies competing against each other. Other systems do not do this. If there is competition, it is between projects within the same technology. A fixed quota will immediately benefit wind energy in any country where it is the cheapest renewable. In many countries, however, energy-from-waste technologies are cheaper and so wind may suffer in the short term.
An unanswered question is how the quota should be divided between member states, especially if cross border trade in green certificates is permitted. If this trading is allowed, then wind energy in Country A would be competing against wind energy (and, of course, other renewables) in Country B. This should spread the cost of supporting renewables across the European Union, but it won't result in an even pattern of deployment. But perhaps this doesn't matter?