Centralised vehicle-to-grid smart charging supported by PV generation for power variance minimisation at the transformer: A user’s perspective analysis

Recent studies show that the electric vehicle (EV) fleet in the EU will reach 37–38 million units by 2035. Most of them are expected to be charged at home, boosting the number of residential charging stations to be installed. In order to decrease their environmental impact, these stations should be powered by clean energy sources, such as distributed photovoltaic (PV) generators. However, the increased penetration of EVs and PVs may cause large power supply and demand fluctuations, stressing the substation transformers. This paper proposes a centralised bidirectional Vehicle-to-Grid (V2G) smart EV charging policy minimising the net-load power variance (NLV) at the transformer. The proposed approach relies on the iterative solution of a Mixed-Integer Quadratically-Constrained Quadratic Programming (MIQCQP) problem that, unlike other research papers, keeps into account users’ charging/discharging requirements, and realistic charging limitations and efficiency. The impact of the resulting EV charging schedules is analysed at a district level for growing EV and PV penetration values, then compared with the results obtained with both unidirectional (V1G) and uncontrolled (UC) EV charging. Key elements of novelty of the work are: (i) the formalisation of the optimisation problem and its scalability potential, allowing for a multi-year analysis; (ii) an accurate assessment of the user self-sufficiency and the EV battery degradation by means of a physics-inspired model; (iii) an evaluation of the potential economic impact for EV owners over multiple years. Applying the proposed V2G strategy to battery electric vehicles (BEVs) reduces the NLV at the transformer by up to 80%, while increasing self-sufficiency by up to 23%, producing a minimal battery degradation. In the current market scenario, if the Distribution System Operator (DSO) offers a fair compensation for the V2G grid support, the potential yearly economic savings for battery electric vehicle (BEV) owners equipped with a residential PV generator range between 10% and 20%. This happens despite the higher V2G charging stations’ upfront costs and the faster BEV battery degradation.