Energy Vol. 12 No. 314. pp. 179-185, 1987 036M442/87 f3.00 +O.OO Printed in Great Britain Pergamon Journals Ltd

CHANGING DIRECTIONS OF THE SOLAR THERMAL TECHNOLOGY PROGRAM

FRANK WILKINS

Program Manager, Solar Thermal Technology, U.S. Department of Energy

There have been many changes in the Department of Energy’s Solar Thermal Technology Program over the last 10 yr. Its focus has been the development of technologies that concentrate the sun’s energy; and that focus has not changed. But there has been considerable change in the pathways taken to making the technologies real alternatives for producing energy. Only a part of these changes have beep due to the evolution of those technologies. Instead, many changes have resulted from economic and political changes that have taken place in the country during this period. As the needs and priorities of the country change, so do the needs and priorities of the Solar Thermal Program. This paper describes how changing events at the national level have altered the technical focus and directions of the Solar Thermal Program. This is not unique to the Solar Thermal Program, or even to the other renewable energy programs at the Department of Energy. It is common to many federally funded research programs.

To being the story, it is necessary to remember what the mood of the country was like when the solar programs were started. In 1973 there was an energy crisis. Waiting in lines to buy gasoline became a national pastime. People began looking for ways of returning to the “good old days” when energy was plentiful and cheap. National attention was focused on energy problems, and organizations such as the Energy Research and Development Agency (ERDA) and then the Department of Energy (DOE) were formed. Advanced technology was going to come to our rescue. The formation of NASA some years earlier had resulted in landing men on the moon and had proven that the mixture of national enthusiasm, technical excellence, and federal funding could overcome very difficult technical challenges.

DOE was started with the same burst of enthusiasm that had accompanied NASA. Unlike the NASA program of the 1960s. however, the energy crisis of the 1970s was solved by political events, such as the weakening of OPEC, before it could be solved by technology. Public focus on energy declined with declining oil prices. In addition, political priorities changed. Increasing national defense readiness and balancing the budget took over the national agenda in the 1980s.

This change had a significant impact on the Solar Thermal Program. Since its inception, the program has been either rapidly expanding or rapidly contracting. Figure 1 shows the funding history of the program. As can be seen, it is nearly a classical bell-shaped curve. The program expanded in the 197Os, and contracted in the 1980s. The changes in funding levels have significantly altered the paths by which goals can be achieved. Even with the changes, however, the ultimate goal of the program has remained the same: to make solar thermal technologies a viable alternative to fossil fuels for producing energy.

The Solar Thermal Program was started with the assumptions that the cost of oil and gas would continue to increase rapidly while the price of solar thermal technologies would decrease due to an aggressive federal program. Figure 2 shows that these assumptions were projecting the possibility of the technologies being economically competitive by the late 1980s.

During the early part of the program DOE’s charter was to develop the technology and to assure that those solar-related goals were met. This included research, technology development, and large-scale system demonstrations.

The large solar thermal budgets of 1978-1981 were primarily the result of several large system experiments. The largest was to prove the technical feasibility of central receivers

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FRANK WILKINS

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Fig 1. Solar thermal technology funding history.

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Fig. 2. 1980 oil price projections and cost goals for new technologies.

and a IO-MWe pilot plant built at Barstow, California. This system uses 18 18 heliostats to focus the sun’s energy on a receiver that produces steam at 1050°F. Although there have been some technical problems, principally with receiver leaks and heliostat corrosion, this plant has done what it was intended to do. It was designed to generate 1OMWe and it has produced as much as 11.7 MWe. It has recently generated 81 MWhr (net) for a day and more than 5OOMWhr for a week, while being operated by the Southern California Edison Company.

