Sunday, February 20, 2011

Why Not Natural Gas?

Increasingly I see people suggesting natural gas, specifically compressed natural gas, CNG, as a better option than EV's for personal transportation needs.  Increasingly I'm convinced it's not as easy as some would make it seem or even a good idea.  Yes we have large reserves of CNG here in the US, and hydro fracturing techniques, (fracking), are freeing up untapped reserves.  Fracking is not without it's problems, I won't go into details here but there are consequences that need to be closely looked into before we forge blindly ahead.  CNG has less energy density than gasoline so tanks need to be larger and provide less range, about the same as a battery powered Tesla Roadster, but with far lower performance.  CNG cars also have lower performance than conventional gasoline versions, the CNG Honda Civic GX has 113 hp compared to the 140 hp gasoline version.  Since it's a highly explosive gas under high pressure the tanks need to be very strong and well protected.  Since it's a gas it needs to be compressed to flow into a tank, which takes energy and time.  The Phill home fueling station will use about 6 kWh's of electricity to provide 100 miles worth of fuel.  An EV could go about 25 miles on those 6 kWh's of electricity.  Refilling a CNG vehicle is not that quick, it will take overnight with an expensive home filling system if your house has a NG pipeline connection.  The Phill would take about 12 hours for a full tank.
Phill Specs
A little more than half of all homes have NG, while almost 100% of US homes have electricity.  There are few public high pressure fast filling stations available, basically a non existent infrastructure that would need to be developed at high cost, while existing pipelines are failing.
The safety issue is significant.  If a CNG vehicle catches fire the potential for damage is much higher than with a gasoline vehicle.  Example: CNG Honda Explosion  Notice the gasoline vehicles next to the CNG vehicle also caught fire but did not explode.  More troubling are the high number of pipeline explosions that seem to occur, possibly with increasing frequency as older pipes fail.  A Google search of "Natural Gas Explosion" brings up a long list, many with shocking video footage.  This site seems to track some of the latest incidents Recent NG explosions  I'm quite happy that I don't have a NG pipe going into my house or even in my neighborhood.
Using CNG in an inefficient ICE vehicle at maybe 20% efficiency makes little sense when it can be use in combined cycle generating plants at 60% efficiency to charge EV's.  Additionally a few pipelines going to a few generating plants are much more efficient and easier to monitor and maintain than millions of pipelines going to millions of homes and public fill stations.  If we are going to use CNG lets not waste it in ICE's, let's use it to displace coal fueled electricity.

Another more detailed look at CNG for transportation:
CNG analysis
*Update:  A recent study suggests that NG may have a larger carbon footprint than previously thought.
NG's higher emissions
Industry insiders question the realities of NG production
Problems with NG production
Smaller NG reserves than previously thought
Hinchey on Gas Reserves 
Additional data on energy required to compress and transport NG by Rick Kermentz on Seeking Alpha:
 The collection network (from a group of wells) is generally low pressure. The gas is scrubbed of sulfur compounds, odorant added, and compressed to 1,500 psi for long distance transport, with additional compressor stations every 40-60 miles. The pressure is dropped backed down to typically 100 psi for city distribution, and often down to 3 psi for residential distribution. A high volume NG filling station probably would access gas at 100-200 psi.

To get a reasonable range in a CNG vehicle, the gas will be pressurized to 5,000-10,000 psi. Not only is there significant energy consumed compressing the gas, the thermal heat of compression is totally lost.

CNG Bus Fire
Bus Fire
CNG Bus Explosion
Bus Explosion


  1. For a lot more on natural gas leaks and explosions, check out this site:

  2. In reading these comments about the limitations of CNG in comparison to the current ICE, it occurs to me that almost all the same limitations apply almost equally well to the battery powered EV compared to the ICE vehicle. Less energy density, limited range, heavy storage containers, very long time to "re-fuel", insufficient refueling infrastructure, etc. It's almost as if you could do a CUT (CNG) and REPLACE (battery EV.) Almost all of these debilitating limitations are avoided, or significantly reduced, by incorporating an ICE powered generator in the EV; yes, that's right, a smartly designed hybrid.

    While the EV battery may not explode in as spectacular a fashion as CNG, we do have 300, 400, 500 volts and more in cables and conduction bars that, in an accident, wait to zap (and worse) any unsuspecting rescuer or home mechanic. Unfortunately, this same danger will exist in most high voltage motor systems, irrespective of whether there is an ICE backup; low voltage systems such as homopolar motors should be investigated.


