Abstract
The growth of distributed generation from variable renewable energy sources, which is necessary to achieve the European Union's planned transition to renewable energy by 2050, poses significant challenges to the electricity system at both the distribution and transmission levels. It is increasingly occurring that distribution grids, especially at the low voltage (LV) level, are no longer able to transport excess solar energy (congestion on lines) as well as to release this energy to the national transmission grid (congestion on transformers), compromising the stability and quality of electricity supply. Thus, although distributed solar generation is essential for the energy transition, some local grids are already no longer able to accommodate new solar plants (saturation of hosting capacity). In addition, the increasing self-consumption and the penetration of new loads such as heat pumps and electric vehicles generate increasing variability in the residual load (demand net of self-consumption) of the DSO's control area. Increased variability, together with unmetered distributed solar generation (DSOs do not monitor plant output), makes the residual load increasingly difficult to forecast. This result in higher imbalances between demand and scheduled supply and voltage fluctuations that must be compensated for by the transmission system operator (TSO) through the use of increased reserve of flexible and dispatchable resources. How to limit the impact of distributed generation on the power system at the transmission level while simultaneously increasing the hosting capacity of distribution grid is still a problem being researched and tested and is exactly the purpose of this study. We propose a groundbreaking solution to address this issue based on the installation of batteries and inverter grid-forming in the primary/secondary stations and on innovative logic of control of the battery management system (BMS). We tested BMS control strategy using the netload data metered at a primary station under the control of a DSO in the north of Italy. We proved that if the system is suitably dimensioned, reduces the number of reverse power flows by 96% and the maximum reverse power by 33%, limiting voltage standard violation or transformer overload. The solar energy generated in the area downstream of the cabin that is fed into the transmission grid (reverse power flows) is reduced from about 4% to less than 0.05%, so that almost all PV fleet’s generation remains in the control zone. At same time, the distribution of solar-induced residual load ramps is practically restored to the levels found in the absence of solar generation at all the time scale (15/60/240 min). Therefore, the TSO is not forced by distributed solar generation to increase secondary/tertiary/unit-commitment reserves.