Fuel CellS WORK
A Fuel Cell is an electrochemical device that converts chemical energy
directly into electricity, in contrast to more conventional electric
generation technologies such as natural gas turbines or fossil fueled
boilers. Direct electrochemical conversion is environmentally attractive
because of inherently low emissions, lower carbon intensity, as well
as less noise and vibration because it is a “solid state”
Fuel Cells have been known since the 1800’s, practical development
began in the 1960’s under the impetus of the Gemini and Apollo
space programs. Fuel Cells occupied a key role providing on board
power and environmental support due to their high energy density to
provide both heat and power, and because their by-product water was
needed for drinking.
Fuel Cells have been in continuous development since the mid-1960’s
incorporating substantial governmental and private industry funding.
The major developers today have focused on four distinct technologies.
The following chart outlines these technologies and the developers
active in each category.
FuelCell Energy Corp.
Rolls Royce Fuel Cells
Fuel Cell CONFIGURATION
a practical point of view, a Fuel Cell is much like a battery with
one important difference. A battery essentially has a fixed amount
of fuel and runs down when the chemical energy stored in it is consumed.
In contrast, a Fuel Cell has its energy continually replenished and,
thus, will continue to generate power as long as fuel is supplied.
a battery, as shown in Figure 1, hydrogen fuel is continuously supplied
to the cell’s negative electrode called the anode. Concurrently,
oxygen from ambient air is continuously supplied to the cathode or
positive electrode. Like a battery, a Fuel Cell consists of two conductive
plates separated by an insulating barrier containing an electrolyte.
The reaction of hydrogen at the fuel anode is:
—› 2H+ + 2e–
and of oxygen at the cathode, air side:
1/2 O2 + 2H+ + 2e– —› H2O
the electrolyte is actually an electrical insulator, the electrons
are forced to travel in an external circuit and thereby produce electric
power. In contrast, the hydrogen ions travel through the electrolyte
to recombine with the electrons and oxygen to produce water vapor.
encourage reasonable rates and efficiency, a highly dispersed platinum
catalyst “ink” is printed on the anode and cathode layers.
The electrolyte, considered a relatively mild material from a chemical
viewpoint, is contained in “blotter like” separators inside
POWER SECTION of a practical Fuel Cell, shown in the insert to Figure
1, needs to generate electric power at reasonable voltage and current
outputs. The production of 1400 amps at 155 volts DC requires an assembly
of 256 cells.
various cell stacks operates from 65°C to over 800°C thermal
management systems within the power plant provides a means: to heat
the unit to operating temperature during startup, to extract heat
during operation, and to provide a thermal source for Combines Heat
and Power HP (CHP) applications.
temperature Fuel Cell technologies typically use an internal reforming
process where the source fuel is introduced directly to the anode
plate. Lower temperature Fuel Cells rely upon an integrated fuel processor
that converts the source fuel into a hydrogen rich reformate needed
by the cell stack.
cell stack produces variable voltage direct current due to its battery-like
characteristic of lower voltage at higher current draws. The POWER
CONDITIONER section, shown in the inset of Figure 1, converts this
variable DC from the cell stack into a very high quality AC electricity
for customer and/or grid use. Also integrated in the Power Conditioner
are computerized controls and protective interlocks to assure that
the power plant operates smoothly during any condition and properly
interfaces with the site’s electrical network during any abnormalities
caused by customer or grid events.
upon the Fuel Cell technology incorporated into a power plant, the
process converts from 30 to 49 percent of the fuel’s energy
to electricity for customer or grid use. Also, between 30 and 40 percent
of the fuel input can be recovered as useful thermal energy for site
use, such as for water heating, space heating, and even air conditioning.
Fuel Cell power plant is self contained, capable of fully automatic
startup and operation, and of maintaining an appropriate grid/customer
interface under all conditions. Required Quarterly Maintenance can
actually be done while the unit is operating. While the cell stack
is an important part, it becomes just one of a number of other system
components that operate together in a fully integrated, unattended
Indeed, a fully operational and automatic Fuel Cell power plant is
an extremely impressive mix of chemical, mechanical, electrical, control,
computer, and manufacturing engineering. In fact, if an example were
to be selected to epitomize a leading edge state of multi-disciplined
engineering, a Fuel Cell power plant would be one of the best examples