Diesel Engine vs. EV: Which is better?

Diesel versus EV, the battle! Which of these two vehicle propulsion types is better than the other?

RELATED: THE DIFFERENCE BETWEEN GASOLINE AND DIESEL ENGINES

As you will soon find out, this question is not as simple to answer as it might seem on the surface. While you are likely to have an opinion on the matter, the truth is more nuanced than it might initially seem.

Are electric cars better than diesel?

In order to determine which is better, we really need to define the metrics we will be using. In other words, better in what way?

If we are talking about carbon emissions, fuel efficiency, noise pollution, and air quality, then EVs are clearly the outright winner. If, however, we are talking about torque or initial price, then diesel-engined cars will win.

Even though diesel cars are major polluters, it must be borne in mind that some components of EVs can be particularly bad for the environment, especially their batteries. 

The answer really does depend on what the vehicle will be used for. For many, fuel economy, range, initial price, and after-sales maintenance costs are likely the decisive factors when buying a new car.

Depending on the type of vehicle, and the desired use, there may be limited options. For instance, if you need a vehicle that packs a lot of pulling power, a diesel engine may be best - hands down. 

However, EV pickup trucks, and even semis, are improving all the time, and are likely to give diesel-engined versions a run for their money very soon.

However, while companies, like Tesla, believe electric trucks will be cleaner and cheaper to operate than their diesel counterparts, it's not a done deal.

Those in favor of diesel engines will tell you that, for long-haul freight fleets, range and recharging still represents a huge hurdle for electric 18-wheelers to overcome.

John Mills, a spokesman for the engine maker Cummins Inc., told Bloomberg that, “Right now, we don’t think it’s viable. It is more viable where you have shorter routes, fewer loads and you’re able to recharge.”

While diesel and EV engines have their pros and cons, the choice often comes down to personal choice and practical requirements from the buyer. Although government intervention is making it more difficult to manufacture some types of diesel vehicles. 

Over the next decade, 24 European cities, with a total population of 60+ million people, will enact bans on diesel vehicles. A large number of countries, including France and China, are following suit. This may make the manufacture and use of diesel vehicles too costly to continue.

Is an electric car really more efficient?

This is a tricky one to answer easily. While there are plenty of claims that EVs are no more efficient than internal combustion engines, many of these sources are biased.

According to the US Department of Energy’s Office of Energy Efficiency and Renewable Energy, “EVs convert about 59%–62% of the electrical energy from the grid to power at the wheels. Conventional gasoline vehicles only convert about 17%–21% of the energy stored in gasoline to power at the wheels.”

However, we are talking here about diesel engines, and they can at least double the power conversion of gasoline engines.

It is estimated that between 85% and 90% of the electricity delivered and stored in an EVs' battery is used by the car's electrical motor. In other words, up to 90% of the energy generated is used for work by the vehicle.

The difference between the overall efficiency claimed by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy and an EVs motor efficiency can be accounted for by losses attributed to charging and discharging the battery and, for some cars, converting AC to DC current and back again.

To hash out the point a bit more, here is an interesting discussion by Brian Feldman on Quora. But remember this discussion concerns gasoline engines. For reference, gasoline vehicles get around 38 kWh per gallon (8.3 kWh/l) and modern diesel engines tend to get around 70 mpg (29.7 km/l).

“Consider the Tesla Model S, which has an available 85 kWh battery and a 265-mile range. 

Consider a similar gas-powered car, which gets 35 mpg. Gasoline contains about 33 kWh of energy per gallon.

Tesla uses 320 Wh/mile of energy (85 kWh/265 miles). The gas-powered car uses 940 Wh/mile of energy (33 kWh/35 miles). 

Once the energy is on board (not counting the efficiency of the power generation, oil refining, or charging), the Tesla is using only about a third as much energy as the comparable gasoline-powered car.”

Based on the average figures supplied for diesel engines, EVs are still more efficient, by about a third.

"But," you might ask, "isn't that electricity generated from fossil-fuel-powered power plants?" While this is certainly true for a large proportion of grid-supplied electricity around the world, is this really fair?

After all, for diesel-powered internal combustion engines, the oil needs to be found, extracted, refined and transported to fuel stations before it is ever pumped into the tank. This may be more or less comparable to the energy used to supply power for electrical generation. 

But as each country's energy mix starts to integrate more renewable and low-emission sources (nuclear, wind, solar, etc), the gap between diesel and EV will continue to expand on this front.

This also doesn't begin to consider the impact of diesel fuels with regards to future sustainability and environmental impact.

How much does it cost to charge an electric car?

