Electricity Sources
  • Current electricity sources. Approximately 42% of all electricity sold in the United States in 2011 came from burning coal.  Coal is cheap, but is also the dirtiest fuel (highest carbon content).  Charging EV batteries from the grid will frequently produce the same or even more greenhouse gases and other air pollutants than running a conventional gasoline car in many parts of the country. The National Research Council released a report in 2009 (Figure S-3) showing that the health costs of running a battery electric vehicle are greater than the health costs of a regular gasoline vehicle, a hybrid electric vehicle and a plug-in hybrid. This same NRC report showed (Figure S-4) that the greenhouse gas emissions from a battery EV are greater than the GHGs from a gasoline hybrid electric vehicle.
  • Greening of the grid. We have assumed that the grid becomes “greener” over time, including increased use of:
  • Renewable energy (wind, solar, geothermal, etc.) increases over time
  • Nuclear energy increases slightly over time
  • Coal plants are either replaced with units that have carbon capture and storage (CCS) capability, or older plants are retrofitted with CCS; all non-CCS coal plants are phased out by 2070:
  • We use the AEO-2012 projections for average US grid mix through 2035, with extrapolations to 2100 assuming that stringent climate change legislation forces utilities to install lower carbon sources. The resulting grid mixes over the 21st century are shown below;  all natural gas combustion turbines are replaced with more efficient combined cycle units by the end of the 2070 time period and all conventional coal plants (without CCS) are replaced by 2070):
  • Note that we are using the projected average grid mix in our calculations; in reality we should be using the marginal grid mixes to reflect the types of electrical generators that are on the margin when electric vehicle batteries are charged. The Greenhouse Gas Protocol specifies that analysts should always use the marginal grid mix and NOT the average grid mix when calculating real-world GHG emissions [1]. For example, the “greenist” generators, solar and nuclear also have the lowest operating costs, and are therefore run first since utilities practice “economic dispatch”, running their lowest cost generators first, and only adding more expensive generators as the load increases;  As a result, fossil fuel based generators such as coal and natural gas plants are usually operating at the margin.  When a new load such as vehicle battery charging is added, then, the fossil fuel generators have to be ramped up [the low carbon sources such as solar, wind and nuclear are already running at full capacity].  However, calculating the marginal grid mix is very complicated, so we have used the projected average grid mixes in this model.
  • Bottom line: using the average grid mix in our model will estimate lower GHGs than in actual practice. Note also that this chart above does not include the added electricity generation that will be needed to support PHEV and BEV charging during the daytime This is based on an EPRI (Electric Power Research Institute) PHEV charging profile.  Thus PHEV and BEV advocates state that some car owners will need to be able to charge their car batteries at work during the day to entice them to purchase those electric vehicles. Or they will plug in their vehicles as soon as they get home from work, which often coincides with maximum demand.  This daytime charging will often correspond to the peak utility load, so new generation capacity will most likely be required to accommodate large scale daytime PHEV and BEV charging.
  • [1] D. Breoekhoff, “The Greenhouse Gas Protocol: Guidelines for quantifying GHG reductions from grid-connected electricity projects,” World Resources Council and the World Business Council for Sustainable Development, August 2007

 

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