The dramatic increase of PV generation implies several challenges in transmission and distribution system operation. As for transmission, major issues relate to the variability, uncertainty, reduction of inertia and regulation capabilities, with consequent higher needs in flexibility resources requirements. Flexibility is considered as the ability of the power system to deploy its resources with the aim to match with changes in “net load” (e.g. load minus DG output including variable generation) ensuring a stable and a secure operation. In particular, high PV penetration significantly affects the daily profile of “net load”: lower net load in central daylight hours involves the risk of over-generation since a minimum amount of traditional generation is required for operational security (e.g. balancing reserve); in the evening, the decreasing PV output, which occurs together with the evening load demand ramp, exacerbates the upward ramps of net load with consequent risk of inadequate system response. The above concerns are further increased by the progressive decommissioning, due to loss of market competitiveness, of thermal power plants i.e. the main traditional resources of flexibility. New, highly performing flexibility resources are therefore gaining more and more importance.
This report provides a review of present and expected scenarios about flexibility in system operation. It summarizes and integrates results of a survey involving national experts in six countries, namely Belgium, Germany, Greece, Italy, Japan, and Switzerland. Information is provided about:
The main conclusions of the report are the following: