A solution to the energy problem is suggested through the technology of photovoltaic electrolysis of water to generate hydrogen. Efficient solar devices are discussed in relation to available solar energy, and photovoltaic energy cost. It is concluded that photovoltaic electrolytic generation of hydrogen will be economically feasible in 1985

Miller, J. L.

Morgan, J. R.

English

NASA Technical Reports Server

SPACE POWER TECHNOLOGY APPLIED TO THE 
ENERGY PROBLEM 
J. L. Miller and J. R. Morgan 
Power Branch 
Electronics and Control Laboratory 
George C. Marshall Space Flight Center 
Marshall Space Flight Center, Alabama 35812 
257 
https://ntrs.nasa.gov/search.jsp?R=19770023350 2020-03-20T07:52:45+00:00Z
SUMMARY 
A technique using aerospace technology is presented for applicability to 
large-scale hydrogen production in 1985 energy systems. Photovoltaic energy 
conversion is baselined with application design data provided. A comparison of 
hydrogen generation techniques, based on a 1985 scenario, is provided. System 
performance and costing characteristics are provided for 1985 application. 
INTRQDUCTIQN 
What has been referred to a s  the "energy problem" would be more 
accurately described a s  the "fuel depletion concern. l 1  The word ''problem'' 
implies "doubt" and "uncertainty" neither of which are proper descriptors of 
the doubtless certainty that our fossil fuel resources a re  rapidly being depleted. 
To say that we a re  running out of energy is equally incorrect. By definition, 
energy is "., .the actual exertion of power.. . whereas fuel is merely an energy 
carrier or substance in which energy is stored. Our entire life style is based in 
large part upon our ability to extract energy from fuel and to cause it to perform 
work (or  other exertions of power) for us. The Designer of the Universe, 
acting out of infinite wisdom and toward a plan that mankind has yet probably 
not even begun to understand, provided not only a finite quantity of fuel in the 
Earth but also an energy source incorporating a fusion nuclear reactor properly 
located about 93 000 000 miles from Earth. 
Until about 200 years ago we knew only how to use the nuclear source. 
We knew how to use it to make our crops grow, to use the seasons and weather 
phenomena such as  winds and the hydrologic cycle, and we could even heat water 
with solar energy. With the advent of knowledge of how to locate, extract, and 
use fossil fuels, our life style a s  we know it today evolved. Along with the 
conveniences, comforts, and expediencies of fossil fuel use came the pollution 
and concern about depleting the supply. With additional knowledge and searching 
we found that a certain amount of a different kind of fuel was also stored in the 
Earth. The major problem with its use is that we cannot figure out what to do 
with the contaminating fission product waste. The major difference between 
fossil fuel use and nuclear fuel use is that the "polluting" effects of fossil fuel 
use are  short-livedand the environment will "self clean" itself in a decade o r  
two after the pollution stops. Nuclear energy use on the other hand produces a 
'7contaminationf' that will require several hundred thousand years to dissipate 
to safe levels in the environment. 
258 
These 77polluting" or  "contaminating" concerns a re  probably not particu- 
larly important (assuming we can continue to contain and guard the nuclear 
waste) because we have such a small quantity of either that their use cannot 
continue far into the future. Using the term quad (quadrillions of Btu or loi5 Btu) 
as a convenient energy quantity, one source [ l ]  puts our fossil energy reserve 
inside U.S. boundaries at  about 10 317 quads (335 for oil, 8670 for coal, and 
1312 for gas) The "known o r  expected to be found" fissionable uranium reserves 
inside U. S. boundaries and obtainable a t  economically viable prices is only about 
884 quads [2]. To look at  the fuel use pattern and trends between coal, petroleum, 
natural gas, etc., over the range of a decade or  two or  even a couple of hundred 
years is to miss the big picture. Figure 1 puts the U. S. fossil fuel use [ 31 in 
proper perspective in relation to the availabjlity of solar energy 141 Even if  
one assumes the 11 201 quads of fossil and nuclear reserve previously mentioned 
to be consumed at  the constant rate of approximately 85 quads per year, the 
supply will last only 132 years. Assuming a linear increase at the escalation 
rate, the supply will last about 56 years or until the year 2033. 
Figure 1. U.S. fossil fuel consumption and 
solar energy available. 
The obvious long range solution is to look to the Sun and to the energy use 
rate at  which the Designer of the Universe has allowed for the planet Earth. The 
only way to increase this ultimate use rate is to go out in space with large 
reflectors and direct more of the energy toward us, but then we would probably 
get too hot. Another alternative is to by-pass the photosynthesis route to fossil 
259 
fuel resupply and go directly to a synthetic fuel generated from sunlight. The 
photovoltaic water electrolysis (PWE) system described in this paper converts 
solar energy into the synthetic fuel hydrogen. A description of the system 
operation, technologies involved, and predicted economics a r e  contained in the 
following narrative. 
