green hydrogen
Green hydrogen (GH2 or GH2) is hydrogen produced by the electrolysis of water, using renewable electricity.  Production of green hydrogen causes significantly lower greenhouse gas emissions than production of grey hydrogen, which is derived from fossil fuels without carbon capture.Green hydrogen’s principal purpose is to help limit global warming to 1.5C, reduce fossil fuel dependence by replacing grey hydrogen, and provide for an expanded set of end-uses in specific economic sectors, sub-sectors and activities. These end-uses may be technically difficult to decarbonize through other means such as electrification with renewable power.  Its main applications are likely to be in heavy industry (e.g. high temperature processes alongside electricity, feedstock for production of green ammonia and organic chemicals, as an alternative to coal-derived coke for steelmaking), long-haul transport (e.g. shipping, aviation and to a lesser extent heavy goods vehicles), and long-term energy storage.As of 2021, green hydrogen accounted for less than 0.04% of total hydrogen production. Its cost relative to hydrogen derived from fossil fuels is the main reason green hydrogen is in less demand. 
For example, hydrogen produced by electrolysis powered by solar power was about 25 times more expensive than that derived from hydrocarbons in 2018.

Definition
Most commonly, green hydrogen is defined as hydrogen produced by the electrolysis of water, using renewable electricity.  In this article, the term green hydrogen is used with this meaning.
Precise definitions sometimes add other criteria. The global Green Hydrogen Standard defines green hydrogen as “hydrogen produced through the electrolysis of water with 100% or near 100% renewable energy with close to zero greenhouse gas emissions.”A broader, less-used definition of green hydrogen also includes hydrogen produced through various other methods that produce relatively low emissions and meet other sustainability criteria. For example, these production methods may involve nuclear energy or biomass feedstocks.

Uses
There is potential for green hydrogen to play a significant role in decarbonising energy systems where there are challenges and limitations to replacing fossil fuels with direct use of electricity. Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals, thus contributing to the decarbonisation of industry alongside other technologies, such as electric arc furnaces for steelmaking. However, it is likely to play a larger role in providing industrial feedstock for cleaner production of ammonia and organic chemicals. For example, in steelmaking, hydrogen could function as a clean energy carrier and also as a low-carbon catalyst replacing coal-derived coke. Hydrogen used to decarbonise transportation is likely to find its largest applications in shipping, aviation and to a lesser extent heavy goods vehicles, through the use of hydrogen-derived synthetic fuels such as ammonia and methanol, and fuel cell technology. For light duty vehicles including passenger cars, hydrogen is far behind other alternative fuel vehicles, especially compared with the rate of adoption of battery electric vehicles, and may not play a significant role in future.Green hydrogen can also be used for long-duration grid energy storage, and for long-duration seasonal energy storage.

Market
As of 2022, the global hydrogen market was valued at $155 billion and was expected to grow at an average (CAGR) of 9.3% between 2023 and 2030.
Of this market, green hydrogen accounted for about $4.2 billion (2.7%).
Due to the higher cost of production, green hydrogen represents a smaller fraction of the hydrogen produced compared to its share of market value.
The majority of hydrogen produced in 2020 was derived from fossil fuel. 99% came from carbon-based sources. Electrolysis-driven production represents less than 0.1% of the total, of which only a part is powered by renewable electricity.
The current high cost of production is the main factor limiting the use of green hydrogen. A price of $2/kg is considered by many to be a potential tipping point that would make green hydrogen competitive against grey hydrogen. It is cheapest to produce green hydrogen with surplus renewable power that would otherwise be curtailed, which favours electrolysers capable of responding to low and variable power levels (such as proton exchange membrane electrolysers).: 5 The cost of electrolysers fell by 60% from 2010 to 2022, and green hydrogen production costs are forecasted to fall significantly to 2030 and 2050,: 26  driving down the cost of green hydrogen alongside the falling cost of renewable power generation.: 28   Goldman Sachs analysis observed in 2022, just prior to Russia’s invasion of Ukraine that the “unique dynamic in Europe with historically high gas and carbon prices is already leading to green H2 cost parity with grey across key parts of the region”, and anticipated that globally green hydrogen achieve cost parity with grey hydrogen by 2030, earlier if a global carbon tax were placed on grey hydrogen.As of 2021, the green hydrogen investment pipeline was estimated at 121 gigawatts of electrolyser capacity across 136 projects in planning and development phases, totaling over $500 billion. If all projects in the pipeline were built, they could account for 10% of hydrogen production by 2030. 
The market could be worth over $1 trillion a year by 2050 according to Goldman Sachs.
An energy market analyst suggested in early 2021 that the price of green hydrogen would drop 70% by 2031 in countries that have cheap renewable energy.