All vehicles have a cost for their running, including electric cars. However, unlike gasoline-powered vehicles, the running costs for EVs tend to be much lower over the lifetime of the vehicle. This is because the vehicles have fewer moving parts to break down or wear out. Owners of electric vehicles also pay less tax, and some also pay less in insurance costs.

Many countries around the world also offer financial incentives to purchase EVs, such as grants or other schemes, to help make the vehicles more affordable. 

The costs of charging EVs can vary, although many cities also offer free charging points. EDF Energy has a fairly in-depth article on just this matter, but for brevity, we give a few exemplar costs here:

Rapid charging points (of the kind you will find on motorways) tend to be more expensive, given their added convenience for EV drivers. 

In the United Kingdom, "Pod Point rapid chargers cost 23p/kWh at Lidl and 24p/kWh at Tesco, which is about £6-7 for 30 minutes of charging (about 100 miles of range)," according to EDF.

For Tesla owners, and where Tesla Superchargers are available, costs range from free to 24p per kWh. This depends on when you bought your Tesla and what tier, if relevant, you are currently on. 

It is advised that you contact Tesla for the most up to date information with regards to costs. 

For non-Tesla owners, charging fees vary depending on the network you use. Registration, subscription, and connection fees may apply. 

When you charge from home, costs will depend on your energy supplier and relevant tariffs. According to the United States Department of Energy: 

"If electricity costs $0.11 per kilowatt-hour, charging an EV with a 70-mile range (assuming a fully depleted 24 kWh battery) will cost about $2.64 to reach a full charge.

This cost is about the same as operating an average central air conditioner for about 6 hours. To compare the fueling costs of individual models of conventional and plug-in vehicles, see the Vehicle Cost Calculator.

For PEV charging, costs can vary slightly. It is recommended you consult the report entitled "Comparing Energy Costs per Mile for Electric and Gasoline-Fueled Vehicles."

The Pros and Cons of EV and Diesel Engines

For ease of reference, and with thanks to allstarcard.co.uk, we have created the following table to explore the pros and cons of both types of engines. This is not intended, in any way, to be comprehensive, and is just for illustrative purposes.

What are the advantages and disadvantages of an electric car?

Advantages

• Zero emissions (excluding grid-supplied generation)
• Minimal noise pollution and a quiet traveling experience
• Zero road tax and congestion charging
• Presents a green image - but not a tangible benefit
• High residual value
• Instant acceleration
• Initial costs can be reduced from Government incentives and tax breaks
• Maintenance costs are much lower over the vehicles lifetime compared to internal combustion engines

Disadvantages

• Expensive to buy
• Limited range
• Extensive time to recharge
• Scarcity of recharging points
• Electricity is usually generated by fossil fuel power stations, so it may offset the purpose of ‘going green’
• Danger to pedestrians of a silent approach

What are the advantages and disadvantages of a diesel car?

Advantages

• Lower lifetime cost than gasoline because of lower depreciation
• Engines last longer and tolerate much higher mileages than petro
• More efficient (by around 25% compared to petrol) so fuel costs are less, providing pump prices stay close. Diesel’s better mpg becomes more pronounced over long-distance journeys. Some diesel engines can even be more fuel-efficient than a petrol hybrid
• Produce less CO2, so road tax is lower than petrol - but depends on the policy
• Higher torque or pulling power means a mid-range acceleration of larger diesel cars is often better than sports cars. This pulling power is why diesel is used for commercial vehicles: it can pull much greater loads than any other option here
• Tend to depreciate at a lower rate than petrol/gasoline engines
• Diesel engines can deal with various fuel types beyond conventional diesel. Biodiesels could be a game-changer for diesel engines in the future

Disadvantages

• More expensive than gasoline to buy (historically)
• Produce nitrous oxides, hydrocarbons, and particulates, so not necessarily greener than petrol and definitely at a disadvantage compared to EVs
• Insurance is higher for diesel engines rather than petrol engines, by up to 15% - because they cost more to replace or repair
• Engines generally require a little less routine servicing but if they do go wrong, repair costs are higher. Latest figures show diesel engines are slightly less reliable than petrol
• Volatile fuel price
• Oil is a finite resource

Please note that the above is a rough summary of each type of engines' pros and cons - it is not comprehensive by any means. At the end of the day, your particular needs and wants will ultimately drive (excuse the pun), your choice of engine. 

But, as time goes by, the high environmental cost of diesel engines is likely to lead to them being phased out completely. And this is another consideration - does it make sense to purchase a diesel vehicle now, when the fuel may become difficult, if not impossible to find in many places?

As oil becomes scarcer and prices rise, and electricity generation moves to exclusively renewable sources, basic economics could also mean that the battle between EVs and diesel engines has already been settled.

Unless biodiesel can "save diesel's bacon" in the future. Only time will tell.