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Why a compressed natural gas plug-in electric hybrid makes sense

Since the Prius arrived about 14 years ago all of the hybrids in America have been gasoline electric. Why not marry the two cleanest methods of propulsion we have?


Practical electric vehicles affordable to families in the middle and lower income levels do not yet exist. Sure, we can use tax and borrow economics to make anything seem affordable, but the truth is almost nobody is going to buy a Leaf at its actually break-even price with no government rebates.

In California the government price supports to the all-electric Leaf buyer and to the manufacturer are now well over 30% of the “price” of the Leaf. The customer's buy-price is about $19,500 for one. Yet, the Prius is the best-selling car in California. Not the best-selling green car – best period. In the US overall the Prius outsells the Leaf by about a 10 to 1 ratio and the Prius outsells all the plug-in and pure EVs in the market combined.

Automakers can build a practical hybrid automobile affordably now. They can and do sell well without massive tax refund incentives and without special stickers for high occupancy lanes - as the Prius has been proving for well over 2 years now. The buying public needs range and the Leaf does not offer that, or the majority of green vehicle buyers don’t believe that it does.

There is a very large group committed to doing the right thing environmentally as the Prius and other hybrids like it have proven. However, look at any electric car website, or on any forum where the battery electric vehicle (BEV) owners and fans vent and one will see that the hatred for gasoline is strong. Why not get rid of the gasoline and oil, but still have great range and solid environmental performance?

A recent article by Parks McCants here at Torque News reminded us that there are already cars that use compressed natural gas and they are cleaner than all the liquid fuel vehicles their size in the market. They come close to the amazingly low level of CO2 produced by hybrid electric cars, outputting about 220 grams per mile. Gasoline electric hybrids beat that by about 10%. Thinking about Parks’ story made me wonder why Toyota, Honda, or maybe some other automaker has not combined a compressed natural gas (CNG) drivetrain with an affordable electric hybrid drive. This marriage would immediately be the cleanest and greenest powertrain in the US market besides full electric, yet could have basically unlimited range and would come at a dramatically lower cost.

Yes, fueling stations remain a problem. However, how is that different than hydrogen, or electric vehicles? Both struggle to provide enough places to fuel up. CNG has two big advantages with regard to fueling. Natural gas is already widely distributed around the US. It is like electricity in that way. Adding in a network of compressed gas stations is relatively easy, much easier than hydrogen would be for example. Furthermore, Honda already has a home refueling system that can be hooked up to any home with an existing Nat. Gas connection.

CNG has political and economic benefits too. It quiets the whole “energy independence” argument, which this author thinks is ridiculous anyway. Unlike diesel, we have enough natural gas production and reserves in North America to expand the fuel to large numbers of vehicles. Second, it is affordable. The fuel and the engine technology are inexpensive.

The benefits of a CNG electric hybrid don’t end there. Think about electric vehicles. One big benefit many EV owners cite (which again we are skeptical of) is a lower cost of ownership due to the lack of need for oil changes and maintenance. CNG vehicles have that advantage as well according to the CNG proponents.

There is one other way that CNG is a possible green fuel. That is as the range extender engine in vehicles like the BMW i3 and Chevy Volt. CNG is a cleaner fuel than gasoline, but more importantly, it also does not need to be purged as often from its internal tanks, so those who use their extended range electric vehicles primarily as EVs would not need to burn their fuel strictly to keep it fresh.

Is this short story the defining work on CNG-hybrids? Of course not. So feel free to pick apart the logic in the comments section below. Peer review and discussion is the backbone of good science.


bruce dp (not verified)    January 29, 2014 - 2:58PM

Today's plugin buyer is different than the initial affluent early-adopters. For today's buyers, it is less about being green and more about saving money.

There are positives and negatives with the writer's stated idea. They base their source for compressed natural gas (cng, ch4) from fossil sources. But little cng is from the U.S., and mostly from our friendly neighbors to the north (Canada) and south (Mexico). All N. American sources, destructive fracking is used (injection into the ground to release more hydrocarbons).

Like hydrogen (h2) cars, their h2 is made/reformed from ch4 (but no one is saying what happens to the gunk left over after the h2 extraction). Like gasoline, cng is subject to the ups and downs of the market. Whereas electricity is stabel and cheap.

There are time honored ways to generate ch4 from bio-sources, but it needs to have the fat cat$ invest in that to make it happen. That will likely not happen without social pressure as ch4 from fossil sources is cheaper than making ch4 from bio-sources.