Another system was built to prove the feasibility of parabolic dish technology. This was the Solar Total Energy Project, at Shenandoah, Georgia. The Shenandoah plant shown in Fig. 4, uses 114 parabolic dishes to supply energy to the Bleyle Knitwear factory. As with any pilot plant, Shenandoah proved valuable in learning the problems associated with a new technology. Technical problems with automated controls and the contamination of the heat transfer fluid provided the knowledge to make improvements in following generations of hardware. Shenandoah is now being operated by Georgia Power, supplying

Changing directions of the Solar Thermal Technology Program 181

Fig. 3. Solar One: the IO-MWe solar thermal central receiver pilot plant near Barstow, California.

Fig. 4. Solar total energy project operating at Shenandoah, Georgia.

the adjacent factory with electricity, steam and cool water for air conditioning. In addition to these two experiments, there were a number of parabolic trough

experiments to provide experimental data and to demonstrate to industry that the technology could supply the needs for process heat. These systems showed that troughs could indeed efficiently collect solar energy-when they were working. Unfortunately, many suffered problems with trackers, controllers, and non-solar-related hardware pro- blems. Many off-the-shelf components that “should” have worked well on solar systems

182 FRANK WILKINS

turned out to be inadequate in the solar environment. Again, these were learning experiences that led to the next generation of hardware being more efficient and more reliable.

These systems taught us a lot, but the lessons were expensive. During the 197Os, in the midst of rapidly escalating oil prices, it was felt these costs were warranted. Beginning in 1981, however, there was a significant change in DOE’s philosophy. It moved away from demonstrations and large-scale experiments to more emphasis on research. It was felt that anything near the commercialization end of the R&D cycle was better left to private industry. In addition, instead of the cost of oil increasing dramatically, the actual price of oil stabilized, and then decreased. Figure 5 shows the actual cost of oil, and a recent prediction of future costs. Even this more recent prediction did not anticipate the dramatic decrease in oil prices in early 1986. This is considerably different from the assumptions made only 5 yr ago. The result was that, even though some of the cost goals had been reached, the technologies were still too expensive in a market of relatively inexpensive oil, gas and coal.

120

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Fig, 5. Projections of oil prices 1980 and 19841985 (the latter from Southern California Edison Co.).

The experiments at Barstow and Shenandoah as well as the trough projects proved the technical feasibility of the technologies. However, the systems were too expensive. It became clear that there was only going to be a near-term market for solar thermal systems if their cost became competitive with fossil energy at prices much closer to today’s prices, not at the very high predicted prices that were anticipated in the 1970s. It also became clear that future DOE Solar Thermal Technology budgets were going to be significantly smaller. There were a number of ramifications of shrinking budgets. Some major parts of the program had to be either phased out or scaled down. Parabolic troughs, for example, were the most advanced of the technologies and the closest to commercialization. It was thus the most vulnerable technology, and it went from a $15 million program to under $1 million in 2yr. The Solar Thermal Program transferred ownership of the trough projects and the Shenandoah dish experiment to the industrial or utility users. Involvement in the 10 MWe pilot plant was scaled down as much as possible under the co-operative agreement with Southern California Edison. Many individual tasks were phased out completely.

When the market did not materialize as expected and R&D dollars dried up, some industrial organizations decided to stop work on the technologies. Similarly, laboratory involvement was cut back. The Jet Propulsion Laboratory, which had been responsible for the parabolic dish program, phased out of the program in 1984. Sandia National Laboratory, Livermore, which had been responsible for the development ofcentral receivers, will be largely out of the program by 1987.

Changing directions of the Solar Thermal Technology Program 183

Fig. 6. Vanguard parabolic dish.

While these contractions led to a generally gloomy atmosphere in the R&D community, there were some bright spots. Chief among them was the operation of Vanguard, an 1 l- mdiameter parabolic dish that set a record for the highest-ever solar to electric efficiency. Vanguard I, Fig. 6, operated at 29% to produce 25 xW. In parabolic trough technology, a trough project called the Modular Industrial Solar Retrofit (MISR) led to the design of troughs that were reliable and achieved efficiencies of 60% while operating at 400°F. Finally, in central receiver technology, a co-operative group of utility, industry and government organizations combined resources and talent in a major experiment at DOE’s Central Receiver Test Facility to prove that molten salt receivers were more efficient and possessed a better storage system than the IO-MW pilot plant.

