Much ado about green hydrogen

India already has a National Green Hydrogen Mission (NGHM) in place, and steps towards implementing it have been in the news lately. At the conference held last week, Puri said public sector undertakings have targeted annual production of one million tonnes of green hydrogen by 2030 (the mission targets 5 million tonnes a year in the country by that year) while Bhupinder Singh Bhalla, secretary in the same ministry, said the government is likely to come out with a mandate on the usage of green hydrogen. Maharashtra, meanwhile, became the first state to announce a green hydrogen policy, last week.

So, what is green hydrogen, and why has its time come?

Amid efforts to cut down on carbon emissions, the world is looking for cleaner sources of energy and hydrogen is one of the first choices. It is the most abundant element on the planet, can be isolated through a variety of processes, and is already being used in industrial processes such as oil refining and metallurgy.

If hydrogen is to be used as an alternative fuel, it will not in itself release carbon dioxide. The catch comes in producing the hydrogen, which does not exist in the free state in nature. The most widely used process involves the burning of fossil fuels, which defeats the purpose. Green, therefore, refers to the process by which hydrogen is produced.

When hydrogen is green

Hydrogen is classified as green, blue or grey depending on the production process. Green hydrogen, like blue or grey hydrogen, is still hydrogen, the difference being that it is produced without burning fossil fuels. The bulk of the hydrogen being produced today, however, is not green.

The commonest process is called steam methane reforming. Methane is made to react with steam at high temperatures, resulting in hydrogen, carbon monoxide and a small amount of carbon dioxide. Hydrogen produced this way is called grey, and it is a carbon-intensive process. If, during the process, some of the carbon released is captured and stored, the hydrogen is classified as blue.

Hydrogen can also be produced with the electrolysis of water, which would split into hydrogen and oxygen. Although no carbon is produced by the electrolysis itself, such processes are not always green. If the electricity needed is produced by burning of fossil fuels, it would again defeat the purpose.

Hydrogen produced by the electrolysis of water will be green only if the electricity is generated from sources like wind or solar, which are not carbon-intensive. Production of hydrogen by electrolysis, however, is yet to be adopted on a large scale, said S Dasappa, professor at IISc’s Centre for Sustainable Technology and chair, Interdisciplinary Centre for Energy Research. He estimated that steam methane reforming accounts for 97% of the hydrogen being produced today.

Hydrogen from biomass

The National Green Hydrogen Mission, approved by the Union cabinet in January, refers to pilot projects undertaken for the production of green hydrogen. Electrolysis of water using renewable energy is one way; the NGHM also mentions thermochemical and biochemical methods for the production of green hydrogen from biomass. Biomass refers to renewable organic resources, and can include agriculture crop residues, special crops grown specifically for energy use, and waste.

At his lab, Dasappa has innovated a biomass-based method under a project which, according to the IISc website, was supported by the ministry of new and renewable energy and the department of science and technology.

It is a two-step process. First, biomass is converted into syngas (a fuel gas mixture rich in hydrogen) with the help of oxygen and steam. Next, the syngas is converted into hydrogen. The first step happens in a novel reactor and the second in an indigenously developed separation unit; both these technologies were developed in Dasappa’s lab.

A kilogramme of biomass contains 60 grams of hydrogen, but Dasappa’s process can produce 100 grams from the same quantity of biomass, the IISc website says. The additional hydrogen comes from the steam used in the process.

The process, in fact, produces carbon dioxide, besides solid carbon. However, hydrogen produced from biomass is considered green because, as the process of growing biomass itself removes carbon dioxide from the atmosphere, which offsets the carbon dioxide released during the production of hydrogen.

Dasappa said his process is net carbon-negative. Citing paddy residue as an example of biomass used, he noted that paddy will already have taken carbon dioxide during photosynthesis. “Whenever something is emitted from biomass, the carbon dioxide has already been accounted for. It is not emitting anything ‘net’,” he said.

For every kilogramme of biomass used, roughly 1.8 kg of carbon dioxide gets offset, Dasappa said. In any case, biomass not used for such a process would have degraded and released carbon dioxide, which would have been worse, he said.

The road ahead

India currently consumes around 5 million tonnes of hydrogen annually, mostly for industrial purposes, and almost entirely sourced from fossil fuels. The NGHM, whose objective is to make India the global hub for the production, usage and export of green hydrogen, aims to build capabilities to produce at least 5 million tonnes per annum by 2030, with the potential to reach 10 million tonnes per annum with the growth of export markets. It targets decentralised production, saying it will explore biomass-based production systems and electrolysers connected to solar or other renewable energy plants.

The two-phase mission proposes to first target industries already using hydrogen. The first phase (2022-23 to 2025-26) aims to create demand while enabling adequate supply by increasing the domestic electrolyser manufacturing capacity. It expects green hydrogen costs to become competitive by the second phase (2026-27 to 2029-30), allowing for accelerated growth in production.

One of the challenges with hydrogen is transportation. It has a low volumetric energy density, which means it occupies a lot of space compared to the energy it can provide. The gas is also corrosive. To make transportation viable, hydrogen needs to be compressed into liquid form, which is an expensive process. In view of these challenges, the mission proposes a cluster-based production and utilisation model, implying that infrastructure for the utilisation of hydrogen, too, would need to be set up. At the same time, the mission also talks about developing infrastructure for transporting hydrogen by ships, trains and pipelines