Projects
Australia
In 2020, the Australian government fast-tracked approval for the world's largest planned renewable energy export facility in the Pilbara region. In 2021, energy companies announced plans to construct a "hydrogen valley" in New South Wales at a cost of $2 billion to replace the region's coal industry.As of July 2022, the Australian Renewable Energy Agency (ARENA) had invested $88 million in 35 hydrogen projects ranging from university research and development to first-of-a-kind demonstrations. In 2022, ARENA is expected to close on two or three of Australia’s first large-scale electrolyser deployments as part of its $100 million hydrogen deployment round.

Canada
World Energy GH2’s Project Nujio'qonik aims to be Canada’s first commercial green hydrogen / ammonia producer created from three gigawatts of wind energy on the west coast of Newfoundland and Labrador, Canada. Nujio’qonik is the Mi’kmaw name for Bay St. George, where the project is proposed. Since August 2022, the project has been undergoing environmental assessment according to regulatory guidelines issued by the Government of Newfoundland and Labrador. Project Nujio'qonik is expected to produce the first green hydrogen in late-2025 and start international export in 2026.

Chile
Chile's goal to use only clean energy by the year 2050 includes the use of green hydrogen. The EU Latin America and Caribbean Investment Facility provided a €16.5 million grant and the EIB and KfW are in the process of providing up to €100 million each to finance green hydrogen projects.

China
In 2022 China was the leader of the global hydrogen market with an output of 33 million tons (a third of global production), mostly using fossil fuel.
As of 2021, several companies have formed alliances to increase production of the fuel fifty-fold in the next six years.Sinopec aimed to generate 500,000 tonnes of green hydrogen by 2025. Hydrogen generated from wind energy could provide a cost-effective alternative for coal-dependent regions like Inner Mongolia. As part of preparations for the 2022 Winter Olympics a hydrogen electrolyser, described as the "world's largest" began operations to fuel vehicles used at the games. The electrolyser was powered by onshore wind.

Germany
Germany invested €9 billion to construct 5 GW of electrolyzer capacity by 2030.

India
Reliance Industries announced its plan to use about 3 gigawatts (GW) of solar energy to generate 400,000 tonnes of hydrogen. Gautam Adani, founder of the Adani Group announced plans to invest $70 billion to become the world's largest renewable energy company, and produce the cheapest hydrogen across the globe. The power ministry of India has stated that India intends to produce a cumulative 5 million tonnes of green hydrogen by 2030.In April 2022, the public sector Oil India Limited (OIL), which is headquartered in eastern Assam’s Duliajan, set up India’s first 99.99% pure green hydrogen pilot plant in keeping with the goal of “making the country ready for the pilot-scale production of hydrogen and its use in various applications” while “research and development efforts are ongoing for a reduction in the cost of production, storage and the transportation” of hydrogen.

Mauritania
Mauritania launched two major projects on green hydrogen. The NOUR Project would become one of the world’s largest hydrogen projects with 10 GW of capacity by 2030 in cooperation with Chariot company. The second is the AMAN Project, which includes 12GW of wind capacity and 18GW of solar capacity to produce 1.7 million tons per annum of green hydrogen or 10 million tons per annum of green ammonia for local use and export, in cooperation with Australian company CWP.

Namibia
Namibia has commissioned a green hydrogen production project with German support.  The 10 billion dollar project involves the construction of wind farms and photovoltaic plants with a total capacity of 7 (GW) to produce. It aims to produce 2 million tonnes of green ammonia and hydrogen derivatives by 2030 and will create 15,000 jobs of which 3,000 will be permanent.

