Renewable electricity supply is a crucial factor in the realization of a low-carbon energy economy. The understanding is growing that a full turn-over of the electricity sectors by 2050 is an elementary condition for avoiding global average temperature increase beyond 2 degrees C. This article adopts such full transition as Europe's target when designing renewable energy policy. An immediate corollary is that phasing-in unprecedented energy efficiency and renewable generation must be paralleled by phasing-out non-sustainable fossil fuel and nuclear power technologies. The double phasing programme assigns novel meaning to nearby target settings for renewable power as share of total power consumption. it requires organizing in the medium term EU-wide markets for green power, a highly demanding task in the present context of poorly functional markets in brown power. The EU Commission's 2007/2008 proposals of expanding tradable certificates markets were not based on solid analysis of past experiences and future necessities. The keystone of sound policies on renewable electricity development is a detailed scientific differentiation and qualification of renewable electricity sources and technologies, for measuring the huge diversity in the field. We provide but structuring concepts about such qualification, because implementation requires extensive research resources. Support for renewable electricity development is organized via feed-in prices or premiums, and via quota obligations connected to tradable green certificates. Green certificates are dependent on physical generated renewable power, but separable and no joint products. Contrary to conventional wisdom we argue their separation in cost analysis but firm linking during trade. A few graphs illustrate the importance of assigning qualities to different renewable power sources/technologies. Feed-in systems based on an acceptable qualification perform generally better than certificate markets imposing uniform approaches on a very diverse reality. For a similar reason, uniform and undifferentiated taxation of non-sustainable energy sources cannot replace renewable energy support schemes capable of differentiation. (C) 2009 Elsevier Ltd. All rights reserved.