I really don't think that CNG vehicles will be a threat to EVs. I have researched many alternative fuels over the years: biodiesel, hydrogen, ethanol, CNG, etc. I think that many of them have some potential, but they have never managed to have more that a brief time in the limelight.
I love biodiesel, and I bought myself an old diesel Mercedes last year, just so I could have a more environmentally responsible commuter car. However, I had to drive 30+ miles to make it to the only non bulk distributor in the area. I could have had the fuel delivered in bulk, but that car got great mileage, and I would not have been able to use up all 250 gallons before its shelf life came up. I had the knowledge, but not the time to produce my own fuel.
I was excited to hear about hydrogen in the 90s, and again when the "Hydrogen Highway" was proposed. However, most of our hydrogen comes from fossil fuels and the costs of running on hydrogen are still prohibatively expensive.
Ethanol seemed like a great fuel, at first. Just a few years ago, we were looking for a family car. My husband is a Chevy man, and the salesman was trying to get me interested in Flex Fuel. "You can save so much money because ethanol is so much cheaper!", he touted. I tapped the sticker on the window. "Um...it looks like you get quite a bit worse fuel economy with E85." Then, I researched about the water and pesticides that are needed to support the ethanol crops. Maybe ethanol wasn't as great as I originally thought.
As for CNG, it is cleaner burning, and it would be nice to rely on a more local source of fuel. I remember when many people scrambled to convert their vehicles to duel-fuel (gasoline and CNG) to take advantage of a nice tax credit. However, many of these people ran primarily on gasoline, due to the ease of refueling and abundance of stations.
For some reason, our society does not seem willing to give up gasoline. Plus, our government seems more willing to spend money on subsudizing petrolium products (including CNG), than other alternative fuels.
So...why the heck did I buy an EV?
1. I wanted a zero emissions vehicle (or at least a much lower emissions vehicle).
2. I was tired of paying so much for a fuel that I knew was harmful.
3. I wanted something that was more energy efficient.
4. I wanted a vehicle I could charge/refuel at home with minimal fuss.
5. I wanted to be part of a movement to show the rest of the world that we can function without burning fuel in our commuter vehicles.
I'm assuming that many other folks had the same reasons for wanting an EV.
How do NGVs (Natural Gas Vehicles) measure up to EVs?
1. Though NGVs do have less tailpipe emissions than gasoline, they have greater emissions than gasoline in their production and transportation.
2. NGVs are cheaper to fuel than gasoline vehicles, though still more expensive than EVs.
3. NGVs are about as efficient as gasoline vehicles. EVs are more efficient than both NGVs and gasoline vehicles. Hooray for the second law of thermodynamics!
4. You can refuel your NGV at home with the right equipment if you already have natural gas supplied to your house. If you do not (I don't), you would have to have it delivered and stored in a tank.
5. NGVs still burn fuel.
So, it would seem comparing NGVs and EVs is like comparing apples to oranges. They each have their own advantages and disadvantages. They are from two different markets.