The end of the oil era is a reality. Consequently, a good number of manufacturers have proposed different technologies to cover this shortage, which is especially acute in the automotive sector. One of these technologies, which has been talked about a lot (but few clear things are said), is hydrogen. But,
What are the truths and lies about hydrogen?
Hydrogen is a chemical element represented by the symbol H. Under normal pressure and temperature conditions, it is a diatomic gas (H2) that is colorless, odorless, tasteless, and non-metallic. Hydrogen is highly flammable, due to its enormous tendency to combine with oxygen to form water (H2O), which is why hydrogen is almost non-existent in the atmosphere, existing mostly in the form of water.
The idea is to use this chemical energy to do work. A fuel cell is an electrochemical energy conversion device. That is, it is a generator that combines hydrogen and oxygen to obtain electrical energy. The only byproducts of this reaction are energy and water, so it appears to be the panacea of energy generation.
The great lie of hydrogen is considering it an energy source. This is not correct, since as we have mentioned, hydrogen does not exist on Earth in its natural form. On the contrary, it is an energy vector, that is, a form of storing energy, just like an electric battery. Therefore, it does not prevent us from having to generate that energy using fossil fuels, nuclear energy, or renewable energies. The problem of energy generation is still there, exacerbated by having to supply the world’s vehicle fleet. Hydrogen does not solve the problem; it does not bring anything new to the table.
As if that weren’t enough, the problem is even more serious. Suppose we obtain hydrogen by decomposing water, using an energy source. This hydrogen, we combine in a vehicle to generate energy. By virtue of what the laws of thermodynamics dictate, the energy obtained is always less than that used for the decomposition of water into hydrogen. In short, we have lost energy. How much? Well, approximately 50% during charging, and 50% during discharging, that is, 75% of the energy. It is much more efficient to use electricity directly in an electric motor. On the other hand, hydrogen can also be obtained from fossil fuels but, once again, it is more efficient to perform the combustion directly. Hydrogen thus becomes an unnecessary step that increases the overall inefficiency of the system.
Since it is clear that it is not an energy source, how does it perform as a form of energy storage?
- Lithium batteries have an overall cycle efficiency of 90%. This means that to use 6 kWh, it would be necessary to use 6.6 kWh, compared to the 25kWh needed using hydrogen for storage.
- Hydrogen, compared to hydrocarbons (such as gasoline or propane), is much more difficult to store. Its low density means it requires a larger and heavier tank to store the same amount of energy. The molecular simplicity of hydrogen allows it to pass through most materials by diffusion.
- Increasing pressure improves volume density, making tanks smaller but, in any case, heavier than their hydrocarbon equivalents. Furthermore, obtaining compressed hydrogen requires energy to run the compressor, which implies dissipation in the cycle.
- Alternatively, hydrogen can be stored in liquid form. However, liquid hydrogen requires cryogenic storage and it boils around –252.882 °C. Therefore, its liquefaction requires a large dissipation of energy because it requires a high energy input to cool it to that temperature. Tanks must also be well insulated to prevent evaporation. Tanks with thermal insulation are usually expensive and delicate. Assuming all that is solved, the density problem remains. Liquid hydrogen has a worse density by volume than hydrocarbon fuels by approximately 4 to 1. These are the main points about the density problem of pure hydrogen: There is about 64% more hydrogen in a liter of gasoline (116 grams) than in a liter of pure liquid hydrogen (71 grams). The carbon in gasoline also contributes to energy combustion.
- The best way to store hydrogen may be captured by some type of material. Research is being done in these areas.
Therefore, it is obvious that hydrogen is not the panacea it is painted to be. On the contrary, it is simply another technology, which will have to be developed in future years, but which will not easily be able to replace the advantages of oil.
To conclude, some quotes from experts on the subject.
“I have been building engines for more than thirty years, and I can assure you that hydrogen engines are economically unviable.” Dieter Zetsche, president of Mercedes (PhD in electrical engineering and chosen by Time Magazine in 2006 as one of the 100 most influential men on the planet)
“Hydrogen is not a natural fuel. It must be produced, and to date it is very expensive. It will not be viable in the foreseeable future, and energetically it is a disaster, because producing hydrogen costs more energy than it later gives.” José María López, deputy director of the Automobile Research Institute of the Polytechnic University of Madrid
“Only 20% to 25% of the energy used as a source to synthesize hydrogen from natural compounds can later be recovered for end use in fuel cells. Since the laws of physics cannot be changed with policies or investments, the hydrogen economy will never make sense.” Ulf Bossel, European Fuel Cell Forum
