Electric vehicle fleet development: how does it affect public charging?

2024-01-10 Toni Simolin and Johanna Mäkinen

The number of electric vehicles is growing rapidly. For example,°the road map for fossil-free traffic (urn.fi)°has set a national target of 700,000 electric cars in Finland by 2030. Electric cars are often charged at home, and this has been considered sufficient to cover the average daily need for charging. However, not everyone has the opportunity for charging at home and longer journeys require the use of public charging infrastructure, for example when shopping at a shopping centre. As electric cars become more common, the charging load will increase significantly from today’s level and more electric car drivers will become reliant on public charging infrastructure. How can the public charging infrastructure meet the challenges of increasing electric vehicle usage?

Electric vehicle fleet development

A study by Tampere University (doi.org)°examined the current state of the electric vehicle fleet and the changes brought about by the development of the electric vehicle fleet from the perspective of charging. According to the study, the majority of electric vehicles (incl. fully electric vehicles and plug-in hybrids) only make use of around 3.7 kW of power in public medium charging, despite there being a lot more available. There is often also not enough time to fully charge an electric car while out shopping. The study evaluated various scenarios where electric vehicle models with different charging powers became more common at different rates. As a starting point, all scenarios assumed that newer electric car models have a higher charging power on average than older models, which is indicated by the current trend.

The study predicted that the size of the electric car fleet would increase 22-fold between 2020 and 2040. However, the daily charging energy at the examined charging station would increase by up to 40–70 times and the peak power by 30–50 times. This means that charging energy and peak power would increase significantly faster than the number of electric cars. In other words, an individual car would charge about 2.3 times more energy in the future than it does today. Similarly, the ratio of peak power to the number of electric cars would increase 1.8 times.

What does this mean, exactly? The energy requirements of the cars are expected to remain the same as the fleet is electrified. In this case, the increase in the share of public charging means that electric cars would not need to be charged as much elsewhere, such as at home, at work or at rapid charging stations. The results also suggest that, at a larger charging station, the ratio of charging energy to peak power is higher, that is, more energy can be charged into the cars in relation to the peak power required. Increasing charging power also enables more flexible charging: the higher the charging power, the more likely it is that the charging load can be transferred to a different point in time, e.g. when cheap electricity is more available or other loads on the grid are lower.

The limits of charging infrastructure may become an obstacle

The limitations of the existing electrical grid must be taken into account when dimensioning the charging infrastructure. Overhauling the electrical grid for electric vehicles is often not financially viable and therefore it is not always possible or cost-effective to build as much charging capacity into a charging station as electric car users would like. This, in turn, can lead to vehicles not always being fully charged in time and the user having to make use of extra charging to reach their destination. This worsens the user experience of electric vehicles.

At public charging stations, the revenues of the charging operator often depend on the amount of energy used for charging. The less energy that is used in charging the cars, the less revenue the charging operator makes. Efficient use of the charging capacity can have a positive impact on charging, both from the point of view of the electric vehicle user and the charging operator.

Algorithm for efficient use of charging capacity

With dynamic load management, the medium charging mode (mode 3) for everyday charging of electric vehicles can be controlled so that the desired power or current limit is not exceeded. However, there are two challenges to the efficient use of charging capacity: the different charging characteristics of electric vehicles and the uneven distribution of the charging load between phases.

Electric vehicles have a variety of charging characteristics that the load management system needs to detect. The study carried out at Tampere University has developed an algorithm that can identify the characteristics of different electric vehicle models and make the charging station more efficient from the point of view of the user (doi.org) and the charging operator (doi.org).


2024-01_Tuni-01_hns-blogi_kirjoittajat_Toni Johanna

Toni Simolin and Johanna Mäkinen,

Tampere University

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