The announcement of the “Europe Green Deal” last December shows Europe’s growth strategies to address climate change and environmental problems through new renewable energy, and to shift to an energy-efficient and competitive economic paradigm. As Korea also announced its “Hydrogen Economy Revitalization Roadmap” in January of last year, and the “Korean Green New Deal” policy in May, public interest in hydrogen-based energy is playing an increasing role in the new renewable energy industry with high expectations for the new renewable energy industry.
After hydrogen was first discovered in 1766, hydrogen gas was used to fly balloons in 1783. Then hydrogen-fueled cars were first released in 1972, but their use was restricted due to other relatively cheaper energy sources. Because hydrogen exists as combined molecules in nature, unlike other energy sources such as petroleum, coal and natural gas, energy should be input to obtain pure hydrogen, so it is considered an Energy Carrier or secondary energy source, like electricity, that can store and transport energy, rather than a primary energy source like petroleum.
Because hydrogen becomes water after combining with oxygen when it is released into the atmosphere, hydrogen energy is often considered clean energy. However, if fossil fuels such as petroleum and coal are used during its production, it cannot be considered completely clean. It can be considered clean only when it is produced using renewable energy, such as solar, water or wind power.
There are many ways of generating hydrogen. In general, it is classified into byproduct hydrogen, water electrolyzed hydrogen and extracted(reformed) hydrogen. Byproduct hydrogen is hydrogen that can be obtained in the petrochemical and steel making processes. It has long been used industrially for petrochemical purification and semiconductor cleaning. Water electrolyzed hydrogen is obtained from water using electricity. Due to high production costs, its production is not economical. Extracted hydrogen is produced from fossil fuels, such as coal and natural gas. Natural gas-extracted hydrogen currently accounts for the largest percentage.
As byproduct hydrogen is a secondary byproduct produced in the petrochemical and steel making processes, its supply is limited. As water electrolyzed hydrogen is uneconomical, extracted hydrogen is currently the cheapest way to produce hydrogen in large quantities. As hydrogen energy is obtained from extracted hydrogen through fossil fuels, it is not completely clean but can be considered low carbon energy with less greenhouse gas emissions than fossil fuels when used as fuel cells.
In general, according to production processes, hydrogen is classified as grey hydrogen if it produces CO₂, and blue hydrogen if it captures and stores CO₂with water electrolyzed hydrogen, or imported hydrogen classified as green hydrogen. The European Union has certified hydrogen as eco-friendly through the CertifHy Guarantee of Origin since 2016. The International Energy Agency (IEA) and International Renewable Energy Agency (IRENA) subdivides hydrogen produced using fossil fuels into Black (coal)/Grey (gas)/Brown (lignite).
Green Hydrogen among these, as hydrogen energy that produces the least carbon emissions, is used for P2G (Power to Gas) technology which electrolyzes water using electricity produced by renewable energy and stores it as hydrogen. This stored hydrogen is transported to where it is needed and used as a fuel cell energy source.