finally 'green hydrogen' is produced entirely from renewable sources. Energy Hydrogen is found in the first group and the first period in the periodic table, i.e., it is the lightest element. Hydrogen is rarely found in its pure form in the atmosphere, H2. In flame of pure hydrogen burning in air, the hydrogen (H2) reacts with oxygen (O2) to form water (H2O) with the release of energy. 2H2 (g) + O2 (g) → 2H2O (g) + energy In atmospheric air rather than pure oxygen, hydrogen combustion may yield a small amount of nitrogen oxides with the water vapor. The energy released allows hydrogen to be used as a fuel. In an electrochemical cell, that energy can be used with relatively high efficiency. If the energy is used to produce heat, thermodynamics places limits on the thermal efficiency of the process. Hydrogen is usually considered to be an energy carrier, like electricity, as it must be produced from a primary energy source such as solar energy, biomass, electrical energy (e.g. in the form of solar PV or via wind turbines), or hydrocarbons such as natural gas or coal. Conventional hydrogen production using natural gas induces significant environmental impacts; as with the use of any hydrocarbon, carbon dioxide is emitted. At the same time, the addition of 20% hydrogen (an optimal share that does not affect gas pipes and appliances) to natural gas can reduce emissions from heating and cooking. Hydrogen is locked up in enormous quantities in water, hydrocarbons, and other organic matter. One of the challenges of using hydrogen as a fuel comes from being able to extract hydrogen efficiently from these compounds. Currently, steam reforming, which combines high-temperature steam with natural gas, accounts for the majority of the hydrogen produced. This method of hydrogen production occurs at 700–1100 °C, and has an efficiency of 60–75%. Hydrogen can also be produced from water through electrolysis, which is less carbon-intensive if the electricity used to drive the reaction does not come from fossil-fuel power plants but rather from renewable or nuclear energy sources. The efficiency of water electrolysis is about 70–80%, with a goal of 82–86% efficiency by 2030 using proton exchange membrane (PEM) electrolyzers. Other methods for producing hydrogen for fuel are also currently being tested. Renewable liquid reforming is the process of taking liquid fuels, like ethanol, and reacting with high-temperature steam to produce hydrogen near the point of