The deployment of renewable energy technology is a well established instrument in climate policy in Europe and elsewhere, yet relatively little attention is given to the cost of the CO2 emissions avoided as a result of RE policies. This workshop assembles a group of electricity system modelers to determine, from an ex post point of view, the amount of CO2 abatement that has resulted from RE deployment in Europe and the cost of that abatement. The purpose is not so much to arrive at a final definitive number as it is to identify the factors that create more or less abatement and more or less cost.