Fuel cells and electrolysers in future energy systems - VBN

4 The nature of fuel cells
In this chapter, the status and future potential of five different types of fuel cells are pre‐
sented. This chapter is based on “The nature of fuel cells” [1] included in appendix I.
In this review, focus is on fuel cell systems for CHP production in future energy systems;
however, the review also includes aspects of other applications of fuel cells. The operation
principles as well as the characteristics and applications of the different types of fuel cells
are considered. High temperature polymer exchange fuel cells (HT‐PEMFCs) seem to have
the best potential in terms of transport and micro‐CHP, while SOFCs have the potential for
replacing existing technologies in distributed local or central CHP plants. Significant chal‐
lenges have to be overcome, before broad commercial use of fuel cells in future energy sys‐
tems can be expected.
4.1 Introduction
In most countries, the energy supply consists of a small percentage of intermittent re‐
sources as well as combustion technologies in vehicles, power plants and CHP plants. The
perspective in replacing conventional technologies with more efficient fuel cells is depend‐
ent on the characteristics of the different fuel cell types available.
Fuel cells generally consist of the cell, in which an electrochemical reaction takes place; the
stacks, in which the cells are combined to the desired power capacity; and the balance of
the plant, which comprises systems for handling fuel, heat, electric power conditioning, and
other systems required around the cell.
Fuel cells are comparable to batteries, except from the fact that they are not limited by the
amount of energy stored in the cell itself. In these cells, chemical energy is converted di‐
rectly into electricity. This provides higher efficiencies than in traditional technologies, in
which the energy content in fuels is converted into thermal energy, then mechanical energy
and finally electricity. The higher efficiencies also imply a significant reduction of emissions.
Although certain types of fuel cells are mainly considered for mobile and others for station‐
ary use, this is not determined yet. The characteristics of the fuel cell types, however, make
certain potential applications more probable than others. Fuel cell types are named after
their electrolyte, which also determines their operating temperature. In Table 1, the main
characteristics of the five main types of fuel cells are listed.
Please note the fact that such comparisons are subject to the different preconditions and
characteristics of the different fuel cells. Thus, these preconditions should be taken into
account when comparing e.g. efficiencies. In Mathiesen and Nielsen (2008) [1], the data
sheets for different fuel cell systems are presented.
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