The Well-to-wheel carbon footprint of Petrol, Diesel, CNG, Hybrid and Battery powered electric cars in India

Ever wondered about the true environmental cost of your daily commute? It's more than just the smoke from the tailpipe. Every day, millions of us in India turn the key in our cars to navigate our bustling cities. Transport is the third-largest carbon emitting sector. Data indicates that within the transport sector, road transport accounts for about 90% of total carbon emissions of which passenger transport contributes almost half. So roughly about 45% of the third largest emitting sector comes from passenger transport which includes our cars, bikes, and buses

To understand our options for reducing this impact, this blog will compare the most common vehicle technologies on our roads today:

• Internal Combustion Engine (ICE) Cars: The traditional vehicles that run on petrol, diesel, or CNG.
• Battery Electric Vehicles (BEVs): All-electric cars that run on electricity stored in a large battery, charged from an external power source.
• Hybrid Electric Vehicles (HEVs): These cars run primarily on conventional fuels such as petrol, diesel or CNG but are supported by a small battery. This battery recharges itself in two ways: through regenerative braking—where energy normally lost during braking is captured—and through the engine, which spins a generator to produce electricity for the battery. As a result, HEVs typically consume less fuel than traditional ICE cars while avoiding the necessity to charge the battery externally like the BEVs. We have not included diesel or CNG hybrid variants in this analysis because they are uncommon on Indian roads, but the insights from petrol hybrids provide a useful baseline for understanding the emissions of these other hybrid types as well.

(Note: We are not covering Plug-in Hybrids (PHEVs) in this analysis, which feature a larger battery that can be plugged in. These cars, in a sense, have the best and worst of both the worlds.)

To compare these vehicles fairly, we must look beyond the tailpipe and analyze their entire carbon footprint.

Understanding Well-to-wheel analysis of the fuel used to drive Traditional, Hybrid or Electric cars

Generally, the carbon emission associated with driving a car is mistakenly attributed only to the exhaust pipe emissions - carbon emitted by burning fuel to produce energy to run the car. These are also called tailpipe emissions and are usually obtained via a "Tank-to-Wheel" (TTW) analysis of the fuel consumed by a car

• Battery-electric vehicles are assumed to emit no carbon because they don't burn any fuel and hence don't generate any emissions. This is only partly true; they emit carbon in another phase which we will cover in a moment. This phenomenon sometimes leads to BEVs being prematurely classifed as a completely green mode of transport
• Internal combustion engine cars emit the maximum carbon of their lifecycle in the TTW phase when they burn the fossil fuel to move the vehicle
• Hybrid cars don't have a battery that is externally charged. Therefore like traditional cars they emit maximum carbon of their lifecycle through the TTW phase to move the vehicle

However, there are further hidden greenhouse gas emissions from the moment oil and gas are extracted ("the well") or electricity is generated through to its transportation, refining and fueling of the cars ("the tank"). This is called a "Well-to-tank" (WTT) analysis.

• This is the point where battery-electric cars are no longer green options. Because India's electricity grid has high transmission and distribution losses, and 70% of the electricity is generated via coal, BEVs emit their entire carbon when they use this electricity later to move the vehicle
• Internal combustion engine cars emit the least carbon of their lifecycle in the WTT phase because the extraction process is not as carbon-intensive. Typically CNG has a marginally higher WTT emission because of the energy required to compress the gas
• Hybrid cars, the ones whose battery cannot be charged externally, don't take the penalty that BEVs take and therefore emit least amount of carbon of their lifecycle similar to traditional ICE cars.

Together this forms the entire lifecycle of the fuel used by a car, also known as Well-to-Wheel (WTW) analysis. However, fuel production and usage doesn't just emit carbon, it also uses freshwater during its production process. Before we compare the carbon emissions and water consumption, let's understand what are the units of measurement

Understanding the Metrics: Carbon and Water Footprint Explained

When we discuss the Carbon and Water footprint of travel, we use specific, standardized units to quantify their footprint:

• Carbon Footprint: This metric is measured in kilograms of Carbon Dioxide Equivalents (Kg CO₂e). It represents the total greenhouse gas emissions (including carbon dioxide, methane, and nitrous oxide) released throughout the entire journey of the energy used for travel: from extracting fuels or generating electricity, to refining, distribution, and the emissions produced when petrol, diesel, CNG, or electricity powers a vehicle. These gases are weighted by their Global Warming Potential to give a single comparable unit.
• Water Footprint: This is measured in kilo litres (KL), with 1 kilo litre equating to 1,000 litres. This figure quantifies the amount of freshwater used to extract and refine fossil fuels such as oil, gas and coal. Our focus here is primarily on "blue water" – surface and groundwater resources.

How these metrics are calculated

• A Carbon emission factor indicates the carbon footprint per litre of liquid fuels such as petrol, diesel; per kg for CNG; and per kWh for electricity
• A Water footprint factor indicates the water footprint per litre of liquid fuels such as petrol, diesel; per kg for CNG; and per kWh for electricity

These factors act as multipliers. When applied to the quantity of fuel consumed (derived by the mileage and distance covered by the vehicle), they help estimate the total footprint.

Comparing the Environmental Impact: ICE vs. HEVs vs. BEVs

Now, let's apply this understanding to a real-world scenario: a typical 20 kilometer office commute in a metro city for all the different vehicle types

Analyzing the results

The data reveals some counterintuitive truths about vehicle emissions in India today.

First, the most surprising result is that BEVs are not necessarily the cleanest option today. This is almost entirely due to the WTT emissions from India's coal-reliant electricity grid. As soon as the full lifecycle is considered, the green credentials of BEVs in the current Indian context do not hold. They also use up the most amount of water amonsgt other fuels because the Indian grid uses a lot of water to produce electricity

Second, diesel emits less carbon than petrol, yet it is discouraged by regulations. Diesel engines release higher levels of harmful pollutants like particulate matter and nitrogen oxides, which cause severe air pollution and health problems. So, while they may be slightly better for climate change, they are worse for public health.

Finally, hybrids emerge as a compelling middle ground. By using a battery that is charged by recovering energy to supplement their internal combustion engine, they reduce the total amount of fuel burned. Therefore they offer a lower carbon footprint than traditional ICE cars without being dependent on the carbon-intensive electricity grid.

Crucial Caveats

1. It is vital to remember that these results are a snapshot of the present. The future of vehicle emissions is dynamic. As India's grid becomes greener with more renewable energy sources, the WTT emissions and the overall carbon footprint of BEVs will shrink dramatically. In contrast, reducing emissions from ICE and hybrid vehicles is unlikely and might need some new technological innovations.
2. The mileage figures used for these vehicles are based on the lower end of the ARIA mileage reported for newer sedans and compact SUVs. This helps us represent a reasonable middle ground, but it doesn’t guarantee that one vehicle category will always emit more carbon or consume more water than the another. Actual environmental footprint can vary based on the actual mileage of the cars under consideration. You can use our activity creation tool to estimate the footprint of your vehicle and save it to your account as well.

Stay tuned for more travel related blogs! You can continue your journey to understand how diet impacts the environment by checking out our blog on the carbon and water footprint of India's favourite non-vegetarian dishes. It's part of a series that compares the carbon and water footprint of popular indian dishes with an aim to help people understand the hidden green house gas emissions and fresh water consumption associated with their food choices

You can even check out all the other activities related to food and travel that have been added by the community or you can sign-up now to personalize and track the environmental footprint of your activities