J. Ignacio Ortega, J. Ignacio Burgaleta and Felix M. Tellez.

Journal of Solar Energy Engineering (Transactions of the ASME), Vol. 130, No. 2, May 2008, pp. 024501 (6pp).

Of all the technologies being developed for solar thermal power generation, central receiver systems (CRSs) are able to work at the highest temperatures and to achieve higher efficiencies in electricity production. The combination of this concept and the choice of molten salts as the heat transfer fluid, in both the receiver and heat storage, enables solar collection to be decoupled from electricity generation better than water/steam systems, yielding high capacity factors with solar-only or low hybridization ratios. These advantages, along with the benefits of Spanish legislation on solar energy, moved SENER to promote the 17MWe Solar TRES plant. It will be the first commercial CRS plant with molten-salt storage and will help consolidate this technology for future higher-capacity plants. This paper describes the basic concept developed in this demonstration project, reviewing the experience accumulated in the previous Solar TWO project, and present design innovations, as a consequence of the development work performed by SENER and CIEMAT and of the technical conditions imposed by Spanish legislation on solar thermal power generation.

Wolf-Dieter Steinmann and Rainer Tamme.

Journal of Solar Energy Engineering (Transactions of the ASME), Vol. 130, No. 1, Feb. 2008, pp. 011004 (5pp).

Solar thermal systems, including direct steam generation in the absorbers, require isothermal energy storage systems. One option to fulfil this requirement is the application of phase change materials (PCMs) to absorb or release energy. The implementation of cost-effective storage systems demands the compensation of the low thermal heat conductivity that is characteristic for the candidate materials for PCM. Solar steam generation for power plants requires latent heat storage systems for a saturation temperature range between 200 deg C and 320 deg C. This paper describes the basic concepts investigated and first results of research activities aiming at the demonstration of a storage system using steam provided by parabolic trough collectors.

Yolanda Lechon, Cristina de la Rua and Rosa Saez.

Journal of Solar Energy Engineering (Transactions of the ASME), Vol. 130, No. 2, May 2008, pp. 021012 (7pp).

The objectives of the analysis reported in this paper are to evaluate the environmental impacts of the electricity produced in a 17MW solar thermal plant with central tower technology and a 50MW solar thermal plant with parabolic trough technology, to identify the opportunities to improve the systems in order to reduce their environmental impacts, and to evaluate the environmental impact resulting from compliance with the solar thermal power objectives in Spain. The methodology chosen is the life cycle assessment (LCA), described in the international standard series ISO 14040-43. The functional unit has been defined as the production of 1kWh of electricity. Energy use needed to construct, operate, and dismantle the power plants is estimated. These results are used to calculate the 'energy payback time' of these technologies. Results were around 1yr for both power plants. Environmental impacts analyzed include the global warming impacts along the whole life cycle of the power plants, which were around 200g/kWh generated. Finally, the environmental impacts associated with the compliance of the solar thermal power objectives in Spain were computed. Those figures were then used to estimate the avoided environmental impacts including the potential CO2 emission savings that could be accomplished by these promotion policies. These savings amounted for 634kt of CO2 equiv./yr.

P. J. T. Straatman and W. G. J. H. M. van Sark.

Solar Energy, Vol. 82, No. 6, 2008, pp. 520-527.

Solar thermal electricity (STE) generation offers an excellent opportunity to supply electricity with a non-CO sub(2) emitting technology. However, present costs hamper widespread deployment and therefore research and development efforts are concentrated on accelerated cost reductions and efficiency improvements. Many focus on the latter, but in this paper we rather focus on attaining very low levelised electricity costs (LEC) by designing a system with very low material cost, while maintaining appreciable conversion efficiency and achieving low maintenance cost. All investigated designs were dimensioned at a 50 MW scale production. Calculated LECs show that a new proposed hybrid of ocean thermal energy conversion with an offshore solar pond (OTEC_OSP) may have the lowest LEC of 0.04 /kWh. Addition of a floating offshore solar pond (OSP) to an OTEC system increases the temperature difference in the Rankine cycle, which leads to an improved efficiency of 12%, while typical OTEC efficiencies are 3%. This higher efficiency leads to much lower investments needed for power blocks, while the OSP is fabricated using very low-cost plastic foils. The new OTEC_OSP design can be located in many sunny coastal areas in the world.

D. Kruger, Y. Pandian, K. Hennecke and M. Schmitz.

Desalination, Vol. 220, No. 1-3, 1 Mar 2008, pp. 612-618.

Solar thermal parabolic trough collectors can be used to provide heat for desalination, cooling and electricity generation. The set-up and some intermediate results of a measurement campaign for the evaluation of a parabolic trough collector - the Solitem PTC1800 - are presented. Optical tests of the concentrator were used to determine the intercept factor, allowing to give recommendations for optical improvements. Thermal testing up to 200 super(o)C with pressurised water showed low radiative and convective losses.