[en] A detailed model of electricity systems is used to accurately assess energy transition policies to 2050 based on the development of renewables in the electricity sector. The model sheds light on the expected and unexpected effects of the complex interactions between policies targeting the development of large-scale renewable energy technologies, the use of a CO₂ constraint to control the environmental effects of renewable energy policies, and the possible use of new sources of flexibility (electricity storage, demand management) in reducing the cost of achieving ambitious targets for renewable energies. The complex modelling used demonstrates the modest levels of variable renewable energy (VRE) in an optimal mix in the context of carbon constraint. Similarly, the differences in the cost-effectiveness of policies aimed at developing renewable energies demonstrates the increased costs of policies targeting 80% of renewables, as well as their poor environmental performance. The use of storage slightly improves the economics of VRE in the system but can, in some cases, lead to higher emissions. (authors)