Green hydrogen, which is hydrogen produced by splitting water into hydrogen and oxygen using renewable electricity, is the most water-efficient form of clean hydrogen, and uses about one-third less water per kilogram of hydrogen produced than blue hydrogen. Therefore, it is important to prioritise green hydrogen to minimise water security threats, a report published by the International Renewable Energy Agency (IRENA) on December 10, 2023, during COP28, said. Bluerisk, a group of water strategy and data experts who assess and manage water risks, and the IRENA, conducted the analysis.
The report is called ‘Water For Hydrogen’.
The hydrogen produced from natural gas along with carbon capture and storage is called blue hydrogen.
Hydrogen’s global water demand to increase within two to three decades
Environmentalists recommend using hydrogen as an alternative energy solution to fossil fuels, but large amounts of water are required to produce it. It is estimated that hydrogen’s global water demand will increase by more than three times by 2040, and rise by six times by 2050, the report said.
This week, at COP28, announcements to increase clean hydrogen production worldwide were made.
How to reduce water risks associated with clean hydrogen production?
To minimise impact on local water resources and water risks, fossil fuel-powered hydrogen production plants should be retired, and replaced with green hydrogen production, the report recommended.
Why is green hydrogen a better alternative than blue hydrogen?
While green hydrogen is also produced from water, the advantage is that electrolysis of a renewable source is performed. Also, green hydrogen consumes less water than other types of hydrogen which aim to reduce greenhouse gas emissions. This makes green hydrogen the best option for water security, and the climate.
Blue hydrogen is the most water-intensive hydrogen, and has a water intensity more than twice that of green hydrogen.
More than a third of planned or operating green and blue hydrogen production projects are located in highly water-stressed regions. This is risky and can lead to water scarcity if the resources are not properly managed. Therefore, when building new clean hydrogen plants, or approving projects, water considerations should be prioritised, the report suggested.
According to the report, China’s Yellow River Basin accounts for less than four per cent of the country’s total water resources, and over 80 per cent of the country’s hydrogen produced from coal is made in this water-stressed region.
It is likely that by 2040, more than 23 per cent of Europe’s green hydrogen projects, and 14 per cent of its blue hydrogen projects, will be in areas under high or extremely high water stress.
By 2040, 99 per cent of India’s existing and planned green and blue hydrogen capacity is likely to be under extremely water-stressed conditions.
The adoption of air cooling and improved electrolysis efficiency will help reduce water dependency during green hydrogen production. This is because a one per cent increase in electrolysis efficiency results in a two per cent reduction in water requirements, the report said.
Globally every year, hydrogen production requires 2.2 billion cubic metres of fresh water, which is used as an input and cooling medium. The amount of water used for global hydrogen production annually accounts for 0.6 per cent of the energy sector’s total freshwater withdrawal.
Green hydrogen is produced through proton exchange membrane (PEM) electrolysis, a technique in which the electrolyte is a solid speciality plastic material, water reacts at the positively charged electrode or anode to produce positively charged hydrogen ions (protons) and oxygen, electrons produced at the negatively charged electrode or cathode travel through an external circuit towards the anode, and the hydrogen ions move to the cathode, according to the US Department of Energy.
Green hydrogen has the lowest water consumption intensity. The average water consumption intensity of green hydrogen is 17.5 litres of water per kilogram of hydrogen produced.
Green hydrogen can also be produced through alkaline electrolysis, a process in which water is decomposed into hydrogen and oxygen in an electrolytic cell, and an alkaline electrolyte, such as an aqueous solution of sodium or potassium hydroxide is used.
Green hydrogen produced through alkaline electrolysis has a water consumption capacity of 22.3 litres per kilogram of hydrogen produced.
Blue hydrogen is produced through steam methane reformation, an endothermic process in which methane reacts with steam under three to five bar pressure in the presence of a catalyst to generate hydrogen, carbon monoxide, and a small amount of carbon dioxide. The carbon dioxide is captured and stored.
The water consumption capacity of blue hydrogen is 32.2 litres per kilogram of hydrogen produced.
Hydrogen can also be produced through coal gasification, a process in which coal is made to react with water, air or oxygen, and syngas, a mixture of carbon monoxide, carbon dioxide, hydrogen, methane, and water vapour is produced. When hydrogen is produced through coal gasification, 50 litres of water are withdrawn per kilogram of hydrogen produced, and 31 litres of water are consumed per kilogram of hydrogen generated.
Therefore, the water consumption intensity for hydrogen produced through coal gasification is about two times that of PEM electrolysis’ water consumption requirements.
When carbon capture is performed, the water withdrawal requirement during hydrogen production through coal gasification increases to 80.2 litres per kilogram, and the water consumption capacity increases to 49.4 litres of water per kilogram of hydrogen produced.
In order to achieve the Paris Agreement’s goals, green hydrogen is the best option.