Fuel Cell Electric Vehicles

Along with battery electric vehicles, there is a lot of buzz about use of fuel cell technology for driving electric vehicles. Both battery EVs and FCEVs are equally green and are considered as potential replacement to IC engine vehicles.

Although battery electric vehicles and fuel cell electric vehicles appear nearly same, they majorly differ in production and harvesting of electricity. As the name goes, fuel cell EVs use fuel cell as their energy source. One of the most common fuel used for fuel cell is hydrogen. The hazardous effects of pollutants from conventional fuel vehicles have caused the scientific world to move towards environmentally friendly energy sources. Though we have various renewable energy sources, the perfect one to use as an energy source for vehicles is hydrogen.

About Hydrogen:

One of the major reasons for hydrogen being used as fuel is its energy density. Hydrogen has energy density of around 33000watt hour/kg. Because of this major reason it has been used earlier in space programs and submarines. Comparing this to other energy sources, petrol has energy density of 3000watt hour/kg and Li ion batteries stand with just 200–300-watt hour/kg.

Knowing more about Fuel cell:

If we have to define fuel cell then, it is an electrochemical device that can produce electricity by allowing chemical gases and oxidants as reactant. With anodes and electrolytes, the fuel cell splits the cation and the anion in the reactant to produce electricity. Fuel cells use reactants, which are not harmful to the environment and produce water as a product of the chemical reaction. The reaction between hydrogen and oxygen can be used to generate electricity via a fuel cell.

A simple diagram below shows operation of fuel cell

Fig: Operation of Fuel Cell

The most common type of fuel cell for vehicle applications is the polymer electrolyte membrane (PEM) fuel cell. In a PEM fuel cell, an electrolyte membrane is sandwiched between a positive electrode (cathode) and a negative electrode (anode). Hydrogen is introduced to the anode, and oxygen (from air) is introduced to the cathode. The hydrogen molecules break apart into protons and electrons due to an electrochemical reaction in the fuel cell catalyst. Protons then travel through the membrane to the cathode.

The electrons are forced to travel through an external circuit to perform work (providing power to the electric car) then recombine with the protons on the cathode side, where the protons, electrons, and oxygen molecules combine to form water.

Fuel cell EV:

The figure below shows basic fuel cell electric vehicle

Fig: Basic Fuel Cell Electric Vehicle

The electricity generated in the fuel cell of a hydrogen engine can take two routes, depending on the demands of the specific driving situation. It either flows to the electric motor and powers the FCEV directly or it charges a battery, which stores the energy until it’s needed for the engine. This battery, known as a Peak Power Battery, is significantly smaller and therefore lighter than the battery of a fully electric car, as it’s being constantly recharged by the fuel cell.

Advantages of FCEVs:

• As hydrogen has high energy density, FCEVs have a range of about 300–350 miles per fill/charge which is much better than BEVs.
• The range of fuel cell vehicles is not dependent on the outside temperature.
• Another major advantage of FCEVs is its charging time. Hydrogen tanks take merely 4–5 minutes to fill up to their full capacity.

Efficiency of fuel cell electric vehicles:

Fig: Efficiency of Fuel Cell Vehicle considering all conversions

Hydrogen fuel cell EVs look good with greater range and high energy density fuel but considering whole energy conversion cycle in today’s era, they stand with lesser efficiency.

Though hydrogen as an element is abundant in universe, it is mostly available in the form of hydro carbons. Pure hydrogen needs to be manufactured. This is done through two processes, electrolysis and natural gas reforming. During this conversion, almost 20% of energy is lost.

Further the PEM fuel cell are only 80% efficient so more 20% energy is lost in this case.
The most efficient AC/DC converter is itself 92% efficient which counts to more 8% loss.
Hydrogen needs to be compressed for its storage. This compression can be accounted as 12% of more energy. As the hydrogen infrastructure is not well developed, transportation losses account to 5%.

If we consider all the above factors then the final efficiency that we get is just about 35%

Major disadvantages:

As mentioned earlier, considering technological development in up till now, fuel cell vehicles have very low energy chain efficiency. Infrastructure for hydrogen is not well developed and will require considerable amount of investment from all countries.

The natural gas reforming method of producing hydrogen is also not a green process and has large amounts of carbon emissions.

Moreover, the production cost of hydrogen itself is high. The E-ROI of hydrogen is less than 1 which makes it even more difficult for its use as fuel for vehicles. This also makes manufacturing and running cost of FCEVs quite high as compared to battery electric vehicles.

Scenario in India:

Tata Motors, in collaboration with Indian Oil Corporation, just flagged off the country’s first hydrogen fuel cell powered bus. The bus is named Fuel Cell Starbus. The test results generated power of 85 kW at 275 VDC, which is capable of running Fuel cell bus up to 450 km with single refuelling of on-board hydrogen.

India currently has two hydrogen refuelling stations. One, at Indian Oil R&D Centre, Faridabad and other at National Institute of Solar Energy, Gurugram.

India’s largest power producer and a central PSU under Ministry of Power, NTPC Ltd, has invited global expression of interest (EoI) to provide 10 Hydrogen fuel cell (FC) based electric buses and an equal number of Hydrogen Fuel Cell-based electric cars in Leh and Delhi.

The move to launch hydrogen-powered vehicles aims at decarbonizing the mobility segment.

Future of FCEVs:

Though the FCEVs stand below battery electric vehicles in today’s scenario, with growth in hydrogen infrastructure we could see more and more hydrogen-based FCEVs.

Countries like China, Japan are investing in fuel cell technology and are aiming to have around 1 million running FCEVs by 2030.

Although hydrogen fuel cell may not seem suitable for passenger vehicles, it can find its use in heavy duty transport and marine vehicles.

With all these points, as of now we can say that battery electric vehicles are going stay and rule for this decade at least.

Writers: Dhiraj Ghode, Hrishikesh Gawand, Ranveer Ghorpade, Sanika Gaykar, Sankalp Gharmalkar