# Technology for Green Hydrogen Production: Desk Analysis
## 2 Background of Analysis  
### Energy Production from Fossil Fuels and Renewable Sources  
The most popular and widely used fuels for energy production are coal, petroleum, natural gas, and oil [2; 3; 4]. Unfortunately, when these fossil fuels are burned, in addition to energy, they also release industrial gases that pose a potential threat to the natural environment [77]. Undesirable by-products of the combustion of fossil fuels include sulfur (IV) oxide, carbon (II) oxide, carbon (IV) oxide, nitrogen oxides, dust, and ashes, as well as hydrocarbons that have not been burned. The combustion process also emits heavy metals such as radium, thorium, and lead, which are contained as admixtures in fossil fuels. All emitted combustion products change the natural environment irreversibly, polluting the air, soil, and groundwater, and contributing to the accelerated death of plants and animals, an increase in the incidence of asthma, allergies, cardiovascular diseases, and cancer. The effects of air pollution in the form of smog, the ozone hole, acid rain, odors, and the greenhouse effect are particularly dangerous to human health and life [78; 79]. Reducing the amount of pollution in the combustion process of fossil fuels can be ensured by the modernization of outdated industrial plants, waste-free or at least low-waste production, reuse of exhaust gases, or energy saving. Taking into account the fact that the Earth's fossil fuel resources are slowly decreasing and the need to diversify energy to avoid an energy crisis, it is necessary to generate electricity from renewable sources at an affordable price [2; 4]. Primary energy consumption by source on a global scale in 2022, as shown in Figure 2, was already 166,588.47 TWh [80]. Primary energy, assuming that it is unconverted energy available as a resource, was based on the substitution method. It includes energy needed by the end user in the form of electricity, transportation, and heating, as well as inefficiencies and energy lost in converting raw materials into a usable form. Primary energy consumption for fossil fuels including coal, oil, and gas amounted to as much as 137,236.67 TWh, which constitutes over 83% of the total consumption. The highest value of 52,969.59 TWh among depleting fossil fuels was achieved in the case of oil. Primary energy consumption for nuclear and renewables in 2022 was only 6702.34 TWh and 22,649.47 TWh, respectively. It should be noted that primary energy consumption for other renewables should be increased. Electricity production from fossil fuels, nuclear, and renewables in the world from 1985 to 2023 is presented in Figure 3 [81]. Yearly electricity generation, capacity, emissions, import, and demand data for over 200 geographies are contained in this dataset. The share of fossil fuels in global electricity production has not changed much over the last three decades, decreasing only from 64 to 61%, while the share of nuclear has decreased from 15 to 9% and the share of renewables has increased from 21 to 30%. Total electricity production in 2023 amounted to 29,479 TWh, of which 17,879 TWh was generated from fossil fuels, 2686 TWh from nuclear, and 8914 TWh from renewables. One can observe a global upward trend in the implementation of renewable technologies, which is partially offset by a decline in nuclear energy production. Currently, approximately 96% of the total hydrogen production in the world is based on fossil fuels and only 4% on water electrolysis, of which approximately 1% uses energy from RESs for the electrolysis process, in which green hydrogen is obtained in a zero-emission way [82]. According to data published by the International Energy Agency, in 2021 the total global production of hydrogen was 94 million tonnes (Mt H\({}_{2}\)), including 74 Mt H\({}_{2}\) of pure hydrogen production and around 20 Mt H\({}_{2}\) mixed with carbon-containing gases in methanol production and steel manufacturing, as shown in Figure 4 [82]. Emissions associated with hydrogen production based on fossil fuels were above 900 Mt CO\({}_{2}\).