Stimulated by the ambitious decarbonisation targets, European countries have experienced a tremendous growth in distributed generation from Variable Renewable Energies (VRE). To face these new challenges an overall re-designing of the power system is required which would involve more flexible market schemes, adequate cross-border interconnections as well as smarter and even more integrated grids. On this purpose, European TSOs have planned a massive reinforcement of the electric borders mostly based on HVDC technology. Furthermore, the expected full market integration would be a very powerful tool for accommodating renewable energies.
Nevertheless, the great development of dispersed generation (DG) has been introducing new issues in the operation of the power system, mainly due to the uncertainty and the variability of VRE. In fact, the TSOs have to create reserve margins greater than in the past. Furthermore, due to the reduction of the thermal generation in favor of the VRE in the Day-Ahead- Market (DAM), it is less likely that the reserve margins are available to satisfy the security constraints of the system without re-dispatching actions in the Ancillary Services Markets (ASM). Furthermore, in some situations (especially during low consumption periods) the TSOs could not completely exploit the interconnection capacity in order to assure a minimum thermal generation in service or they have to curtail RES generation to mitigate the over generation (OG) phenomenon . All these consequences involve difficulties in the management of the power system and a strong increase of the costs for the final consumers.
In this context, flexibility of resources and new market designs could play an important role for the sustainable integration of VRE. Making controllable the DG and consequently allowing its usage also for providing ancillary services, will contribute to better shape the exchange profiles and therefore to reduce the risks of limitation of the available interconnection capacity during critical periods as well as the risk of system balancing issues. Obviously, a coordinated smart-evolution towards a greater interoperability of transmission and distribution is necessary as well as adequate forecasting, communications and control systems .
Recently, the Italian Regulator suggested a new market design that allows the DG and the renewables resources to take part to the ASM. It seems that the most promising services that VRE and DG could provide in the medium and long term horizons are the downward tertiary reserve and the downward balancing services.
The paper will investigate the Italian interconnected power system on 2023 and 2030 scenarios , assuming the development of the new market design proposed by the Italian Regulator. The study is based on market simulations in which the system is examined considering dynamic mechanisms and technical constrains. The analysis performed will investigate the contribution of VRE to the downward replacement reserve and the re-dispatching actions required, assuming that margins are created not only thanks to the action of the thermal power plants but also through the contribution of wind and the PV power plants. The study will show that, in general, the VRE participation to the ASM decreases the amount of renewable generation curtailed as well as produce significant benefit during the night and near midday.
In conclusion, the new market schemes proposed would improve the integration of the networks with a strong reduction of the ASM costs. Moreover, during critical situations, it could be also achievable a better exploitation of interconnection capacities.