With the term "hydrogen economy" we are referring to the infrastructure necessary to meet the energy needs of the future hydrogen-based society, and it entails the concepts of production, distribution, storage and use.
In addition, if its production is based on renewable energy, the above processes are part of a cycle which is environmentally friendly, the so-called hydrogen cycle.
It is expected that in the future the hydrogen economy will greatly contribute to the exploitation of renewable and environmentally friendly sources of energy and the development of new technologies.
Significant infrastructure changes will have to be made to facilitate the transport and distribution of this new energy.
There are currently several different approaches regarding the form of the grid that is to distribute hydrogen. We will mention two of the basic methods, which have different approaches.
The first approach, with regards to the formation of the grid, is similar to that of today's electrical networks. Many hydrogen generating units, which are capable of producing large amounts of hydrogen, are connected to each other with suitable pipelines.
The network will also include hydrogen distribution control centres.
These centres, in turn, will undertake the task of supplying smaller refuelling stations with hydrogen.
The second approach is a decentralised one, as opposed to the previous approach. Hydrogen, in this case, is produced locally at refuelling centres in quantities sufficient to meet local demand.
A step further is to produce at the exact point of demand, if we are talking about home use. An important advantage of the second approach to the former is the independence it offers. A malfunction at some point on the network will not affect smooth operation in others. Therefore, such a system will continue to function in a satisfactory manner in cases of emergency, such as a natural disaster.
The US, Japan and the European Union (EU) have been involved in a race to develop technologies for the production and use of hydrogen.
Also, countries with potentials as regards to renewable energy have exhibited a vivid interest in hydrogen, aiming at a first stage at de-carbonation of their economies, and in the long-term to export hydrogen to other countries.
Thus, in Norway, a national study was prepared to use hydrogen as an environmentally friendly fuel. Respectively, specific hydrogen production processes are developed by splitting hydrocarbons.
Iceland aims to become an exemplary model of the hydrogen economy, aiming to be fully independent of petrol, by using hydrogen produced from electrolysis using hydroelectric and geothermal energy.
An interesting application currently under development is that of electrolysis devices known as "Power-to-Gas". Hydrogen produced from electrolysis devices, combined with renewable energy sources, is introduced into the natural gas network.
This approach allows for the natural gas pipelines to be used as large "storage tanks", avoiding the construction of new infrastructure.
The quantity of hydrogen introduced depends on the regulations implemented in each country.
This problem can be overcome by the methanisation reaction, where hydrogen and carbon monoxide/carbon dioxide is converted into methane.
Stored hydrogen in the form of gas can be used for heating, transport or even be transformed back into electricity. Power-to-Gas technology is today a promising solution for large-scale renewable energy storage.
Hydrogen offers an opportunity to overcome problems regarding energy supply, climate change and air pollution faced by countries.
The only waste created from producing energy with hydrogen and oxygen is wastewater and heat.
Oxygen is abundant in the atmosphere, while hydrogen can be detached from hydrocarbons, such as natural gas reforming, releasing however significant amounts of carbon dioxide, from water with the electrolysis process, or using solar energy through the thermochemical water disintegration into oxygen and hydrogen.
To this end, the EU is proposing legislative measures and regulations to develop an extensive strategy for the hydrogen economy. It is noted that the EU has been supporting hydrogen research since 1989, with a continuous increase in funding.
Finally, hydrogen can also be used in a completely different manner to produce energy. This is done by nuclear fusion where, at very high temperatures and pressures, hydrogen isotopes give out helium and emit energy.
This energy is transformed into electricity for use on a large scale. The operation of the first experimental nuclear fusion plant is expected in 2025.