A Snapshot of the Electric Car on the Electric Grid

Zak Edson, Director Product Planning, January 29, 2010

The Tesla Roadster goes more than 200 miles (380 km) on a single charge. The average person drives about 40 miles (60km) in a day. This leaves a range of about 160 miles (257km) after an average day of driving in a Tesla Roadster. Meaning that at the end of the day when a Roadster is plugged in to be charged up, it is really only to top off the battery.

Why is this significant?

It is important to understand the amount of energy a battery draws when charging and how this affects the electricity grid.

The typical home is allocated 100-200 amps from the neighborhood’s transformer. Say an electric car is charged from a 50 amp (32 amp in Europe) circuit breaker. This is only 50 amps of the allotted 100-200. And if charged at night, not much other electricity is being used in the house. When charging a Tesla Roadster, the car only draws as many amps as are available. Once plugged into a 50 amp outlet, the car only draws 40 amps (due to the National Electric Code (NEC)). And drawing 40 amps is drawing 40 amps, be it an oven or electric car. A home can’t draw more amps than it is allocated. Utilities are well informed of the maximum amperage of any given home, and the homeowner may not make any changes to the service without appropriate permits and approval by the utility.

With that, many utilities require they be informed when a person purchases an electric car, and often the billing rates are modified to accommodate the electric car. This also gives the utility the opportunity to make sure that the house and neighborhood transformer are appropriate for the electrical needs. In fact there are forward looking utilities working with Tesla to learn of the charging needs of a typical electric vehicle and its owners. Here at Tesla we are seeing a very positive response from utility companies who want to work with us to continue to make electric cars a positive impact on our society and environment.

And lastly, the convenience of an electric car. A great time to use energy is during off peak hours. Not only is there a surplus of cheaper electricity, it’s also quite convenient. Much like how the Tesla Roadster is set to a specific amperage, when the driver comes home at the end of the day, the charging can be set to begin at a specific time, automatically. Tesla owners simply drive home, plug in the car and set it to begin charging during off-peak hours. In the morning, the car is ready to go with the equivalent to a full tank of gas, without ever stopping at a gas station!