Time was also spent reorganizing the Solar Thermal Program to give it more research emphasis. Ideas were required for new concepts that would increase reliability and maintain efficiency while significantly reducing the cost of the systems. This had a very beneficial effect. It led to a new wave of creativity that had been somewhat submerged under the complacency of large budgets and the success of the Shenandoah experiment and the Solar One pilot plant.

One of the more dramatic innovations was the change in direction of concentrators, both heliostats and dishes. For 10 years R&D was focused on concentrators using silvered- glass reflectors. Silvered glass is highly reflective and durable. It is also expensive and heavy. Research is now aimed at replacing silvered glass with silvered polymers and using more efficient structural techniques to hold it. As shown in Fig. 7, this has the potential of decreasing the cost of heliostats by 50%. It will have a similar impact on dish technology. For example, the LaJet Co. has developed a membrane-based dish (Fig. 8) that is much lighter and less expensive than dishes using glass reflectors.

Another innovation addresses the size and weight of the receiver for central receivers.

184 FRANK WILKINS

Gloss / Metal Technology

$400/mz $240-160/m

Fig. 7. Heliostat research and development.

Fig. 8. LaJet membrane point-focus disc-Solar Plant One.

New research is looking at concepts that can absorb much more energy per square foot of absorber. The higher the energy absorbed, the smailer the receiver needs to be for the same power rating. Figure 9 shows the evolution of receivers that may lead to a direct absorber concept which is more efficient than previous receivers while being only a fraction of the size.

Changing directions of the Solar Thermal Technology Program 185

SOLAR 1 PGBE / BECHTEL

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Fig. 9. Central receiver R&D.

DIRECT ABSORPTION ISALT RECEIVER)

VERY HIGH FLUX ABSORPTION

An effort is also underway to learn more about the potential of concentrated solar energy. Thus far, nearly all solar thermal applications have converted concentrated solar energy into heat to be used directly for industrial processes or to be converted into electricity. The solar spectrum is very complex, consisting of high-energy photons in the U.V. down to less energetic, but more plentiful, photons in the i.r. We have long been aware of the negative effects of this. Many materials, for example, degrade much more rapidly in concentrated flux that in an oven at the same temperature. Research is now beginning to determine if these effects can be used in a beneficial manner. There is, for example, indication that certain hazardous wastes, when subjected to concentrated solar flux, degrade efficiently. The U.V. portion of the spectrum initiates a chemical reaction, and the remainder of the spectrum supplies heat to complete the reaction. In this way all of the energy is used efficiently, while taking advantage of the high thermodynamic quality of the energy source.

Research is also determining the benefit of a clean source of heat than can supply heat transfer rates in excess of 14MW/m2 and temperatures greater than 5000°F. As of now this is basic research. Perhaps it will lead to an efficient technique for splitting water to produce hydrogen and to the photo-catalysis of water and air to produce ammonia. However, very little is known about concentrated solar energy. To take full advantage of concentrated solar flux, we must learn more about it.

The Solar Thermal Technology Program has undergone considerable change since its inception. Some of the change was a consequence of political philosophy, some was from economic realities, and some was from technical breakthroughs. There are times when the uncertainty and change lead to frustration and inefficiency. It is not, however, an insurmountable problem. It requires a flexibility in outlook that can accept multiple paths to a goal. It also requires keeping up to date with the changing conditions and how they affect the various technical options

It was once said that progress is the art of preserving order amidst change and preserving change amidst order. There has been considerable change in the Solar Thermal Technology Program, yet there has been considerable progress. In the future there will be more change, and more problems. There will also be more progress and, with luck, a bit more order. But regardless of the problems ahead, the goal is worth the effort. As has been shown, predictions of the future are often inaccurate; particularly if they are precise. But there is only a finite amount of fossil fuel left in the ground, and some day other sources of energy will be needed. Solar thermal energy can be one of those sources. To make that a real option is the goal of the Department of Energy’s Solar Thermal Technology Program. The goal can be attained.