Off-grid solar charging of electric vehicles at long-term parking locations

Abstract

This work analyses the effectiveness of an off-grid solar photovoltaic system for the charging of electric vehicles (EVs) in a long-term parking lot. The effectiveness of charging is investigated through analysis of the states of charge (SoC) at departure of EVs plugged in at the parking lot over the simulated year. Although the share of vehicles leaving with inadequate charge over the entire year is small, this share is relatively high during low irradiance winter months. We show that an increase in efficiency of the solar modules used in the system and an increase in the minimum duration of time spent at the parking lot are effective within limits at improving charging adequacy. We then formulate three strategies to allocate the available energy in the system with the objective of reducing the number of vehicles leaving at lower SoCs: 1) curtailment of charging beyond 80% state of charge, 2) prioritised charging of vehicles at low SoCs and 3) prioritised charging based on both SoC and time before departure. We identify the strategy prioritising vehicles with low state of charge to be most effective, but performance in the worst month remains a challenge for the location considered.