Energy

Production from water

Hydrogen can be produced from water by splitting the molecule into its components (hydrogen and oxygen) through different processes, among which the most consolidated is electrolysis.
Electrolysis is the scission of water through the use of electric energy according to the following reaction: water plus electric energy equal hydrogen plus oxygen.
Electric energy could be produced in plants that exploit renewable sources. In order to obtain a cubic metre of hydrogen in the gaseous state 4-5 kW/h of electric energy are needed.
The main problem is still the cost. It is true that water electrolysis produce pure hydrogen, but the price will be acceptable only when technological innovations allow to produced electric energy from renewable sources at extremely low costs.
An experimental system to separate water is thermo-electrolysis: by applying the electrolysis on high temperature vapour (900/100°C) the result is hydrogen with 2.4 kW per cubic metre. However electrolysis efficiency is directly proportional to temperature: at 15-20°C, in order to separate water, 83% of the reaction energy must be electric energy, while at 1000 °C the percentage is reduced to 65%. High temperature vapour could be obtained from geothermal fumaroles or concentration thermo-solar power plants.
Other experimental processes are:  

• photo-conversion that separates water by using biological organisms or synthetic materials 
• photo-electrochemical techniques that generate electric power by using catalysing systems or semi-conductors that, associated to the sunlight, are be able to separate water molecules.
• thermolysis that separates water molecules by using heat. It requires very high temperatures, i.e. around 3000°C (with many problems deriving from such temperatures)