Evaluating the impact of control algorithms on cost savings of AC solar charging: a simulation-based study of savings in reference to bidirectional charging, constraints and options

With the increasing spread of electromobility and renewable energies such as photovoltaics, the efficient charging of electric vehicles with solar power is becoming increasingly important. For owners of electric vehicles, self-consumption of photovoltaic electricity is particularly attractive, as the cost of grid electricity is usually significantly higher than the feed-in tariffs. Efficient utilisation of solar power generation requires that the charging power of the electric vehicle can be adapted to the available PV surplus power in the best possible way. This minimises the use of expensive grid electricity during the charging process and maximises self-consumption of solar energy. The charging process is often controlled by external energy management systems. This case should be considered in this paper. Depending on the communication standard between the wallbox and the vehicle, it is not always possible to vary or reduce the charging power in any terms of level and speed. This limitation is partly due to the minimum charging power, which is restricted by the PWM signal to 1.38 kW for single-phase connections and 4.14 kW for three-phase connections during IEC-compliant charging. However, this constraint is resolved with the more advanced ISO 15118-20-compliant charging process. Additionally, the vehicle’s charging status can be transmitted to an energy management system, allowing for further optimization opportunities. Given the various types of wallboxes, energy management systems employ control strategies that are tailored to the specific technical setup to effectively manage the charging process. This study shows that, depending on the wallbox and charging method used, the savings with unidirectional solar charging can vary by several €100. Charging process with ISO communication options offer an advantage over IEC-compliant communication. As many charging points have already been installed in Germany, not all of them can communicate via the modern ISO 15118-20 standard and cannot be updated. For these wallboxes, recommendations for configuring the control algorithm are derived from the results, and the potential savings are presented to help evaluate whether replacing the wallbox with a newer model is justified. Additionally, it is shown that the savings potential of solar charging, as calculated by a mixed-integer optimization model, is often overestimated. In fact, the cost savings for older AC wallboxes can be €100 to €200. This would make their replacement with a bidirectional one more economical.