Fuel cells and electrolysers in future energy systems - VBN

7 Technology Description
7.1 Introduction
CHP plants have proven to have good and efficient abilities to integrate fluctuating energy
sources. The expansion of CHP systems is important to increase the overall fuel efficiencies in
both energy systems with high amounts of fluctuating wind power and in systems with low
amounts of fluctuating wind power. The efficiencies of the CHP plants themselves can be
improved significantly by means of fuel cell technologies. These can improve the overall fuel
efficiency further and reduce the environmental impacts connected to the production of energy.
In these cells chemical energy is converted directly into electricity instead of traditional
technologies where the energy content in fuels is converted into thermal energy, then
mechanical energy and then electricity.
Although several types of fuel cells are currently being developed and demonstrated, for large
stationary appliances or micro-CHP one kind of fuel cell is especially promising because of its
high efficiency and fuel flexibility, solid oxide fuel cells (SOFC). Other kinds for fuel cells are
more suitable for mobile or smaller distributed generation. The most promising fuel cells within
these applications are proton exchange membrane fuel cells (PEMFC), because of their rather
simple design and quick start-up.
For the task of integration of wind
power and other fluctuating renewable
energy sources the different fuel cells
have different capabilities. Fuel cells,
like other technologies, cannot be seen
as an isolated improvement, but has to
be assessed within the energy system
surrounding it. In this section the
advantages and disadvantages of using
fuel cells for balancing fluctuating
renewable energy sources is assessed.
7.2 Fuel cell characteristics,
efficiencies and applications
All fuel cells have in common that the
core consists of a cell with an electrolyte
and two electrodes, the anode and the
cathode. In Figure 1-1 the reactions in
different fuel cells is illustrated. In the
cell the hydrogen and oxygen is
Figure 7-1: Schematics of different fuel cell types.
converted to water producing electricity
and heat. The conversion of hydrogen takes places in a chemical process, where the catalytic
active electrodes convert hydrogen into positive ions and oxygen into negative ions. The precise
reactions depend on the type of fuel cell. The ions cross the electrolyte and form water and
possibly CO2 depending on the fuel and fuel cell. Only protons can cross the electrolyte creating
a voltage difference between the anode and the cathode in the cell. This voltage difference can
create the current in a fuel cell system. [1]
Long term perspective for balancing fluctuating renewable energy sources:
Fuel cells for balancing fluctuating renewable energy sources
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