SOLAR RESEARCH By Christoph Richter and Diego Martinez Plataforma Solar A German-Spanish co In the province of Almeria in southeast Spain, on the edge of the Tabernas Desert, lies the Plataforma Solar de Almería (PSA). On this over-250-acre site, the full force of the Andalusian sun has been exploited since 1980 for the testing and optimisation of a variety of high-temperature solar technologies under nearly practicable conditions. More than 20,000 square metres of mirrors of various shapes in different test facilities concentrate the direct solar radiation to generate high and extremely high temperatures. These facilities in the middle of a barren landscape, some of which seem to have come from the 22
de Almería operative venture future, make up the largest test centre in Europe for concentrating high-temperature solar technologies and one which leads the world in its variety. Every year, the site fascinates not only solar enthusiasts, but numerous scientific and private visitors. DLR played a major role in its planning and construction, and has been making use of the facility since the very beginning with on-site scientific staff to conduct its own solar technology testing and development work. It works in close co-operation with its Spanish partner, CIEMAT, which owns and operates the facility today. 23
SOLAR RESEARCH The founding of the PSA can be traced back to international efforts to find ways of using alternative sources of energy following the first oil price crisis in 1973. In order to evaluate and enhance the potential of solar thermal power plants, the International Energy Agency (IEA) launched an international project in the second half of the 70s with the aim of building a solar tower and a parabolic trough test facility, each designed to produce 500 kilowatts of electricity. At the time, there were nine countries participating (Belgium, Germany, Greece, Italy, Austria, Switzerland, Sweden, Spain and the USA). The Spanish government provided a test site for this project, which was known as the Small Solar Power System (SSPS) and was co-ordinated by DLR. The site was in the Tabernas Desert, which not only offered excellent insolation conditions (more than 3,000 hours of sunshine and more than 1,900 kilowatt/hours of direct solar radiation per square metre and year), but also promised to create new jobs in a region whose use as an impressive scenic backdrop for many of the Westerns and action films produced in the second half of the 70s was declining sharply. Test operations at the SSPS facility began in 1980. In addition, at the initiative of the Spanish government, a purely Spanish project went into operation in 1982. This was the CESA I (Central Electrosolar de Almería) power tower plant, which was designed to produce one megawatt of electric power. From 1985 to 1987, the CESA I facility was used to test the first major German-Spanish project, GAST (Gas Cooled Solar Tower). At about the same time, the SSPS facility was transferred to Spain by the IEA, thus uniting the organisation of the two facilities into today s PSA. Parallel to this, a bilateral agreement was negotiated between Germany and Spain for the joint scientific use of the PSA for the development, testing and demonstration of concentrating high-temperature solar technology. In the context of this CHA (Convenio Hispano-Aleman), which took effect in 1987, it was agreed that there should be two managing institutions as equal partners, namely the CIEMAT on the Spanish side and the DLR on the German. The CHA for joint Spanish-German management of the PSA remained in force until the end of 1998. During that time, the test capacity of the PSA was expanded considerably through the construction of a solar furnace, a number of dish/stirling units 24
and the DISS facility for the direct generation of steam, thereby increasing its leading position internationally, especially with regard to technological diversity. This was also made possible to an increasing extent by the financial participation of the EU from about the end of the 80s, which, through various projects, contributed roughly one third of the annual budget, totalling approximately three to four million Euros over the years. Apart from numerous solar projects, the PSA also came to the attention of the general public as a major European research facility with a test programme conducted for the European Space Agency aimed at investigating the effects of the temperature shock on the outer ceramic shell protecting the Hermes space plane during its re-entry into the atmosphere. The specific possibilities of space-related research work were also used intensively by scientists from the Max Planck Institute as of the late 90s to study Cherenkov radiation with the aid of the large heliostat mirror array in the CESA I field. After 1999, the CIEMAT assumed sole management responsibility for the PSA, because the German government of the day had already decided in 1997 to terminate the CHA in its existing form. The desire of the two PSA partners (DLR and CIEMAT) to continue their successful co-operation came to fruition in the form of a joint arrangement to conclude more specifically project-related cooperation agreements, each running for a period of three years. In this context, DLR makes a considerably reduced financial contribution to the running costs of the PSA and