As such, the renewables sector has focused on developing renewable and clean energy resources such as solar, wind, nuclear, hydropower and biofuels as alternatives to fossil fuels. However, hydrogen is set to make a return to the mainstream as the international community seeks to respond to the world’s energy and climate challenges, particularly in light of the targets set by the 2015 Paris Climate Agreement and recent climate activism around the world.
What is the ‘Hydrogen Economy’?
There are several reasons hydrogen is again receiving serious consideration as an alternative energy source. In addition to a global desire for more environmentally friendly fuel sources, improvements in hydrogen technologies, increasing government support for climate-friendly fuel diversification (e.g., in countries such as Japan, Korea and Germany) and changes in global energy policy, in emission standards and in the global technology landscape (such as the rapid deployment of intermittent renewables that require grid-scale storage for system stability) all help to support the argument for developing the hydrogen economy. It is also generally recognized that hydrogen has the potential to decarbonize a range of industries.
A rising star of the renewable energy sector, hydrogen is a versatile and environmentally friendly resource which produces only pure water and heat when combusted. Although hydrogen has been traditionally used as a feedstock in several industrial processes (such as ammonia synthesis and the refining of crude oil), recent developments have shown that hydrogen can also be used for a number of applications, including electricity generation, transportation and storing energy from intermittent renewable sources.
How is Hydrogen Produced?
Natural Gas Reforming Process
At present, the majority of the world’s hydrogen is produced through the natural gas reforming process, which involves using high-temperature steam to produce hydrogen from a methane source such as natural gas. This method is currently the cheapest and most efficient method by which hydrogen is produced and can be coupled with carbon capture and storage technology to reduce the carbon emissions produced in the hydrogen production process.
Hydrogen can also be produced by means of ‘gasification,’ which is the process of, for example, releasing gaseous hydrogen compounds from coal or biomass utilizing high-temperature steam and oxygen in a pressurized gasifier. The resulting gas contains hydrogen, which is then reacted with steam to separate the hydrogen. This process can also be coupled with carbon capture and storage technology to reduce carbon emissions produced through the gasification process.
Renewable Liquid Reforming
Like with natural gas reforming/gasification, this process involves reacting renewable liquid fuels, such as ethanol, with high-temperature steam to produce hydrogen near the point of end use.
Another commonly used method of producing hydrogen is electrolysis, which uses electricity to split water into hydrogen and oxygen. This method also provides the potential for establishing a zero-emission fuel chain if the electrolysis process is powered by renewable energy generated from solar or wind. In doing so, the process of both producing and then subsequently using hydrogen to generate energy would not produce any greenhouse emissions.
It should, however, be noted that, currently, the production of hydrogen from water requires the use of fresh water as the base material. The direct production of hydrogen from seawater requires the development of new technologies to achieve commercial viability. In geographies where fresh water is itself a precious commodity, the production of hydrogen requires a two-step process: (i) the production of fresh water by means of desalination technology, followed by (ii) the application of electrolysis for hydrogen production. Despite this additional step, the process has the benefit of being capable of implementation by utilizing existing and proven technologies.
Extraction from Ammonia
Ammonia is a colorless inorganic compound of nitrogen and hydrogen (NH 3), usually found in gaseous form with a pungent odor. Much research has been undertaken into finding methods of extracting hydrogen from ammonia, such as that undertaken by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia. The CSIRO has created a metal membrane that filters out pure hydrogen gas from ammonia, which can then be used, for example, in fuel cell vehicles.
The advantages of extracting hydrogen from ammonia are that:
- Due to its chemical composition, the production of hydrogen from ammonia does not release greenhouse gas emissions.
- It is much easier to transport hydrogen in the form of ammonia that in a pure gaseous or liquid form (as will be discussed in greater detail below). If hydrogen can be produced from ammonia at the point of need (using, for example, the hydrogen membrane technology from CSIRO), it will be easier and cheaper to organize supply chains to support the use of hydrogen.
Extraction from liquid organic hydrides
Technologies for the extraction of hydrogen from liquid organic hydrides such as methylcyclohexane (MCH) are under consideration. MCH is produced from toluene and hydrogen, and both toluene and MCH exist in a liquid form at ambient temperatures and pressures. Hydrogen is removed from the MCH through a catalytic process, and the resulting toluene can be reused as the base for the production of MCH.
MCH is also capable of safe storage and transportation using existing technologies. However, at present there is no commercial scale project utilizing an MCH value chain.
Fermentation involves converting biomass into sugar-rich feedstocks that can then be fermented to produce hydrogen.
Potential Methods of Hydrogen Production
High-Temperature Water Splitting
This method aims to use high temperatures that are generated by sources such as solar concentrators or nuclear reactors to drive chemical reactions that split water to produce hydrogen.
Photobiological Water Splitting
This method intends to make microbes, such as green algae, consume water in the presence of sunlight to produce hydrogen as a byproduct.
Photoelectrochemical Water Splitting
Similar to high-temperature water splitting, photoelectrochemical water splitting aims to produce hydrogen from water using special semiconductors and energy from sunlight.
Uses of Hydrogen
A hydrogen fuel cell produces electricity by combining oxygen and hydrogen, with this combustion process generating electricity and producing only water and heat as byproducts. Small hydrogen fuel cells can power items such as laptops and cell phones, while at the other end of the spectrum, larger hydrogen fuel cells can provide electricity for powering buildings. As such, hydrogen has the ability to generate power on small, medium and large scales, which makes it a very attractive option for helping countries and corporations meet their decarbonizaton targets.
