In the wake of the Paris agreement, France has set a zero net greenhouse gas emission target by 2050.This target can only be achieved by rapidly decreasing the share of fossil fuels and accelerating the deployment of low-carbon technologies. We develop a detailed model of the power sector to investigate the role of different low emission and negative emission technologies in the French electricity mix and we identify the impact of the relative cost of these technologies for various values of the social cost of carbon (SCC).We show that for a wide range of SCC values (from 0 to 500€/tCO2), the optimal power mix consists of roughly 75% of renewable power. For a SCC value of 100€/tCO2, the power sector becomes nearly carbon neutral while for 200€/tCO2 and more, it provides negative emissions. The availability of negative emission technologies can decrease the system cost by up to 18% and can create up to 20MtCO2/year of negative emissions, while the availability of new nuclear is much less important. This study demonstrates the importance of an effective SCC value (as a tax for positive emissions and remuneration for negative emissions) to reach carbon neutrality for moderate costs. Negative emissions may represent an important carbon market which can attract investments if supported by public policies.

Many studies have demonstrated the feasibility of fully renewable power systems in various countries and regions. Yet the future costs of key technologies are highly uncertain and little is known about the robustness of a renewable power system to these uncertainties. To analyze it, we build 315 long-term cost scenarios on the basis of recent prospective studies, varying the costs of key technologies, and we model the optimal renewable power system for France over 18 meteorological years, simultaneously optimizing investment and dispatch.Our results show that the total cost of a 100% system is not that sensitive to the power mix chosen in 2050. Certainly, the optimal energy mix is highly sensitive to cost assumptions: the installed capacity in PV, onshore wind and power-to-gas varies by a factor of 5, batteries and offshore wind even more. But the total cost will not be higher than today, and choosing a non-optimal electrical mix does not significantly increase this total cost. Contrary to current estimates of integration costs, this indicates that renewable technologies will become by and large substitutable.