  3. Low voltage systems have inherent inefficiencies, and as far as high voltage most conversions are under 200 volts and most OEM's are under 400 volts. They've also been crash tested successfully.
    Batteries and electronics are in no way as potentially explosive as CNG, but of course no system that holds large amounts of energy in a small package is 100% safe.
    You missed the big difference though, efficiency and infrastructure.
    An EV charged from a CNG plant is far more efficient than any ICE, and a hybrid simply adds complexity and higher degree of danger. It's much easier to distribute CNG to a few large plants than to build out the infrastructure and pumping stations to distribute it to millions of individual vehicles. Further more the infrastructure already exists, every home and business has electricity. You can literally drive your new EV home and plug it in without doing anything else.

  4. Sorry, but I think you missed the whole point of my remark which is that almost all of your "non-explosive" comments about the deficiencies of CNG apply equally well to battery powered EVs; but not to hybrid EV (sorry, I don't accept your very narrow definition of what constitutes an EV.) Your response seems to focus on my flippant comment about explosions which I only made because that's what almost half of what your comment is about. Forget about the exploding CNG tanks for now. How do you address the operational limitations of the battery powered EV that are similar to those of the CNG system that you so correctly identified?
    I'm aware of the limitations of low voltage systems (I'm an excessively degreed EE) which is why serious research into low voltage power systems would be so useful (even if it doesn't pan out.)
    Look. I believe in EVs. I just don't think that current, or near future, battery technology can do the job of energy storage and timely charging. Today's batteries are only about a factor of ten better than the batteries built for electric cars over a hundred years ago by Edison. That is why the ICE is needed for a vehicle that is not restricted to simple commuter use or blingy showoff.


  5. "How do you address the operational limitations of the battery powered EV that are similar to those of the CNG system that you so correctly identified? "

    Easily. As I already mentioned EV's do not have the same infrastructure limitations that CNG vehicles have, and while they do have range limitations the actual limitations are less because, as already mentioned, you can more easily find electrical outlets than CNG filling stations. Even homes and businesses with NG service don't have any vehicular fill capacity while an EV can plug into a standard existing outlet. It's also much easier to install a higher power circuit than it is to install a CNG pumping station. It took me about half an hour to snap in a 30 amp 220V circuit breaker, run a few feet of wire, and hook up an outside plug for my car. Before I did that I just plugged into a regular 120V outlet or a 220V dryer plug.
    Additionally, if you are going to deal with similar limitations why not do so with a vehicle that uses NG in a substantially more efficient manner, and has the capability of using many other fuels including renewables?

    As for research into low voltage systems, I don't see the point in pursuing something that's not likely to pan out, especially since it's not really an issue. It's easy enough to design inertia switches and/or fuses that break up the pack into lower voltage segments after a crash, and the few Roadsters that have been crashed, some quite severely, have not posed any special hazard. As mentioned, crash testing has shown packs to be well protected in other vehicles.

    Since you've been actively reading my blog you really should be able to answer some of your questions from my previous posts regarding range and battery technology. Quite simply I'm not that concerned with range since current EV's can "only" cover about 95% of most drivers daily needs. I don't think we need to rule out a product just because it might not possibly work for 5% or our needs. My own 50 mile max range conversion handles probably 99% of my driving needs, and like most people I own more than one vehicle. Until we have unsold EV's sitting on the lot because they don't have enough range then range really isn't an issue. Real EV's, the LEAF being the only one somewhat widely available in the US right now, are selling as fast as they can make them. Most of the people who worry about EV range limitations don't own one.

    Regarding my "narrow" view as to what constitutes an EV, I'm fine with you calling a "hybrid" a "hybrid EV", since that's what it is, that's what "HEV" stands for. The term "hybrid" differentiates it from a pure EV, and that difference is significant, as you yourself point out. If you think you need a hybrid that's fine with me, but like most hybrid buyers what you really want is an EV, you just don't trust them yet or think their range is enough for you. At some point range and fast charge stations will increase enough that even you will feel comfortable with an EV. I'd be interested to know what your numbers actually are.

  6. As a car guy and lover of all vehicles, I cried when GM massacred all those poor EV1's. Therefor I welcome all forms of car technology. The way I see it Natural Gas could save all cars (meaning the "current cars not just new ones.") With turbo technology possibly making up power losses. EV or hybrid for small cars, CNG and CNG hybrid for mid to true American fullsize cars. Also more conversion companies mean jobs which we badly need.

  7. Well if we cut back our oil usage for newer vehicles there will actually be plenty of oil for the shrinking fleet of older vehicles for quite a long time. Since CNG is still a limited fossil fuel resource we need to use it as efficiently as possible, and that is not going to be pressurizing it and pumping it to millions of inefficient ICE vehicles. There are still the issues of infrastructure and safety as well.
    I agree we need jobs, battery construction and recycling and EV factories would provide many good ones.