SuperGrid – Storage Technology for Linear Fresnel Power Plants

Duration: May 2011 - April 2014  
Contracting Authority/ Sponsors: Fraunhofer-Gesellschaft, Program "Märkte von Übermorgen", Fördernummer 823 813, Project "Supergrid"  
Project Partners: Fraunhofer-Institut für Integrierte Systeme und Bauelementetechnologie IISB, Erlangen; Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung, Institutsteil Angewandte Systemtechnik IOSB/AST, Ilmenau; Fraunhofer-Institut IWM, Freiburg; Fraunhofer-Institut für System- und Innovationsforschung ISI, Karlsruhe  
© Photo Fraunhofer ISE

Fig. 1: Schematic diagram of a direct molten salt power plant (left) and a dual-loop power plant (right).

© Photo Fraunhofer ISE

Fig. 1: Simulated power versus operating hours per year for the reference, DMS and dual-loop power plants located at Daggett, USA.

In contrast to PV power plants, solar thermal power plants can also supply electricity as required during periods with little or no solar radiation due to the integration of thermal storage units. Different storage solutions are appropriate for different types of collectors. We have investigated various storage technologies and power plant concepts for linear Fresnel collectors and compared their levellised costs of electricity to those of a modern reference power plant (parabolic trough power plant with an indirect storage system).

A reference system was compared to a direct molten salt (DMS) power plant with direct storage in two tanks (Fig. 1, left), and a dual-loop power plant, consisting of a combination of thermal-oil and molten-salt solar fields with an indirect/direct storage system (Fig. 1, right). The reference design is based on that used in the Andasol power plants in Guadix, Spain. For each power plant design, the optimal number of loops to achieve the lowest levellised cost of electricity (LCOE) is determined by calculating the annual yield. As a result, the net annual electricity yield varies from case to case. Each of the power plants included a 1000 MWhth molten salt storage unit and a 50 MWel power block. The ”ColSim-CSP“ software developed by Fraunhofer ISE was used for the simulations.

Fig. 2 presents the power versus the operating hours per year for the reference, DMS and dual-loop power systems located in Daggett, USA. The lowest LCOE for the assumed parameters is achieved with the dual-loop concept. The direct molten salt concept also achieves low LCOE, is less complex and is best suited to providing power flexibly. If the costs of the solar field and the heat exchanger system could be reduced by about 15%, the direct molten salt concept could present the best option.

About SuperGrid

Further aspects of the SuperGrid project in different business areas focus for instance on "High-efficiency Power Electronics for Medium-Voltage Applications". The topic of computer modeling of potentially suitable energy systems is addressed in the article "Energy-economic Analysis of a Future Supergrid between North Africa and Europe".