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1915

INDUSTRY COMMENT LETTER:
ENERGY DEVELOPMENTS

SOLAR ENERGY OPPORTUNITIES
The rising costs and uncertain availability of conventional energy sources have led to
increased interest in solar energy options as a means of helping to meet future energy
demands. The importance of these options will increase as the required developments
proceed and as conventional sources and other alternatives are found to present potential
problems in terms of resource conservation, public health, international trade and politics,
environmental protection, and social equity .
Industry is taking initiatives to develop products and provide services in several important
solar energy application areas. These activities will increasingly be reinforced by government
support of research and development and sponsorship of demonstration projects. At
present, the funds allocated to these activities by the government are· still only a small
percentage of the total federal energy R&D budget, but successful demonstration of solar
energy applications should lead to significant increases in the funding levels.
The initial commercial opportunity in solar energy will be in the heating and cooling of
residential and commercial buildings. This market has a potential value of over $1 billion by
1985. Longer-range potential exists in power plants run on solar heat, wind, or ocean
thermal gradients; direct conversion of solar energy to electricity; and use of solar energy to
grow renewable fuels.
Introduction

Government and industry groups in many countries are investigating a number of concepts
for harnessing solar energy. Several U.S. companies are beginning to commit significant
resources to new solar energy-related activities, and government funding of solar energy
research has increased dramatically over the last three years, reaching about $50 million in
fiscal 1975. A bill providing $60 million for demonstration ·projects for solar-heated and
cooled buildings over five years was passed in September, and a $1 billion across-the-board
program for solar energy research and development over five years was enacted by Congress
in October. In addition, Japan has announced its Project Sunshine, for which multibillion
dollar expenditures are being planned over the next 25 years; Australia is planning an

Arthur
Q LlttleInc.Acorn Park • Cambridge, Massachusetts 02140
AIHIN

URU IIS

CAIi.MAS

!ONOON

MIXKOCIJY

PARIS

• ( 617) 864-.5770 I First Cambridge Corporation, an ADL Subsidiary

RIODEJANF.IRO

SANfRANCISCO

TORONlO

WASHINCt'ION WlESIIAlllN

 2

exp~ded. sol~ ene~gy _program; similar efforts are under way in Western Europe; and the
Soviet Umon ts contmumg to pursue a significant solar energy development program.
The degree to which solar energy applications can be successfully moved beyond the
researc~ and development phase will depend upon the availability and nature of competing
alternative energy sources and the cost/benefit trade-offs required to arrive at a coherent
energy policy. Solar energy is abundant enough to provide self-sufficiency and clean enough
to meet the most stringent environmental standards. The challenge lies in finding methods
for converting this energy efficiently and economically into useful forms.
The amount of energy the United States land area receives annually from the sun is some
500 times as much as the energy consumption projected for the year 2000. One square yard
of land exposed to direct sunlight receives the energy equivalent of about 1 horsepower.
However, solar energy is not easily convertible and is not "free." It can be considered a
widely distributed resource somewhat akin to low-grade mineral deposits. The collection
and conversion of solar energy into useful forms must be carried out over a large area,
entailing significant capital investment for the conversion apparatus. In addition, since solar
energy is not constantly available on Earth, some form of storage is needed to sustain a
solar-powered system through the night and during periods when local weather conditions
obscure the sun. This storage capacity involves an additional capital cost.
The widespread . use of devices that utilize solar energy will require considerable development to strike the appropriate balance between technology, the environment, and society's
needs. Results are unlikely to come about quickly, not because of the lack of advanced
technology, but rather because of too little industrial experience with such technology. The
nation lacks both the -capacity to mass-produce systems at a cost low enough to create a
large market and also the institutional arrangements needed for the rapid introduction of
solar-powered systems. The government has an important role to play in developing and
demonstrating solar energy on a commercial scale; establishing a central source of standards
and research literature; aggregating the market among federal agencies; identifying and
reducing institutional barriers at the federal, state, and l~cal levels; and developing legal
concepts to define and protect "sun rights."
Concurrent with successful demonstrations, both producers and consumers must be encouraged to take the next logical steps toward developing a mass market through selected
and effective subsidy programs. Government policy designed to protect proprietary rights
would greatly increase industrial participation. Above all, before making major investments,
industry needs to be assured that government policy will remain consistent as the market for
solar technology develops.
The potential payoff of research and development in solar energy applications has been
recognized and such R&D is now being supported on a significant scale. It is thus becoming
increasingly realistic to assess several of the options for solar e~ergy conversion.

