There has been discussed earlier that that hydrogen is more efficient fuel in terms of energy production provided per weight and that the emission of greenhouse gasses is almost non-existent. So what are some of the reasons that we do not produce our main energy demand through hydrogen? In this chapter, a couple of differences between the use of (bio)- methane and hydrogen will be discussed. There will be looked into some of the advantages and disadvantages of the use of these gases. let us first look into the differences in means of energy efficiency.
When a molecule and atoms interact, the chemical bonds between the two can be altered, broken, reorganized, and/or re-established. Hydrogen gas for example is made of two hydrogen atoms bonded together with a covalent bond. In general, such a connection is depicted as H: H, where the dots represent the electrons that are shared between the two atoms. When the hydrogen atoms are to be separated by for example burning the gas with oxygen present, bonds between the two hydrogen atoms will be broken. The bonds between the oxygen atoms are also broken, when those two gasses are to be burned together the oxygen will make its electrons available for the hydrogen to be bonded too. This reaction will create a water molecule and will create the following chemical equation: H2 + 1/2 O2 −heat→ H2O + 286 kilojoules(KJ). (M.C Akanyıldırım, 2015) So the burning of one mole of hydrogen with half a mole of oxygen will create one mole of water and release energy equal to 286 KJ. The weight of 1 mole of hydrogen gas is just about 2 grams. Unfortunately, hydrogen gas does not often naturally occur in our direct environment.
The main competitor of hydrogen is bio-methane for energy production. Just as hydrogen, bio-methane needs to be made in a process. The techniques of this production have been discussed in chapter 3.1 for bio-methane and 3.2 for hydrogen. But just as hydrogen bio-methane can be burned to release its energy. The chemical reaction that causes this release is as follows; CH4 + 2O2 −heat→ CO2 + 2H2O + 810 KJ. In this reaction, 1 mole of methane and 2 moles of oxygen are burned and release 1 mole of carbon dioxide and 2 moles of water accompanied by 810 KJ of energy. The energy released by methane is about 3 times higher than for hydrogen. One methane molecule does also weigh about 16 grams per mole, in comparison to hydrogen is that 8 times more weight. If you were to burn the same amount of hydrogen, so about 16 grams, you will end up with 2,288 KJ of energy. The combustion of methane does also produces carbon dioxide, so it is not as clean as hydrogen. if the only contributory factor is the amount of energy released by the material itself in a sense of energy efficiency, hydrogen takes the first place. But more benefactors play a role in the use of gas for energy production. For example the cost of the product.
So hydrogen may very well be a clean and efficient source of energy, but to make this fuel type accessible to the general public it should also have a reasonable price. The current price per kg of hydrogen according to a 2017 study of the European Commission (European Commission, 2017) is between €5 and €12 with an average of 9,50 €/kg. in comparison, the price per kg of biomethane is around 1,10 €/kg. so hydrogen is quite expensive to be used as a fuel. But the price per kg does not say everything about its energy-producing capabilities.
In a better situation, a comprehensive fuel price will be determent by the energy content of the fuels and the energy efficiency of for example the engine used. In this scenario, there would be given a better inside into the actual capability and thus the correct price of the fuel type. In the report by the European Commission, they do so by calculation of the fuel price in euros per 100km. according to the following formula;
By using this calculation the price of hydrogen per 100 km came to €4,28, and for biomethane at €5,77 per 100 km. So per 100km of driving it would be cheaper to use hydrogen than biomethane. But would it also be cheaper to use as the main source of energy producer? The above method is only based upon the energy content of the fuel and the efficiency of the process. But specialty engines perform better with their fuel type in comparison to other fuels. so to give every fuel type the same treatment they should be displaced as their energy content in kilowatt-hour(kWh). By doing it in this way the fuels its energy content and price ratio would be directly linked to each other without the differences of potential efficiencies. In the report, they had done this by determining this in €/10kWh. By doing it like this hydrogen would cost 2,85 €/10kWh and biomethane would cost only 0,90 €/10kWh. (European Commission, 2017) The price of hydrogen is as of 2017 just over 3 times more expensive than the use of biomethane. This price has not been reduced much in more recent years.
There could be made an argument that in present-day more and more research is done in the field of hydrogen production and use. And thus it could well be that the price of hydrogen will go down. But the same argument could be made for bio-methane so the differences in price will always be an accompanying factor. But in terms of cost biomethane is currently the cheaper and so more interesting option for consumers and producers.
In present-day cost and efficiencies are important factors but the effect it has on the environment can certainly not be overlooked. Mentioned before in this article and more recently in chapter 5.1. the burning of hydrogen to produce energy will only release water as a by-product and biomethane will release CO2 and water. So on the pure burning side hydrogen does take the upper hand. Because the reduction of CO2 is of great importance for the environment, and methane releases it so that would not be beneficial. But there are a couple of extra factors that must be taken into account.
For example, the method of combining renewable energy sources such as solar power and water electrolysis to create hydrogen does sounds like a dream come true doesn’t it, but there are a few problems associated with this way of production, first, this entire setup does take up an enormous amount of extra space, not to mention the upfront cost of setting up the power plant, and the last point is that the power plant will need water to function and in times and places where excess water usage is discouraged it would be better to look at alternative solutions. Such a solution could well be biomethane, yes it does release CO2 upon combustion. But you should not forget that CO2 is also used to produce biomethane, so the average net CO2 release is zero. Also if you were to use natural gases to produce energy CO2 would be released into the atmosphere that was previously trapped in the earth, where it did not harm our environment.
