Exploring Green Hydrogen

A vector of renewables in the drive for clean power

If recent developments such as the launch of the National Hydrogen En­ergy Mission and bringing green hy­­­­­­drogen within the ambit of renewable purchase obligations are anything to go by, Indian policymakers seem to be aligning their vision with the global green hydrogen drive. It was in 2016 that the Ministry of New and Renewable En­ergy laid out a strategic road map for electrolytic hydrogen-fed fuel cells technology, initiating an indigenous green hy­drogen ecosystem.

Although the infrastructure for hydrogen production exists in India, it (about 5 to 6 million tonnes per annum) is mo­­­s­t­ly produced  from fossil fuel-based technologies. Thus, what we get is “grey” hydrogen. The process chain is colour-classified on the basis of the quantum of carbon emissions, with “green” hydrogen producing zero carbon. As a result, green hydrogen is the current focus of all international climate forums.

India stands well poised at the mo­me­nt, with an ambitious goal of 450 GW of installed renewable energy capa­city by 2030 and falling renewable energy pri­ces, making the clean energy tra­nsi­tion a possibility. Electrolyser tech­no­logies such as alkaline electrolyser (AE) or proton exchange membrane (PEM) electro­lyser can utilise renewable energy-based electricity to produ­ce electrolytic hydrogen with zero emi­s­sions, popularly kno­wn as green hy­dro­gen. Green hydrogen, thus produc­ed, can augment distributed renewable energy generation centres, and divert renewables enabled through hydrogen transmission and storage technologies to energy requirement hotspots. Green hydrogen fuel can thus act as a carrier of clean energy (or a renewable energy vector) in both power and non-power applications.

By doing so, green hydrogen can also counter intermittency issues in renewable energy generation. With the incre­a­se in renewable energy installations, the Indian grid will eventually gain a major share from variable renewable energy (VRE) sources, adding to difficulties in real-time balancing of the grid in the future. Though battery storage solutions (such as lithium-ion) provide intra-day balancing with high cycle times, for long spells clean hydrogen can be explored. There are various promising technologies that can be developed to store hy­­­­­dro­gen for this purpose, such as geological storage including salt caverns and mined or rock caverns, high pressure storage in steel tanks and cylinders, liquefied or cryogenic hydrogen storage, and upgraded natural gas pipelines.

Salt caverns range in depth from 500 to 2,500 metres. Currently, salt caverns are unexplored in India. Rock or mined caverns can be explored in new or existing hydrocarbon reserves. Indian Oil Corpo­ration Limited (IOCL) is already operating India’s first high pressure hydrogen storage unit in India with its refuelling station in Delhi. Further, Visakhapat­nam, Mangaluru and Padur-Udupi have been identified as potential locations for hydrogen storage. Green hydrogen storage in cryogenic tanks can be explored and scaled in the medical and aeronautical industries. Currently, metallic and carbon fibre reinforced composites are utilised for aeronautical propellant tan­ks, and liquid oxygen is transported at low temperatures for medical applicati­ons. Taking the Aatmanirbhar Bharat Ab­hiyan ahead, NTPC Limited is carrying out a pilot to improve the blending of hy­drogen in the natural gas grid in India.

Status of technology integration

The key technology in green hydrogen generation is the electrolyser. Although three technologies exist – AE, PEM, and solid oxide membrane (SOE) – only AE and PEM are commercially deployable at present. PEM has better characteristics and response time for ramp-up and ramp-down functions with grid balancing requirements, but is more expensive than the other technologies. AE and PEM electrolysers can be explored further commercially as they are at technology-readiness levels of 9 and 8 respectively, (with 10 denoting the highest deployability). While SOE is still in an emerging state, AE is more mature, with one of the world’s first large-scale AEs dating back to 1962 at the Nangal heavy water plant facility in Rupnagar district, Punjab. Further, AE requires lower capital costs and better technological know-how.

