Compressed Natural Gas

I think the ICE and gasoline are dead and I believe EVs are the only way forward.
A friend asked me about CNG vehicles, so lets look at them.

Why would we use CNG? Because it is domestically produced, burns cleaner than gasoline, and is cheaper than gasoline ( about half the price ).

What is compressed natural gas? Natural gas is a fuel that is different from gasoline. Gasoline is a liquid at room temperature, if left uncovered it will evaporate and make flammable ( possibly explosive ) vapor, but you can store it in an airtight plastic can with a lid. Natural gas is actually a gas at room temperature, it is liquid at -250F ( -158C ). In order to store any significant quantity it needs to be kept under pressure. A CNG car stores it at 3600 psi ( 250 atmospheres ), the tank has to be big heavy and strong, because 3600 psi of anything contains a powerful explosive force if ruptured ( without even igniting the resulting vapor ).
As natural gas pipelines get further away from the source ( a station that compresses it ), it divides into smaller pipes at lower pressure.
Natural gas pipeline in your neighborhood is 60 psi, and it enters your house at about 2 psi.
Propane in a tank for your barbeque stores propane at about 128 psi, and the tank is rated to handle about 300psi. The filling stations refuse to fill one older than 10 or 20 years ( depending on your local whims ) because they dont want to rupture an old worn out tank.
The CNG tank on a car will need to be replaced after about 15 years, when it nears that 15 years it will need to be carefully inspected. An old CNG tank is dangerous. CNG Tank Expiry

You can buy a CNG burning Honda Civic GX for about $25000 ( It qualified for a $4000 federal tax credit that may have ended at the end of 2010 – reducing the price to $21000 )
It has a 12.6 second 0-60 and gets about 180-240 miles range on its 8 GGE ( gasoline gallon equivalent ) of CNG ( compressed natural gas ) at 3600 PSI. The CNG tank is huge and eats your trunk, so you only get 6 cubic feet of cargo space. An 8 GGE CNG cylinder would be about 17.5 inches in diameter and 42 inches long – probably with a few inches of protective structure around it, and it cant be squashed into unused spaces like a gas tank. That makes it use about 4 to 8 times the volume of a gas tank in your car.
The nearest CNG station to me ( about 20 miles away ) is $1.99 per GGE.
Here is a link to a CNG filling station map and prices: CNG Map
There are 830 CNG filling stations in the U.S., but a large portion of them are not available for public use.
In fact there is no CNG station within 400 miles to the east, west or south of me, so my maximum range in those directions is 1/2 of my cars range. ( I am in Seattle )
You may not live near enough to one of them to want to go every 6 days ( 12000 miles per year = 32 miles per day ) – if I lived 20 miles further away that nearest CNG station would not be useful to me.
You can buy a home CNG filling unit that will cost you about $6000 installed. It can refill your car in about 16 hours. But it uses 800watts to do that, so in 16 hours it would consume 12.8kWh of electricity.
You can buy a $10000 unit that refills twice as fast, but I do not have any data on its electricity consumption.

So for $31000 you can have a car that will take you no more than 120 miles from your home ( probably only 100 ). If you get stuck there is no way for someone to bring you a can of some CNG.
If one of the public CNG stations is on your path, you can go further.
If you refill exclusively at home, you will spend $932 per year on fuel to drive 12000 miles ( $857 on the CNG at $2/GGE and $75 on the electricity ( at 11 cents per kWh ) to run the compressor! ).

Now lets compare it to a Nissan Leaf.
A Nissan Leaf is $32000 ( minus a $7500 federal tax credit, reducing its cost to $24500 )
It does the 0-60, in about 10 seconds and it goes about 80-100 miles on a charge ( with a 14.5 cubic foot trunk )
With a $1000 240V charge plug you can recharge the Leaf in about 8 hours ( They are going to upgrade the next years model to charge in half the time – if the Leaf had the same onboard charger as a Tesla, it could recharge in less than 2 hours from a 240V charger ). With a standard 120V plug on a 20amp circuit you can recharge it in about 16 hours. There are many dozens of the 240V public chargers within 100 miles of me if I wanted to use one.
With a Level 3 fast charger, you can recharge the Leaf in about 20 minutes, but there are very few of those right now, although they promise to add them along the I5 corridor over the next year.
The standard plug 120V can be found in every garage in America, meaning anywhere you go you can recharge your Leaf overnight and get home. So a round trip that includes an overnight stop is the same convenience as the 2x range CNG car.
The Leaf is rated at 34kWh per 100 miles, so $448 per year in electricity to go 12000 miles at 11 cents per kWh.

Neither car is useful for long cross country trips right now. The Leaf can do it, using existing infrastructure ( RV parks and other plugs of opportunity ), but it would be inconvenient. The CNG car can not do it at all.

After 5 years ( without inflation ) you will spend $4663 fueling your CNG car, or $2240 fueling your EV.
Including the home CNG filling station, they cost about the same amount of money.
In the very near future, the batteries will improve and the EVs will become cheaper and longer range, but the best you can hope for for CNG cars is more public filling stations – they arent going to figure out how to compress the CNG more.

Building a CNG station is more complex than a gasoline station, and thus likely to cost even more. You need a big compressor to compress the gas to 3600 PSI. In order to refill the car in a short time, it needs to have a big 3600+ PSI tank so it can have pre-compressed gas ready to push into the car. Gas stations are in the ballpark of a million or two million dollars to build.

A Level 3 charging station is a coke machine sized box that costs in the ballpark of $20k-$50k. They arent really very complicated, so if we buy them in quantity that price will plummet. ( However – an individual level 3 charging station can serve fewer cars per day than a CNG station with multiple pumps can. )

It is a lot cheaper ( several orders of magnitude ) to put in scattered level 3 charging stations and serve a vast geographic area ( like a few thousand and cover the entire country ) adding more capacity as the number of EVs grow than it is to try to cover the entire country with CNG stations, so I think the future for EVs in that regard is also much brighter.
Lastly note that if you took the natural gas and turned it into electricity at an efficient powerplant, the same CNG that would drive the Honda Civic GX 180-240 miles would drive the Leaf about 430 miles.

From the same fuel source, an EV will drive further than a CNG car and thus be cheaper to operate. EVs can use electricity from whatever source we choose: wind, solar, hydro, coal, natural gas, nuclear, tides, geothermal… Cars with roughly equivalent utility are already roughly the same cost, but EVs are rapidly improving in capabilities and price. The infrastucture to support a huge amount of convenient EVs is much cheaper to build.

CNG as a fuel for cars is a dead end.


2 responses to “Compressed Natural Gas

  1. You about covered it! And with PV solar, in 10 years or so, your power is free. No one can guarantee the future price of NG, but the bet is that it will get more expensive.

  2. I have always wondered what happened to the CNG pickup trucks that I remember maybe in the early 70’s, seems like someone told me that it
    costs only $200 to convert you carb to run on CNG…..Been trying to
    figure out why with the price of gas today more people are not going
    back to that….How would you calculate GGE ?

    Good Post…isn’t the CNG 2X the cost of the EV ?

    “After 5 years ( without inflation ) you will spend $4663 fueling your CNG car, or $2240 fueling your EV.
    Including the home CNG filling station, they cost about the same amount of money.”


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