Hydrogen

Hydrogen is a colorless, odorless, light gas, and it has a very high specific energy (about 3 times higher than methane). Hydrogen does not exist in nature in a free state, but it must be extracted from other compounds (typically water and fossil sources such as methane), even if many biochemical production processes are being investigated. Hydrogen can be used (in a combustion engine, in a boiler, in a welding torch) as any other gas with a good calorific value, but its more useful application – from the energetic point of view – is the use in fuel cells for DC electricity generation, with water and heat as its only waste products. The storage of hydrogen (which is the lightest element in the periodic table of elements) is a partially overcome challenge, but at the price of high investment costs resulting from the use of advanced material or of very heavy tanks. Hydrogen can also be liquefied and transported in this form, in order to maximize the amount of storable energy per unit volume; however, the liquefaction process is expensive because hydrogen liquefaction temperature is equal to 20 K only.

The multiplicity of technological solutions that can lead to hydrogen production and to the transformation of hydrogen itself into other forms of energy (in fact, hydrogen is an energy vector, not an energy source) makes it extremely interesting to analyze and develop integrated energy systems based on the use of hydrogen as a temporary energy storage medium.