However, despite its higher capital in­vestment requirement and lesser maturity, the concerted global focus is on PEM for the power sector due to its easy grid integration. It has a lower start-up time (one second to five minutes) and faster ramp-up and ramp-down time of response (100 per cent up-down in one second). It is more promising in the long run as it can offset frequency imbalances in the grid, which may arise due to higher VRE components.

Further, PEMs also have a lower plant footprint of 0.048 m2/kW, compared to 0.095 m2/kW for AE (IEA, 2020). They also have higher output pressure (30 to 80 bars), which is better suited for conversion and stationary storage of hydrogen in gaseous form at 100 bar pressure. The current electrical efficiency of AE is in the range of 63–70 per cent and can climb up to 80 per cent in the long term with advancements, while the efficiency of PEM ranges between 56 per cent and 60 per cent and can rise up to 74 per cent (IEA, 2020). Electrolyser technology can operate in both grid-connected and islanded mode; while the grid connection provides a higher load factor, standalone systems can get exemption from grid charges. The excess electricity from stand-alone green hydrogen systems may be sold to the grid to further reduce the cost of hydrogen production.

Among renewable energy sources, solar-run systems have the advantage of comparatively higher persistence with lower seasonal variation, but also have low plant load factors. On the other hand, wind-based electrolysers have higher variations, but higher plant load factors. Therefore, the major capital cost of technology – electrolyser and battery storage – may be higher overall at the onset, and so options with hybrid technology (solar and wind combined) can be explored. Currently, hydrogen storage in salt caverns is being explored in the UK and the US, with India lagging behind. India can explore rock caverns or empty hydrocarbon reserves after due diligence.

Hydrogen can also be stored in high pressure steel tanks, but at a comparatively lower energy density (15 per cent equivalent of fossil fuels). The stored hy­drogen can be directed as a generated renewable energy vector, transported in vehicles at 350 to 700 bar pressure. It can also be transported in a liquid state at minus 273 degrees in cryogenic tankers. However, in the long run, transportation technologies utilising pipelines need to be explored, in addition to high pressu­re (in excess of 700 bar) storage in steel tanks. The storage medium largely deci­des the duration and discharge speed of the fuel. Green hydrogen can also be stored and carried in mediums such as ammonia, methanol and liquid organic hydrogen forms.

Existing power projects in green hydrogen

India has initiated various pilot projects. Currently, the Bhabha Atomic Research Centre (BARC) is exploring the performance of alkaline water electrolysis and steam-based high temperature electrolysis, as well as advancements in PEM. Similarly, IOCL is working to im­prove the efficacy of electrolysers. Fur­ther, the Council of Scientific and In­dustrial Research – Central Elec­tro Che­mical Research Institute is exploring design parameters to utilise salt water from the sea to generate hydrogen at electrodes. The University of Luc­k­now is analysing variations of alkaline water electrolysis with oxides based on transition metals. A consortium of In­dian Institutes of Technology (Kan­pur, Mad­ras and Jodhpur IITs) and BARC is working on solar-based hydrogen generation on a large scale. There is also ongoing research, pri­marily at IIT Kha­ra­gpur, into the storage and transportation of gaseous hy­dro­gen at a higher density. The design aspects of a metal organic framework-ba­sed high pressure, type-3 hydrogen storage cy­lin­der are being analysed.

The way forward

India needs to recognise the role of hy­drogen in energy transition, as a cost-effective inter-seasonal storage and a balancing option. For transitioning to green hydro­gen, we need to indigenise the ma­n­u­­facturing technology of electrolysers. The government and industries must join hands to drive the dep­loy­ment of these technologies for com­me­rcialisation. We must also enable public-private partnerships to create a demand for green hydrogen by driving towards cleaner sources. Penalising carbon emissions can provide an opportunity for green hydrogen to compete and grow alongside the existing grey hydrogen framework.

Vishu Mishra, Research Engineer and Rishu Garg, Research Scientist, Energy and Power Sector, Center for Study of Science, Technology and Policy (CSTEP)

 

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