In Wisconsin, only a Utility can sell electricity by the kW. Wisconsin has demand based commercial Tiered utility rates Tier 1 is < 60 kW, Tier 2 is > 60 kW,
When you’re supercharging at 250 kw
Your getting just over 4kW per Minute that works out to $0.32 kw. Of course as the charge Tapers your cost per kW creeps up. Until you hit the Tier 1 rate. then you hit the 60kW which equals 1kW per min at the lowest per minute rate $0.23. Tesla does its best to balance the tier rate pricing to be on par with per kW rates in other states.