Comparing the Overall Energy Efficiency of Plug-in Hybrids and Full Electric Vehicles

When it comes to comparing the overall energy efficiency of plug-in hybrid vehicles (PHEVs) and full electric vehicles (EVs), it's crucial to understand that the comparison is not straightforward and involves several complex factors. This article aims to provide a comprehensive overview, ensuring clarity and balance in the discussion.

Defining Energy Efficiency

The term 'energy efficiency' is often misunderstood or misinterpreted. It can refer to how much money you spend, how much energy is expended, or how much fuel is burned. These are all valid measures, but they can sometimes conflict with each other. Stakeholders with a bias (such as those who love EVs or those who bash them) may often overlook certain factors or overemphasize others.

Internal Combustion Engine Vehicles (ICEVs)

An internal combustion engine (ICE) powered vehicle typically carries its power source, which is gasoline or diesel fuel. The engine burns this fuel to generate heat, which is used to expand air and push a piston. The movement of the piston is then converted into rotational energy. The efficiency of an ICE is measured as the ratio of the energy in the fuel to the rotational energy created. However, what is usually reported is the maximum efficiency, which can vary widely depending on speed and power requirements. This is why ICEVs often have transmissions to adjust their operating point.

Efficiency of ICEVs

The maximum efficiency of a gasoline ICE is typically around 30%. Some hybrid designs have achieved up to 40% efficiency. Notably, the efficiency of ICEVs can vary significantly based on factors such as speed and load.

Battery-Electric Vehicles (BEVs)

A battery-electric vehicle (BEV) does not carry a fuel tank but instead carries a battery that is charged by plugging it into an external power source. The battery generates electricity, which is then used by the motor to create rotational energy. Efficiency is measured as the ratio of the electrical energy to the rotational energy created. Comparing the efficiency of a BEV to that of an ICE is not appropriate because they operate on fundamentally different principles. Additionally, the efficiency of a BEV can also vary, though perhaps not as much as an ICE. BEVs typically don’t have transmissions to reduce variations because the benefit is seen as less significant.

Efficiency of BEVs

I believe that the typical maximum efficiency of a BEV is around 90 to 95%, but I am not particularly familiar with the specifics.

Hybrid Vehicles (HVs)

A hybrid vehicle improves the efficiency of the ICE by being better than a transmission at reducing variations. This is a key point to consider when comparing PHEVs and BEVs.

Plug-in Hybrid Vehicles (PHEVs)

A PHEV can be considered three different vehicles:

BEV Mode: When charged like any other BEV, a PHEV’s efficiency should be similar to any other BEV because there is no fundamental difference in the electric motor’s efficiency. Self-Charging BEV Mode: When the vehicle carries its own source of electricity to charge the battery, the efficiency comparison becomes apples-to-oranges, as it involves comparing gas-generated electricity to whatever is available at home. Hybrid Mode: Such a vehicle can achieve some net efficiency improvement over the self-charging BEV mode, although it would not use this mode if it didn’t have a net efficiency benefit.

In 2015, the Union of Concerned Scientists conducted a study on 'Gasoline vs Electric Emissions.' This study shows regional power grid efficiency requirements for an ICE to be equivalent to a BEV based on how power is generated. The study suggests that most regions can meet these efficiency requirements with a hybrid.

Conclusion

The overall energy efficiency of PHEVs and EVs depends on various factors, including the driving conditions and the source of electricity. While EVs may have an edge in certain situations, the overall efficiency of a PHEV can be influenced by whether it runs purely on battery power or relies on the ICE.

Key Takeaways

Efficiency is a complex concept that can be measured in different ways. ICEVs have maximum efficiency around 30% to 40%, while BEVs typically range from 90% to 95% efficiency. PHEVs can behave like three different vehicles, each with its own efficiency profile depending on driving conditions and mode of operation.

Understanding these nuances is crucial for making informed decisions about which type of vehicle is best for your needs and environmental impact.