Understanding the Energy Capacity of Electric Vehicles Compared to Traditional Cars

Introduction

Individuals interested in electric vehicles often ask two important questions: “Why are most electric vehicles (EVs) limited in their top speeds?” and “Why do they have a shorter range compared to internal combustion engine (ICE) vehicles?” Answering these queries requires considering the energy content of various fuels and the corresponding energy stored in high-voltage battery packs that typically power EVs.

Energy Content of Petrol and Diesel

To start, let's examine the energy content of the two most prevalent fuels worldwide. One liter of petrol contains approximately 9 kWh of energy, while one liter of diesel holds nearly 10 kWh. For context, a compact car with a typical 40-liter petrol tank carries about 360 kWh of energy, whereas the same size tank filled with diesel offers an equivalent of around 400 kWh.

Energy Content of High-Voltage Batteries

In contrast, a standard high-voltage battery in a modern compact EV stores between 50-80 kWh of net energy. The term “net” is crucial here, as not all of this energy is available for the drivetrain; there are upper and lower buffers within the battery pack. The upper buffer is typically lower than the bottom buffer to prevent catastrophic damage from deep discharges, leading manufacturers to allocate a larger buffer at the bottom. In general, a larger buffer enhances battery longevity. However, increasing buffer size means less net energy available for propulsion, which compels manufacturers to add more modules, resulting in increased weight and space requirements. To optimize usage, manufacturers recommend maintaining battery charge between 20% and 80%, allowing users to adjust their habits to extend battery life.

Comparing Propulsion Methods

The following table compares petrol, diesel, and electric propulsion methods using the Peugeot 208 as an example, although these figures are consistent across various models with different fuel types. All data is converted to kWh for straightforward comparison.

Conclusion

With current battery technology, the fuel tanks of ICE vehicles contain nearly ten times more energy than a typical battery in an electric vehicle. However, electric vehicles benefit from significantly higher efficiency. As seen in the table, the electric vehicle consumes nearly three times less energy than a comparable ICE vehicle over the same distance. This is expected, as electric motors can achieve efficiencies of up to 94%, compared to 38-40% for contemporary turbocharged, direct-injection petrol and diesel engines. To match the range of a petrol model, an electric vehicle would require approximately 128 kWh, and to equal the range of a diesel vehicle, around 158 kWh. The actual requirement could be even higher due to weight penalties from larger batteries, making it virtually impossible to achieve similar range with today’s battery technology. However, emerging solid-state battery technologies hold promise for bridging this gap significantly while also improving charging times.

The following table illustrates the charging power comparisons for different fuel types.

Today’s advanced electric vehicles can charge at power levels up to 270 kW. In contrast, a 50-liter petrol tank is equivalent to a charging power of approximately 13,500 kW, while diesel is around 15,000 kW, enabling ICE vehicles to refill in about 2 minutes. The disparity in charging speed heavily favors ICE vehicles.

While charging an electric vehicle overnight can mitigate some of these issues, the size of the electric “tank” makes actual charging time differences less pronounced than charging rates may suggest. Nevertheless, the quest for faster charging solutions continues, and advancements are on the horizon.