Renault Group

Hydrogen or electric cars? It’s time to clarify

25 May 2021
5 min
The profound change in the way we think about mobility is reflected in particular by the rise of two technologies. Hydrogen vehicles and “conventional” electric vehicles have made a place for themselves, notably in Europe. So how do we choose between these two modes of powering an electric motor? Which one best anticipates the future of the automobile? And what if, in reality, these technologies could complement, rather than oppose, one another? Read on for a clarification.
by Renault Group

The different terms: electric vehicle, hydrogen fuel cell vehicle and hydrogen vehicles with a battery

These days, when we talk about a hydrogen fuel cell vehicle, we mean a form of electric car. This type of vehicle, commonly known as an FCEV (fuel cell electric vehicle), uses hydrogen to power a 100% electric motor. On top of this, at Renault, the hydrogen-powered utility models (consisting of Kangoo Z.E. Hydrogen and soon Master Z.E. Hydrogen) incorporate both a hydrogen tank with a fuel cell and a battery that can be charged on the electric grid. In everyday speech, however, “electric car” is often used to refer to a vehicle that is powered by a battery alone, and “hydrogen car” for a vehicle with an onboard hydrogen tank as well as a battery.

The principles and advantages of hydrogen fuel cell cars

A hydrogen fuel cell electric vehicle uses dihydrogen (H2) as fuel. The fuel cell is supplied with this hydrogen, and oxygen from the surrounding air. These gases, upon contact inside the fuel cell, provoke an electrochemical reaction which produces an electric current, heat and water vapor. This electric current is then used to power an electric motor which then propels the vehicle.

This technology contains numerous intrinsic advantages. Firstly, the vehicle’s exhaust only emits water vapor. Hydrogen vehicles are classed as “zero emission” cars, because they produce neither atmospheric emissions of CO2nor pollutants*. In addition, an electric motor combined with a fuel cell is particularly efficient, resulting in much lower energy consumption than a combustion-powered car. What’s more, filling up the tank with hydrogen only takes three to five minutes — in other words, no more than topping up a combustion-powered version — for several hundred kilometers of range. Another advantage is the nature of the electric motor: its excellent torque offers the driver dynamic and responsive road handling

At Renault, hydrogen power does not replace the battery, it adds to it. Kangoo Z.E. Hydrogen combines the 30 kW battery of Kangoo Z.E. with a 5 kW hydrogen fuel cell (a further 5 kW of energy, for example, could be used to heat the interior during winter.) The vehicle can therefore travel 230 kilometers after recharging the battery on the electrical grid, plus another 140 extra kilometers with a full hydrogen tank.**

The principles and advantages of electric cars

In a “conventional” electric vehicle, electric energy is not produced by a fuel cell, but stored in a battery after charging from an electricity supply, whether this be a public charging station or a plug socket at a private location. The electric motor receives this stored current and uses it to propel the vehicle. As a complement, the electric motor also receives current recovered using its reversal properties, where every deceleration or application of the brakes generates energy that is then transformed into electricity.

A 100% electric car emits zero exhaust gas: it is carbon-free when being driven and gives off no air pollutants. The efficiency of an electric motor is also three to four times superior to that of an equivalent combustion engine, offering controlled consumption and considerable power. Lastly, these cars have the advantage of being able to access a growing variety of charging infrastructures, whether on the highway, in the city or at home (with the installation of a Wallbox, for example.)

Hydrogen: a safe technology

The need to keep hydrogen under high pressure requires vehicles to be equipped with advanced safety devices. Manufacturers therefore use very high quality materials to ensure the gas circulates safely. Emergency dihydrogen purge circuits as well as protective components prevent shocks or potential leaks from causing accidents. The Renault utility vehicles, for example, have a system that dilutes and disperses hydrogen in under a minute — an additional safety guarantee for these models classified “zero risk” according to the European regulation (CE) n° 79/2009. You can feel just as confident as in a combustion-powered, hybrid or battery electric vehicle.

The maturity of the electric car

Not all of the technology in electric cars and hydrogen vehicles is at the same stage of development. The principle of using electric motors for propulsion dates back to the automobile’s early days. Mass production of this type of electric vehicle started in the 1990s. However, it was not until the 2010s that “hydrogen” electric cars, fitted with a fuel cell, were mass-produced. These days they are particularly suited to utility purposes, specifically for professional needs.

