The Solar Energy Panel was organized jointly by the NSF and NASA in January 1972, and comprised of nearly 40 scientists and engineers possessing expertise in solid state physics, chemistry, microbiology, power engineering, architecture, photovoltaics, and the thermal sciences as well as several economists, environmentalists, and sociologists (see Appendix B). The Panel was charged with assessing the potential of solar energy as a national energy resource and the state of the technology in the various solar energy application areas, and with recommending necessary research and development programs to develop the potential in those areas considered important. The scope of the Panel's activities was defined to include all applications of direct solar energy, as well as power from wind, ocean thermal differences, and useful energy from replenishable organic materials. This report presents the findings of the Panel.

Current projections [1] of the total U.S. energy demand, see Figure 1, show a growth from approximately 64 X 1015 BTU in 1969 to nearly 300 X 1015 BTU in the year 2020. A significant portion of this increase is projected to be derived from nuclear energy, with the rest being supplied by fossil fuels some of which are being rapidly depleted. In view of the Nation's and the world's growing concern with environmental and health/safety factors as well as our anticipated increasing dependence on imported petroleum and gaseous fuels, it is important to evaluate the potential impact of solar energy utilization, since it is an inexhaustible source of enormous amounts of clean energy [2].

The average yearly incidence of solar energy in space and on the ground in the continental U.S. is:

The 17 thermal watts/ft.2 results in an average daily (24 hour) energy supply of 410 thermal watt-hours/ft.2. This value is approximately twice the amount needed to heat and cool an average house. Converting the 17 thermal watts/ ft.2 into electricity at a 10% conversion efficiency would result in an average daily electric output 'of approximately 1,140,000 kilowatthours per square mile. In 1969, the Potomac Electric Power Company sold a daily average of 30,000,000 kilowatt-hours to 425,000 customers in an area encompassing 643 square miles. Within 27 square miles or about 4% of the above PEPCO serviced area devoted to a solar electric generation system, PEPCO could in principle provide the necessary electric power. Under the same assumption of a 10% conversion efficiency and U.S. average solar incidence, in 1969 the total electric energy consumed in the U.S. could have been supplied by the solar energy incident on 0.14% of the U.S. land area.

There has been little Federal support of solar energy utilization other than for powering artificial satellites. Commercial and philanthropic support of solar power generation has been almost negligible. Programs in Australia, the USSR, France, and Israel have all substantially exceeded U.S. effort. In principle, solar energy can be used for any energy need now being met by conventional fuels [3]. Three broad applications have been identified by the panel as most promising from technical, economic, and energy quantity standpoints. These are: (1) the heating and cooling of residential and commercial buildings, (2) the chemical and biological conversion of organic materials to liquid, solid, and gaseous fuels, and (3) the generation of electricity. The Applications chapter of the report is organized into three primary sections corresponding to these broad application areas. Within each section, one or more methods or processes for

converting solar energy to the desired form are presented in the following format:

• Description of Concepts

• Status

Limiting Factors and Recommended Approaches

• Goals and Projected Impacts

• Short Range (3 year) R&D Program Recommendation

• Long Range (10-15 year) R&D Program Recommendation

Phased Program Plan

The Panel is confident that solar energy can be developed to meet sizable portions of the Nation's future energy needs. This report is

intended to document this confidence. It must be recognized, however, that severe time limitations prevented a thorough and critical formulation and review of the technology, economics, relative prospects, and development tasks in each concept. Closer study is expected to eliminate certain areas from further attention, while some new and promising approaches may be added. A more detailed, in-depth examination of these and other methods for converting solar energy to useful forms is high on the agenda of our recommended research and development program. An introduction to the potential and uses of solar energy may be found in references [4] & [5].

CONCLUSIONS

• Solar energy is received in sufficient quantity to make a major contribution to the future U.S. heat and power requirements.

• There are numerous conversion methods by which solar energy can be utilized for heat and power, e.g., thermal, photosynthesis, bioconversion, photovoltaics, winds, and ocean temperature differences.

There are no technical barriers to wide application of solar energy to meet U.S. needs.

• The technology of terrestrial solar energy conversion has been developed to its present limited extent through very modest government support and some private funding.

• For most applications, the cost of converting solar energy to useful forms of energy is now higher than conventional sources, but due to increasing prices of conventional fuels and increasing constraints on their use, it will become competitive in the near future.

• A substantial development program can achieve the necessary technical and economic objectives by the year 2020. Then solar energy could economically provide up to (1) 35% of the total building heating and cooling load; (2) 30% of the Nation's gaseous fuel; (3) 10% of the liquid fuel; and (4) 20% of the electric energy requirements.

• If solar development programs are successful, building heating could reach public use within 5 years, building cooling in 6 to 10 years, synthetic fuels from organic materials in 5 to 8 years, and electricity production in 10 to 15 years.

• The Federal government take a lead role in developing a research and development program for the practical application of solar energy to the heat and power needs of the U.S.

• The solar energy R&D program provide for simultaneous effort on three main objectives: (1) economical systems for heating and cooling of buildings, (2) economical systems for producing and converting organic materials to liquid, solid, and gaseous fuels or to energy directly, (3) economical systems for generating electricity.

Research and development proceed on various methods for accomplishing the above objectives and that programs with phased decision points be established for concept appraisal and choice of options at the appropriate times.

• For those developments which show good technical and economic promise, the Federal government and industry continue development, pilot plant, and demonstration programs.

• Environmental, social, and political consequences of solar energy utilization be continually appraised and the results employed in development program planning.