25 January 2018
DLR scientists of the Institute of Solar Research and industrial partners have developed a new insulation for the radiation receiver of a solar tower power plant. The radiation receiver is located in a cavity at the top of the solar tower. The cavity insulation used has to be able to withstand high loads like direct concentrated radiation, temperatures above 1000 degrees Celsius with strong fluctuations and weather influences. The product is market-ready and is being distributed by Eugen Arnold GmbH.
Previous types of insulation suffered damage after a short period of operation. The damage ranged from gaps which reduce the efficiency of the power plant to damage to safety-critical areas such as the receiver suspension, which could cause a complete failure of the system.
Success requires a harmonious blend - Cavity made of a new mix of materials passes solar tests
The new insulation consists of a multi-layered material mix. Its design compensates known problems of directly irradiated insulation, for example uneven shrinkage and embrittlement. The outermost layer is a high quality ceramic sheet or fabric based on ceramic fibres. It is resistant to high temperatures and prevents the underlying layers from discharging fibres. The inner layers consist of different kinds of high temperature wool as well as microporous materials. The scientists had determined in preliminary tests what temperature range the materials were most suitable for. The insulation was divided into several segments to facilitate transport and installation. Each segment fit into the lift of the solar testing tower, thereby making a special construction crane unnecessary.
The new product was tested at the experimental tower power plant of the Plataforma Solar de Almería (PSA) in Spain. The PSA is owned and operated by CIEMAT. The researchers exposed the insulation to 100 hours of concentrated solar radiation under realistic conditions, resulting in material temperatures in excess of 1000 degrees Celsius. They recorded the temperatures at various depths as well as the temperature distribution on the surface. At the same time, the flux density of the incident radiation was determined. It was the first time that the real load of a solar irradiated cavity could be displayed and analysed with high resolution. The concept of the new cavity insulation proved to be very successful in the tests. There were no damages in the test phase and no material failure occurred even in areas of heavy loads.
The development was funded by the Federal Ministry for Economic Affairs and Energy. In addition to DLR as project coordinator, the companies Eugen Arnold GmbH and Walter E.C. Pritzkow Spezialkeramik were involved.