PWE SYSTEM DESCRI PTION 
There a re  two basic technologies involved in converting sunshine into 
hydrogen fuel. Figure 2 shows a block diagram of the PWE system. Solar 
energy is converted into dc electrical energy by photovoltaic devices called 
solar cells and the dc energy is then used to electrolyze water in electrolysis 
cells. An artist's concept of how a large plant might look is shown in Figure 3. 
The fuel production plant envisioned here occupies approximately 11 acres and 
has an annual production capability of about 170 000 lb of hydrogen or an energy 
equivalence of about 1800 barrels of oil. The solar array form occupies about 
10.5 acres of the tract and has a peak output of about 1.5 MW at noon on a 
sunny day. 
The solar cells a re  silicon devices developed for the space power market 
and currently beginning to be used in terrestrial applications, Efficiencies of 
12 to 16 percent are  currently achievable a t  prices of $10 to $15/watt of peak 
Figure 2. Photovoltaic/electrolytic hydrogen generation plant. 
260 
WATER 
ELECTROLY ZER 
WATER 
SUPPLY 
HYDROGEN 
USER 
Figure 3. Photovoltaic-electrolytic hydrogen generator. 
performance. It is anticipated that by 1985 cell efficiencies of 18 percent at 
prices between $0.20 and $0.50/W of peak performance will be available. 
The Low Cost Silicon Solar Array Project managed by JPL for ERDA has the 
objective of bringing the price of an encapsulated solar array to under $1. 60/ft2 
by 1985 with an assured lifetime of over 20 years [ 51. 
Looking at  the solar energy available in North Alabama, Figure 4 shows 
the weekly averages of available energy at a fixed southerly facing angle of 45O 
on the roof of Building 4487 at the Marshall Space Flight Center. These data 
were obtained for the entire year of 1975 and show that even the worst weeks 
have over 100 W-h/ft2/day available and the best ones range up to 500 W-h/ft2/day. 
The overall annual average for the year of 1975 is 360 W-h/ft2/day. One advan- 
tage that a photovoltaic system has over a pure thermal absorber is the fast 
response time. Figure 5 shows the energy available between 6:OO a.m. and 
7:30 p.m. on April 16, 1975, which was a perfect day with 590 W-h/ft2 integral 
under the curve. This is an ideal day for either a photovoltaic or  thermal 
absorber system. However, Figure 6 is more typical of the average day. In 
this case the integrated available energy of 324 W-h/R2 has a considerable 
amount tied up under the sharp spikes which the 10 ps response time of PWE 
system can extract. Also, solar cells will give a proportional output for the 
dimly illuminated overcast days of inclement weather. 
261 
Figure 4. Available solar energy weekly average 
45" Huntsville, Alabama, 1975. 
TIME OF DAY 
Figure 5. Solar energy available, day 106, April 16, 1975, 
Q =  590 W-h/ft2 45" fixed. 
To arrive at an economic viability prediction for the 1985 time period, 
the 1977 situation was used as the point of departure and cost information was 
generated for both time periods. Figure 7 shows the resulting prediction that 
costs per kW-h of dc energy generated by solar array forms will decrease from 
approximately $0.48 to $0.74/kW-h in 1977, to $0.03 to $0.07/kW-h in 1985. 
The 1977 estimate is based upon the 12 to 16 percent efficiency spread and $ 1 0  to 
262 
TI ME OF DAY 
Figure 6. Solar energy available, day 90, March 31, 1975, 
Q = 324 w-H/ft2 45" fixed. 
70 
60 
P:H) 
T 
3 
-. 40 
Y 
v) 
's 
" 3 0  
20 
10 
1975 1980 1985 
YEAR 
Figure 7. Photovoltaic energy cost trend, 
$15/W capital cost information given earlier. The 1985 estimate is based 
upon 14 to 18 percent efficiency and rF 0.20 to 9; 0.50/W capital cost. In addition 
to these estimates, it was assumed that standard panels of 3 ft  x 10 ft  mounted 
in clusters of 5 panels per lean-to would be connected by underground wiring to 
the water electrolysis plant. The lean-to's were assumed to be spaced apart 
twice their width to prevent shadowing one another. The result is a 33 percent 
area utilization factor. For an assumed field of 25 rows of 40 lean-to's per row 
263 
an effective area of 150 000 ft2 of solar array can be deployed in a field of 
approximately 10.5 acres. To arrive at a total life cycle cost it was assumed 
that each lean-to could be built for $100 to $400 and wired into the electrolysis 
system for an additional $50 to $100. This results in an overall installation 
cost of $150 000 to $500 000 for the entire field. A fixed maintenance cost of 
$30 000 per year was assumed. 
