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It is hard to see how that can happen...since it is already about 50-60% efficient (on the generation side).
There are some losses in the compression and liquefaction side. On the regeneration side the fuel cells are about 60% (peak) efficient.

Mike

 

Is methane sustainable? Hell yes. It is cheapest when we simply drill a hole in the ground and grab the fossil stuff - natrural gas. There was so much coming out of the ground in texas that the state had to make laws not to waste it. North dakata still just burns a lot at the well, they need to at least come up to texas environmental standards.

Methane also comes from catalytic or enzymatic decomposition of agricultural waste or products. Most common enzymatic is simply a sewage system naturally decomposing with bacteria providing the enzymatic path. This is more expensive than digging a hole in the ground, but There is plaenty of waste and dumps to provide the stuff at a higher cost.

Finally there is chemical production of methane from water and carbon dioxide, with oxygen as a biproduct. This starts with electrolysis or catalytic cracking of water to hydrogen and oxygen. Then two hydrogen molycules can be combined with a carbon dioxide molecule using electricity (hey use renewable wind for both if you want, and you get a molecule of methane and O2.

Efficiency can not rise very much as the reactions are already quite well understood and very efficient. What can happen is wind electricity can become cheaper, biodigetion of waste can get cheaper, etc.

 

But the nature of gas storage means CNG cars lose passenger or trunk space for shorter ranges than the gasoline version. Wait a minute...

 

There are 5 ideas for using methane for transportation.

1) Pickens plan - place lng/cng stations on long haul truck routes and in air polluted cities. Convert heavy and medium vehicles to lng or cng. Biggest problem is politics preventing national funding, koch brothers are leading pac against. This plan increases ghg slightly verus diesel but greatly decrease oil dependance. and tail pipe pollution Texas and California are supporting with some other states, but low oil prices slow progress even in regional use.

2) Use natural gas and renewables to power plug ins. This is supported by DOE and EPA, despite some PACs attacking it, especially the auto dealers.

3) bifuel for trucks and SUVs, cng for busses. This is making slow progress, but will be hampered until number 1 is done to really bring down costs. cng cars only seem to work in Iran where the government fully supports the infrastructure. CNG cars are as expensive and hybrids and produce more ghg, but have less interior room. They therefore only work for larger vehicles where hybrid does not work as well.

4) methanol flex fuel. China is the leader here. There is a bill in congress going nowhere, as it is opposed by the ethanol and the hydrogen lobbies. California ran a sucessful test, but cancelled when gas got cheap and there were dreams of a hydrogen highway threatened by methanol competing for fuel.

5) Hydrogen. Virturally no chance for the next decade, but maybe in the future.

1,2 and 3 are the low hanging fruit.