Efficiency of gasoline and battery power supply

The efficiency of gasoline-powered cars is surprisingly low. All the heat discharged as waste gas or entering the radiator is wasted energy. The engine also uses a lot of energy to turn various pumps, fans and generators to keep them running. Therefore, the overall efficiency of automobile gas engine is about 20%. In other words, only about 20% of the thermal energy in gasoline is converted into mechanical work.

Battery-driven electric vehicles have quite high efficiency. The efficiency of battery is about 90% (most batteries will generate some heat or need heating), and the efficiency of motor/inverter is about 80%. This gives an overall efficiency of about 72%.

But that's not all. The electricity used to drive the car must be generated somewhere. If it is produced in a power plant that uses combustion process instead of nuclear energy, hydropower, solar energy or wind energy, only about 40% of the fuel required by the power plant is converted into electric energy. In the process of car charging, it is necessary to convert AC electricity into DC electricity. The efficiency of this process is about 90%.

So if we look at the whole cycle, the efficiency of electric vehicles is 72% of that of automobiles, 40% of that of power plants and 90% of that of automobiles. This gives an overall efficiency of 26%. According to the type of power plant used, the total efficiency varies greatly. For example, if the electricity of a car is generated by a hydropower plant, it is basically free (we don't burn any fuel to generate electricity), and the efficiency of an electric car is about 65%.

Scientists are studying and improving the design to continue to improve the efficiency of fuel cells. One method is to combine fuel cells with battery-driven vehicles. Ford Motor Company and Airstream are developing a concept car driven by hybrid fuel cell transmission system, called HySeries Drive. Ford claims that the fuel economy of the car is equivalent to 4 1 mile per gallon. Vehicles use lithium batteries to power cars, while fuel cells charge batteries.

Fuel cell vehicles may be as efficient as battery-driven vehicles that rely on non-fuel power plants. But it may be difficult to realize this potential in a practical and affordable way. In the next section, we will discuss some challenges of realizing fuel cell energy system.