Renewables Integration in Distribution Grids

In recent years, due to the increased fossil fuel demand, international awareness has been focusing on the security of energy supply and on energy-related CO2 emissions, which are expected to more than double by 2050. To deal with these issues, the interest is in the diffusion of renewable energy sources (RES), especially photovoltaic and wind. The number of prosumers is increasing all over the world: they are electric users with small production plants directly connected to their systems. They are active users, so they are able not only to absorb energy from the grid (like passive users) but also to inject it.

All the small production plants connected to medium and low voltage distribution networks constitute the distributed generation (DG). In Italy, most photovoltaic systems are connected to distribution networks: over 22 000 systems connected to medium voltage concentrate 55% of the total installed photovoltaic power (over 20 GW), and only a few systems are connected to the high voltage grid (less than 8% of the installed power). The presence of mini-wind or water turbines is also growing; for example, 2 GW of wind power connection requests were received in 2020 by the Italian distribution network operators.

Power production from photovoltaic and wind power plants is variable and not programmable, since it depends on weather conditions. This poses serious problems to the electricity system, especially when a considerable share of the electricity demand is covered by these variable sources. Furthermore, reverse power flows (from medium and low voltage networks to high voltage networks) are increasingly frequent. These problems can be mitigated or solved by various types of technologies, such as energy storage systems. At the end of 2020, almost 40 000 electricity storage systems were installed in Italy, for a nominal power of over 180 MW; in particular, the number and installed capacity of storage systems increased by 50% from 2019 to 2020.

Digital technologies, combined with electrical components, are becoming increasingly important. Electrical grids become "smart grids" since allows to monitor, manage in real-time and optimize energy production and power flow, improving the integration of renewable sources. Smart grid technologies can be classified into technology areas, with different maturity levels: wide-area and monitoring and control (in rapid development), information and communication technology integration (mature), renewables and distributed generation integration (in rapid development), distribution grid management (in moderate development), Advanced Metering Infrastructure (mature), charging infrastructure for electric vehicles (in rapid development) and customer-side systems (in rapid development). The deployment of these technologies is expected to create improvements in six key-value areas: reliability, cost-effectiveness, environmental impact, safety and security.