Fuel cells

Sustainability: clean energy research for long-term bond

by Yves Martin, L'Argus de l'Automobile, 6.2.2003

What will succeed oil in the heart of our cars? If several systems are in line, none can win, the challenge is so difficult to meet.

The transport issue

Having become an indispensable tool, transport is being hunted down by its n ° 1 enemy, pollution. Indeed, the ever-increasing production of carbon dioxide (C02), responsible for the greenhouse effect that causes global warming, has become a major environmental issue. This is why a large number of industrial countries - with the exception of the United States - signed the Kyoto agreement in 1997, in which they pledged to reduce their production of C02.

After this convention, the European authorities introduced draconian anti-pollution standards for the automobile.

However, limiting polluting emissions from cars is not an end in itself. In addition, as Pierre Zerlauth, technical coordinator during the Michelin Challenge, points out "local pollutants (Editor's note: at the level of the car itself) are better controlled". The pollution generated by the production chain - from storage to the distribution of the energy used in the car - must also be taken into account. We then speak of global energy balance, that is to say pollution "from well to wheel".

"From well to wheel"

Studies have been carried out on different energy sources in order to determine the most advantageous in terms of reducing C02 emissions.

Among these are LPG (liquefied petroleum gas), NGV (natural gas for vehicles), electricity, hydrogen (either used as a fuel or in a fuel cell).

However, as Philippe Pinchon, director of the engine-energy results center at IFP (French Petroleum Institute) underlines: “When we talk about energy balance, we have to take into account four factors: the greenhouse effect. , energy efficiency, cost and availability of energy. "

This is where it gets complicated ! Take for example the electric motor: the most environmentally friendly there is. Depending on the method adopted for the production of electricity, the ecological balance can be disastrous. For example, that produced in Germany, from thermal power plants running on coal, shows a negative balance with a C02 production of 460 grams per kilowatt per hour, which corresponds roughly to the European average. Conversely, the electricity produced by French nuclear power plants emits only 100 g / kWh. The most disastrous result is that of Greece where the production of electricity generates around 900 g / kWh of C02.

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Following this reasoning, we realize that the use of a fuel cell is not as ecological as that.

Indeed, two methods exist to produce hydrogen, the base fuel for a fuel cell: either it is generated on board the vehicle, via a reformer (device which extracts hydrogen from hydrocarbons), or it comes from power plants and then distributed as a conventional fuel (in gaseous or liquid form). If the first solution reduces the production of C02, it emits many other pollutants harmful to the environment due to the incomplete control of reforming. This is why it is preferable to produce hydrogen in a power station where the process is better controlled, but in this case the (insolvent?) Problem of the distribution and storage of hydrogen arises.

Referring to Table emissions C02 below, we see that the use of liquid hydrogen is of no interest.

Indeed, the energy required to liquefy the gas is significant and increases the CO50 production of this sector by 2%. The advantage therefore comes back to the use of compressed hydrogen. Again, depending on the country and the source of extraction, the toll varies from one extreme to another. So,the best result is obtained when hydrogen is produced from natural gas using electricity from French nuclear power plants. However, this solution has the drawback of an exorbitant cost price, from 24 to 29 EUR per gigaJoule (against 7 EUR / GJ for the production and distribution of unleaded super 95 and 98, and 6 EUR / GJ for diesel fuel. , and 13 EUR / GJ for LPG).

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The solution is therefore to combine several solutions in order to derive the maximum benefit from these sectors.

Thus, the car that would offer the best ratio between cost, pollution and efficiency should adopt a hybrid diesel engine and electric motor with a large capacity battery (capable of storing a lot of energy) and equipped with a battery. fuel powered by compressed hydrogen. The only hybrid car marketed in France (Editor's note: at a still very high price), the Toyota Prius is still very far from this refinement.

Comparative table of transport technologies (click to enlarge)

Diesel ; Diesel FT Fischer-Tropsch diesel (synthetic diesel); DME dimethyl ether (synthetic fuel); EMVH methyl esters of vegetable oils: gasoline; ETBE ethyl-tertio-butyl-ether (obtained from the fermentation of beet sugar or corn and petroleum); ethanol EtTOH; natural gas ; LPG; H2 fuel; H2 compressed; Liquid H2; methanol MeOH; gasoline

The worrying increase in C02

For a century, the greenhouse effect has tended to get carried away, causing a general rise in temperatures, via the increase in carbon dioxide (C02) contained in the atmosphere. This gas alone is responsible for half of this phenomenon.

The CO02 concentration is now a quarter higher than it was in the last century. A level of pollution never reached in the last 600 years.

This carbon dioxide comes mainly from the use of fossil fuels (coal, fuel oil, natural gas) in various sectors of activity: industry, energy and transport. These represent more than a quarter of C02 emissions in industrialized countries, and this proportion continues to increase. The many prospects outlined by the International Energy Agency (IEA) predict a sharp increase in total C02 emissions in the next decade: between 31% and 42% ...

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From Rio to Kyoto, a slow evolution

In June 1992, in Rio de Janeiro, 178 countries and 50 international companies committed themselves to sustainable development and signed an agreement aimed at stabilizing greenhouse gas concentrations, all sources of production combined (international action plan called Agenda 21). This framework convention then recommended that developed countries reduce their level of emissions to that of 1990.

Three years later, in Berlin, the States embarked on a new process that should lead to the reduction of C02 emissions. A protocol was adopted in December 1997 at the end of the Kyoto conference. Only the United States has not signed it.

The European Union, for its part, is committed to reducing its CO8 production by 2% by 2010. This reduction will be distributed according to the emission levels recorded in 1990 in the various member countries, their need for development and demographics. Thus, the objective for Germany is a decrease of 21%, that of Greece, an increase limited to 25%, and that of France, equality.

The car fleet accounts for around 12% of the continent's total human-made CO2 production, and 2% globally. In 1995, a new European car emitted 165 g / km, against 191 g / km for a Japanese, and 260 g / km for an American.

In July 1998, the Association of European Automobile Manufacturers (ACEA) made a commitment to the European Commission. This includes a dual objective. Initially, the Association is committed to producing cars intended for the European market whose CO2 emissions will not exceed 120 g / km in 2012 (ie an average consumption of 4,9 l per 100 km). It then undertook to respect an intermediate level for cars sold in 2008, with an average level of CO2 emissions of 140 g / km, or an average consumption of 5.7 l per 100 km.

Learn more about fuel cells

- comparative article Sciences et Avenir
- CHP study with a fuel cell

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