The cost of ch4 fuel per mile fairly close to gasoline when ch4's 70% energy density is factored in. The real gain is that ch4 is so much more clean compared to other fuels, oil and filter changes don't need to be as often, and the engine (ice) last much longer (less gunk = less friction = less wear).

The writer mentioned using existing phev/pih that use a gasoline ice (suggesting convert to use cng).
I suggest that to really do this right, take a note from the Russian's who's original idea for their 'yo' pih was a diesel ice, that had two fuels tanks. Thus the 'yo' could run off either: electricity, diesel, or cng.

The biggest killer to getting automakers to produce EVs, or cng vehicles, is because they are so clean. A clean ice, wears less = needs less replacement parts, thus the automaker makes less profit on selling replacement parts.

I applaud the writer's idea to also offer cng plugins, along with other plugins, but I strongly suggest that a diesel ice be used so it can run either cng or diesel. And lets offer the buyer the option to bump up the electric-range to something more real, like 50 miles.

Aaron Turpen    January 30, 2014 - 3:57PM

In reply to by bruce dp (not verified)

"All N. American sources, destructive fracking is used (injection into the ground to release more hydrocarbons)."

Not exactly true. I live in Wyoming. There are many, many wells here pulling natural gas without anything more than a drilled hole and a pump. This is also true of many sources in Nevada. I'm sure there are others.

I also take issue with the "bump up the EV to 50 miles" thing. The thing most EVangelists seem to have such a hard time wrapping their minds around is that nobody wants a car that can only go 100 miles (or less) before requiring hours of recharge. The world paradigm is 300 miles per "tank" (charge). Beat your head against the wall trying to convince people that they only need what they use to commute all you'd like, the market reality is that for generations, we've expected 300 miles. Period. There's a reason Tesla didn't bother making a 100 mile version of the Model S or Roadster. Musk, for all his nerdiness, is fully capable of seeing past that myopic "but this is what the numbers say" viewpoint.

Parks McCants    January 30, 2014 - 4:04PM

Growing up in Huntington Beach Ca., we had a gas and oil well on the grounds of my High-school.
In most cases the region's residual gas was burned off. There was no market for it. In later life we had a natural gas well on a neighboring acreage in Briceland, Ca. It was utilized to heat and power the town of Briceland in pre-grid days.

Much of the United States was without grid power prior to the Farm Act of the 1940's; following W.W.2.
Many farms and small town relied on gas as their primary energy fuel source.

None of this " natural" gas was forced from the earth by fracking. Let's do it...

David Martin (not verified)    January 31, 2014 - 6:12AM

The reason hybridisatiion has caught on is because petrol is more expensive than in the 'good old days'.
Hybridisation costs money, so since natural gas is cheap, the cost benefit ratios don't work.
There may also be some space considerations, as the NG tanks are bulky.
That would apply more to any schemes to make a hybrid plug in though, as batteries are also bulky.

David Martin (not verified)    January 31, 2014 - 12:38PM

In reply to by John Goreham

If you are paying $2,000 a year in fuel to run your car then, say, a $3,000 cost to hybridise it saving half your cost per year returns $1,000 per year - pretty good.

If you are using natural gas which costs $1,000 a year, then the same $3,000 cost to hybridise is only saving you $500 if you save half your fuel burnt.

The numbers I give are only indicative, but show the problem.

BTW, in answer to another response, natural gas tanks are way, way more bulky than petrol tanks.

John Goreham    January 31, 2014 - 2:14PM

Aha. You're right. Very good point. I still think it would be a good seller due to the green aspect of the design. Also right about the tanks. I have not ben there in a while, but I used to visit Japan and they had Nat Gas taxis. The tank was in the trunk.

AusKiwi (not verified)    December 11, 2015 - 11:34PM

In reply to by John Goreham

I am a taxi driver on the Gold Coast in Australia and by chance today I am driving one of the few LPG fuelled Prius taxi's in our fleet. Australian service stations mostly have LPG so it makes a lot of sense. Although the taxi base has its own LPG pump which doesn't get as much use as it did 10 years ago since the bulk of the fleet are now petrol fuelled Prius's whereas they used to be six cylinder Ford Falcon sedans powered by LPG. Sign of the times. I suspect the average motorist wouldn't save enough money to justify the cost of an LPG conversion on top of the Prius hybrid system, but this 2011 Prius has already done 260,000 kms and will do the same again before it's retired, so the LPG at about 80c a litre or so as opposed to $1.30 for petrol definitely makes economic sense for a taxi fleet.

