The liquefaction process is very energy intensive and as a consequence it requires a lot of exergy.

Because hydrogen is transported in a liquid form, the liquefaction process is also taken into consideration in this work. When in any of the processes electricity is produced, this electricity is used for the electrolysis process of water to produce hydrogen (and oxygen). The biomass systems are divided into two categories: (a) electricity production through biomass combustion, (b) biomass gasification for the direct production of hydrogen. The solar energy systems that are used are photovoltaic and thermal. The renewable energy sources that have been used are: wind power, solar energy, hydroelectric power, and biomass. This comparison is based on the exergy efficiency of each process. The objective of this work is the comparison of hydrogen (H 2) production processes using various renewable energy sources. Renewable energy sources (RES) could be the feedstock for the two methods previously mentioned. Hydrogen can be produced through methane reforming or through the electrolysis of water with the use of electricity or it can be produced directly by gasification from biomass. The route by which hydrogen is produced is the determining factor for its environmental performance.

Hydrogen is an important energy carrier which could play a very significant role in the reduction of emissions of greenhouse gases.

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