Use of hydrogen in cars

Hydrogen has the highest combustion energy per unit mass of any fuel. A hydrogen car is essentially an electric car that uses the conversion of hydrogen in the fuel cell to generate electricity. The drive is locally emission-free with ample range and fast refueling. The downside is the high purchase price and lack of hydrogen infrastructure. In order to carry hydrogen in a passenger car, it must be compressed, which entails higher tank weight and energy losses.

Amount of energy in hydrogen

Hydrogen has the highest energy content of all fuels (33kWh/kg). This means that 1 kg of hydrogen carries 33 kWh of energy to power a passenger car for 100 km using hydrogen in the fuel cell (the fuel cell is about 50% efficient).

Using hydrogen in a fuel cell

Hydrogen mobility today is based on the use of hydrogen in a fuel cell, where hydrogen and oxygen react to produce electricity, heat and clean water. The electricity thus produced is used in an electric motor to power the vehicle. Hence the name FCEV (Fuel Cell Electric Vehicle). Alternatively, the hydrogen can be burned in a conventional engine, but this is less efficient and none of the major car companies are developing this route. The drive is locally emission-free, less noisy, has sufficient range (currently 600 km), and allows fast refuelling (as with petrol). The price of 1 kg of hydrogen is about 9.5 EUR, so 1 km of driving the FCEV will cost similar to a petrol car. The disadvantage is the high purchase price of the car (around €60,000). A drop in the price of hydrogen and fuel cells can only be expected as mass production of FCEVs starts and the infrastructure is put in place.

‍

‍

Hydrogen emission footprint

Hydrogen has a positive effect in terms of a lower emission footprint (well-to-wheel), i.e. when emissions from hydrogen production and distribution are taken into account. According to the US DOE, the well-to-wheel energy intensity of hydrogen mobility is 37% lower than that of gasoline internal combustion engines, even when using fossil hydrogen produced by steam reforming of natural gas (the least environmentally friendly production option). At the same time, CO2 emissions are reduced by 44%.

Hydrogen compression for lower volume

For a range of 500 km in a petrol car we use 35 litres of petrol weighing 24.5 kg, the plastic tank weighs around 10 kg. The same range is provided by 5 kg of hydrogen, but due to its low density it is about 55 m3. In order to carry hydrogen in a passenger car, it is therefore necessary to compress it and thus reduce its volume (pressure of 350 or 700 bar). However, an FCEV with a range of 500 km will still have a tank approximately 4-5 times the volume of a petrol vehicle (approx. 120 l) and 10 times the weight of a composite pressurised tank (approx. 100 kg) compared to a conventional petrol tank.