The embodied-energy debate continues to rage. For those unfamiliar with the concept, embodied energy is the total energy required to produce a product and deliver it to its point of use.
Years ago, I was in the company lunchroom when one of my co-workers began talking about the need to replace our foam coffee cups with ceramic mugs. Another colleague argued the ceramic cup required washing in hot water with soap that had to be manufactured and transported, that the cup was glazed, and that when the cup broke, it would end up in a landfill forever. In the end, we used two cups: disposable (non-foam) for visitors and ceramic for employees.
In early 2010, I had written an article titled “The Benefits of Ice-Based Thermal Energy Storage” for HPAC Engineering. One of the review comments pointed out I had not accounted for the energy required to manufacture the thermal-energy-storage equipment, the energy/emissions involved in mining the resources, and the additional concrete, drywall, etc. that went into the system. It was a valid point, so I added a sidebar explaining that for each of the more than 82,000 lb of concrete required, 2,150 Btu was expended.
This brings me to the realization my Prius may not be as environmentally responsible as I once believed. In a recent issue of IEEE’s Spectrum magazine, a number of scientific studies call into question whether electric cars actually reduce greenhouse-gas (GHG) emissions. The U.S. Congressional Budget Office says electric-car subsidies “will result in little or no reduction in the total gasoline use and GHG emissions of the nation’s vehicle fleet over the next several years.” However, the Union of Concerned Scientists says an electric car yields less carbon dioxide than any gasoline-powered car.
The problem with comparing electricity with other fuel options is that we’re not considering the source of the electric energy being used to charge car batteries. Is the energy being produced by burning coal? Natural gas? Nuclear power? Solar photovoltaics (PV)? That certainly makes a difference in comparing carbon footprints. And even solar PV charging, it if could be done on a commercial scale, has a downside: PV cells contain heavy metals, and their manufacturing process releases high-global-warming-potential GHG.
The other major problem with electric or hybrid cars is their traction power systems. And that’s where embodied energy comes in. Batteries require materials (e.g., lithium, nickel) that are energy-intensive to process and difficult and expensive to discard (as are spent batteries themselves). Also, there’s the additional energy required to manufacture the carbon composites and aluminum components required to reduce the weight of electric vehicles to compensate for the weight of the batteries, which is why a National Academies study published in 2010 concluded the lifetime health and environmental impact of electric cars could be worse than that of gasoline-powered cars!
So what’s the answer? I don’t know, but I’m going to keep driving my hybrid. I stop at the gas pump about a third as often as my wife, who drives a small SUV. So even if I’m not reducing transportation’s carbon footprint, I am doing my small part to reduce our dependence on foreign oil … and saving money in the process.