Over time, charging and battery infrastructures offering ever-greater range have enabled the rise of “conventional” electric vehicles, which represented more than 5% of European automobile sales in 2020 (an increase of 90% on the previous year.)

Electric or hydrogen: what about energy storage?

“Conventional” electric cars work using a battery alone. Electricity is stored directly within the car, inside the traction battery. This type of vehicle is “filled up” through charging, which quite simply uses current from the electrical grid via charging stations that are increasingly common in public spaces, or using plug sockets at private locations such as the home.

In terms of energy storage, the hydrogen fuel cell electric vehicle behaves according to very different principles. This kind of vehicle runs on hydrogen, not electricity from the grid. Before filling up the tank, the dihydrogen needs to be stored, which is a challenge in itself: the chemical element is very light, with 11m3 required to store one kilo. Engineers have therefore developed different techniques to reduce this volume and to facilitate the transportation and storing of dihydrogen. There are two main methods currently in use: either the tank pressure is increased, which “compresses” the gas in a reduced space, or the hydrogen is liquified in a container at an extremely low temperature, for the same result in terms of space-saving.

Electric or hydrogen: CO2 emissions comparison

With regards to emissions released when running, electric battery cars and hydrogen fuel cell electric vehicles emit zero air pollution from the exhaust. However, a calculation of their overall CO2 emissions should be carried out to include their entire life cycle, in other words from design to recycling, and should also take into consideration the way in which the vehicle’s energy is transformed to power mobility.

It is therefore the way in which the energy that propels them is produced which largely explains the carbon footprint of these vehicles. Take an electric vehicle using electricity from the grid to charge its battery. If the power plants that supply this electricity are low-carbon (nuclear and renewable energy sources such as wind, hydroelectric and solar power,) then the car’s life cycle is considered virtuous from an environmental point of view. This is why the carbon footprint of an electric vehicle is calculated based on the energy mix of the country where it charges. In many European countries — Germany, for example, where the production of electricity from renewable energy sources is increasing at a steady rate — the electric car will see its carbon footprint decrease as the percentage of these sources in the energy mix increases. Conversely, trips undertaken by the driver of a combustion-powered vehicle will always have the same carbon footprint over time, regardless of geography.

For hydrogen fuel cell vehicles, electric energy is created without emissions inside the vehicle using its onboard hydrogen. It is the production of this hydrogen that explains the CO2 emissions attributed to this type of vehicle. As yet, the simplest way to produce hydrogen — rare as a naturally-occurring H2 molecule on Earth (even if the hydrogen atom is very common in space) — involves reforming natural gas through chemical transformation to extract the dihydrogen molecule. Evidently, this results in more carbon emissions than during energy production using renewable energy sources.

There are, however, low-carbon ways of producing hydrogen, in particular through water electrolysis. This is the principle of batteries…but the other way round. Electrolysis requires electricity to produces dihydrogen molecules. If this electricity is “green” (from wind power, solar energy etc.), the CO2 emissions attributed to the production of this hydrogen are minimal. This is called “green hydrogen”, a future solution for making this means of propulsion even cleaner!

Electric or hydrogen? Why not both

While industrial development of the hydrogen car is more recent than that of the battery-powered electric vehicle, the two technologies now coexist on the market, offering complementary approaches for different needs. Electric battery power continues to be the best solution for individuals as things stand. At the current time, hydrogen is aimed first and foremost at business fleets or professionals, especially when their premises possess a hydrogen charging station. This means of propulsion also suits drivers with regular routes, like deliveries for example, with access to a suitable refill station.

The current Renault utility vehicles and future models developed in partnership with fuel cell leader Plug Power (who have already rolled out over 40,000!) thus benefit from the advantages of this technology: considerable range (370 kilometers for Kangoo Z.E. compared to 230 kilometers on battery alone**) combined with a hydrogen tank recharge of just five to ten minutes. This is added to an already-integrated battery charge system that is lighter than that of “conventional” electric vehicle, giving it greater usable charge. Professional drivers can charge up on-site overnight, for example, and fill up on hydrogen during the day. This modular nature is particularly appreciated during periods of intense use.

Rather than competing, hydrogen and electric battery technologies complement one another. The overall winner is the driver!


*Neither atmospheric emissions of CO2 nor pollutants while driving (excluding wear parts).

**WLTP range: Worldwide harmonized Light Vehicles Test Procedure. The standard WLTP cycle consists of 57% urban driving, 25% suburban driving and 18% highway driving.

Copyrights : Anthony BERNIER

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