The end of oil the oil era is a reality. With this, 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 widely talked about (but few clear things are said), is hydrogen. But,
What are the truths and lies of hydrogen?
Hydrogen is a chemical element represented by the symbol H. Under normal pressure and temperature conditions, it is a diatomic (H2) colorless, odorless, tasteless, non-metallic gas. Hydrogen is highly flammable, due to its enormous tendency to combine with oxygen to form water (H2O), which is why hydrogen is almost nonexistent 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 byproduct of this energy reaction is water, so it apparently is the panacea of energy generation.
The big lie of hydrogen is to consider it a source of energy. This is incorrect, since as we have mentioned, hydrogen does not exist on Earth in natural form. On the contrary, it is an energy carrier, that is, a way to store energy, just like an electric battery. Therefore, it does not avoid the need to generate that energy through fossil fuels, nuclear energy, or renewable energies. The problem of energy generation remains, 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 were not enough, the problem is even more serious. Suppose we obtain hydrogen by decomposition of water, using an energy source. This hydrogen, we combine it in a vehicle to generate energy. According to the laws of thermodynamics, the energy obtained is always lower than the energy used for the decomposition of water into hydrogen. In short, we have lost energy. How much? Well, approximately 50% in the charge, and 50% in the discharge, 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 combustion directly. Hydrogen thus becomes an unnecessary step that increases the overall inefficiency of the system.
Since it is clear that it is not a source of energy, how does it behave as a way of storing energy?
- 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 as storage.
- Hydrogen, compared to hydrocarbons (such as gasoline or propane), is much more difficult to store. Its low density means that a larger and heavier tank is required to store the same amount of energy. The molecular simplicity of hydrogen allows it to permeate most materials through diffusion.
- Increasing the pressure improves the volume per density, making the tanks smaller but, in any case, heavier than their hydrocarbon equivalents. Also, obtaining compressed hydrogen requires energy to use 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 at around -252.882 °C. Therefore, its liquefaction requires a large energy dissipation because it requires a high energy supply to cool it to that temperature. The tanks must also be well insulated to prevent evaporation. Tanks with thermal insulation are usually expensive and delicate. Assuming all that is resolved, the density problem remains. Liquid hydrogen has worse volume density than hydrocarbon fuels, about 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 the gasoline also contributes to the combustion of energy.
- The best way to store hydrogen may possibly be captured by some type of material. Research is being done on these aspects.
Therefore, it is obvious that hydrogen is not the panacea that is painted for us. On the contrary, it is simply another technology that will have to be developed in the coming years, but that will not be able to easily replace the advantages of oil.
Finally, some quotes from experts on the subject.
“I have been making 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 in 2006 by Time Magazine 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 become viable in the foreseeable future, and energetically it is a disaster, because producing hydrogen costs more energy than it then gives.” José María López, deputy director of the Automotive Research Institute at the Polytechnic University of Madrid.
“Only 20% to 25% of the energy used as a source to synthesize hydrogen from natural compounds can be recovered later for its final 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