rthur D l ittl Ir

 3
Heating and Cooling

The most promising near-term application for solar energy is in the heating and cooling of
buildings. About 90 buildings in the United States already include solar heating systems, and
solar hot water heaters are in wide use in Japan, Australia, Russia, and Israel. Several
demonstration projects are in various stages of completion: several schools have been
equipped to use the sun's energy for a portion of their hot water, heating, and cooling
needs, and systems in public buildings, office buildings, and residences in many locations
will shortly provide information on the degree of success achieved in solar-heated and
cooled buildings.
A typical solar heating and cooling system includes the following componen ts:
•

Solar Collector - a means of capturing solar thermal radiation in an enclosure with a glass or plastic cover. Since the cover is transparent to the
incident solar radiation, but opaque to the re-radiate d energy, the solar
collector, like a greenhouse, serves to trap solar energy and turn it into heat.

•

Heat Storage System - a mat erial th at has a high specific heat or experiences
a change of phase. It ac~epts collected solar heat as available and allows it to
be with drawn as needed .

•

Source of Auxiliary Energy - fuel or electri city to provid~ heat during
exten ded cloudy period s and to avoid the need for uneconomically large
collectio n and storage facilities.

•

Heat-actuated Air Conditioner - a unit that can be driven by the collected
solar heat.

•

Auxiliary Equipment - the piping , controls, heat exchangers , heat transfer
fluid , valves, pumps, motors, and other equipment needed to couple the
essential elements to an operating system.

These systems can be integrated into buildings designed for efficient thermal control
through the choice of appropriate insulating materials for windows , roofs, and floors
without sacrificing aesthetic architectural design.
Major innovations take con.siderable time to be introduced into the housing industry and to
be accepted by the builder and buyer. However, several factors favor the application of solar
energy to provide hot water, heating, and cooling in buildings:
•

rapidly rising fuel costs;

•

energy conservation measures;

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•
•
•

industrialization and increased sophistication of the construction industry;
public pressure for environmental quality; and
government actions supporting development of solar-energy applicati ons.

The basic economic case for substituting solar energy for conventional energy sources rests
on the desirability of substituting capital for nonrenewable fuels. The capital costs of
installed solar equipment are largely attributable to labor utilized in the production of th e
equipment and components and in the installation of the equipment. The financial burden
and the materials and energy used in building the solar equipment present themselves clearly
at the time of the initial installation. However, once installed, solar equipment provides cost
savings over the many years of its operation. Moreover, a comparison of the costs of solar
and conventional systems does not adequately reflect the hidden costs - environmental,
social, or political - which are not now charged against the conventi onal fuels. As broaderbased cost accounting is adopted, the cost benefits of solar heating and cooling of buildings
will become increasingly favorable as compared with those of competing fuels. In addition,
the effects of lessening the reliance on imported fuels will lead to a more favorable trade
balance.
The annual capital charges for the solar equipment range from $300 to $600 for typical
residences - expressed as the additional mortgage payments over a ten-year period attributable to the incremental cost of the solar equipment. At this level solar heating and cooling
could now be competitive with conventional systems, part icularly with electric resistance
heating. Heating and cooling costs can be minimized when solar energy accounts for
approximately 50% of the to tal heatin g or cooling load . Beyond this level, the increased ·
capital investment for the solar equipment tends not to be effectively utilized.
Industry has indicate d that it can develop products based on present technology and that it
has the capacity to supply the required resources and equipment. Arthur D. Little, Inc., has
brought togethe r in one project 90 industrial organizations from around the world that
could make a solar heating and cooling industry a reality. The objectives of this project are
to define the technology base, establish market prospects and economic projections , and
pro vide the data on which product development and business decisions can be based. An
indust ry based on this near-term solar application not only could be profitable to those
contributing to it , but also would provide an important means of reducing consumption of
nonre newable energy resources.
The market for solar heating, cooling, and hot water will depend on the prices and
availability of competitive fuels, government policies, and the effectiveness of manufacturi ng and marketing strategies. About 20% of the present national energy consumption is
account ed for by household and commercial uses. Theoretically, up to 75% of the energy
for th ese purpo ses could be provided by solar energy. We estimate the potential market for
solar climate control at over $1 billion by 1985.
·

 5
The environm ental benefits of this use of solar energy are measured by the environmental
damag~s c~us~d by t?e fuel replaced. Damage to the environment by solar ~quipment
ope rati on is virtually mconsequential compared to any of the conventional fuels: such use
of solar_energy does not cause air, water, or thermal pollution; it does not require solid
':a st e disposal, fuel storage , pipelines , transmission lines, or other forms of fuel transportation ; and it does not create potential hazards. Furthermore , use of solar equipment reduces
land use of the total energy supply system as it is installed primarily on building roofs.
Power Plants
Heat Engines

