I read with interest the letter last week extolling the virtues of electric vehicles (EVs). It painted a very rosy picture of the future that may not have been completely accurate. Our electric grid is able to support a small percentage of EVs but any large number is untenable.
I don’t want to get too technical, but a basic understanding of the electric grid is necessary. I spent half a century in the electric utility business and need to point out that our grid is an extremely synchronized and balanced system; to maintain the parameters necessary for proper operation of electrical equipment, generation supply must almost exactly equal demand. Theoretically, when you turn on a 100-watt light, a power plant somewhere must increase generation by 100 watts. If area demand exceeds generation capacity by even a small percentage, the result is a blackout.
A fairly efficient EV (e.g., Tesla S) uses a little over 300 watts/mile. Over the course of a year driving 15,000 miles, it consumes about 5000 kW hours. This is an amount equal to around four month’s usage of the average house. So for every three EVs, we put the equivalent of another home on the grid. The U.S. has around 300 million autos, so even if only half (150 million) are changed to EVs, we have added the equivalent of 50 million new homes to the grid.
A large power plant, like the new Duke plants, produces enough power (850 megawatts) to supply about 650,000 homes. Simple math shows we will need a minimum of 80 new plants, and in reality to account for maintenance and outages, probably 100. These numbers assume most charging will occur in the evenings and not during the day at peak load times — probably unrealistic. The U.S. builds the equivalent of 35 Duke Citrus plants every year to replace retiring units and to support increased demand. The 100 number will be in addition to those.
The use of solar is often suggested as a solution but it also has drawbacks — a solar field capable of providing a single megawatt covers around 4 acres; i.e. an 850 megawatt solar plant would cover around 3,500 acres — and since it only works during the day, it actually supplies a maximum of 425 megawatts per (sunny) day!
Yes, EVs are way cool and futuristic, but don’t plan on getting rid of that gas guzzler.