Flexibility assessment in nuclear energy dominated systems with increased wind energy shares

This study analyses the system integration of wind energy in terms of load balancing and power plants scheduling. The case study is the French power system, which relies on high rates of nuclear power, representing 78% in the total generation (2008). The study evaluates the ability of nuclear reactors to follow the load under several configurations of power plants in 2030 with at least 28 GW wind power representing 11% in the total generation. A dynamic optimization dispatching model is built with a detailed discrete-time formulation under the nuclear power ramp up and down constraints. Results show that operating the French power system with high infeed of wind power by 2030 seems technically feasible but relies heavily on the capacity of nuclear reactors to follow variations, on energy storage to insure flexibility and on the market capacity to allow generators to adapt continuously to the demand. Simulations show that balancing the wind power variation is less a matter of installing more flexible capacities, as load factors might decrease and reduce the investors' interest when prices are relatively low. Balancing becomes more an issue of ramping rates and unit scheduling, power market regulation and real-time market interactions with the day-ahead and intra-day markets.