Saturday, August 17, 2013

Re: [Geology2] Re: your opinions



On 8/16/2013 10:46 PM, fossrme wrote:
 

Sounds like you have some experience in this. What does it mean when you say the plants operate at 31-33% efficiency? How does that translate into information about CO2? What mpg does that assume? Can you walk us through how you can compare the amount of CO2 coming from the plant to the amount coming out of the car.


Efficiency is just the ratio of output energy to input. The greater the efficiency, the less CO2 produced per unit of useful output. Internal combustion engines typically average about 20% efficiency. Since a small part of that comes from hydrogen combustion, we should probably compare to about 21% efficiency from carbon. Then, if coal power plants alone work at 31-33% but lose about 10% in transmission/storage, we would be comparing 21-23% overall efficiency in electric vehicles to 21% for IC engines. Presumably both would have additional losses to friction in gears and air movement, but we can assume those are about the same.  So, the electric will produce very slightly less CO2 for each joule of output kinetic energy running on coal power alone. When you throw in nuclear and hydro power, the difference in CO2 becomes more distinct.

Of course, there are other considerations, particularly the potential environmental and health hazards associated with battery technology. So, it is not clear at all whether the costs and other downsides of electric outweigh the CO2 benefit.

Chuck


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