Hydrogen as an energy carrier

In short: Hydrogen can store and transport energy. When it is burned or used in a fuel cell, the exhaust is essentially just water.

In more detail: Hydrogen is the lightest element and the most common in the universe. On Earth, however, it occurs almost only in compounds, such as water or natural gas. It therefore first has to be produced using energy, which makes it not an energy source but an energy carrier, rather like a battery.

In detail

• Electrolysis: Electricity can split water into hydrogen and oxygen. If the electricity comes from wind or sun, it is called green hydrogen.
• From natural gas: Today most hydrogen is made from natural gas, which releases carbon dioxide (grey hydrogen). If this CO₂ is captured and stored, it is called blue hydrogen.
• Fuel cell: In a fuel cell, hydrogen and oxygen react with each other in a controlled way. This directly produces electricity, heat and water, without an open flame.
• Storage is demanding: Hydrogen takes up a great deal of space. It is compressed into tanks under high pressure or cooled to about minus 253 °C until it becomes liquid.
• Losses: Converting electricity into hydrogen and back loses a large share of the energy. Where electricity can be used directly, for example in battery cars or heat pumps, that is usually more efficient.
• Key uses: Hydrogen is considered most useful where electricity is hard to use directly: in steelmaking, the chemical industry, for fertiliser and possibly for ships and aircraft.
• Long-term storage: Surplus green electricity from sunny and windy periods could be stored as hydrogen for weeks or months.
• Safety: Hydrogen is highly flammable but disperses upwards very quickly. Tanks and pipes must be especially tight and well monitored.
• Connections: Energy storage and chemistry come together here (stromspeicher-und-eigenverbrauch, chemische-reaktionen-grundlagen, periodensystem-grundlagen).