Page 289 - Alternative Energy Systems in Building Design

HYDROGEN ECONOMY 263

or exceeding 60 percent. A special solid oxide fuel cell known as a tubular solid oxide
fuel cell uses tubes of compressed solid oxide disks, resembling metal can tops, which
are stacked up to 100 cm high.
Another experimental fuel cell technology, referred to as a planar solid oxide fuel
cell (PSOFC), has promising potential for producing small-scale power generators at
the 3- to 5-kW scale. They are intended for stationary power generation, for use as
power supplies in remote areas, and as auxiliary power for use in vehicles. SOFC appli-
cation at present is not considered to be suitable for use as a prime power source.
Recently, SOFC technologies have made significant progress in product development
and are being manufactured commercially by a number of companies. At present, the
main obstacle to the use of this technology is the high heat production resulting from the
chemical reaction of hydrogen and oxygen, which must be mitigated. The fuel cell,
owing to significant power-production capacity and high efficiency, will, in the near
future, be used in motor vehicles and as a source for electric power generation.

ALKALINE FUEL CELLS

Alkaline fuel cells (AFCs) use potassium hydroxide in the electrochemical catalytic
conversion process and have a conversion efficiency of about 70 percent. In the last
few decades, NASA has used alkaline cells to power space missions.
Until recently, owing to the high cost of production, AFCs were not available com-
mercially. However, improvements and cost reductions in fuel cell production have
created a new opportunity for commercializing this technology.

DIRECT METHANOL FUEL CELLS

This type of fuel cell uses a proton-exchange electroconversion process similar to the
one discussed earlier and uses a polymer membrane as the electrolyte. However, with-
out a re-former mechanism, the anode acts as a catalyst that separates the hydrogen
from the liquid. It should be noted that until recently, owing to the high cost of
production, AFCs have not been available commercially. However, improvements
and cost reduction in fuel cell production have created a new opportunity to commer-
cialize this technology. Direct methanol fuel cells (DMFCs) operate at a relatively low
temperature (120–200°F) and have about 40 percent efficiency. At more elevated
temperatures, these fuel cells operate at higher conversion efficiency.
In the United States, the future commercialization of DMFC technology will de-
pend on genetically modified corn, which can be fermented at low temperatures. Such
a breakthrough could indeed make the technology a viable source of electrical energy
production, which could contribute significantly to the reduction of air pollution and
minimize the expensive import of crude oil.

REGENERATIVE FUEL CELLS
This technology, which is still at its early research and development stage, is a closed-
loop electroconversion system that uses solar-powered electrolysis to separate hydrogen