Present Situation
The new legal framework defined in Spain by the Royal Decrees 436/2004 (BOE of 27/03/2004) and 2351/2004 (BOE of 24/12/2004) has given an important boost to the Spanish industrial activity related to solar thermal power plants. The bonus of 0,18 €/kWh established for the electricity produced with concentrating solar power plants in any of their three options (parabolic-troughs, central receiver or Stirling dishes), together with the possibility of gas hybridization up to a maximum of 12% - 15%, has consolidated the interest of industries and investors in solar concentrating technologies. The result of this interest is the promotion of 5 solar thermal power plants with central receivers and parabolic-troughs in Spain.
Medium Concentration:
With regard to parabolic-trough collectors technology, the technical and commercial maturity reached by solar power plants (mainly due to the valuable experience gathered by the SEGS plants in California) contrast with the lack of development in other fields that are also interesting for this type of solar collectors, such as industrial heat processes and air conditioning.The lack of solar collectors and industrial equipments with adequate characteristics for this type of applications make an intense R&D activity necessary to achieve the same level of development than in electricity generation. Spain, like many other Countries located in the so-called Earth Solar Belt, have climatic conditions that make very attractive these other applications of parabolic-trough collectors.
If we add to this fact the experience gained by CIEMAT at the Plataforma Solar de Almería (PSA), it seems evident that at present it is convenient to work in the development of components for air conditiong and industrial process heat applications. For this reason, we are participating in Task 33/4 ('Solar Heat for Industrial Processes', SHIP; www.iea-ship.org/) of the International Energy Agency, to exchange experience and know-how with other international institutions working on these fields.
At the same time, direct steam generation in the absorber tubes of the parabolic-trough collectors is being consolidated as a very important wayfor cost reduction and maintenance simplification of this type of solar collector plants.
High Concentration:
Central receiver systems, after the scaling-up and demonstration phase, are now ready to start their commercial exploitation. Testing of more than 10 experimental small solar power plants of this type (0,5 - 10 MWt), mainly in the 80s of last century, served to demonstrate the technical feasibility of this concept and its capability to operate with large thermal storage systems. The biggest experience took place at the Plataforma Solar de Almería and in the Solar One and Solar Two plants in Barstow (California).The R+D projects carried since then, have allowed components and procedures enhancement, so that a global efficiency of 23% (conversion from solar to electricity) is predicted for design point and a value of 20% for annual global efficiency. Nevertheless, the greatest challenge for central receiver systems at present is the start up of the first generation of commercial plants connected to the grid under market conditions and with routine operation. The three central receiver technologies that are preparing their first commercial plants are based on the use of molten salts, saturated steam and air-cooled volumetric receiver.
The high investment cost is still a handicap for the complete commercial exploitation of central receiver systems. The first commercial applications, which are ready to come out, still show a specific cost of) 3.000 Euro per kW of installed power, and an electricity production cost between 0,18 to 0,20 Euro/kWh. Cost reduction in the technology is, therefore, essential for the commercial expansion of these solar systems. Since we are well aware of this problem, PSA permanently keeps a R+D program related to central receiver technology, aiming at cost reduction and efficiency improvement.
Solar Fuels and Solarization of Industrial Processes:
As far as solar furnaces are concerned, the number of applications for these high concentration solar systems is increasing and new reactors are being developed to supply heat to industrial processes requiring thermal energy and to eliminate contaminants by using concentrated solar radiation. The main objective is to demonstrate the technical feasibility of solar furnaces to supply thermal energy to industrial processes that work at high temperature and are different from electricity production or metallurgical treatments.At the same time, the control systems are being improved to keep the temperature and solar flux more stable at the focus.
Due to the valuable experience gathered during the past years and the experimental facilities available, PSA is at a leading position also in this solar field at present. Test facilities wil be soon improved with the start up of a new solar furnace with vertical axis and provided with a 3,5 m diameter high-quality concentrator, which is placed at the top of a 18 m tower. It is expected that a concentration of 8000X will be achieved with this new solar furnace because it does not need a mirror to rotate 90º the focus from the original vertical focal plane to the horizontal plane.
The concentration and nominal power of this furnace is thus increased. Since hydrogen is a clean source of energy, its production is considered of high priority in Spain and Europe at present. Nowadays, 95% of the hydrogen consumed is produced from natural gas and a great effort is needed to develop new non-pollutant production processes.
This is the goal of the new R+D projects in this field. The way how a economy based on hydrogen can be implemented is currently under discussion and there is not a global agreement about the feasibility of R+D projects to develop new technologies for massive hydrogen production.
The significant technical development of renewable energies in Spain, together with the searching of ways to increase the value of the national coal, are key factors when selecting hydrogen production processes suitable with our national interests, just as Iceland has approved an ambitious program to use geothermal energy for hydrogen production. Under the same premises, France has launched the Pan-H Program aimed at hydrogen production using nuclear energy.
As far as Spain is concerned, there are several R+D projects currently underway: there are several projects at the Plataforma Solar de Almería aimed at using solar energy for hydrogen production, the company EHN is investigating the use of wind energy for hydrogen and CEDER (Centro Español de Energías Renovables) is participating in the integrated European project CHRISGAS which is investigating the use of biomass for hydrogen production. There are also demonstration projects promoted by REPSOL with in-situ methane reforming in fuel stations; the Spanish pilot plant ELCOGAS (coal gasification) is also worthwhile to be mentioned here.
It must also be mentioned that CIEMAT, in collaboration with the French CEA and the Italian ENEA, is preparing the set up of the Experimental Platform SUSHYPRO, and a work plan to test hydrogen massive and clean production systems using thermal processes at high temperature and without CO2 emissions.
Following the strategic guidelines defined in SUSHYPRO, the Plataforma Solar de Almería has started several R+D projects in the last two years to develop new technologies for hydrogen production using thermo-chemical processes based on concentrated solar radiation (Projects PDVSA, INNOHYP y SOLTER-H). These activities are performed within the Group of Solar Fuels, which is included in the Unit of Solar Concentrating Systems.
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