, , ,

I was out doing a guardrail survey last week when a Nissan Leaf passed us. I was stunned by how quiet it was. Especially stunned because I didn’t notice it behind me until the last second. Thankfully, I was out of the lane at the time.

My concern about electric vehicles is not so much about their inaudibility as their efficiency. I am concerned that they are being touted as paragons of efficiency while being none such. The efficiency ratings of full electric cars like the Leaf are well over 100 MPG (equivalent). How can this be, when they weight just as much, if not more, than similarly sized internal combustion cars?

I looked at the stats for the Leaf and a car I know well, the Hyundai Elantra (don’t hate). The Leaf weighs 3,300 lbs and the Elantra 2,500 lbs. The Elantrra infamously claimed to get mileage of 40 MPG highway and 33 city. I have seen 40 MPG in that car once, and am lucky to get 33 MPH highway after a long smooth run on I-95. The leaf is rated by the EPA at 99 MPG highway and 106 MPG city. The reason city driving is more efficient for electric and hybrid cars is regenerative braking.  Everytime a Leaf brakes, it recharges its battery.

But how is this possible? The Leaf weighs a third more than the Elantra and is almost three times as efficient? Is electricity magic? Only with sleight of hand.

Consider where an electric vehicle gets its power: power plants, miles away. The combustion of coal or natural gas to boil water, make stream, turn a turbine and make electricity is only the start of where the Nissan Leaf gets its fuel. That electricity has to then be pushed through transformers, miles of aluminum wires, and more transformers to get to the homes and garages stabling these Leaves. The standard generation and transmission losses in getting electricity from burnt carbon to household power is something like 75%

The numbers I have for this are in kWh/Mile, but they are useful. The rated efficiency of a battery electric vehicle like the Leaf is 0.18-0.46 kWh/Mile. This is great compared to the comparable rating of a 25 MPG car (like the Elantra), which is rated at 1.35 kWh/Mile*. The Elantra is the location of the combustion, so if it gets 25 MPG, I know it is using as much energy as I gave it. With an electric car, you have to take transmission losses into account. Multiplying 0.18 and 0.46 times 75% generation and transmission losses, you get 0.72 and 1.84 kWh/Mi.  Or 18 to 46 MPG.  Firmly in the neighborhood of my big, bad, dirty Elantra. Electricity is not magic after all.

Now, if most of the energy was generated by solar or wind, as is the case in California, there would be less CO2 impact, but still nearly as much energy lost in transmission. The transmission losses from these alternative sources may be greater, as their plants are more spread out, relaying on longer transmission lines to get power to the people. If the energy is generated by local microgeneration plants, with very short transmission lines, then energy loss from generation to consumer would approach 25%. Then, and only then would I claim electric vehicles as a clear improvement over internal combustion engines.

After some prompting from my associate from another continent, Lars Fields, I did some calculations as to what an all electric fleet of cars would need to be powered entirely by local solar power.

Americans travel about 2,795,883,000,000 (2.8 trillion, or about half a light year) miles in their cars every year. If we take the best case efficiency with zero transmission losses (0.18 kWh/Mile), we would consume 503,258,940,000 kWh of energy in powering an all electric fleet.

Assuming 22 kWh generated per square foot of solar, we would need 802 square miles of solar panels to power that fleet. That is actually not that bad. That is about 70 SF per car. You could easily get that by roofing every 162 SF parking space in America.

An electric car is still a car. At average highway speed, it still requires over 2% of an acre per passenger to deliver people where it is going. All those acres need to be impervious. Increasing the impact on our nations waterways. It is still designed to move an average of 30 MPH, and much faster, spreading out land uses and making America unusable for all but other cars. Its average speed is still tantalizingly close to 35 MPH, the most common posted speed limit in America and the 50/50 kill speed for pedestrians in America. For these reasons, I will probably never see the electric car as the “sustainable choice”. I am concerned that many environmentalists have made this mistake.

If you want to actually save energy build cities to allow walking and biking. Make prosperous places, not just highways linking more prosperous metros.


* based on the handy conversion number of 33.4 KWh / gallon of gas.