Transport (Fuel Cells Electric Vehicles)
Many automobile companies, such as Hyundai, Toyota/Lexus, Honda and Mercedes-Benz, have undertaken substantial investment to develop hydrogen-powered vehicles, which possess both a longer range and much shorter refueling times when compared to electric vehicles. These vehicles are called ‘Fuel Cell Electric Vehicles’ (FCVs) and contain hydrogen fuel cells and hydrogen storage tanks that are capable of being refilled in a manner similar to cars fueled by gasoline.
Hydrogen Energy Storage
Hydrogen Energy Storage (HES) is the process of storing energy in the form of hydrogen. Stored as hydrogen for use in fuel cells, for example, hydrogen is an alternative to battery storage. Intermittency, one of the key issues facing wind a solar power generation (i.e., the sun doesn’t always shine nor the wind blow), can be resolved either by:
- Using hydrogen fuel cells for power generation during periods when power cannot be produced from wind or solar.
- Using wind and solar to produce hydrogen, e.g., from hydrolysis, and then utilizing the power per point 1 above.
Production of hydrogen utilizing wind and solar when coupled with hydrogen storage and transportation solutions (discussed further below) effectively also allows wind and solar energy to be “transported” in the form of hydrogen and converted back into electricity (for example, by fuel cell) when needed. The HES process can also be utilized to store energy from other renewable and non-renewable energy sources.
Advantages of Using Hydrogen
As the third most abundant element on Earth, hydrogen can be found in resources including water, natural gas, coal and biomass, meaning that there is no possibility of running out of hydrogen, unlike fossil fuels, which are limited in their supply.
The biggest advantage of using hydrogen as an energy resource is its ability to decarbonize a variety of industries, including the transportation and power generation industries. As detailed above, hydrogen fuel cells combine hydrogen with oxygen to produce energy, with the only byproducts of this process being water and heat. This makes hydrogen a very attractive alternative to fossil fuels, particularly given that if hydrogen is produced using energy from renewable resources (as explained above), then not only will industries be decarbonized, but the whole chain of producing and using hydrogen as an energy resource will be one that does not produce any harmful emissions or pollutants. As such, hydrogen possesses significant potential to assist with decarbonizing numerous industries and is, accordingly, an attractive renewables option for many countries and corporations around the globe.
Efficiency Powering Existing Renewables
Challenges Facing Hydrogen
Storage and Transportation
- Pipeline: This method involves using a pipeline to transport hydrogen, similar to pipelines that are used to transport oil and gas, and is the least expensive way to deliver large volumes of hydrogen.
- High-Pressure Tube Trailers: This method, which is generally expensive, involves transporting compressed hydrogen by truck, railcar, ship or barge in high-pressure tube trailers and is generally used for distances of 200 miles or less.
- Liquefied Hydrogen Tankers: This method involves cooling the hydrogen to a temperature where it becomes a liquid. While the liquefaction process is expensive, it enables hydrogen to be transported more efficiently (in comparison to using tube trailers) over long distances by truck, railcar, ship or barge.
A substantial amount of the energy infrastructure currently in place around the world is designed to support the use of fossil fuels, such as oil pipelines and coal power plants. As explained above, specialized equipment and infrastructure is required to transport and store hydrogen, let alone generate power.
Uptake of Technology
Furthermore, the uptake in the technology required to produce, store, transport and use hydrogen as an energy resource on both industrial and commercial scales has not been as fast as anticipated given the cost and complexities involved in building such infrastructure. In addition, there has been reluctance to invest in such infrastructure until there has been a wider uptake in hydrogen power, such as an increase in the number of FCVs on the road and/or the number of hydrogen fuel cells being used to generate power. As the costs associated with hydrogen continue to decrease, it is hoped that governments, corporations and individuals will begin to take up and install the technology required to support a hydrogen economy at a faster pace.
Safety and Environmental Concerns
Advances in the technology used to generate energy from hydrogen as well as the implementation of strict standards and regulations regarding the use, transportation and storage of hydrogen have helped to reduce these risks and regulate the use of hydrogen so that it is used both safely and in an environmentally friendly manner. However, the perception regarding the environmental and safety problems associated with using hydrogen still persist and will need to be addressed in order for hydrogen to be used on a wide-scale and commercial level.
What Does the Future Hold for Hydrogen?
It is clear that hydrogen has the potential to form a substantial part of the global energy mix as countries and corporations strive to meet their climate change and decarbonization targets. The many applications and benefits of using hydrogen to generate energy make it particularly appealing and are core reasons governments and corporations globally are making substantial investments into hydrogen. Hydrogen’s versatility and multiple applications, along with its ability reduce greenhouse emissions, increase energy security and support the deployment of renewable energy sources such as wind and solar make it very likely to play a significant part in the world’s future energy mix.
While hydrogen faces various challenges (particularly as to the costs of its production, storage and transportation in addition to the infrastructure required to support its use as an energy resource), recent developments have shown that progress is being made on all of these, providing the foundation for hydrogen to become a widely used energy resource around the globe. Consequently, it appears that the outlook for the future of hydrogen as an energy resource remains promising.