Feb-2024

The challenges of transitioning to green hydrogen

Green hydrogen is a significant and promising source of renewable energy, but it faces several economic, technical, and regulatory challenges.

Himmat Singh
Formerly CSIR-Indian Institute of Petroleum

Article Summary

Green hydrogen produced from the electrolysis of water using renewable energy can be used directly as a fuel or converted into derivatives, namely, ammonia, methanol, synthetic diesel, and jet fuels. These are promoted by governments and industries as renewable chemicals and sustainable alternative fuels for long-haul trucking, shipping, and air travel. Hydrogen is also viable as a means to store renewable energy and could even be used for cooking and heating homes. Costs are dropping significantly, with electrolyser prices down 50% and renewable energy costs falling 50-60% over the last 10 years. Further decreases are anticipated. However, economic, technical, and regulatory hurdles remain for the developing hydrogen economy.

Introduction
Preserving our planet is a formidable challenge for humanity, with the Intergovernmental Panel on Climate Change (IPCC) stressing the need to limit global temperature increases to 1.5°C above pre-industrial levels to avoid the most severe climate consequences (IPCC, 2022). Green hydrogen emerges as a valuable tool in this endeavour.

Hydrogen serves as a clean-burning molecule and versatile energy carrier, applicable in a wide range of energy and industrial uses. Its potential and challenges stem from two primary energy characteristics: hydrogen has a high specific energy (energy content per unit of mass) but a low volumetric energy density. This means that hydrogen requires pressurisation or liquefaction to become a practical fuel (NITI Aayog, 2022), while hydrogen carriers may prove more economical for longer-distance transport.

Hydrogen promises to decarbonise sectors that have historically been challenging to decarbonise. However, it is crucial to note that a staggering 99% of hydrogen production currently relies on fossil fuels, which are associated with significant pollution. Green hydrogen, produced from the electrolysis of water using electricity from renewable energy sources, presently represents a mere 0.1% of global hydrogen production (Nelson, 2021). Nevertheless, it holds immense potential for addressing the intermittency issues of renewables. It facilitates policies and practices to advance the production and uses of hydrogen where direct electrification is problematic. Hydrogen can be used directly as fuel for heating industrial processes such as the production of iron, steel, aluminium, and glass, as a fuel in hydrogen fuel cells, or converted into derivatives such as ammonia, methanol and synthetic diesel and jet fuels. As such, there is a need to prioritise green hydrogen project deployment at scale, leveraging multi-sector opportunities to simultaneously scale supply and demand.

Hydrogen production and demand
Hydrogen is the universe’s lightest and most abundant element. It is highly reactive, so it is rarely found in its elemental form and must be extracted from compounds. Its role in decarbonisation depends on the environmental friendliness of the production method, leading to different classifications (NITI Aayog, 2022):
• Black/brown hydrogen is produced from the gasification of coal or lignite. The process produces hydrogen but also produces high levels of carbon dioxide (CO2) and, as a result, has the highest ‘carbon intensities’, greater than 18kg CO₂/kgH₂ (see Figure 1).
• Grey hydrogen is produced from methane or natural gas via the steam methane reforming process (SMR) with carbon intensities ranging from 11 to 9kgCO₂/kgH₂.
• Blue hydrogen uses an additional process to capture the CO2 emissions from gasification or reforming to reduce the carbon intensity of the process ranging from 10 to 0.6 kgCO₂e/kgH₂, determined by the effectiveness of the carbon capture process. The captured carbon must then be sent for permanent storage (CCS) or utilisation (CCU).
• Turquoise hydrogen is produced by the pyrolysis of methane, producing hydrogen and elemental carbon, thus avoiding CO2 emissions. This process is in the early stages of commercialisation. The carbon intensity of turquoise hydrogen is determined by the source of methane and the supply of heat to drive the pyrolysis process, and can range from 1.5 to less than 0.6 kgCO₂e/H₂ (Singhania, et al., 2023), (Schubak, 2022).
• Green hydrogen is generated by the electrolysis of water using electricity. The carbon intensity for hydrogen from electrolysis ranges from 1 to 0.3, depending on the share of renewable energy in the electricity mix. Electrolysis is the only process that uses water in place of hydrocarbons as the hydrogen source.

Table 1 illustrates the range of carbon intensities for the different colours of hydrogen. There is a progressive fall in carbon intensity values, moving from black or brown to grey, then blue to turquoise or green hydrogen. Carbon intensities may approach zero for turquoise or green hydrogen compared with as much as 18-20 KgCO₂/KgH₂ for coal. While using colours to differentiate routes to produce hydrogen has been valuable, a consensus is emerging that carbon intensity is more appropriate (IEA, 2023). Given that there is a range of intensities for any given production route, this will drive the necessary shift towards production methods with the lowest carbon intensity, for example, ensuring that renewable electricity is used for electrolysis. This is reflected in the increasing level of investments in hydrogen electrolysis projects worldwide.

Alkaline and polymer electrolyte membrane (PEM) electrolysers are both commercially available technologies. Worldwide, the three biggest manufacturers in 2022 were all Chinese companies, with a combined manufacturing capacity of 4.1 GW (Klevstrand, 2022). Global investments amounted to $1.2 billion, representing a doubling in commissioned capacity to 1.2 GW, with 25% of this capacity installed in China (Klevstrand, 2023). Advanced electrolyser technologies such as solid oxide and anion exchange membranes are nearing commercial deployment.