Page 288 - Alternative Energy Systems in Building Design

262 FUEL CELL TECHNOLOGY

delivered to end users. According to the DOE, present U.S. use of hydrogen for hydro-
cracking is roughly 4 million metric tons per year. It is also estimated that 38 million
metric tons per year of hydrogen production would be sufficient to convert enough
domestic coal to liquid fuels to significantly reduce U.S. dependence on foreign oil
imports. However, it should be noted that the coal liquefaction process presents sig-
nificantly more emissions of carbon dioxide than does the current system of burning
petroleum.
Based on 2006 statistics, 48 percent of global hydrogen production was derived
from natural gas, 30 percent from oil, and 18 percent from coal. Water electrolysis, as
discussed earlier, accounted for only 4 percent of the total.

PHOSPHORIC ACID FUEL CELLS
This type of fuel cell uses phosphoric acid compounds as the catalytic conversion mem-
brane. Phosphoric acid fuel cells generate electricity with a conversion efficiency of about
40 percent. The large amount of heat produced by the process (about 400°F) is used for
steam production, which, through cogeneration, is used to produce additional electricity.
To date, hundreds of commercially available phosphoric acid fuel cells (PAFCs) have
been installed throughout the world and are used by power utility companies, airport
terminals, hotels, hospitals, municipal waste dumps, offices, and other such buildings.
Recently, many automotive manufacturers, such as Toyota, DaimlerChrysler, and others,
have used PEMFCs in their hybrid automobiles (using a combination of a fuel cell and
an internal combustion engine) and are racing to produce more efficient production
systems that ultimately will be used in transportation technology as the principal means
of power generation.

MOLTEN CARBONATE FUEL CELLS

Fuel cells employing this electroconversion use molten carbonate as a catalyst to sepa-
rate the hydrogen electrons from the molecule. The cells operate at a very high temper-
ature (1200°F) and are considered to be very efficient. Heat generated as a by-product
of fuel cell operation is recovered and used in heat exchangers that provide heated water
for use in many commercial and industrial applications, substantially augmenting over-
all operational efficiency.
Molten carbonate fuel cells (MCFCs) operate on hydrogen, carbon monoxide, natural
gas, propane, landfill gases, marine diesel fuels, and coal gasified products. In Italy and
Japan, multimegawatt MCFCs have been installed successfully and tested as stationary
stand-alone power-generation systems. At present, there are a number of stationary
MCFCs in operation in California, used as base-load electricity and heat energy.

SOLID OXIDE FUEL CELLS
This technology uses a hard ceramic solid oxide material as an electrolytic conversion
catalyst and operates at extremely high temperatures (1800°F). Solid oxide fuel cells
(SOFCs) are cable of producing several hundred kilowatts of power at efficiency near