I've just done this in real life :)

This really depends on how perfect the interviewer wants it to be. Meaning that I can do it taking 3 mins… or 30 mins.

Number of chargers = Charging demand / (Charging capacity of a single charger* capacity utilization) 

Now the tricky part is how to you estimate capacity. Because it can be done in “kms of power”, in Kilowatts, etc…. I would probably do it in “full charges” and assume a full charge takes 4h (considering slow and fast charger average*) and provides 500 kms.

*Please note that one could deep dive and consider the multiple types of charges according to use case (in transit, parking, etc… I am assuming that most of chargers will be in parking and will be slow)

Capacity of a charger = 16 working hours / 4h *365 = 4 charges / day * 365 = ~1400 charges per year

Capacity utilization = ~70%

Therefore used capacity = 1400*70% = ~1000 charges/year

Charging demand = number of electrical vehicles * average kms driven a year by an electric car / 500 * % of charges done outside home

1.000.000 * 10.000 / 500 * 40% = 80.000.000

[Please note that a better way to do this would segment the charging demand between families and professional users…]

So number of chargers = 80.000.000 / 1.000 = 80.000 chargers

The tough part in this exercise is that one can be wildly wrong and have to idea… and there is a ton of assumptions above that the acceptable range of answers is so high that it is very easy to be completely wrong. Now, remember that the objective here is to show your thought process. You don't need to know how long it takes to charge an Electric Vehicle, you don't need to have a strong sense of capacity utilization not how frequently do people charge outside their home. That is why you should validate (or ask for support when defining) your assumptions with the interviewer.

Hope this helps, and happy to get any feedback on my own answer.

(edited)

Hi there,

I think this is an interesting question that may be relevant for many people. I would be happy to share my thoughts on it:

• Personally, I would approach the first part of the question from a demand-based perspective (i.e., identifying the number of electric cars per household), and the second part of it from a needs-based perspective (i.e., assessing the average mileage of an electric car and the share of private vs. public charging stations). However, I would also appreciate seeing your proposal for it.
• However, please keep in mind that most major strategy consulting companies have not used standalone market size estimations for a long time. While this does not mean it never happens, this type of case study question may not be very meaningful for both the candidate and interviewer, as only a few skills are being tested.
• That being said, simpler market size estimations may still be a part of a case study, for instance when estimating the revenues of the client company is required.

If you would like a more detailed discussion on how to best prepare for your upcoming interviews, please don't hesitate to contact me directly.

Best,

Hagen