15.04.2021 | Storing renewable energies

Hydrogen basics

The expansion of renewable energies is one of Axpo's strategic pillars. In order to make electricity from renewable sources such as photovoltaics continuously available, technologies like battery storage and hydrogen are important. Hydrogen? Below some facts on the subject.

Green hydrogen, which is produced with power from renewable energy sources, is considered a key technology for the energy turnaround and de-carbonisation in view of Switzerland's climate neutrality targets. Axpo intends to develop know-how in this area and realise leading-edge projects. 

Hydrogen is not necessarily green because as an energy source it is – like electrical energy – not primary energy, and has to be generated using primary energy. In 2020, 96% of the hydrogen used was produced based on fossil energy sources (see box below).

Lighter than air

Hydrogen (H) is the most abundant element in the universe – it is a component of water (H2O) and nearly all organic compounds.

It is the chemical element with the lowest atomic mass. Atomic hydrogen H does not occur under normal atmospheric conditions. On Earth it exists in molecular form: as H2, an invisible, colourless, odourless gas (more here). Hydrogen is 14 times lighter than air and can be stored and transported. Pro unit of mass, hydrogen holds a great deal of energy (calorific value), for example 3 times more than petrol and 7 times more than wood pellets.

Hydrogen is produced by splitting water( H2O) into the elements oxygen (O) and hydrogen (H2). However, lots of energy is need to spilt the molecule H2. Processes like steam reforming, coal and biomass gasification are used.  When the process takes place with the help of electric current, we call it electrolysis.

After splitting water into hydrogen and oxygen, the hydrogen (H2) can be stored or transformed into methane (CH4) with CO2. Methane is similar to natural gas and can be fed into the existing natural gas grid.

Conversion to electricity

Conversion of hydrogen into electricity can take place by means of a thermochemical process or a fuel cell. The fuel cell is an electro-chemical device for the direct conversion of the fuel cell's chemical energy into electricity.

Similar to batteries, fuel cells produce direct current at low voltages. A battery consumes a chemical substance that is contained in the cell unit. In contrast, fuel is continuously directed to the cell unit in fuel cells, similar to gasoline or diesel fuel in a combustion engine.


In principle, hydrogen is suitable as a direct energy carrier and as a raw material for carbon-neutral applications, in connection with the sectors heat, mobility, power and industry (sector coupling), as well as a medium for storage and transport.

Particularly in the fossil fuel dominated area of mobility (commercial vehicles, public transport, shipping and aviation), hydrogen is seen as an alternative fuel and a useful addition to e-mobility in the medium and long term. First steps with hydrogen-powered passenger cars are underway, for example at Hyundai or Toyota.

In addition, green hydrogen can make a significant contribution to the de-carbonisation of energy intensive industries such as steel, and also to the achievement of climate protection targets.

Hydrogen categories 

Green hydrogen is produced by means of electrolysis using only power from renewable energies. Independent of the chosen electrolysis technology, the production of hydrogen is CO2-free since 100% of the electricity used comes from renewable sources.

Grey hydrogen is produced from fossil fuels. As a rule, natural gas is heated and converted to hydrogen and CO2 (steam reforming). The CO2 is then released into the atmosphere and intensifies the global greenhouse effect: The production of one tonne of hydrogen results in about 10 tonnes of CO2.

Blue hydrogen is grey hydrogen that captures and stores its CO2 (carbon capture and storage CCS) during the production process. The CO2 generated in hydrogen production does not enter the atmosphere and production can be considered CO2-neutral.

Turquoise hydrogen is hydrogen that is produced through the thermal decomposition of methane (methane pyrolysis). Solid carbon is produced instead of CO2. In order to be CO2-neutral, the heat supply to the high temperature reactor must come from renewable energy sources and the carbon must be permanently bonded.

Yellow or pink hydrogen is produced with electricity from nuclear power.

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