> Petroleum for transportation currently accounts for 27% of US energy usage
> 25% * 27% = 7% more electricity
There is no relation between amount of petroleum used and amount of electricity generated in the data provided by you. All you can say is we need the equivalent amount of 7% extra of total energy used today. You did not provide any data about how much of total energy used is electricity . If electricity is 7% of total energy usage, then we need 100% extra to charge all the cars.
> 25% * 27% = 7% more electricity
There is no relation between amount of petroleum used and amount of electricity generated in the data provided by you. All you can say is we need the equivalent amount of 7% extra of total energy used today. You did not provide any data about how much of total energy used is electricity . If electricity is 7% of total energy usage, then we need 100% extra to charge all the cars.
TLDR: your math is wrong.