The main advantage of biomethane over hydrogen Is that not a lot of new facilities have to be built to produce and distribute biomethane. The gas can directly be injected into the already existing gas infrastructure used for natural gases. This would prevent a massive amount of extra infrastructure build-up, that would have to be performed for hydrogen. the use of the already existing infrastructure would also become with great energy and cost-effectiveness, once again saving steps that do have to be taken for hydrogen. another great point is that the usage of natural gas lines would already be hooked up to consumers, so the transition to a renewable source would be rather smooth and easy. Other than for hydrogen, where an entirely new pipeline system and consumer access would need to be build or modified to fit the characteristics of hydrogen. (Stephens-Romero et al., 2011; Trinomics et al., 2019)
The point made at the beginning of this section about the usage of water for hydrogen production is also a great factor in the environment. (Oesterholt et al., 2018) It would be true that countries located near water would be able to relatively easily filter and pump the water to be used for hydrogen production. But the point about that could also be made. Most of our water is saltwater. If that water were to be used, it should be filtered to remove all salts from it, to make sure it does not affect the hydrogen production. All that salt has to go somewhere. The most likely scenario is that the salt would be pumped back into the ocean or stored in warehouses. In the case of the warehouse, extra space will need to be made to hold the excess salt. And I the case of the ocean, the effect of extra salination could be catastrophic for the organisms that live within it. In case a country is landlocked and has no excess to disposable water sources, it would not be possible to create hydrogen and is dependent on other countries. This dependency would mean that extra infrastructure would need to be built, which would again have all kinds of environmental effects. The last point of the hydrogen production and the use of water is that water is overall a precious resource. The use of it for energy production should greatly outweigh the need of it for basic survival and other hygienic infrastructure. There are also ways of producing hydrogen without water, employing steam reforming, which is in present-day the most used way of hydrogen production. But steam reforming does need natural gas or other fossil fuel to be able to work. So this method would greatly contribute to the addition of CO2 into the atmosphere and not cause it to be reduced.
Biogases such as bio-methane do have another positive contribution to the environment, which hydrogen does not pose. Bio-methane can be produced from various organic waste sources. The degradation of organic waste through the process of anaerobic digestions gives a couple of advantages to bio-methane. (Sárvári Horváth, Tabatabaei, Karimi, & Kumar, 2016) One of the main upsides would be that the nutrient-rich digested residues, that are leftover from agricultural harvest could be used to fertilize farmland. This way nutrients would be recycled back into the land, that otherwise would have been lost. This recycling would in turn cause that farmers have to use less intense manners to make their fields ready for the next harvest. (Paritosh et al., 2017).
Although Hydrogen as a source of energy using renewable energy does have a great benefit over biomethane in the sense of clean energy production. The current overall negative environmental impact of the usage of hydrogen is far greater than the potential of bio-methane. Because of processes that occur in the background. So in the sense of energy production in an environmental way biomethane is currently the best solution.
In this chapter, we have determent that hydrogen is the most energy-efficient in the sense of pure energy production, but biomethane has the best price and is currently the best option for the environment. But as the demand for more sustainable and environmentally friendly resources grows, also more research will be done. This research will mainly consist of ways to produce energy as efficient and environmentally sound as possible. And although investigating multiply methods of accomplishing this might not be the most efficient, it certainly is the way to go. To stay in the scope of biomethane and hydrogen. it seems like one can never truly replace the other. Both have great opportunities on their own. But both also have their current limitations.
To start with hydrogen. The storage and transport of hydrogen is currently a critical issue. The major problem is the low density of hydrogen gas. Three possible solutions have been proposed. These potential hydrogen delivery systems include compressed tube trailers, liquid storage tank trucks, and compressed gas pipelines. One major disadvantage of each system is the high upfront capital costs needed to produce and develop the large scale systems that could hold the pressure difference created by the low density of hydrogen. the current best option for storage is focused on the use of metal hybrids. It would take more effort to convert the hydrogen into a binding element, but the advantages you get are a high volume efficiency, easy recovery, and a greater safety guaranty. The safe use of hydrogen may very well be the most important aspect of the use because it is one of the most explosive gasses known.
There have been made great strides in the production of biomethane using lignocellulosic biomass(Muni Ramanna Gari Subhosh Chandra, n.d.). and yet there are far ways to go in the development of higher rate gas conversion from biomass. Also, research into the best bioreactor technology within the anaerobic digestion process has to be done to optimize the production. To create biomethane from the degradation of organic material, microorganisms work together. But not a lot is known about these interactions and their metabolic processes (Chen, 2015). However recent developments in molecular biology have shed light on the implementation of tools used to understand complex microbiological systems. (Franco-Duarte et al., 2019) This information could lead to more optimized and controlled processes in the future. Unfortunately, the amount of organic matter currently needed for the production of biogases, such as biomethane is limited. (Sárvári Horváth et al., 2016). Because of this new substrates and new effective technologies are needed to keep up with the growing demand for biomethane in the world.
Both biomethane and hydrogen have their advantages and disadvantages when it comes to research. hydrogen needs to be better storable, and biomethane needs more efficient ways of production. There cannot be said which one the two would be better to invest more time into research, because if you spend more time on one of them, it could be that you miss important aspects of the other. Both have challenges to overcome. So for prospects, it might be best to keep looking into both of them, because you will never know when you find something that could change the entire game.