The prospect of focusing the sun's energy to generate steam for a power plant has long been
intriguing. A solar-powered steam engine, using a large mirror to focus solar radiation on a
boiler, was the central attraction of the 1878 Paris World Exposition. Similar plants were
built in California in 1901 and in Egypt in 1913.
Large-scale terrestrial solar power plants have been proposed to work in conjunction with
conventional power plants - in Russia about 15 years ago and more recently by researchers
at the University of Arizona and the University of Houston. Several design approaches for
solar-energy-concentrating mirrors and thermal storage devices are now being investigated by
Honeywell, General Atomic, and others under contract to the National Science Foundation.
In one approach, arrays of linear parabolic sun-tracking mirrors would focus solar radiation
onto heat-absorbing tubes. These tubes, coated with a solar radiation-absorbing material,
were designed to heat to about I 000°F a circulating fluid which would transfer the heat to a
thermal storage system. Alternatively , heat pipes could be used to transfer the heat from the ·
tubes to the thermal storage area. The heat would be withdrawn from storage during cloudy
days and at night and transferred to a working fluid, which would drive turbine generators
to produce electricity.
To overcome the heat losses associated with collecting the heat from a large number of
parabolic mirrors, an alternative approach is being investigated by several aerospace firms .. In
this method, mirrors focus sunlight onto a central boiler placed on top of a tall tower,
producing temperatures of 1000°F. A one-square-mile mirror field and a 1500-ft tower
would be needed to provide a useful power output of 100 Mw. Such power plants,
incorporating six hours of energy storage, are projected by the National Science Foundation
to have a capital cost of $1000/kw in 1974 dollars. Much engineering remains to be done to
identify optimum system .·parameters, evaluate specific component designs and energy
storage approaches, and establish the economics of various systems to decide on the
specifics of a pilot plant.
If these ongoing investigations are successful, a 5-Mw demonstration plant is expected to
begin construction during the next five years at a cost of $25 ~illion, funded by NSF, and if
these are shown to be successful, a large-scale power plant will be produced by 1985. Plants

 6

of th is_typ~ could also be part of total energy systems delivering both heat and electricity
for residential and commercial uses.
The~e appro~ches work at their design efficiency only on clear days, indicating that the
choice of smtable locations will favor the desert areas of the Southwest. The environmental
imp~cts of solar heat-engine power plants are related primarily to land use, the effects of
shadmg predominantly desert areas, and induced demographic pattern changes.

Wind Energy
Solar energy is also available indirectly through the winds, since solar energy sustains the
winds. Of the average solar energy reaching the Earth - 1 kw per square meter of surface
area - 2-20 watts per square meter are converted into kinetic energy. Winds are remarkably
repeatable and predictable, and the moving air can be extracted by wind generators installed
in suitable locations. A wind power system could incorporate an energy storage system: for
example, the electricity produced and not used directly could be used for the electrolysis of
water to produce hydrogen for transmission through pipelines as an alternative fuel.
The theoretical power potential in the winds over the continental United States and within
200 miles of its shores exceeds, by a factor of at least ten, projected U.S. electricity demand
in the year 2000. A practical goal would be to supply 5% of the electrical energy demand by
wind power ( this would exceed the contribution of hydroelectric power plants).
In 1915, wind power was used to generate 100 Mw of electricity in Denmark. In the 1940's,
an 1100-kw machine was operated experimentally in Vermont. Buildup of ice during a
winter storm resulted in failure of the blades. Wartime scarcity of material did not permit
replacement of the blades.
A wind generator requires a minimal wind speed of about 10 mph in order to produce
power. Wind velocity increases logarithmically with height above ground; the structures to
support efficient wind generators would have to be more than 100 ft high, raising the cost
of the system and also presenting aesthetic problems for use in populated areas.
Where the winds are moderate to strong, large machines are most economic, but substantial
advances in the design of very lightweight airfoils at Princeton University (being proved by
Grumman Aerospace Corp.) indicate that small-scale wind power generation also may be
feasible. The typical sizes for a wind generator can range from 20 kw to about 2 Mw.
There are no critical technical feasibility problems in the design of wind generators. The
major questions are associated with the degree to which cost reductions can be made and
uncertainties eliminated. The National Science Foundation is sponsoring studies and experiments at NASA Lewis Research Center to reduce these uncertainties. Present estimates
are that wind generators, without energy storage and located in the prairie states, in the
Lake Ontario region, and in upper Michigan, will cost $500-700/kw, rendering them
competitive with other remote power-generation methods.

