BEV Charging Basics

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.

Pad mounted distribution transformer
Pad mounted distribution transformer

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.

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11 thoughts on “BEV Charging Basics

  1. Hi Donn,
    Like the new format.
    I keep wondering: if a gallon of gas is used to fuel a power station, how many miles would a BEV go compared to using the gallon in a gas-fueled car? Also, what are the real costs of the 2 options?
    Regards,
    Steve

  2. Thanks. Appreciate comment n new website.
    Not sure I understand the question.
    The per mile cost of electricity is less than the per mile cost of gasoline, though the actual amounts vary depending on the vehicle. Here’s from a website on the subject.
    “Based on national average electricity rates of 12 cents per kilowatt-hour (kwh), a 114 MPGe (combined) Nissan Leaf costs 90 cents per 25 miles, which works out to 3.6 cents per mile, or $3.60 per 100 miles.”

    “Now compare that to a reasonably frugal conventional car:”

    “Based on national average gasoline prices of $3.72 per gallon, a 33 mpg (combined) Honda Civic costs $2.79 per 25 miles, or 11.1 cents per mile, or $11.16 per 100 miles.”

    • Hi Donn,
      Power plants and cars use different fuels. For this case, let’s assume both use the equivalent of diesel fuel. The power plant burns it to create steam, turn turbines and generators, sends the power over the grid to the BEV charger to the BEV’s batteries to its motors to move the BEV a certain distance. In a diesel auto, the gallon goes in the tank to its motor to move the auto a certain distance. It’s hard for me to understand how the losses of creating, delivering, and converting the electricity to motion is more efficient than a diesel auto. What are the sources of the efficiency?
      Thanks Donn

      • With respect to a single gallon of diesel fuel, the diesel car is more efficient. Coal-fired power plants are 33% efficient, but there are line losses that can cut efficiency as much as another 6% plus transformer losses, plus battery charging losses, while the diesel or gasiline powered car is around 30 to 40% efficient.
        Actually, using efficiency as the sole metric, BEVs make no sense.

        • Donn,
          That’s what I thought. A strong article to make these facts clear would go a long way to erase the relative mileage figures that most everyone thinks justifies BEVs.
          Thanks,
          Steve

  3. The California power grid is already in such bad shape that during the summer it’s in danger of massive failure. I really don’t want to see what will happen if you add even 10,000 electrics to the mix. It won’t be pretty. There are dozens of reasons electrics are idiotic

    • Thanks for your observation about the California grid. No question Ca;ifornia has structual problems that will eventually lead to failures of some sort. Many people disagree with my stement, but time will tell.

      • Anyone disagreeing with you, Donn, doesn’t know anything about power systems. Power systems are not impressed by infantile SJW posturing, virtue signaling, green NGO propaganda, venal politicians, rent seeking renewables hustlers, etc.

        I assume the bosses are stifling any contrary voices to their happy days projections of California’s energy future. The biggest gamble? Continued importation of relatively cheap power over highly loaded interconnections. Surrounding States won’t be suckers forever. And massive blackouts are assured, as has happened in the past.

        • California already has structural problems in it’s delivery system. Lack of power to deliver is not the only reason for rolling brown outs, stress and overheating at and beyond max capacity is a definite factor. And the greenies with their plug ins won’t forgo their cars without the circuit where the power company can shut it off at need, like for a/c.

  4. Pingback: Home Car Charging: A Primer - Master Resource

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