August 2, 2018

Safety in solar power plants – silicone oil passes final qualification test

There are currently no uniformly applicable standards or regulations for approval and market introduction of novel heat transfer fluid for operation in solar thermal parabolic trough power plants. In principle, the medium must be independently qualified in terms of its chemical and thermodynamic properties. A considerable large-scale technical effort is required for the mandatory demonstration of a thermal oil under realistic power plant conditions. Scientists from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), together with international partners from research and industry, have successfully demonstrated the practical suitability and functionality of a new silicone oil-based heat transfer medium in the southern Spanish province of Almería.

Operational safety is an important issue in the development of components and heat transfer media used in solar power plants. The comparatively new solar thermal power plant sector has hitherto lacked clear and internationally recognised procedures and standards for the qualification of a new type of heat transfer medium. This is due to the fact that almost all existing parabolic trough power plants use an identical heat transfer fluid type.

The PROMETEO test facility at the Plataforma Solar de Almería (PSA), which is one of the large laboratories of the Spanish Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), offers developers ideal opportunities to demonstrate the safe operation of a new heat transfer fluid.

Field trial

A burst pipe was simulated as part of a field trial conducted by WACKER Group, DLR and CIEMAT (Spain). The leakage, simulated using a very fast opening valve, caused the 420 degree Celsius hot heat transfer fluid to escape without igniting.

For the experiment, special attention was paid to the full-scale conditions in order to illustrate the circumstances in commercially operated facilities on a one-to-one basis. The accident scenario was based on the worst possible failure that has occurred to date. The entire process, from the initial idea of the trial to its set-up and implementation, was monitored and supported by TÜV Nord.

The trial was one of the final steps in the complete qualification of the silicone oil HELISOL®5A, a heat transfer fluid for parabolic trough power plants developed by the WACKER Group in Munich. The oil had previously passed the so-called 'proof of concept' successfully during an aptitude test, in which it was solar operated for 480 hours at an operating temperature of 425 degrees Celsius in the demonstration plant (totalling 1100 hours of solar operation).


Scientists from the DLR Institute of Solar Research and CIEMAT are running the PROMETEO test facility at the Plataforma Solar de Almería as part of the SITEF (Silicon Fluid Test Facility) and SIMON (Silicon Fluid Maintenance and Operation) projects.

In addition to DLR as project coordinator and Wacker Chemie AG, the companies involved at the industrial end are TSK Flagsol, TÜV NORD, Senior Flexonics GmbH, innogy SE, Rioglass Solar and flucon GmbH. At the research end, the Spanish CIEMAT (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas) – the owner of the PROMETEO test facility – has been cooperating with DLR for more than two decades to increase the efficiency of solar power plants.

The main aim of the project, which is funded by the German Federal Ministry for Economic Affairs and Energy and the Spanish Ministry of Science, Innovation and Universities, is to increase the efficiency of parabolic trough power plants while reducing operating costs.


Michel Winand

Corporate Communications Aachen, Bonn, Cologne, Jülich, Rheinbach and Sankt Augustin
German Aerospace Center (DLR)
Corporate Communications
Linder Höhe, 51147 Cologne
Tel: +49 2203 601-2144

Christoph Hilgert

German Aerospace Center (DLR)
Institute of Solar Research
DLR Institute of Solar Research
Linder Höhe, 51147 Cologne