Hybrid Cars Running on Battery Power: Efficiency Explained

Hybrid vehicles, both plug-in hybrids (PHEVs) and those that are marketed as 'full hybrids,' can indeed run on battery power alone under certain conditions. However, it is crucial to understand that running completely on battery power does not necessarily maximize efficiency and can vary significantly based on the specific hybrid system involved. This article will delve into how hybrid cars utilize battery power, the efficiency behind it, and why hybrid systems are designed the way they are to enhance overall performance.

Power Utilization in Hybrid Cars

There are three main paths through which power flows in hybrid cars: mechanical, electrical, and deferred. These paths each involve some degree of loss, with the deferred path being the most inefficient.

1. Mechanical Path

In this path, power from the Internal Combustion Engine (ICE) is transmitted directly through the gearbox and differential to the wheels. This path is usually less efficient due to the mechanical losses in the variable gears.

2. Electrical Path

For the electrical path, power from the ICE is used to generate electricity, which is then converted to mechanical power through a motor. This path is less direct but can offer more control over power delivery.

3. Deferred Path

The deferred path involves charging the battery at one moment and discharging it later, allowing for more complex energy management. While this can be efficient in certain scenarios, it often results in the highest losses due to the energy conversion processes.

Why Hybrids Utilize Multiple Paths

Hybrid systems are designed to utilize more than one path simultaneously, allowing for more efficient power delivery. The ICE in a hybrid vehicle is designed to operate at its optimal power output, which typically ranges from 20 to 40 percent of its maximum power rating. However, during normal driving, the ICE needs to generate 5 to 10 percent for cruising and up to 50 percent for acceleration. By utilizing both mechanical and electrical paths, hybrids can optimize performance and efficiency.

For example, when a hybrid vehicle is cruising, the ICE can generate more power than necessary, which is then used to charge the battery. During acceleration, the ICE can generate less power, and the battery can provide additional power, balancing efficiency and performance. This is why the deferred path is utilized in hybrid systems.

Efficiency Considerations

While the deferred path allows for more complex energy management, it is important to understand that it is not "free" energy. The efficiency gains achieved through different paths may not always outweigh the losses. For instance, some full hybrids have a feature that forces the car to operate solely on battery power, but this can negatively impact fuel economy, as emphasized in the 2016 Prius Owner's Manual.

Achieving the best efficiency in hybrids often involves fine-tuning when to use different power paths. Aggressive driving may compromise efficiency, whereas more conservative driving can optimize the use of the hybrid system. Understanding how and when to use the various power paths is key to achieving the best fuel economy and performance.

Comparing Hybrid, PHEV, and BEV Efficiency

When comparing the efficiency of different types of hybrid vehicles, it is crucial to consider the entire process. Efficiency ratings often omit the losses involved in the "deferred" path, focusing instead on the final mechanical and electrical paths. While PHEVs and plug-in hybrid electric vehicles (PHEVs) can be cheaper to operate due to some of the easier-to-manufacture components, the overall efficiency can be misleading without taking into account the entire process.

Understanding the mechanics of power utilization in hybrid cars can help owners make more informed decisions about driving habits and vehicle performance. By balancing the use of mechanical, electrical, and deferred paths, hybrid vehicles can offer significant efficiency gains over traditional ICE vehicles.