WRC main class in 2025

[Mirek]

The Fórmula-E powertrain allow those cars to race 45 min. In Rally, With more braking (regeneration) and slower top speeds (energy consuption) PLUS next season fast charge tech that will be used (tech in development - using motorsport to do so).. Could that kit perform?
I cant math properly like an engineering but my bias is more on the "wrc can be electric with current tech and under some little tweaks on the format" but hardcore fans simply dont want to lose the engine sound.

There is not more regeneration in rallying than on circuit. That is misconception and it's exactly opposite because you can never achieve near ideal circuit conditions in rally.

Let's have a look on the formula E because that also works in the real life. The battery has 54 kWh, nearly the same as the Kreisel RE-X1. Why can it have so relatively small battery? Because there is way higher renegeneration level on the circuit and because the car is basically all made of carbon (the rest of the car weights nearly nothing).

I have counted 200 kg for 48 kWh in my previous estimation (taking into account roughly 250Wh/kg density). So what is the weight of the formula E battery? The battery alone has 250 kg, quite similar to my estimation, BUT there is the cooling which allows all that fast charging, high-level of recuperation and high power delivery (max. power in race mode is 220 kW). Together with the cooling the battery pack weight is 385 kg! That's for just 54 kWh capacity.

So why can the Formula-E run that long time with such battery? The car alone without the battery pack and the driver is only 440 kg heavy! That means that the whole car has a weight just a bit higher than the battery pack alone. Similar weight of the car is of course completely unreal for rallying. Realistically we can not expect the cars to be reasonably lighter than the Kreisel RE-X1 which has a weight of 1330 kg with a battery slightly smaller than the one from Formula-E. Formula-E delivers 220 kW of race power. That's not that bad for a 900 kg heavy thing including the driver but hardly anything breathtaking. The RE-X1 has however 1500 kg (including the crew) which is 600 kg more! 220 kW is roughly equivalent to the Rally2 cars, Rally1 cars are much stronger and both are about 100 kg lighter.

Now the recuperation. We can easily count the average power output of the formula-E car. The race has 45 minutes, the battery has 54 kWh. If they run it dry they take in average 72 kW of power. Surprisingly low value, isn't it? According to Kreisel their car uses in average 120 kW on a stage (value counted from their stated 1,2 Wh/km for an average speed of 100 km/h). Why so much more? Because the car is much heavier and because the recuperation on circuit is much more effective. And even those 120 kW (70% more than formula-E) is not enough to fight the rally2!

So if we put the Formula-E battery into a rallycar we get something very similar to Kreisel RE-X1. Is that surprising? I don't think so. It shows that there are certain common limits for everyone.