therefore also has a substantially reduced formal influence on the utilisation of the various test facilities. Despite this sharp cut-back on the German side, the quality and quantity of the scientific work conducted by the two partners at the PSA has in practice been at least maintained or even increased at the present time thanks to some very successful project acquisition efforts. This is not in the least due to the mutual trust that has developed among the German and Spanish employees working there in the course of their many years of co-operation. This period has also witnessed such important new milestones in the further development of high-temperature solar technology as the demonstration of direct steam generation and the delivery of solar energy to gas turbines at temperatures of 1,000 degrees centigrade; it has also seen the design, construction Fig. previous page: View over the Plataforma Solar (PSA) at Almería, Spain Fig.: Testing and developing in Andalusia, one of the driest and sunniest areas in Europe (six days of rain a year on average). 25
SOLAR RESEARCH and testing of the European parabolictrough collector Eurotrough and the dish/ Stirling system EuroDish, product developments which it is hoped to introduce on the global market. Test facilities The 83-metre-high solar tower of the CESA I facility, which can be seen for miles around, is something like a symbol of the PSA. It is where a total of 300 40-squaremetre heliostats concentrate the solar radiation, providing about seven megawatts of thermal energy for tests on the four test levels available on the tower, which have already been used for numerous large-scale solar experiments. The somewhat smaller CRS solar tower facility, which still dates from the SSPS project, has ninety heliostats of the same size and two test levels, offering good conditions for smaller projects and test objects. The most emblematic facility in the parabolic trough sector is without doubt the DISS loop, which has now been extended to a total length of approx. 700 metres, and whose roughly three megawatts of thermal power is used for the direct generation of steam at 100 bar and more than 400 degrees centigrade. The 75- metre-long Eurotrough collector and the 50-metre-long LS3 collector are important test facilities for experiments on highperformance absorber tubes, the development of photogrammetric measuring methods and tests on a high-temperature storage system using solid storage media, which recently went into operation. In the dish/stirling field, two EuroDish facilities with mirrors eight and a half metres in diameter are currently in continuous operation and are being used to test new components, and another four facilities of an older design can be equipped for specific test requirements. This is only a brief survey of the most important facilities for research into solar thermal electricity production. Other resources, such as a solar furnace and solar chemical test facilities for water detoxification, round off the range of systems available at the PSA. For the professional operation of these facilities, there is at present an on-site team of about 20 scientists and engineers from CIEMAT and twelve from DLR, while some 40 more Spanish colleagues are employed for the supporting work in 26
operation, maintenance and administration. Numerous students and, especially in the summer months, scientists from a variety of national and European programmes and other European research institutions receive funding to stay as guests, so that at any one time the total active work force at the PSA can often comprise more than one hundred individuals. Outlook At the end of March 2004, a new Spanish Electricity Law regulating the framework for feeding electricity into the grid took effect, creating attractive conditions for building solar thermal power plants and noticeably increasing the interest of German, Spanish and international project developers, technology suppliers and utility companies in the possibilities and market opportunities offered by this technology, and not only in Spain. Against the background of increasing efforts to protect the climate, and in view of the fact that oil prices are once again very high at present, the development leading to the construction of new solar thermal power plants has been given fresh impetus throughout the world, as illustrated in particular by the Global Market Initiative (GMI), which was signed by a number of countries at the Renewables 2004 conference in Bonn with the goal of installing 5,000 megawatts of generating capacity over the next ten years. This dynamism is also apparent at the PSA, which has seen a growing number of enquiries from various parties requesting technical advice, co-operation on projects and reports in the media. Against this background, DLR and CIEMAT are striving for renewed intensification of their co-operation and expansion of the test facilities at the PSA in order to meet the growing demand for research and development in this field. The prospects for a truly sunny future in German-Spanish cooperation have seldom been as good as they are today! Dr. Christoph Richter is the head of the DLR Delegation at the Plataforma Solar de Almería (PSA), Spain, and Diego Martinez is the Director of the PSA. 27 Ill.: Heliostats reflect and concentrate the sunlight to high energy densities.