Oman
An association of companies announced a $30 billion project in Oman, which would become one of the world's largest hydrogen facilities. Construction was to begin in 2028. By 2038 the project was to be powered by 25 GW of wind and solar energy.

Portugal
In April 2021, Portugal announced plans to construct the first solar-powered plant to produce hydrogen by 2023. Lisbon based energy company Galp Energia announced plans to construct an  electrolyser to power its refinery by 2025.

Saudi Arabia
In 2021, Saudi Arabia, as a part of the NEOM project, announced an investment of $5bn to build a green hydrogen-based ammonia plant, which would start production in 2025.

Spain
In February 2021, thirty companies announced a pioneering project to provide hydrogen bases in Spain. The project intended to supply 93 GW of solar and 67 GW of electrolysis capacity by the end of the decade.

United Arab Emirates
In 2021, in collaboration with Expo 2020 Dubai, a pilot project was launched which is the first "industrial scale", solar-driven green hydrogen facility in the Middle East and North Africa."

United Kingdom
In March 2021, a proposal emerged to use offshore wind in Scotland to power converted oil and gas rigs into a "green hydrogen hub" which would supply fuel to local distilleries.In June 2021, Equinor announced plans to triple UK hydrogen production. In March 2022 National Grid announced a project to introduce green hydrogen into the grid with a 200m wind turbine powering an  electrolyser to produce gas for about 300 homes.Vattenfall planned to generate green hydrogen from a test offshore wind turbine near Aberdeen in 2025.

United States
The federal Infrastructure Investment and Jobs Act, which became law in November 2021, allocated $9.5 billion to green hydrogen initiatives. In 2021, the U.S. Department of Energy (DOE) was planning the first demonstration of a hydrogen network in Texas. The department had previously attempted a hydrogen project known as Hydrogen Energy California. Texas is considered a key part of green hydrogen projects in the country as the state is the largest domestic producer of hydrogen and has a hydrogen pipeline network. In 2020, SGH2 Energy Global announced plans to use plastic and paper via plasma gasification to produce green hydrogen near Los Angeles.In 2021 then New York governor Andrew Cuomo announced a $290 million investment to construct a green hydrogen fuel production facility. State authorities backed plans for developing fuel cells to be used in trucks and research on blending hydrogen into the gas grid. In March 2022 the governors of Arkansas, Louisiana, and Oklahoma announced the creation of a hydrogen energy hub between the states. Woodside announced plans for a green hydrogen production site in Ardmore, Oklahoma. The Inflation Reduction Act of 2022 established a 10-year production tax credit, which includes a $3.00/kg subsidy for green hydrogen.

Public-private projects
In October 2023, Siemens announced that it had successfully performed the first test of an industrial turbine powered by 100 per cent green hydrogen generated by a 1 megawatt electrolyser. The turbine also operates on gas and any mixture of gas and hydrogen.

