A cost comparison is made between a terrestrial solar cell array power system and a variety of other power sources for the ATS-6 Satellite Instructional Television Experiment (SITE) TV terminals in India. The solar array system was sized for a typical Indian location, Lahore. Based on present capital and fuel costs, the solar cell array power system is a close competitor to the least expensive alternate power system. A feasibility demonstration of a terrestrial solar cell array system powering an ATS-6 receiver terminal at Cleveland, Ohio is described

Masters, R. M.

English

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NASA TECHNICAL	 NASA TM X-71720
MEMORANDUM
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COST COMPETITIVENESS OF A SOLAR CELL ARRAY
POWER SOURCE FOR ATS-6 EDUCATIONAL TV TERMINAL
by R. M. Masters
Lewis Research Center
Cleveland, Ohio 44135
ripril 1975
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COST COMPETITIVENESS OF A SOLAR CELL ARRAY POWER SOURCE
FOR ATS-6 EDUCATIONAL TV TERMINAL
by R. M Masters
Lewis Research Center
National Aeronautics and Space Administration
Cleveland, Ohio
ABSTRACT
A cost comparison is made between a terrestrial molar cell array power
system and a variety of other power sources for the ATS -6 Satellite Instruc-
tional Television Experiment (SITE) TV terminals in India. The solar array
system was sized for a typical Indian location, Lahore. Based on present
capital and fuel costs, the solar cell array power system is a close com-
petitor to the least expensive alternate power system. A feasibility demon-
str0 ion of a terrestrial solar cell array system powering an ATS -6 receiver
terminal at Cleveland, Ohio is described.
INTRODUCTION
The ATS -6 satellite launched in May of 1974 is a link in an experiment
to study the effectiveness of satellite relay of educational and instructional
programsto schools, learning centers, and community antenna distribution sys-
tems. In the United States the experiment will operate until early 1)75 as a
Health Education Telecommunications (HET) program. Later the satellite will
be moved to the opposite side of the world and operate as part of the Satellite
Instructional Television Experiment (SITE) in India (ref. 1). Either the HET
or SITE receiving equipment, with monochrome TV, will require a total of 200
watt-hours of electrical energy per day when operated 3 hours per day.
Many SITE terminals in India will be located in villages where skill
levels are low, money is scarce, and electrical power in many instances is
nonexistent. Areas without power will require dependable, locally generated
electric power to operate the TV receiver terminal. The problem was examined
by the Indian National Committee for Space Research (INCOSPAR) (ref. 2) in a
study which considered a variety of power sources and estimated their costs
for this application. The study concluded that a kerosene engine-generator-
battery combination was the most economical method of producing electrical
power in the quantity needed.
Although the study considered solar cells, they were rejected as a can-
didate because of the high cost. The costs that were available to the study
group were those costs associated with space uses of solar cells. Since that
time the number of terrestrial applications and the market for solar cells
has increased. As a result, arrays designed specifically for terrestrial
applications can now be obtained at a cost far lower than space solar cell
array costs.
$155 $208
240 321
315 422
152	 222
135	 200
150
	
