Évaluer le coût des politiques climat-énergie à base de renouvelables. Du bon usage des modèles d’optimisation sectorielle

Many countries have adopted a low-carbon transition policy in the power sector that is inefficient because it is mainly based on the promotion of variable renewable energy sources (VRE) at large scale, alongside carbon pricing which has only a minor role. This paper focuses on exercises to evaluate these policies in comparison with policies that place all low-carbon technologies on an equal footing, which is done with complex modelling of electricity system with large share of VREs. Three exercises show that the optimal shares of VRE are low (maximum 15%), whatever the level of the carbon price, even after taking into account the sources of flexibility (storage, demand management, integration with neighbouring systems, intersectoral coupling) that enhance the value of the VREs. But these results contrast with those of a very thorough exercise by Ademe which, without testing scenarios with realistic assumptions on flexibility, would prove that the power system can economically rely on VREs alone, without dispatchable low-carbon technologies, including nuclear. This comparison highlights the importance of the assumptions made about the various sources of flexibility and the institutions needed to coordinate their development with that of VREs, assumptions that explain the results in favour of VREs and against dispatchable low-carbon technologies.