Efficiency of conversion chain and choice of hydrogen generation

The efficiency of the hydrogen motor is only about 25 %.

The efficiency of hydrogen storage and transport is 95%.

The efficiency of the total conversion chain including fuel generation and transport strongly depends on the efficiency of the hydrogen generation process.

The following table gives the efficiencies for different ways of hydrogen generation and the corresponding total efficiency:

Source: data from: Althammer, Hattensperger 1998.

These values show that direct conversion from fossil sources is much more efficient than conversion via power generation and electrolysis.

CO₂ emissions

As far as Greenhouse gases are concerned, the best option is electrolysis using power from renewable sources (water, wind, nuclear) which produces only minor quantities of CO₂ during transport etc.

Hydrogen combustion

As far as emissions are concerned, H2 is the ideal fuel. Even without after-treatment, there are only some minor emissions from lubricant combustion (HC 0,04 g/kWh; PM<0,05g/kWh), and NOx (0,4 g/kWh).

Resource saving

Apart from environmental impact, the long-term availability of the resources used has to be taken into account. Since hydrogen is a means for storing energy rather than an energy source, its advantage does not lie in unlimited availability but in offering a technology, which is compatible with any energy source (fossil or renewable).