Reaching carbon neutrality in France by 2050 : optimal choice of energy sources, carriers and storage options.

Summary To contribute to the goal of containing global warming to 1.5°C, the French government has adopted the objective of zero net greenhouse gas emissions by 2050. As the main greenhouse gas is carbon dioxide, and most CO2 emissions are due to the combustion of fossil fuels, this thesis focuses on achieving carbon neutrality of French energy-related CO2 emissions by 2050. This thesis aims to study the relative role of different low-carbon options in the energy sector to achieve carbon neutrality. Specifically, this thesis first studies the French power sector, first in a fully renewable system, and then in one incorporating other mitigation options, i.e. nuclear power and carbon capture and storage. I study the impact of uncertainties related to the development of renewable energy costs and storage options and address the robustness of an all-renewable power system to cost uncertainties. Later, adding other low-carbon options in the electricity sector, I analyze the relative role of different options. Similarly, to encourage investment in renewable energy sources such as wind and solar power, I study the investment risk associated with the volatility of prices and volumes of renewable electricity technologies, and the performance of different public support schemes. The analysis in this thesis goes beyond the power system and also considers the entire energy system in the presence of sectoral coupling. During this thesis, I have developed a family of investment and operation optimization models to answer different questions concerning the French energy transition. These models minimize the cost of the considered system (power system or energy system as a whole) by satisfying the supply/demand balance at each hour for at least one year, respecting the main technical, operational, resource and land use constraints. Thus, the short and long term variability of renewable energies is taken into account. Using these models, I answer the questions raised above. These models are not used to find a single optimal solution, but several optimal solutions under different scenarios of weather conditions, costs, energy demand, and technology availability. Therefore, the importance of robustness to uncertainties is central to the methodology used, as well as optimality. The results of my thesis show that renewable energy sources are the main enablers of the energy transition, not only in the power system but also in the whole energy system. While the elimination of nuclear power only marginally increases the cost of a carbon-neutral energy system, the elimination of renewables is associated with high inefficiencies in both costs and emissions. In fact, if renewable gas is not available, even a social cost of carbon of €500/tCO2 will not be sufficient to achieve carbon neutrality. This is partly due to the negative emissions it can produce with carbon capture and storage, and partly due to the economics of internal combustion engines fueled by renewable gas. The central message of this thesis is that achieving carbon neutrality at the lowest cost requires a largely renewable energy system. Therefore, if we are to prioritize investments in low-carbon options, renewable gas and electricity technologies are of utmost importance.