Using fuel cells in... renewable energy systems Background

Using fuel cells in...
renewable energy systems
Generating renewable electricity is an important way to reduce carbon dioxide (CO2) emissions and many countries
are installing wind and solar power plants to help meet targets for cutting CO2. One drawback of these energy sources
is their variability: the wind tends to blow intermittently and solar power is only available during the daytime. Hence
renewable power plants either have to be over-engineered to take account of this lower capacity factor, or they
must be supported by spinning reserve power stations, typically fast-response open-cycle gas turbines – which goes
against the environmental aims of the projects.
Ideally, excess renewable energy generated during times of plenty can be stored for use during periods when
sufficient electricity is not available. But storing this energy is a difficult task: batteries and similar technologies
perform well over short timescales, but over periods of weeks or months a different approach is necessary. Energy
storage in the form of hydrogen is one such possibility: excess electricity is fed into an electrolyser to split water
into its constituent parts, oxygen and hydrogen. The hydrogen is then used in fuel cells to produce electricity when
needed, releasing the stored energy back to the grid.
This process allows excess energy produced in wind farms and
solar power plants to be stored and used, instead of wasted.
Increasing the utilisation of renewable power plants helps
to maximise the return on investment and lower the cost of
electricity. The need for spinning reserve is also reduced as
these facilities now have stored energy which can be readily
converted back to electricity when required. Hydrogen can also
be produced in a number of ways from biomass, allowing for
the integration of this energy source in a complete renewable
energy system. The most efficient way to convert hydrogen
back to electricity is via fuel cells. This is not confined to grid
electricity: in certain cases the stored hydrogen can be diverted
for sale as fuel to fuel cell electric vehicle owners.
Technology Used In This Application Today
Fuel cells and electrolysers are complementary technologies. An electrolyser cell is much like a fuel cell run in
reverse, using electricity instead of producing it. Commercial electrolyser technology is widely available and includes
both proton exchange membrane and alkaline electrolysers.
As pure hydrogen is the fuel produced in this scenario, any type of fuel cell can be used to convert this into electricity
in stationary power generation. For fuel cell vehicles, the technology of choice is proton exchange membrane fuel
cells (PEMFC).
Wind-to-Hydrogen Hybrid Power Plant
Berlin Brandenberg Airport, scheduled to open in late
summer 2012, is to run a fleet of fuel cell vehicles
using hydrogen produced in a nearby hybrid power
plant. This plant converts excess wind energy into
hydrogen and stores it for later use.
MYRTE (a French acronym for Renewable Hydrogen
Mission for Integration into the Electric Grid) is located
on the French island of Corsica, in the Mediterranean
Sea, and combines solar power with electrolysers,
hydrogen storage and fuel cells.
The project is a partnership between CEA (the French
Nuclear and Alternative Energies Commission), energy
company AREVA and the University of Corsica. MYRTE
contains a 560 kW photovoltaic power plant which has
been connected to the Corsican electricity grid since
December 2011. The system can provide electricity
during the day but, using the electrolysers and AREVA’s
hydrogen energy storage system, excess electricity can
be stored and returned when required, for example
during the night, using fuel cells.
The aim of this initial project is to prove the concept,
but there are plans to develop the system further
with a second phase planned for 2013. This will see
the inclusion of AREVA’s Greenergy Box, an integrated
hydrogen energy system housing electrolysers, fuel
cells, fuel storage and heat management systems
inside a standard container.
The wind–hydrogen hybrid power plant, located in
Prenzlau, Germany and opened on 25 October 2011,
is primarily a 6 MW wind power plant. ENERTRAG
AG has partnered with DB Energie GmbH, Vattenfall
and TOTAL Germany on the project with DB Energie
seeking to use the electricity to contribute to
decarbonising the railway network. The rail network
needs a predictable and reliable source of power and
it is encouraging to see DB Energie recognising the
solution a combination of hydrogen and renewables
can offer. During periods of excess wind, the three
wind energy plants (each of 2 MW nominal power)
generate carbon dioxide-free hydrogen through a
series of electrolysers. This stored energy, effectively
acting as renewable base-load energy, can be used in
a number of ways:
• The hydrogen can be mixed with biogas and fed
into cogeneration plants which produce electricity
and heat. The electricity can then be fed back
into the grid at times when little or no wind is
available; the heat is fed into a district heating
network, increasing the overall efficiency of the
hybrid power plant.
• The hydrogen is also used as a fuel by TOTAL
hydrogen refuelling stations in Berlin and Hamburg
which support fleets of fuel cell vehicles.
Images: Corsica (University of Illinois); Angela Merkel lays the first stone at the Hybrid Power Plant (Bundesregierung); representation of Berlin Brandenburg airport
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MAY 2012