Page 283 - Alternative Energy Systems in Building Design

FUEL CELL APPLICATION 257

previously, is more expensive because it involves the use of an excessive amount of
electricity. For instance, the production of 1 kg of hydrogen requires about 50 kWh of
electricity. In order to accelerate the hydrolysis process, platinum is used as a catalyst
for the electrolytic separation of water into hydrogen and oxygen. As discussed previ-
ously, other means of hydrogen production through hydrolysis involve the use of other
renewable-energy resources such as wind, solar, and geothermal energies.
While hydrogen as an element is abundant on earth and in the universe, in general, the
manufacture of hydrogen does require the consumption of a hydrogen carrier, such as a
fossil fuel or water. Fossil fuel resources, such as methane, produce CO , an air pollutant.
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However, when used as fuel, they produce only pure water as a by-product of oxidation.
BIOLOGIC PRODUCTION FROM ALGAE

Another hydrogen-production method, referred to as biologic production, involves the
use of an algae bioreactor. The process, discovered in 1990, involves depriving the algae
of sulfur, leading them to produce hydrogen (as opposed to the production of oxygen
seen in normal photosynthesis). This process has been further refined to a level at which
the commercial production of hydrogen is now economically viable. The conversion
efficiency of the biohydrogen process generally ranges from about 7 to 10 percent.
In most instances, biohydrogen bioreactors, other than those with algae, also can
use animal feedstock. In this process, bioreactors make use of special bacteria that
feed on hydrocarbons and exhale hydrogen and CO . The CO generally is sequestered
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by several methods, leaving hydrogen gas.
ELECTROLYSIS OF WATER AND ASSOCIATED CHALLENGES
Commercially, the predominant methods of hydrogen production are based on
exothermic chemical reactions of fossil fuels, which provide the required energy for
the chemical conversion of feedstock into hydrogen. In this process, which involves
large-scale hydrolysis, most of the energy required is produced by hydropower or
wind turbines. As mentioned earlier, 50 kWh of electricity is required to manufacture
1 kg of hydrogen, which translates into approximately 9 cents/kWh. Since this process
makes use of literally nonpolluting electric power, despite the inefficiencies of elec-
tricity production and electrolysis, it is in fact the least expensive and safest way to
produce hydrogen fuel.

HIGH-TEMPERATURE ELECTROLYSIS (HTE)

Hydrogen can be generated from energy supplied in the form of high heat, as a by-
product of solar thermal concentrating, and from nuclear and electricity production
technologies. In contrast with low-temperature electrolysis, discussed previously, the
elevation of water to extreme temperatures allows water to convert the extreme heat
energy into chemical energy (hydrogen), which results in 50 percent conversion effi-
ciency. Since most of the energy in the HTE process is supplied in the form of heat,
lesser amounts of energy are required to convert heat to electricity and then to a chemical
reaction. At present, HTE has been demonstrated only in a laboratory environment.