Hur dimensionerar vi framtidens elnät? Fallstudie med avseende på e-mobilitet

Sammanfattning: During the last few years, the interest for electric vehicles has increased enormously, there are even talk of prohibiting fossil fuels in the coming years. There is a risk that the charging of these electric vehicles can strain the electric grid. The simulations of the grid with added power demand from the electric vehicles concludes that there will not be a problem on the low- and medium voltage grid. The distribution of the customers’ charging times has greater impact on how strained the grid is becoming than the charging power of each car. It might be a problem for transformers with a high number of connected customers since even low charging powers will accumulate to a noticeable power. The network must be designed to supply the customers with electricity even at peak consumption. Over the last few years many network companies have measured hourly consumption but this has not always been the case. Previously the peak power for a group of customers has been estimated with help of the so called Velander formula from their yearly consumption. By comparing this calculated power with the hourly measured values, it was concluded that the formula still gives an indication of the amplitude of the highest power. Since electric vehicle charging change the previous relation between power and energy with the high but seldom peaks, Velander formula is not usable for electric vehicles. It is therefore in the net owners’ interest to be informed when charging stations is installed. It is of great importance to look at the sum of the power demand and not only on each customer’s power demand. When networks are built they usually are over dimensioned, mostly because the margin it gives of uncertainties in expected consumption. The relatively low extra cost is also a factor. This is mainly the reason why there has been such a good margin to allow an expansion of electric vehicles in the grid.