Wheel to Well Analysis
When you examine the relative efficiencies of compressed natural gas and electric vehicles you have to look at the total cycle of energy; that is how much energy we expend to remove natural gas from the ground, how much energy we expend generating electricity, how much energy we expend transporting natural gas or electricity and how much energy electric or natural gas vehicles use while driving. Generally, to examine the efficiency of a process we divide the energy we get out that process by the energy we put in to the process. When we have a complicated chain of processes, the total efficiency is the product of the efficiencies of each process.
If we consider E(rem) to be the efficiency of removing natural gas from the ground, E(gen) to be the efficiency of the generators that produce electricity, E(trans) to be the efficiency of transportation, E(stor) to be the efficiency of storing natural gas, and E(drive) to be the efficiency of the vehicle; then we have total efficiencies of:
Total efficiency for compressed natural gas:
E(rem) X E(trans) X E(stor) X E(drive) = 92% X 97% X 87% X 19% = 15%
Total efficiency for electric:
E(rem) X E(gen) X E(trans) X E(drive) = 92% X 50% X 92% X 44% = 19%
Here it is assumed that electricity is generated by burning natural gas in a combined cycle power generator. This means that for this example both compressed natural gas and electric have a natural gas removal efficiency (E(rem)) of 92%.
But, electricity can be drawn from many other sources. For this comparison we use the same initial efficiency so that we can compare the two technologies more easily. We must also note that electricity cannot be stored economically. This means that when generators produce electricity they must do so on demand.
Data taken from:
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1428016
http://www.memagazine.org/supparch/mepower03/gauging/gauging.html
When you examine the relative efficiencies of compressed natural gas and electric vehicles you have to look at the total cycle of energy; that is how much energy we expend to remove natural gas from the ground, how much energy we expend generating electricity, how much energy we expend transporting natural gas or electricity and how much energy electric or natural gas vehicles use while driving. Generally, to examine the efficiency of a process we divide the energy we get out that process by the energy we put in to the process. When we have a complicated chain of processes, the total efficiency is the product of the efficiencies of each process.
If we consider E(rem) to be the efficiency of removing natural gas from the ground, E(gen) to be the efficiency of the generators that produce electricity, E(trans) to be the efficiency of transportation, E(stor) to be the efficiency of storing natural gas, and E(drive) to be the efficiency of the vehicle; then we have total efficiencies of:
Total efficiency for compressed natural gas:
E(rem) X E(trans) X E(stor) X E(drive) = 92% X 97% X 87% X 19% = 15%
Total efficiency for electric:
E(rem) X E(gen) X E(trans) X E(drive) = 92% X 50% X 92% X 44% = 19%
Here it is assumed that electricity is generated by burning natural gas in a combined cycle power generator. This means that for this example both compressed natural gas and electric have a natural gas removal efficiency (E(rem)) of 92%.
But, electricity can be drawn from many other sources. For this comparison we use the same initial efficiency so that we can compare the two technologies more easily. We must also note that electricity cannot be stored economically. This means that when generators produce electricity they must do so on demand.
Data taken from:
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1428016
http://www.memagazine.org/supparch/mepower03/gauging/gauging.html
