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Energy efficiency

Groundwater management


Electrolysis: the next phase of the green transition

Hydrogen and electrolysis are not new inventions. Hydrogen dates back 13 billion years to the Big Bang and has been used in industry for decades in the post-industrial world.
18 September 2023

An electrolyser is a device that uses electricity to split water into oxygen gas and hydrogen gas. To keep the gases separate and prevent mixing, there is a special membrane in between called an electrolyte. It helps to balance the charges and keeps the gases from getting mixed up or contaminated. When using renewable energy for electrolysis the hydrogen produced is called green hydrogen.

Types of electrolysis:

  1. Alkaline: a liquid electrolyte splits water with an electrical current. Free from costly
    metal materials and configurable in large stacks, it provides long-term stability and
  2. Solid Oxide: a ceramic electrolyte transfers oxygen ions to the anode at high temperatures. While complex, it offers high efficiency and good heat utilisation.
  3. Polymer Electrolyte Membrane (PEM): a solid polymer membrane conducts protons.
    Operating effectively at high current densities and variable power levels within seconds,
    it pairs well with renewable energy.

Old technology given new life

There is nothing new about producing hydrogen from wind power — in Denmark, at least. Back in 1894, the inventor Poul la Cour used electricity from a wind turbine to split water into oxygen and hydrogen gas. The gases were separately collected in tanks, stored in bottles, and used to light buildings, such as the Askov Folk High School.


How green hydrogen can be utilised

While producing green hydrogen through electrolysis is not a new technology, the hydrogen currently used in industrial processes is predominantly fossil-based, being derived from gas and coal. Today’s hydrogen supply accounts for 1.7 percent of the global annual energy consumption and emits 830 million tonnes of CO₂ annually. Only about 1 percent is based on renewable energy. As global renewable energy continues to grow rapidly, the potential for substituting fossil-based hydrogen with green hydrogen represents vast opportunities for emissions reductions.

Green hydrogen can be utilised in many parts of the energy system, either in its pure form or as a building block in further refining processes. As a fuel, green hydrogen is
completely free of harmful emissions; a vehicle fuelled by hydrogen, for example, only emits water vapour.


The importance of water

Water is the basis of electrolysis and presents its own challenges and opportunities. The purity of the water is essential, and this raises questions on how to supply the necessary quantities of sufficiently pure water. As drinking water is a very scarce global resource, Danish efforts to develop suitable solutions for electrolysis focus on purifying wastewater and using groundwater from areas where the water level is problematically high and cannot be used for consumption. In this way, electrolyser plants can contribute to a new water ecosystem which uses low-quality water from other sectors, including wastewater from private households. While technologies within wastewater treatment and water purification already exist in Denmark, the Danish water industry is also working on new technologies to solve these challenges.

Green hydrogen is Danish hydrogen

This case is a part of the white paper “Green hydrogen is Danish hydrogen”. Discover Denmark’s plans to produce green fuels and decarbonise global transport and energy-intensive industries.

Explore the white paper

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