The capital cost of the solar cell panels was calculated from the expected 
peak performance and the price per peak watt stated earlier. The performance 
on a per square foot basis was obtained by calculating the best and poorest cell 
packing densities achievable with the round terrestrial cell. This range is 
from 0.78 to 0.87. 
Finally, the capital plus maintenance cost on a per square foot per month 
basis was arrived at  by amortizing the capital over an anticipated life of 20 years 
at  assumed interest rates of 8 and 10 percent and then adding the monthly 
maintenance cost to that. Overall average performance was obtained by multi- 
plying the average energy available by the packing factor and by the cell 
efficiency. 
There a re  reflective louver concentrator concepts which a re  attractive 
and could reduce energy costs in the early timeframe. Description of these 
alternatives is beyond the scope of this paper. However, assuming a reflective 
louver cost of $2/ft2 plus $0. 33/ft2 for installation and an additional $250 per 
lean-to for a tracker and a 10 year lifetime, the best that can be expected in 
the 1977 timeframe is $0.30/kW-h. Concentrators offer no advantage in 1985 
because the added capital and maintenance cost compared to the anticipated low 
solar cell array cost results in driving the energy cost upward. Using the same 
assumptions previously stated for concentrator cost and life in the 1985 time 
period, the previously stated $0.03 to $0.07/kW-h would increase to $0.04 to 
$O.OS/kW-h. To evaluate the overall 1985 economic viability of the PWE system, 
a break even transfer cost of $O.O3/kW-h was taken as  being the most optimistic 
justifiable number. 
Conversion of the solar energy to a useable fuel may be accomplished 
through several mechanisms [6,7,8] . Considerable research is being conducted 
in thermal decomposition and photosynthesis of water. However, without a 
major technology breakthrough, the most promising hydrogen generation technique 
is water electrolysis. The capital investment and operating cost sensitivities of 
other generation techniques cannot compete with electrolysis in the 1977 or 1985 
markets. Even electrolysis cannot be cost effective for large hydrogen volumes 
in the 1977 time period when compared with hydrogen generation from fossil fuel 
sources. With rising fossil fuel costs and their limited availability, electrolysis 
will prove cost effective in the 1985 or earlier time periods. 
264 
There are three candidate electrolyzer technologies being currently 
developed; alkaline matrix, solid polymer electrolyte, and solid oxide electrolyte. 
For the 1977 commercial market, the alkaline matrix technology represents the 
most commercially developed. "Off-the-shelf' units using this technique are 
currently available for production rates up to 1.4 MBtu hydrogen/h, The solid 
polymer electrolyte technology will prove most cost effective during the 1980 to 
1990 time period. Beyond 1990, the solid oxide electrolyte technology will 
becorr,e commercially available. An artist's concept of a typical hydrogen 
generation facility is shown in Figure 8. 
Figure 8. Electrolytic hydrogen generator. 
The alkaline matrix technology requires bulky subsystems and recircula- 
tion of electrolyte to produce reasonable sized electrolyzer units. For small 
hydrogen generation rates (less than 1.0 MBtu hydrogen/h) this technique will 
prove competitive beyond 1985. This system is a derivative of the alkaline 
matrix electrochemical technology developed by NASA and currently being used 
in the Space Shuttle fuel cells to provide electrical power. 
The solid polymer electrolyte (SPE) technology for electrolysis is a 
direct derivative from the NASA Gemini program. ERDA is planning extensive 
development in SPE technology in association with EPRI. EPRI is an organiza- 
tion of electric power utilities which was formed to pool their research funds to 
meet their common goals. This technology emphasis is expected to reduce 
capital equipment costs to approximately $30 to $60 per MBtu hydrogen as 
shown in Figure 9. 
265 
1 
1970 1975 1980 1985 1990 
YEAR 
Figure 9. Projected SPE electrolyzer capital costs. 
Selection of a design operation point is made on a basis of current 
density, capital equipment costs, and electrical power requirements as  shown 
in Figure 10 191. The example shown uses a current density of 1500 mA/cm2 
which results in capital costs of $62/MBtu hydrogenh and an energy require- 
ment of 298 kW-h/MBtu hydrogen generated. Using these parameters with an 
CURRENT DENSITY - MAlSQ CM 
Figure 10. Electrolytic hydrogen costs, 1985 basis. 
