I have one friend who just bought a Tesla S and he mentioned something that doesn't get widely publicized for the Tesla's that typical charging is 85% of battery capacity. So keep in mind the typical range of a Tesla is 85% of the stated range. I asked him what kind of charging system he had and he had the 240V that is similar to an electric dryer circuit. I told him I had another friend with a Nissan Leaf who was a bit more on the cheap side so he charging his leaf on 120V. It takes 20 hours for a complete charge and is also recommended to not exceed the 80% battery charge.

What I found interesting in a Nissan Leaf Forum is there is 300 watts of overhead for the 120 Volt and 240 Volt charging.

The question starts.

7 hours for 240V and 20 hours for 120V. I thought it would be exactly half for the lower voltage?

The answers posted are.

The 120v charging is limited to 12amps (1.44kW). 240v charging is done at 16a (3.84kW). That comes to 2.67 times slower, plus 120v charging is less efficient...there's a fixed overhead for the cooling system that brings the practical difference close to 3 times slower.

2). There is a parasitic load of about 300W that runs during charging. These pumps draw the same power regardless whether the charging is done with 120VAC or 240VAC. This power takes a larger fraction of the available power away from charging when using 120VAC, This further slowing charging. Interestingly, this causes 240VAC charging to be more efficient.

The last comment on 240VAC being more efficient got me curious to calculate the PUE of 1.44kW (120V) vs. 3.84 kW(240V) with a 0.3 kW overhead for the cooling and electrical distribution.

120V had a PUE of 1.26.

240V had a PUE of 1.08.

When you do the math on an individual basis this is not big deal, but add up all the 120V charging of electric vehicles and the numbers add up fast.

Google has a PUE of 1.08 for its Hamina Data Center. Would it ever want to go back to a PUE of 1.26?

It is painful to think about charging at 120V vs. 240V both from a time perspective and waste of energy.