Charging a battery-powered vehicle (BEV) starts outside the home at the distribution transformer.
Actually, it starts at the power plant where electricity is generated.
The issues are:
Are there sufficient power plants to charge BEVs?
Is the distribution transformer serving the home large enough to charge a BEV at home?
The first question has been answered, in general terms, as yes, unless there is a large number of BEVs concentrated in a specific geographic area. See Hidden Costs of EVs and PHEVs – Part I for an explanation of this issue.
It would appear that there could be 87 million BEVs on the road if spread uniformly across the country, before new power plants would have to be built to accommodate the additional load caused by charging the batteries of BEVs.
The load on the distribution transformer is determined by the voltage and current of the charging outlet or home charging station. The charging stations also determine how long it takes to recharge the BEV. At 40 amps, it would take around 7 hours to fully charge the battery. At 72 amps, it would take around 3 hours. (This data is from the Tesla website. Other BEVs may have differing charging requirements.)
The first instance requires the equivalent of a 10 KVA transformer. In the second it’s around 17 KVA. Single-phase distribution transformer sizes are 5, 15, 25, 37 1/2, 50, 75, 100 and 167 KVA.
It’s not unusual to have four homes serviced by a single transformer, which is frequently a 50 KVA unit.
The fact is, no utility knows how fully their distribution transformers are loaded. With the advent of larger and larger TVs, the addition of more computers and other electronic gear, the load on distribution transformers has been slowly but constantly increasing.
It might only take one homeowner adding a BEV using the simplest, lowest voltage and amperage charging system to overload an existing 50 KVA transformer.
If all four homeowners add a BEV and the existing 50 KVA transformer is 75% loaded, it could easily require that the 50 KVA unit be replaced with a 100 KVA transformer.
Consider what happens when a family has two BEVs. It could require dedicated transformers for each home, or at least adding an additional distribution circuit.
These are costs the utility bears. They are hidden from the usual calculations of the impact that BEVs have on the utility system.
Another consideration is that older homes may have service entrance boxes rated 100 amps, while new homes are likely to have a service entrance of 200 amps.
The owners of older homes are likely to have to pay for a new service entrance large enough to handle the current when charging their BEV.
An earlier article on this subject, see Hidden Costs of EVs and PHEVs – Part II, considers other aspects of charging BEVs, such as charging during the day rather than at night. Since adding load to distribution transformers also adds load to substation transformers, there is the potential for having to replace substation units that cost a million dollars.
People buying BEVs that cost $100,000 aren’t concerned about the cost of adding charging stations to their homes, but people in the market for BEVs costing $35,000 may find the additional cost burdensome.
Whether this will affect the adoption of BEVs is another question that only time will answer.