I recently read the Cleaner than what article in the Economist which talked about a study that said electric cars powered by coal plants produce more CO2 than fuel-powered cars. This study is incorrect because it falls into a trap I have fallen into in the past. Energy consumption is not directly related to energy production.

I fell into this logic in my previous employment with Philips LED. With Philips, I would meet with cities to help them understand how switching from traditional bulb street lighting to LED would cut down on the cities energy production and thus decrease their CO2 emission. In 2010 I attended the Street and Area Lighting Conference in Huntington Beach. I sat next to Michael Stevens, head of lighting at Southern Company, while Robert Koenig of the Clinton Climate Initiative spoke about selling carbon credits created from cities switching to LED street lighting. Michael laughed under his breath. His laugh shocked me. I had recently started a career that I thought was saving the world by reducing energy consumption through LED street lighting. To me it was the lowest of the low hanging fruit in reducing our emission of CO2. So I asked Michael why he was laughing. He told me he was that energy consumption and energy production are two very different things. He drew me this very simple graph.


Energy consumption varies like a wave, with the lowest points when residents and businesses are asleep and the highest around mid-afternoon when everyone is most active. Southern Company, like most energy producers use a mixture of  production methods to meet the demand. Southern Company has a base production turbines that provide most of the power that is to be consumed. These turbines never turn off and they do not vary with demand. Southern Company turns on auxiliary turbines to meet peak demand energy consumption during the day. These turbines vary with the energy demand. To lower CO2 emission due to energy production you must lower peak-time demand. 

Michael said even though energy consumption drops off at night, the base turbines are still on, producing energy and emitting CO2. That excess energy is lost because we have not created the technology to store great amounts of energy efficiently. Michael said when a city reduces their night time energy consumption by 10% by switching to LED street lights, it will have no effect on CO2 emission, because the turbines were still on.  This is the same trap that Christopher Tessum, Jason Hill and Julian Marshall of the University of Minnesota have just fallen into with their recent study in the Proceedings of the National Academy of Sciences. This study found that a battery-powered car recharged with electricity generated by coal-fired power stations is likely to cause more than three times as many deaths from pollution as a conventional petrol-driven vehicle. Just like LED street lighting carbon credits, this study directly relates energy consumption with CO2 emission without taking into account when the energy is being produced.

In this case electric vehicles are usually plugged in at night consuming the excess energy produced during off-peak hours. This energy is stored in their batteries for use during peak hours during the day.  The net result of charging your electric car at night not only removes the CO2 that would be produced by a petrol-driven car during the day it is also consuming excess energy that would normally be lost by the coal power plant at night. 

Furthermore, if all cars were switched to electric cars, the general public would make much better use of the lost energy produced during off-peak hours of the base production turbines as well as removing the petrol-burning cars from the roads all together. Electric vehicles could behave as one massive battery for the power company. 

In the future, a more effective study would measure when electric cars are plugged in. It could also look at what can be done with aligning power companies with the electric car chargers. Perhaps they could provide free energy between 2 and 5AM to electric car chargers.