Aaron Turpen    January 31, 2014 - 3:00PM

Actually, new methods for making CNG tanks allow them to be shaped and formed just as gasoline tanks are. LPG is just a byproduct of NG extraction, btw, and is actually more likely to come from cracked crude oil or fracked NG. LPG also settles to the ground when it leaks, creating a "puddle" effect of highly flammable fuel whereas CNG disspates in air when it decompresses. CNG is also easier to transport in pipelines and such whereas LPG is usually transported by tractor-trailer, but is easier to store. The two, like any other fuel, have their drawbacks and high points.

Your analysis of the ROI is good, though. One advantage of CNG is that it can also be used to create H2 for fuel cells or power a fuel cell itself. That would eliminate the need for a combustion engine altogether.

David Martin (not verified)    January 31, 2014 - 4:02PM

The point about LPG which is germane is that it is far more energy dense than NG and does not require a high pressure tank.

If you are making the tank for CNG in some rather more exotic shape than a cylinder or similar then the costs increase due to the extra materials needed to maintain integrity.

I think the way forward is fuel cells, as you outline, in partnership with batteries, taking over where the energy density/cold and hot weather performance of batteries lag.

Aaron Turpen    January 31, 2014 - 10:11PM

In reply to by David Martin (not verified)

The real trouble with CNG is that most energy companies aren't interested in producing and selling it to the consumer vehicle market. They'd much prefer to sell to fleets, where they can do a complete chain (energy extraction, delivery, storage, pumping) instead. NG (be it liquefied or compressed) has far more promise in delivery trucks and heavy vehicles than it does in passenger cars.

David Martin (not verified)    February 1, 2014 - 4:00AM

In reply to by Aaron Turpen

Probably fair enough from an American perspective.
Here in the UK our alternative is LPG, which works pretty well as the cars are dual fuel, so that you can switch back to petrol if you are in a place where it is not available.
In spite of its being half the price of our petrol, which runs at around $8/gallon, not many bother.
It takes up a bit of the trunk and has to be serviced once a year, which obviously costs some money, so it really works for 12,000 miles per annum plus drivers.
There are very few about though, so it is down to the drivers, not the petrol companies.
In many places in Europe the have very extensive natural gas supplies, in Germany for instance around a tenth of stations have NG pumps, and the cars are usually dual fuel so there are not too many worries about running out.

They are still not that popular, but maybe that will change with the new VWs which were designed from the ground up to be able to take an NG drivetrain.

So at least in Europe there is reasonable availability of NG/LPG fuels, so lack of take up is not down to the oil companies.

John Goreham    February 1, 2014 - 9:27AM

In reply to by Aaron Turpen

I completely agree with Aaron that Nat Gas makes more sense first as a truck and fleet fuel. It also sort of pisses me off that the only government agency that drives around my town all day, 6 days a week, has a fleet of gasoline burning, non-hybrid sh1? box small trucklets that smell when they go by - all the while that same monolith keeps using my tax dollars to fund EVs and other alternative vehicles. (Post office if you didn't guess).

DENNIS CLAYTON (not verified)    February 28, 2015 - 6:51PM

I have been thinking about a cng plug in hybrid for awhile. I thought the only way to do this was to takea plug in hybrid and convert the gas engine to a cng engine

Parks McCants    March 2, 2015 - 1:07PM

In reply to by DENNIS CLAYTON (not verified)

Welcome Dennis. Right you are. To date we know of no manufacturer that offers a CNG plug-in or hybrid cars and light trucks, However, in speaking with Honda, the company is considering many combinations of co-generating engines including CNG for future model offerings. Thank you for reading.

Jim (not verified)    June 2, 2015 - 6:05PM

In California the government price supports to the all-electric Leaf buyer and to the manufacturer are now well over 50% of the “price” of the Leaf. The customer's buy-price is about $11,500 for one.

Is this correct? $11,500 for a brand new Leaf in California? How's the math work here?

Alisdair (not verified)    November 9, 2015 - 12:03PM

In the big cities of Spain, there are many taxis that are Toyota Prius hybrid converted to LPG. It really works. I recently took one at Madrid's airport and it run on LPG in the motorway, then electric in the city's centre traffic jam.

Paul Dodson (not verified)    October 20, 2016 - 8:07AM

The demands of electric vehicles are increasing in different countries. Due to its beneficial features and specification, people are starting using electric cars; but the common problems with electric cars are charging systems, and due to lack of charging stations most of the electric vehicle owners are facing problems. Therefore, different types of new advanced features are introducing day by day to deal with these problems.

Kristofer Cassel (not verified)    May 24, 2020 - 1:13PM

Great article and great idea! Here in sweden we use "biogas" which is made from household waste. It powers all gas-cars and also the buses in Linköping, my home town. This is another great argument for gas-electric hybrids.