285
110
	
190
366	 500
T ^^
-;
The objective of this report is to use current estimates of solar cell
power system costs to assess the competitiveness of solar power for the SITE
application. This involves a cost comparison of a solar cell power system
with systems examined in the INCOSPAR study, after adjustment for general
inflation and fuel cost increases since 1969.
ADJUSTMENT FOR INFLATION AND 
FUEL 
COST INCREASES
One of the tasks in the 1969 INCOSPAR study (ref. 2) was to determine
the most economical means of supplying power to run the ATS-6 receiver termi-
nal. This was accomplished by determining the cos-c, in India for the various
power systems and fuel. Capital costs were determined and an interest charge
of 8% per annum on the capital cost charged over the lifetime of the original
equipment. Operating costs of fuel were determined on a yearly basis. The
total yearly operating cost was computed for each system by adding the annual
fuel cost, annual interest, and the capital cost divided by the estimated use-
ful life.
Using the data of reference 2, relative costs of the various systems are
adjusted to reflect current capital and fuel costs and are presented in Table I.
Capital cost inflation is assumed to be 34% 0% per year) and the cost of fuel
is assumed to be double the 1969 costs. In each case the cost was determined
f.r a system of 200 watt-hours per day capacity. Annual interest on the orig-
inal investment is assumed to be 10%.
TABLE I. - ANNUAL COST FOR 200 WATT HOUR PER DAY REQUIREMENT
1974
Electrical Power from Distribution Lines
1 mile
2 miles
3 miles
Gasoline Engine Generator Set with Battery
Diesel Engine Generator Set (1.5 kW generator)
with Battery
Diesel Engine Generator Set (automobile generator)
with Battery
Kerosene Engine Generator Set with Battery
Manual Power Bicycle Generator with Battery
Water Poorer (Too specialized an application)
Wind Power (Average wind speed too low)
Lead Acid Battery with Recharging Station up to
10 Miles Distant
200	 268
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SIZING OF THE SOLAR CELL ARRAY POWER SYSTEM
The solar cell array power system for SITE is a mechanically simple, low
maintenance unit with no moving parts. The system consists of a solar cell
array, storage batteries and a zener protective diode.
System design starts by first specifying the load requirements of the
SITE TV terminals. In each case the basic premise is that the TV terminal
will be operated for 3 hours each day. The TV terminals require a normal
65 wa;;ts of power, giving a basic daily requirement of 200 watt-hours. In
order to determine the solar cell array and battery sizes to meet this re-
quirement, the expected insolation of a selected location must be found.
For the SITE terminals insolation conditions reported in reference 3 were
used.
Locations in the northern areas of India were considered since direct
broadcasts are scheduled for the region. The insolation readings for the
city of Lahore were used in the design because they are representative of
the average insolation of many reporting stations of northern India, such
as Delhi, Allahabad, Jullundur, and New Delhi. Table II lists the average
daily insolation of Lahore.
TABLE II. - AVERAGE DAILY INSOLATION, IN LANGLEYS
(cal/cm2/day)
Annual
Month	 J	 F	 M A	 M	 J	 J	 A	 S	 0	 N	 D	 Ave.
Lahore 320 410 510 610 660 650 550 470 550 48o 390 310 501
To determine the array size for this location computational methods des-
cribed in reference 4 were used. Briefly, this consisted of using the insole-
tion data to compute the average monthly energy available from a solar cell,
taking into account factors such as temperature, sun angle, latitude of loca-
tion, turbidity, cloud cover, and cell efficiency. From the average monthly
energy input the array size and storage battery capacity is calculated based
on battery depth of discharge, charge efficiency, temperatures and specific
load profile. The solar cell array poorer system is designed, then, on the
basis of an annual watt-hour budget whereby the array generates, over the
course of a year, enough watt-hours to satisfy the annual load requirements
and battery charging inefficiencies.
A typical se,, 1',P rw-_ay and battery specifications for a power supply
sized for Lahore,o"4 a with a load profile of 200 watt-hours per day would
be as follows:
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ARRAY
5.6 centimeter round silicon cells (terrestrial quality)
10% cell efficiency
40 cells in series (four 10-cell modules 12-volts/section)
5 cells in parallel (five 12-volt sections)
1.08 square meters (0.0197 square meters/v7att)
55 watts-peak array output
BATTERY
12 volts nominal
500 ampere-hour total capacity
SOLAR CELL ARRAY POWER SYSTEM COSTC
Annual costs of the solar array system are dependent upon the life-
time estimates of both the array and battery. The silicon cell array life-
time is estimated to be in excess of 10 years. Based on past experience,
battery lifetimes of 5 years or more can be expected. The battery operat-
ing conditions are not strenous, entailing only shallow discharges with
near full charge maintained most of the time. For this study a ten-year
solar cell array life and five-year battery life is assumed.
System costs are based on present and projected commercial prices
for solar cell arrays and present battery prices. Present prices for
arrays are $17 per peak watt of output (ref. 5) for 12-volt lead acid
batteries, S5 cents per ampere-hour. Future array cost estimates are
based on the goals of the Photovoltaic Energy Conversion Program of the
Energy Research and Development Administration: $5/watt by 1977, to $2/
watt by 1979 and $.50/watt by 1984. These cost reductions are expected
to result from the automation of present production techniques.
Table III shows the annual costs for a solar cell array power system
computed using the same assumptions as for the systems in Table I.
TABLE III. - ANNUAL COST OF A SOLAR CELL ARRAY POWER SYSTEM FOR
A LOAD OF 200 WATT HOURS PER DAY AT LAHORE INDIA
Array Cost	 $17/w	 $10/w 	 $5/w	 $2/w
Array
	 93	 55	 27	 11
prorated/10 years
Batter
	