266 
8 percent amoritization of capital costs over the projected life of 20 years, 
hydrogen generation costs a r e  determined based on various electrical power 
costs as shown in Figure 11. Using the 1500 mA/cm2 operating point and an 
assumed electrical power cost of $0. 02/kW-h, the hydrogen production cost is 
slightly more than $9.OO/MBtu hydrogen. 
"F ELECTRICAL POWER COST 
t ------- 40M'L 
t 
t I 10 MIL 
i 
I 
I 5 MIL 
! 
t i 4 
500 1000 1500 2000 
CURRENT DENSITY - MAISQ CM 
Figure 11. Hydrogen generating cost, 1985 basis. 
The cost of producing hydrogen from fossil fuels is shown in Figure 12 
[ 9, lo] .  Production from natural gas is accomplished by methane reformation. 
Fuel oil oxidation is used for fuel oil sources. These curves reflect the impact 
of fossil fuel costs, but do not show labor inflationary factors which will occur 
between now and 1985. Such factors will increase the slope of the fossil fuel to 
hydrogen conversion curves. Based on these curves and the projected energy 
costs of fossil fuels for 1985, it is expected that electrolytic hydrogen production 
will be cost competitive with fossil fuel hydrogen production techniques 191 . 
The principle hydrogen users in 1985 are expected to remain as they are 
today, i. e. , industrial consumption for manufacturing semiconductor devices 
and fertilizer and for heat treatment processing. Residential uses for electrical 
power and heating/cooling applications are not expected to materialize before 
1990. Similarly, transportation users for electrical or internal combustion 
' 267 
10 - SOLAR ELECTROLYTIC 
HYDROGEN GENERATION 
1985 PROJECTED 
FUEL OIL COST 
7 FUELOIL 
METHANE 
REFORMAT I ON 
FUEL OIL 
0x1 DATION 
I 
Loo 2.00 3.00 4.00 5.00 
FOSSIL FUEL COST - blMBTU 
Figure 12. Fossil fuel hydrogen cost. 
powered vehicles a re  not expected to mature by 1985 [ l o ]  . With major users 
being in the industrial market, it is conceivable that small systems of the type 
described in this paper will provide a substantial portion of these hydrogen 
consumers. 
CON CLU S I ON 
Photovoltaic/electrolytic generation of hydrogen will prove economically 
feasible by 1985. The physical technologies exist today for such a system, 
although it is not cost competitive. The extensive development efforts by ERDA 
and EPRI during the next 5 years will reduce the cost of NASA derived technology 
to a competitive situation. Photovoltaic generated power will cost in the range 
of $0.03 to $O.O'l/kW-h and electrolytic hydrogen will be available at $9.OO/MBtu 
which will be competitive with fossil fuel sources. 
268 
REFERENCES 
1. U.S. Energy Outlook: An Initial Appraisal 1971-1985. Prepared by the 
National Petroleum Council's Committee on U. S. Energy Outlook, 
November 19 7 1 . 
2. Hattle, H. C. and Howard, J. B.: New Energy Technology - Some Facts 
and Assessments. MIT Press, 1971. 
3. Glaser, P. E.: The Future of Power from the Sun. Proceedings of the 
Intersociety Energy Conversion Engineering Conference, 1968. 
4. Terrestrial Applications of Solar Technology and Research. Prepared 
by Auburn University Engineering Systems Design Summer Faculty 
Fellows in conjunction with the Program Development Directorate, 
George C. Marshall Space Flight Center, NASA, September, 1973. 
5. Derman, Samuel: Major Solar-Cell Programs Strive to Lower Cost, 
Improve Efficiency. Electronics Design, March 15, 1976. 
6. Funk, James E . : The Generation of Hydrogen by the Thermal Decompo- 
sition of Water. 9th IECEC Conference Proceedings, 1974. 
7. Lotker, Michael: Hydrogen for the Electric Utilities - Long Range 
Possibilities. 9th IECEC Conference Proceedings, 1974. 
8. Ficket, A. P., and Titterington, W. A,: Electrolytic Hydrogen Fuel 
Production with Solid Polymer Electrolyte Technology. 8th IECEC 
Conference Proceedings, 1973. 
9. Titterington, W. A. and Nuttall, L. J.: General Electric's Solid 
Polymer Electrolyte Water Electrolysis. Conference on the Electrolytic 
Production of Hydrogen, Chemical Society, London, England, 1975. 
10. Hoffman, George A. : Hydrogen-Rich Automotive Fuels: Future Cost 
and Supply Projections. 9th IECEC Conference Proceedings, 1974. 
269 


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