Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 775
Page 775
Appendix H
A Solar Hydrogen System
To convert solar radiation to electricity, one makes use of
photovoltaic materials akin to the solar cells used to energize
battery-free pocket calculators. However, as an energy source,
solar radiation is relatively dilute. Impressive amounts of
(desert) land area would have to be devoted to this use in order to
replace fossil fuel supplies. For example, it is estimated that the
complete replacement of such supplies in the United States would
require total collector fields on the order of 50,000 square miles,
about 1 percent of the total U.S. land area (Ogden and Williams,
1989). On the other hand, obtaining the same power from biomass
grown on energy farms would require more than 10 times that area.
Even obtaining synfuels from coal would, in 14 years, use up the
24,000 square miles of land thought to be available for strip
mining.
Once the solar energy system generates electricity, the
electricity can be used to generate hydrogen. Hydrogen is a
transportable, clean-burning fuel that can be used as energy for
vehicles, planes, and many other devices. This appendix describes
the cost-effectiveness of one such system.
Photovoltaic Materials
Prior to 1980 the only commercially available solar cells were
those made of high-grade single-crystal silicon. Fabrication of
these crystals requires large amounts of time, material, and
energy. Much more promising for application to solar power is the
later technology of thin-film amorphous (i.e., noncrystalline)
silicon cells. The films, typically 1 micron (0.0001 cm) thick, are
prepared by deposition from silicon vapor onto a substrate such as
glass, plastic, or stainless steel, a process that lends itself
easily to mass production. A square meter of cell area would
require only 3 g
OCR for page 776
OCR for page 777
OCR for page 778
Representative terms from entire chapter:
solar radiation
Page 776
of silicon, a very abundant element. The efficiency of
conversion of the power in solar radiation to electricity has
increased from 1 percent, for the first cells produced in 1976, to
almost 12 percent for modest-area laboratory modules and almost 14
percent in 1987 for small-area laboratory cells. Higher
efficiencies, estimated at 18 to 20 percent, may be attained in a
few years with multilayer cells, each layer tuned to a different
part of the solar spectrum.
Commercial Photovoltaics
The Alabama Power Company has a 100-kW amorphous-silicon
generating field in operation at present. Efficiencies of currently
available commercial photovoltaics range from 5 to 7 percent.
Present-day manufacturing facilities are typically of modest
capacity, on the order of 1 MW/yr, at a cost of $1.50 to $1.60 per
peak watt. Within a few years, plants of 10-MW capacity per year
may be on line. These plants are expected to produce cells of 6
percent efficiency for about $1.00 per peak watt. A 50-MW power
plant to sell electricity to the Southern California Edison Company
(Chronar Corporation, anticipating a photovoltaic cost of $1.25 per
peak watt) and a 70-MW/yr production plant (ARCO Solar, Inc.) are
in the planning stage. Looking to the end of the 1990s and the
possibility of production levels of many hundreds of megawatts per
year, Ogden and Williams (1989) project that costs could drop to
the range of $0.20 to $0.40 per peak watt, based on reduced outlays
for specialty glass, labor, and depreciation, together with
commercial efficiencies increasing to 12 to 18 percent. Allowing
for electrical wiring losses and for dirt and dust on the modules
would reduce their overall efficiencies by an estimated 15 percent,
that is, to 10.2 to 15.3 percent. Land costs, site preparation,
array wiring, support structures, and other construction represent
additional area-related costs that would come to about $50/m2 with present technology, but economies
of scale might bring these down to $33/m2.
On the other hand, these figures are pertinent for the U.S.
Southwest, and supplying power to other parts of the country means
finding means other than electric power lines for energy transport.
Also note that these costs are much lower than that used in the
Mitigation Panel's analysis as described in Appendix J. Rather than
using projections of cost, the panel made a deliberate decision to
use only current cost in estimating the cost-effectiveness of
different energy options.
Hydrogen Costs
The cost for the electrolytic production of hydrogen depends on
the capital cost of the electrolyzer and the cost of the DC
electricity to run it. There
Page 777
is little economy of scale beyond a hydrogen production rate of
2 MW. Similarly, the scale economies for photovoltaic power
disappear beyond levels of 5 to 10 MW. The hydrogen production
units could then be highly modularized, with typical unit
capacities of 5 to 10 MW and per-unit capital costs of $4 million
to $12 million, depending on photovoltaic module costs. Projected
costs for solar hydrogen produced in the Southwest would range from
$31.80/GJ (equivalent to $3.88 per gallon of gasoline) with 6
percent efficiency for the photovoltaic module producing DC
electricity at $0.089/kWh (1990) to approximately half those costs
by 1995 and to $9.10/GJ ($1.11 per gallon of gasoline equivalent)
based on 18 percent module efficiency for the year 2000.
Compression to 70 atmospheres, for transport through a 1000-mile
pipeline, would add another $0.16 to $0.20 to the cost per gallon
of gasoline equivalent.
Phasing In
One of the very attractive features about a solar hydrogen power
economy is that it lends itself to a gradual phase-in. Even today,
photovoltaic power is very economical for specialized purposes
including corrosion protection, spacecraft, navigation buoys, and
small remote water pumps or electric power sources. Installations
for supplying peak-load daytime power to utilities are marginally
economic at the present time. Daytime power for residential use
would be economic at solar module costs of $0.70 to $1.50 per peak
watt.
Hydrogen-powered transport, although feasible today for
lightweight vehicles with modest ranges, would benefit greatly from
improvements in the technology for hydrogen storage. One
anticipates that hydrogen-powered transportation would be
economical first for fleet vehicles and, as such, could be tested
initially in major cities in the Southwest without recourse to
pipelines for hydrogen transmission.
Summary
Photovoltaic hydrogen power offers a number of advantages. The
energy source is radiation from the sun, the materials involved are
abundantly available, and the burning of hydrogen fuel is—with
the exception of nitrogen oxides—free of polluting or
greenhouse gas emissions, including CO, CO2, volatile organics, SO2, and particulate matter. The basic
technology exists today, and some small-scale applications of solar
power are economical even at the present time. Implementation of
solar hydrogen power on a larger scale would lend itself to gradual
phase-in, and one can expect to see increasingly important
applications become economical as improvements are made in solar
module efficiency and in hydrogen storage technology.
Page 778
Reference
Ogden, J. M., and R. H. Williams. 1989. Solar Hydrogen: Moving
Beyond Fossil Fuels. Washington, D.C.: World Resources
Institute.
