Petrol-electric hybrid vs CNG conversion: Pros and cons

The government recently said it is framing norms to convert petrol and diesel cars to petrol-electric or diesel-electric hybrids. And one company, Revolo, is ready with a kit that can be retrofitted in any petrol or diesel car, but costs about Rs. 60,000 to Rs. 80,000.

Now, if you look at CNG cars (which are essentially dual-fuel hybrids running on either petrol or CNG), the cost of converting a petrol car to a CNG car works out to almost the same as that of converting a petrol car to a petrol-electric hybrid. Also read: Govt framing norms for hybrid cars

Which one of these system should you pick? We take a look at the pros and cons of both, comparing a Maruti Alto fitted with the Revolo hybrid system and one fitted with a sequential CNG system.

Revolo petrol-electric system

The petrol-electric hybrid system from Revolo (a KPIT Cummins offering) uses an electric motor coupled with the petrol engine through a drive-belt connected to the crankshaft pulley. The electric motor draws power from a battery pack (two 12V batteries) in the boot or from a single Lithium ion battery. This battery pack can be charged overnight from a standard household socket and it also gets recharged when the car is moving – especially during braking. Also see: Convert any car to a hybrid with Revolo’s system

Pros of the petrol-electric system

Revolo claims an additional fuel efficiency of 35% compared to a regular petrol Alto in the city. Given the city mileage of about 17 kmpl for a regular Alto one can get about 23 kmpl using this system. This would result in savings of up to 30% on fuel bills per year. Running costs would come down by 30% overall, given that electricity to charge the system is nearly 1/10^th the cost.

Also the system is quite compact and does not take up as much space as a CNG system would – there is no big cylinder in the boot as the battery pack is small and can be fitted in one corner of the boot saving space.

The system, once fully charged, can run much longer than a CNG system would as it also gets trickle charged during the day when the car is running.

Cons of the petrol-electric system

The cost projection for installing such a system of between Rs. 60,000 to Rs. 80,000 is fairly high. You need to drive over 2000 km a month to realize the benefits of the system. With this kind of driving you would save about Rs 2,100 per month, making the system pay for itself by the third year of use. However, in the fourth year, expect your savings to drop considerably, as you would need to spend about Rs. 14,000 on new batteries. And this is a recurring cost every three to four years. Also read: Do hybrids really give better fuel efficiency and lower running costs?

CNG-petrol dual fuel systems

With a CNG conversion, the car can run on natural gas or petrol. Running it on CNG often gives slightly better fuel efficiency – in the case of the Alto about 22 km per Kg of CNG. With CNG prices at about Rs. 40 per Kg, it is nearly Rs. 30 cheaper than petrol per litre. Also read: Kinds of CNG kits, advantages and disadvantages

Pros of a CNG system

CNG conversion allows for pure CNG driving, without a drop of petrol being burned unlike the petrol-electric system, where you only get a boost from the electric motor, but are still consuming petrol. Therefore the savings (given the cost difference with petrol) are much higher. You realize the investment in CNG much faster than you would with a petrol electric system.

CNG filling networks are quite widespread in about 35 cities now, which means much easier access to gas. Electric charging points are not easily accessible unless you have a garage or easy access to a plug point. It also takes about 5 minutes to tank up on CNG, while it takes about 8 hours for a full-charge of the batteries.

Cons of a CNG system

The size of the CNG tank takes up almost the entire boot in an Alto, leaving no space for luggage. It also is substantially heavier and takes its toll on the suspension of the car. When one travels out of town this becomes an issue as CNG networks don’t exist outside of major cities, forcing the driver to drive on petrol and negate any savings.

Now that you’ve seen the pros and cons of both the systems, which do you think would suit your needs better? CNG or a petrol-electric assist hybrid system? Share your thoughts. Also read: Toyota Prius only hybrid, but Maruti may join in