35	 35	 35	 35
prorated/5
 years 
Interest
	
111	 73	 45	 29
10% of original cost
Total	 $239	 $163	 $107
	 $75
-4-
Using Table III solar cell array power systcm annual costs may be
compared to the least expensive system in Table I, the kerosene engine-
generator at $190 per year operating cost. At today's prices the annual
cost for a solar array system for Lahore India would be 26% more than for
the kerosene-engine generator system. With an array price of $101W the
annual cost of the solar array system would be 14% less than for the kero-
sene-engine generator system. With array prices at $2/watt, the annual
cost would be less than half that of the generator system. These results
show that the solar cell array power system is presently competitive with
the alternate power systems and can be expected to be substantially less
expensive than the others in the near future.
Logistics considerations of refueling or skilled maintenance, as re-
quired for the generator type systems, are unnecessary for the solar cell
array power system. Only periodic checks of the electrolyte level in the
batteries and perhaps occasional cleaning of the array surface would be
needed.
A SOLAR POWERED ATS-6 RECEIVER TERMINAL DEMONSTRATION
To illustrate the feasibility of a solar cell array power system for
a SITE or a HET receiver terminal a demonstration system was put into opera-
tion at the Lewis Research Center, Cleveland, Ohio (figure 1). The system
consists of the antenna, solar panel, and battery box located outside and
the receiver and TV monochrome monitor located within the adjacent building.
The solar array charges lead acid batteri,that supply power to a D C. to
110 V. A.C. converter which operates the receiver and TV unit.
In figure 2 a close-up of the solar array shows the south oriented
array, at a tilt angle of 64° for Cleveland latitude, mounted on the an-
tenna mast. The array consists of four 12-volt (nominal) sections connected
in parallel, providing 44 watts of peak power. Each section can be seen to
consist of four 10-cell modules which are in connected series to provide a
40-cell string. Additional sections may be added in parallel to increase
the charging capacity of the array to suit most design needs.
The solar array in figure 2 is slightly smaller (20%) than required for
the Lahore, India location. This array was sized for local demonstrations
which have a shorter operating period than prescribed for the SITE applica-
tions. The 55-peak-watt output for the Lahore design would be provided by
five sections as previously described.
CONCLUSIONS
The solar array power system proposed for the ATS-6 TV terminal load is
a viable power supply that should be considered in competition with other
systems specified in reference 2. The much lower production costs of pres-
ent terrestrial solar cell arrays, as compared to costs of space cell arrays
used in previous power system cost estimates makes solar powered systems
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a close competitor to the cheapest of the alternate power systems. And,
in the near future, it is expected that solar array power systems will
drop in cost significantly below the least expensive alternate system.
The simplicity, clean and quiet operation, minimal maintenance, and
low yearly operating cost make the solar cell power system an excellent
system for operating the ATS -6 Educational. TV receiver terminal.
REFERENCES
1. The ATS-F Data Book, NASA Goddard Space Flight Center, Greenbelt,
Maryland 20771.
2. Study of Community Broadcast Satellite Systems for India, June 30,
1969, Indian National Committee for Space Research (INCOSPAR) and
General Electric Company, Space Systems Organization.
It
3. Lof, George 0. G.; Duffie, John A.; Smith, Clayton, 0.: World Dis-
tribution of Solar Radiations, Solar Energy Laboratory, The University
of Wisconsin Report No. 21, July 1966.
4. Forestieri, A. F., and Ratajczak, A. F.: Terrestrial Applications of
FEP-Encapsulated Solar Cell Modules, NASA TM X- 71608, September 1974.
5. Telephone communication with Dr. Joseph Lindmayer of Solarex Corporation.
—6—
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Figure 1. - Demonstration System of HFf Receiver Terminal
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Figure 2. - Close-up of Solar Array on HET Receiver lermina
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Cost competitiveness of a solar cell array power source for ATS-6 educational TV terminal

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