 7

The land use for wind generato .
rs is comparable t O th t O f f:' •
,
adverse environme ntal impa t
a
iossll fuel plants. No significant
•
c s are expected be
d th
•
bvely, wind generators could b
yon
e aesthetic effects noted. Altema1
conditions are excellent
d the o~ated about 1O0 miles off the Atlantic coast, where wind
an
ere 1s a huge
t·
could be anchored Th
con menta 1 shelf to which floating generators
·
e power could be d 1·
d
electr olyzed to prod
h d
e ivere to shore by cable, or sea water could be
result in undesirabl uce. y rogen for pipeline delivery, assuming such methods would not
e environmental effects.
Ocean Thermal Gradients

The temperature

differen ce b e t ween t h e sun-heated upper layer of ocean water and the cold
d~eper water offers another opportunity for indirect use of solar energy. This temperature
difference can be used to power very large heat engines. The concept of using the sun-heated
ocean was first put forth in the early l 900's. Experimental power plants were built in 1929
off the coast of Cuba and in 1956 off the coast of Africa. These plants failed because of
design limitations and, in the case of the Cuban plant, damage by a hurricane.
The National Science Foundation is sponsoring research programs to explore several design
concepts and cost parameters for plants of 100 Mw or larger. Hundreds of specially designed
platforms (with a generating capacity of 500 Mw each) could be anchored in the Gulf
Stream to extract this energy. The warm surface waters would be passed through heat
exchangers which boil a fluid such as propane or ammonia to drive huge turbines coupled to
generators. The cold water pumped from the ocean depth (about ~000 ft) would be
circulated through heat exchangers to condense the working fluid. The process would
require heat engines that would operate over a temperature difference of about 40°F, for
which a feasible system efficiency would be about 2%. The major challenge would be to ·
develop very effective heat exchan gers and to design the large tur bines to extract energy
from the working fluid. In addition, the materials would have to be able to withst and the
effects of seawater for prolonged period s and be kept free of marine growths. No significant
enviro nmenta l effec ts of this energy generation metho d have yet been identified.
Direct Conversion

Solar energy can be converted directly to electricity by means of solar cells (pho tovoltai c
conve rsion). In contrast to thermodynamic conversion , photov oltaic conversion involves no
moving parts, circulating fluid, or consumption of mate rial. Furth ermore , a solar cell can
oper at e for long periods without maintenance.
The first successful silicon solar cell was demonstrated in 19?3 at Bell Telephon e Labora tories. Today , silicon solar cells are a necessary part of the power supply systems of most
spacecra ft . As a result of space programs, there is now a substantial technological base for
further developments. The two primary research goals are increased efficiency and lower
costs. Efficiencies of 16% have been obtained · at Comsat laboratories. The theoretical
maximum for a silicon solar cell is 23%.

 8

Silicon solar cells presently cost about $20,000/kw. With further expansion of the markets
for unattended packaged power supplies - e.g., communication equipment, navigational
aids, and signaling devices - costs are projected to drop to about $5,000/kw over the next
several years. New techniques for the production of single-crystal silicon as achieved in the
continuous ribbon process by Tyco Laboratories (being commercialized in a joint venture
80% owned by Mobil Oil) and automated assembly of solar cells being studied by NASA and
NSF could reduce prices to less than $1 ,000/kw over the next IO years. Once a large enough
market has opened up to justify major investments in the production machinery, the cost of
silicon solar cells could decline to as little as five times the cost of plate glass (sand is the
basic raw material for both products).
Several other solar cell materials are under development. A modified gallium arsenide solar
cell researched by IBM has resulted in an efficiency of 18%. Today, gallium is expensive, but
it is as abundant as lead and is available from the slag piles of aluminum smelters. There is
promise that it can be developed as an alternative solar cell material, particularly for use in
spacecraft. Copper oxide-cadmium sulfide thin-film cells which are being investigated at the
University of Delaware represent another possibility. Although the efficiency of these cells
is less than 7%, they can be produced by vacuum deposition, which is projected to lower
production costs relative to silicon crystal cells.
Solar cells could be used in combination with a solar collector to supplement electricity
requirements of a building. Large installations of concentrating mirrors combined with solar
cells could lead to low-cost direct solar-energy conversion systems. For e~ample, one square
mile of land (e.g., desert area) covered with such devices that have an efficiency of 10%
could generate 180 Mw when the sun shines. Such large installations could have significant
impacts on land-use patterns and future demography. Shading of areas by solar energy
collecting surfaces could affect the ecology, particularly in desert areas.
Terrestrial conversion systems suffer from the diffuseness and irregular availability of
sunlight, which require them to have large solar energy collecting areas and some form of
energy storage (e.g., water pumped to an elevated resei;-voir, compressed air, electrical
storage batteries, or a system to produce hydrogen by electrolysis of water). Consequently,
solar energy conversion systems able to generate power on a substantial scale will be
economical only in a limited number of geographical locations.
Such Earth-bound obstacles can be overcome by locating the conversion systems in outer
space where solar energy is constant. One approach for the continuous conversion of solar
energy is to place a satellite solar power station in synchronous orbit 22,300 miles from the
Earth's equator. Solar collectors would convert solar energy directly to electricity, which
would be fed to microwave generators incorporated in a transmitting antenna. The antenna
would direct a microwave beam to a receiving antenna on Earth, where the microwave
energy would be converted back to electricity. (The microwave power density within the
beam is so low that microwave levels beyond the receiving ~ntenna can meet the severest
international standards for exposure to continuous microwave radiation.) Microwaves can be

