POWER April 2021 - 35

FUEL CELLS
2. A pilot fuel cell project is shown here.
Fuel cell systems can be easily scaled up by
adding more modules. Courtesy: Rolls-Royce
Power Systems
pass from anode to cathode. The water
content of the membrane required for
this ion conduction is responsible for limiting
the operating temperature to a maximum
of 100C. The amount of precious
metal (such as platinum) required for the
catalyst has been steadily reduced in recent
years. This has already led to a significant
reduction in costs and remains
the focus of development efforts.
For Rolls-Royce Power Systems applications,
the PEM fuel cell is ideal thanks
to the high power density, high scalability,
modular design capability, and resultant
flexibility. Fuel cells can, for example, be
built directly into battery-powered or electrified
energy systems. The cell achieves
high electrical efficiency (about 50%) and
high current density, and is also very safe
to use. This makes it suitable not just as
a source for stationary power-say in the
form of an emergency generator or an uninterruptible
power supply-but also ticks
all the boxes for mobile use aboard ships.
In order to increase the power density
even further, today's fuel cell systems
sometimes feature air compressors or
even electric turbochargers. As with internal
combustion engines, the compressors
or turbochargers pump air into the air system
at a pressure of 2 bar to 3 bar. Several
individual fuel cells can be connected in
series to form a stack, thus increasing the
voltage. To achieve more performance,
the stacks can also be connected in parallel.
This increases the amount of current
generated to multiples of that achieved by
serial connection.
In developing and applying fuel cell
technology, Rolls-Royce Power Systems
draws on in-depth expertise and years
of experience (Figure 2). Between 1999
and 2011, 26 high-temperature fuel cell
systems-molten carbonate fuel
cells
(MCFCs)-were installed and successfully
operated in various areas of application.
The combination of electricity
and pressurized steam is used in a wide
range of processes in industry and in
April 2021 | POWER
the health sector. The systems have
run an average of about 22,000 operating
hours, and all performance data and
empirical values have been recorded and
analyzed. While market conditions and
the general framework at that time did
not support full production, all lights are
now green for introducing PEM fuel cells
into mass-market settings as an alternative
source of drive power.
Fuel Cell Applications
Their characteristic features mean PEM
fuel cells are suited to various applications
currently powered by combustion
engines. Among other things, fuel cells
could play a key role in zero-carbon data
center, demand response, and marine
propulsion systems.
Data Centers. Data centers are part of
safety-critical infrastructure worldwide, including
in hospitals, airports, and telecommunications
centers. Many data centers
use diesel gensets for emergency power.
The combustion of fossil fuel (diesel) inevitably
results in exhaust gas emissions. If
fuel cells were used for the backup power
supply, the only things given off are heat
and humid spent air. The fuel cell system
has no moving parts, which minimizes mechanical
maintenance. Fuel cells are also
more efficient than engine-based backup
systems. A further advantage is that fuel
cell systems can be scaled with ease. More
modules mean more power, and fuel cell
systems can easily be added later and grow
with the data center.
Demand Response. A high degree of
flexibility is required for the increasing
use of renewable energy sources. When
surplus wind or solar power exists, rather
than curtailing production, the electricity
could be used to produce hydrogen
through electrolysis, which could be
stored. When needed, this energy could
be made available again at short notice
in the form of electricity with the aid of
a fuel cell system. This load management
or " demand response " activity using
smart grids could be one of the key
factors for converting energy systems to
sustainable methods of production.
A demand response solution using
PEM fuel cells in combination with batteries
is ideal for stabilizing grids and
cushioning power peaks. Consumers
can use the system to cover their requirements
even when generation output
from renewables is low. The PEM
fuel cell generator offers the ability to be
connected to locally operating systems
or to microgrids.
Marine Propulsion. Alternative propulwww.powermag.com
sion
systems are attractive and necessary
not just for cars and trucks, but also for
ships. Shipping accounts for 2% to 3% of
global CO2
emissions, and this proportion
is set to rise significantly by 2050 with the
increase in global trade. Onboard fuel cell
systems combine numerous benefits. In
addition to their sustainability and environmental
friendliness, fuel-cell-based marine
propulsion systems are gaining favor due
to their high level of passenger comfort
and high modularity. They are quiet, they
produce no smelly exhaust gases, and
they are virtually vibration-free. This emission-free
propulsion system enables vessels
to be used in sea, lake, and river areas,
where some other systems are frowned
upon due to adverse environmental impacts.
A
fuel cell marine propulsion system
is made up of several parts. At the heart
of the system is the fuel cell, which
converts hydrogen into electricity. This
power is fed via the onboard electrical
distribution system to large consumers,
such as the electric motors driving
propellers and winches, and also to the
smaller " domestic " consumers. The onboard
distribution system also features a
power storage device, typically a lithiumion
battery, to store power temporarily.
This battery permits a time lag between
generation and consumption of power,
thus opening up the possibility of timing
the operation of individual components
for maximum efficiency. This calls for a
smart power management system for
controlling individual components.
Fuel Cell Outlook
Fuel cell technology is increasingly gaining
traction in view of pollutant emissions
and climate protection requirements.
When it comes to making the best use of
renewables for low-emission, zero-carbon
production of electricity and heat, the fuel
cell is the front-runner in terms of efficiency
compared with other systems, making
it an attractive proposition for a variety of
applications. Even today, fuel cells can
be used to ensure efficient energy supply
within stationary standalone facilities,
as well as their mobile use powering land
vehicles and ships. The big advantage
of hydrogen-powered fuel cells is that
CO2
emissions, whether from vessels or
stationary power plants, reduce to zero
where green hydrogen is used. ■
-Michele Bozzolo, Georg Fink, and
Benjamin Oszfolk are fuel cell system
engineers, and Philippe Gorse, PhD is
head of Fuel Cell Technologies, all with the
Power Systems division of Rolls-Royce.
35
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POWER April 2021

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