Government support
In 2020, the European Commission adopted a dedicated strategy on hydrogen. The "European Green Hydrogen Acceleration Center" is tasked with developing a €100 billion a year green hydrogen economy by 2025.In December 2020, the United Nations together with RMI and several companies, launched Green Hydrogen Catapult, with a goal to reduce the cost of green hydrogen below US$2 per kilogram (equivalent to $50 per megawatt hour) by 2026.In 2021, with the support of the governments of Austria, China, Germany, and Italy, UN Industrial Development Organization (UNIDO) launched its Global Programme for Hydrogen in Industry. Its goal is to accelerate the deployment of GH2 in industry.
In 2021, the British government published its policy document, a "Ten Point Plan for a Green Industrial Revolution," which included investing to create 5 GW of low carbon hydrogen by 2030. The plan included working with industry to complete the necessary testing that would allow up to 20% blending of hydrogen into the gas distribution grid by 2023. A BEIS consultation in 2022 suggested that grid blending would only have a "limited and temporary" role due to an expected reduction in the use of natural gas.The Japanese government planned to transform the nation into a "hydrogen society". Energy demand would require the government to import/produce 36 million tons of liquefied hydrogen. At the time Japan's commercial imports were projected to be 100 times less than this amount by 2030, when the use of fuel was expected to commence. Japan published a preliminary road map that called for hydrogen and related fuels to supply 10% of the power for electricity generation as well as a significant portion of the energy for uses such as shipping and steel manufacture by 2050. Japan created a hydrogen highway consisting of 135 subsidized hydrogen fuels stations and planned to construct 1,000 by the end of the 2020s.In October 2020, the South Korean government announced its plan to introduce the Clean Hydrogen Energy Portfolio Standards (CHPS) which emphasizes the use of clean hydrogen. During the introduction of the Hydrogen Energy Portfolio Standard (HPS), it was voted on by the 2nd Hydrogen Economy Committee. In March 2021, the 3rd Hydrogen Economy Committee was held to pass a plan to introduce a clean hydrogen certification system based on incentives and obligations for clean hydrogen.Morocco, Tunisia, Egypt and Namibia have proposed plans to include green hydrogen as a part of their climate change agenda. Namibia is partnering with European countries such as Netherlands and Germany for feasibility studies and funding.In July 2020, the European Union unveiled the Hydrogen Strategy for a Climate-Neutral Europe. A motion backing this strategy passed the European Parliament in 2021. The plan is divided into three phases. From 2020 to 2024, the program aims to decarbonize existing hydrogen production. From 2024-2030 green hydrogen would be integrated into the energy system. From 2030 to 2050  large-scale deployment of hydrogen would occur. Goldman Sachs estimated hydrogen to 15% of the EU energy mix by 2050.Six European Union member states: Germany, Austria, France, the Netherlands, Belgium and Luxembourg, requested hydrogen funding be backed by legislation. Many member countries have created plans to import hydrogen from other nations, especially from North Africa. These plans would increase hydrogen production, but were accused of trying to export the necessary changes needed within Europe. The European Union required that starting in 2021, all new gas turbines made in the bloc must be ready to burn a hydrogen–natural gas blend.In November 2020, Chile's president presented the "National Strategy for Green Hydrogen," stating he wanted Chile to become "the most efficient green hydrogen producer in the world by 2030". The plan includes HyEx, a project to make solar based hydrogen for use in the mining industry.

Regulations and standards
In the European Union, certified ‘renewable’ hydrogen, defined as produced from non-biological feedstocks, requires an emission reduction of at least 70% below the fossil fuel it is intended to replace.  This is distinct in the EU from ‘low carbon’ hydrogen, which is defined as made using fossil fuel feedstocks. For it to be certified, low carbon hydrogen must achieve at least a 70% reduction in emissions compared with the grey hydrogen it replaces.In the United Kingdom, just one standard is proposed, for ‘low carbon’ hydrogen. Its threshold GHG emissions intensity of 20gCO2 equivalent per megajoule should be easily met by renewably-powered electrolysis of water for green hydrogen production, but has been set at a level to allow for and encourage other ‘low carbon’ hydrogen production, principally blue hydrogen. Blue hydrogen is grey hydrogen with added carbon capture and storage, which to date has not been produced with carbon capture rates in excess of 60%. To meet the UK’s threshold, its government has estimated that an 85% carbon capture rate would be necessary.In the United States, planned tax credit incentives for green hydrogen production are to be tied to the emissions intensity of ‘clean’ hydrogen produced, with greater levels of support on offer for lower greenhouse gas intensities.

Research
A 2023 study reported two uses of a conductive adhesive-barrier (CAB) that converted >99% of photoelectric power to chemical reactions. One experiment examined halide perovskite-based photoelectrochemical cells that achieved efficiency of 13.4% and 16.3 h to t60. The second was formed using a monolithic, stacked, silicon-perovskite tandem (two layered cell, with each layer absorbing a different frequency range), achieving peak efficiency of 20.8% and continuous operation of 102 h.

See also
Hydrogen economy
Alternative fuel
Carbon-neutral fuel
Fossil fuel phase-out
Combined cycle hydrogen power plant

References
External links
Green hydrogen explainer video from Scottish Power