 9

converted directly to d.c. electricity with an efficiency of 85%. Th1s very high conversion
efficiency greatly reduces the undesirable effects of thermal pollution associated with all
kn own th ermodynamic processes for power production .
The absence of gravitational forces and of the active environmental influences present on
Earth permits the deployment in space of very large lightweight solar collector structures
which could not be installed on Earth. Because of the continuous availability of solar energy
in synchronous orbit, only about I 0% of the area of solar cells necessary to achieve the
equivalent power output on Earth would be required. Furthermore , there would be no
requirement
for energy storage. Such a satellite could be designed to generate
3,000-20 ,000 Mw of electrical power on Earth. A system of satellites maintained in
stationary orbital locations could deliver power to various geographic locations , with the
receiving antenna placed either on land or on platforms over water near major load centers.
A space transportation

system based on a second-generation space shuttle/space tug
combination would be used to orbit the satellite, probably not before 1990. The capital cost
of a 750-Mw prototype satellite, including the orbital and ground-based systems, space
transportation, and assembly, is projected to be $1500/kw in 1974 dollars. The energy
payback period for system components and space transportation propellants is on the order
of one year. Further cost reductions for larger-output satellites could be achieved by
advanced space transportation systems.
The feasibility of such a satellite solar power station was assessed by a g:oup of companies
(Arthur D. Little, Inc., Grumman Aerospace Corp., Raytheon Co., and Textron, Inc.) with
partial support from NASA. This feasibility assessment indicates that this concept is worthy
of consideration as an alternative energy production method, and that it could be cost
competitive with other advanced energy production systems. A preliminary assessment of
environmental impacts - such as troposphere and stratosphere pollution from space transportation system exhaust products; microwave effects on plants, birds, and aircraft; and
radio frequency interference - indicates that these could be controlled and reduced to
acceptable levels.
On a recent demonstration carried out by Raytheon at the Goldstone antenna site in
California, a microwave beam was transmitted across one mile and converted directly to
electricity with 75% efficiency. Within six months, an efficiency of 80% is expected to be
achieved with microwave beams of about 15 kw. A pilot experiment could be performed in
orbit in less than 1O years. Using state-of-the-art technology, a prototype satellite could be
demonstrated in the early i 990's and a commercial system could come on line before the
year 2000.
Production of Renewable Fuels

Fo si1 fu Is originated millions of years ago as the result o( solar energy-induced photosynthc is. To supplement fossil-fuel deposits, photosynthesis could be used to produce

 10

organic materials such as plants or trees that could then be converted to clean gaseous,
liquid, and solid fuels by pyrolysis or similar processes. One ton of dry organic material
could yield about 10,000 cu ft of methane gas or 2 bbl of fuel oil. With a 2% photosynthetic
conversion efficiency and good growing conditions, one acre could produce 20 tons/year of
organic materials. Although some investigations along these lines are under way, we expect
considerably more time to be required before this approach could be commercialized.

Peter E. Glaser

..
.
.
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form without our prior permi~sion •~ wn:n;~ ;:po~sible individuals in the subject companies .
bte;:~:~:
to the data
nerally av ilable to the public or re e~se
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eliable and we have applied our best profess1ona _Ju
nted Where
f information on which our material is base are r
or comprehensiveness of the information prese
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