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Proceedings of a Workshop: Potential Applications of Concentrated Solar Energy PLENARY SESSION STATUS OF EUROPEAN R&D IN SOLAR CHEMISTRY AND INDUSTRIAL INTEREST IN THIS TECHNOLOGY Paul Kesselring Paul Scherrer Institute Villigen, Switzerland ABSTRACT A short, noncomprehensive summary of the European situation is given and some technical aspects of the European R&D activities are sketched. In conclusion, the long-term prospects for solar chemistry are considered to be good, which justifies an increased R&D effort. The expectations of short-term, strong impact applications, however, should not be boosted. INTRODUCTION The picture of the status of European R&D in solar chemistry as described in this contribution is mainly based on contacts and knowledge gained by international cooperation, in particular within the International Energy Agency (IEA). Thus, whereas it may not be comprehensive, it will characterize the general situation properly to a good extent. GENERAL In order to understand the European R&D situation, it helps to sketch briefly a point of view with regard to solar chemistry (which is more or less widely accepted in Europe): If solar energy is expected to replace some of the functions which fossil fuels fulfill in today's energy systems, then the production of synthetic secondary energy carriers is indispensable. These functions are mainly seasonal storage and long distance transportation, in conjunction with many applications such as individual traffic or domestic heating. The idea is to import solar energy from the well-insulated, usually less industrialized southern parts of Europe or North Africa to the cold, energy-demanding and, in general, heavily industrialized parts of northern Europe. These are considered to be quite important, however clearly long-term prospects for solar energy. In contrast, solar electricity production is expected to have a moderate mid-term and even a small short-term impact (remote applications and ''solar pioneers''). These considerations, together with the fact that solar chemistry is a "young" technology (which has received much less attention during the last 15 years than solar heating and cooling or electricity generation), have led to the following situation: Only a few larger scale (kW range) experiments exist. There are no practical engineering applications as yet. On the university level there are modest to medium, definitely increasing, basic R&D efforts. However, there is a much larger, as yet untapped, potential of expertise at universities. Many scientists are not aware of the fact that their knowledge and know-how could be very valuable for solar chemistry R&D and its application.
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Proceedings of a Workshop: Potential Applications of Concentrated Solar Energy Industry begins to pay attention to the development but, in general and for the time being, is reluctant to invest as there is no short-term market in sight. Money mostly comes from government authorities who can afford an interest in long-term energy issues. In general, funds have been increasing during the last five to ten years. As an example, Switzerland spent almost nothing on solar chemistry ten years ago. Today the annual budget is about 2 million dollars, which corresponds to roughly $0.30 per inhabitant. Provided good proposals will be available, this budget could possibly double or triple during the next five years. SOME TECHNICAL ASPECTS R&D Issues The R&D objectives in Europe are similar to those in the United States, although priorities might be different. The main issues are synthetic secondary energy carrier (e.g., hydrogen or methanol; probably higher priority than in the U.S.). production of high value chemicals; and detoxification of hazardous waste (probably lower priority than in the United States). To reach these goals, all different forms of solar chemistry are investigated: photochemistry (near ambient temperature) thermochemistry (using solar heat) electrochemistry (using solar electricity) and the combinations thereof: photoelectrochemistry photo-assisted thermochemistry high temperature electrochemistry Topics 1, 2, 4, and 5 are the fields receiving most attention at present. Topics 3 and 6 are not always considered to belong to solar chemistry, which is a mistake (at least in my opinion). The solar-specific boundary conditions may lead to requirements which go beyond those of ordinary electrochemistry, and their consequences should not be underestimated. Photochemistry and Photoelectrochemistry In Europe the splitting of water and the reduction of CO2 seem to be the dominant issues. The "scientific background" is given by 20 years of research in photography, photochemistry with lasers, and investigations of natural photosynthesis. Research is concentrated in universities and scientific research institutes. Basic research problems clearly dominate. They are the same in Europe as in the United States, e.g., charge transfer questions in redox systems or corrosion mechanisms in photoelectrochemistry. Countries involved are Germany, Italy, Switzerland, Sweden, Great Britain, and France. The order given corresponds more or less to the importance of the efforts in the respective countries (according to a necessarily somewhat subjective judgment of a colleague of mine, working personally in the field). International contacts are made and cooperation is stimulated mainly by the biannual International Conference on Photochemical Conversion and Storage of Solar Energy, the proceedings of which usually appear in the Journal of Photochemistry (last conference: Palermo, 1990). High Temperature Thermochemistry and Photo-Assisted Thermochemistry In Europe, topics 5 and 6 are intimately connected to the International Energy Agency's Small Solar Power Systems Project (IEA-SSPS-Project).
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Proceedings of a Workshop: Potential Applications of Concentrated Solar Energy European countries involved are mainly Germany, Spain, Switzerland and, to a small extent, Sweden. The scientific and technical background consists, on the one hand, of experience gained in solar thermal electricity generation (collection and handling of solar high temperature heat) and, on the other hand, of knowledge from nonsolar thermochemistry. A typical example of the latter are the nuclear process heat applications, studied mainly during the 1970s. Examples: Steam-reforming of methane and the sulfuric acid watersplitting cycle ("GA-process") are being adapted to the special solar conditions (experiments under way and in preparation, respectively). Compared to the conventional processes, they have additional difficulties (e.g., transients) but also definite advantages (e.g., direct absorption of radiation in volumetric receiver-reactors). The main issues here are of a technological, and not of a basic scientific, nature. A completely different situation exists with respect to the combination of thermochemistry and photochemistry at high temperatures or, to a somewhat lesser extent, to light-induced/assisted catalytic reactions at medium temperatures. In this interesting and promising field we have neither good theoretical understanding nor can we draw upon past experimental experience. There is the intention to improve this situation considerably by a double effort within the five-year follow-up program of the IEA-SSPS project, which is currently under discussion. The first part consists of a basic R&D program, centered around gas/gas or solid/gas reactions at high temperatures combined with high solar fluxes and catalyzed reactions under high solar fluxes and medium temperatures (e.g., < 300°C). The second part should bring a larger-scale experiment, demonstrating the potential of this more recent branch of solar technology. The main institutions involved in this program will be (and are already) universities and research institutes. There are indications that some companies will participate also. Remark Concerning Comparison Criteria for Different Solar Technologies In the years to come, we will have the problem of judging and selecting the different evolving chemical processes with respect to their future potential for practical applications. It is my personal opinion that we should do more to develop sound criteria for this selection process. Very generally speaking, the properties inherent to solar radiation lead to the following requirements: Minimize the use of material in collecting solar energy (low power density of radiation) Use as much of the solar spectrum as possible Minimize response times at the "front end" of a process (transients) It would lead us too far into detail to show that including such solar-specific criteria into a ranking procedure might change its outcome considerably. In the past, this has been neglected too often. CONCLUDING REMARKS In Europe, solar chemistry in recent years has been and still is on the upswing. However, it is a young technology still in need of a major effort in basic R&D. Near-term applications will very probably be limited to niches. In this situation it is important not to oversell this technology—in particular to resist the temptation to sell it as a short-term solution to the "greenhouse problem." The real importance of solar chemistry lies in its long-term potential to substitute functions that are fulfilled now by fossil fuels. Thus, in the long run it actually may help to mitigate the CO2 problem. In order to shorten the basic R&D phase and accelerate practical application, an increased R&D effort is justified. However, a crash program based on exaggerated expectations would do more harm than good. What we need are not crash programs but continuity of R&D on a reasonable funding level.
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