Timing matters in charging an electric vehicle at home

2024-02-07 Toni Simolin

There are many changes happening in the electrical system, such as the increase in consumption due to electric car charging loads and changes in electricity production due to renewable energy sources. Together, these create challenges in maintaining the power balance in the electrical system. In order to mitigate peaks in power, more and more grid companies have introduced a demand tariff.

Demand tariff levels out electricity consumption

According to the National Travel Survey, households with two cars drive an average of 90°km per day. If both vehicles are electric, this would require around 20 kWh of charging energy. If charging is not controlled in any way, the fuses in a detached house property would likely be pushed to their limits. The cost of charging might also be unnecessarily high. However, the amount of electrical energy itself is often not very significant if its timing is controlled intelligently. In single-car households, the average driving distances (~40 km) and thus also the charging energy requirements (~9 kWh) are significantly lower, making it more likely that the need for charging can be covered, for example during the quiet hours of the night.

The demand tariff means that the electricity user pays a separate price according to the peak of electricity consumption. For example, the price of peak power could be €1.3/kW multiplied by the peak power of the month. The demand tariff has been found to improve the cost-relatedness of electricity transmission pricing, as the electrical grid must be dimensioned according to maximum consumption. This pricing model gives electricity users a direct financial incentive to level out electricity consumption to avoid unnecessary consumption peaks. The demand tariff is often combined with time-of-day electricity, which divides the price of electricity into more expensive daytime electricity and cheaper nighttime electricity.

Charging control and cost savings

The medium charging mode intended for everyday electric vehicle charging supports charging control, where the charging current can be adjusted or the charging process can be temporarily stopped completely. This makes it possible to time home charging in such a way that the price does not get too high and the fuses do not blow.

A°joint study°by Tampere University and the Technical University of Dortmund examined the implementation of charging control and the potential cost savings of using commercial electric vehicles and charging stations. The study showed that, with charging control, savings of up to 60% can be achieved in electricity transmission in a household with two cars and using a demand tariff combined with time-of-day electricity compared to uncontrolled charging. This gives electric vehicle drivers a clear incentive to control the charging load, which also benefits the electrical grid.



Toni Simolin
Tampere University

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