In the low power range, from a few
milliwatts to some hundred
watts, fuel cells are potential substitutes for today’s rechargeable
batteries. The portable business has been one of the fastest-growing markets
last decades. Lap-tops,mobile
phones, handheld cameras and other small electrical devices are sold in
millions each year.
PEM fuel cell system integrated into a lap-top, Fraunhofer
DMFC Battery charger for mobile phones, Mechanical
charger for lap-tops, Smart Fuel Cell.
addition to dimensional factors like size and weight, properties such as
operating, response and start-up time are the most important characteristics
portable devices. The integrated power source also has to have a suitably low
operating temperature, so the PEMFC and the DMFC are the only two types which are
to batteries, the separation of the converter and the fuel tank in fuel cell
systems results in more freedom during the design phase. The size of the fuel cell itself
output while the amount of fuel in the tank limits the operating time (or in
other words maximum energy). For
batteries, both power and energy are closely connected to the geometric
design. A lap-top
uses a minimum of 20 W and can normally
be operated for 2-3 hours, while mobile phones only need 2-5 W and have a standby time of
at most 10 days. Fuel cells have a higher theoretical energy density
than today's batteries, and in contrast to the relatively long recharging time for batteries, fuel cells are “recharged” by refilling the
some time of operation, the capacity of rechargeable batteries decreases due
to the many charging cycles. More research
has to be done to confirm this, but fuel cells potentially have a much longer
lifetime. Due to the separation of the fuel converter and the tank, self-discharging
is also not a problem. Both PEMFC and
DMFC are considered to be promising for portable applications.
Their advantage compared to other fuel cells is the high power output at low operating temperatures.
The PEMFC offers the highest power density of the fuel cell stack, but is
still limited in respect of storage of hydrogen. Metal hydrides, which are
mostly used, suffer from high weight as the content of hydrogen is only some
weight-percent. Liquid methanol has a very high energy density and is also easy to store.
However, the DMFC has a much lower power density than
the PEMFC and usually has to operate with diluted methanol (methanol and
water mixture). Due to the
liquid fuel, the DMFC system is simpler than the PEMFC. The choice of fuel cell
type depends on the application and operating conditions.
Camcorder PEM fuel cell system, Fraunhofer
PEMFC for lap-top with methanol
DMFC docking station for
Fuel Cell and Medion.
development in the portable business is still growing strongly, and more
features are added to the applications all the time. This of
course increases the demands on the power source. Forecasts indicate that today's
battery technology no longer will be able to keep up with the power
cells are likely to enter the portable market, but there are still some problems that
have to be solved. Most of the early prototypes were PEMFC, which have
experienced problems with heat and water management. In the last couple of
years, there has been more focus on DMFC. Before any of the fuel cell systems
are preferred to batteries, improvements must be made concerning size,
water, carbon dioxide (for DMFC) and heat management,
operating stability and of course costs.
Home office fuel cell power box,
PEMFC for professional cameras, Fraunhofer ISE and
portable electronics companies are involved in fuel cell research and many
have presented some results or a complete prototype. In addition, there are several companies and research
institutes working on fuel cells in the low power range. There are already
many companies that have passed their first announced date for releasing fuel cell
product. At the moment, a more realistic forecast is that the first fuel cell powered portable applications
will become available in