Solar-Wärme bei 100 bis 800°C im Megawatt-Maßstab für deutsche und europäische Produktionsstandorte

Nutzung von Solar-Wärme aus konzentrierenden Kollektoren für Produktionsprozesse im Megawatt-Maßstab - Grundlagen und Technologie - Erzeugung und Verwendung klimaneutraler Prozesswärme an Produktionsstandorten - Realisierte Praxisbeispiel

Parabolrinnen-Qualitätskontrolle in der Serienfertigung Q-Foto

Mittels photogrammetrischer Methoden lassen sich quantitative Größen für die Qualifizierung der Genauigkeit eines Parabolrinnen-Kollektors schnell und zuverlässig messen. Für eine Serienfertigung der Parabolrinnen wurde eine automatisierte photogrammetrische Messeinrichtung entwickelt. Sie wird in die Kollektorproduktionslinie integriert und ermöglicht es, Montagefehler im Produktionsprozess sofort zu erkennen, um rechtzeitig deren Ursachen zu beseitigen. Der Einsatz eines solchen Systems stellt daher eine sinnvolle Maßnahme zur Dokumentation der Fertigung sowie zur Sicherung des energetischen Ertrags des Solarfeldes und damit des ökonomischen Erfolges eines Kraftwerkprojekts dar

Air Leakage Detection in Building Façades by Combining Lock-In Thermography with Blower Excitation

Air leakage in building envelopes is responsible for a large portion of the building’s heating and cooling requirements. Therefore, fast and reliable detection of leaks is crucial for improving energy efficiency. This paper presents a new approach to determining air leakages in a building’s envelope from the outside, combining lock-in thermography and thermal excitation by a blower door system. The blower creates a periodic overpressure within the building, inducing periodic temperature variations of the surfaces near the leaks on the outside surface, the façade. With the temperature variations excited at a known frequency, Fourier transforms of the time-series of the thermal images at the excitation frequency result in amplitude and phase images highlighting the areas affected by leaks. Periodic excitation and detection by an IR camera is known as lock-in thermography and is widely used to characterize semiconductor devices and in non-destructive testing. Excitation is usually achieved by optical, electrical, or mechanical energy input. For this work, measurements of outside façades have been performed with three excitation cycles of a period of 40 seconds at a 75 Pa pressure difference, leading to a total measurement time of only 2 minutes. Measurements have been performed with air temperature differences of 5 to 7 K at highly variable conditions of irradiance, wind, and cloud cover. The measurements show higher detection quality and less impact from changing ambient conditions than the state-of the-art differential infrared thermography measurements. With the method highlighting the variations in the amplitude image only at the excitation frequency, variations caused by environmental effects are filtered out. A temperature difference as low as a few Kelvin is therefore sufficient, and large façades can be examined from the outside. This amplitude image is already clearer than an image created with differential thermography. A further reduction of unwanted artefacts in the image is demonstrated using phase-weighing of the amplitude by scalar product

Detection of Air Leakage in Building Envelopes using Microphone Arrays

Unintended airflow through building envelopes leads to an increased demand in heating and cooling energy. The most common way to measure air leakage of buildings is the blower door test, which quantifies the overall leakage rate of one room or a building. To reduce air leakage and associated energy loss in new and existing buildings, it is necessary to identify leak locations and prioritize sealing of more substantial leaks. However, detection and quantification of individual leaks with smoke tracers or infrared thermography are challenging, time-consuming, and depend on the operator’s experience. Acoustic methods have been identified to have the potential to localize and quantify individual leaks without the need for pressure or temperature differences. In this work, the acoustic beamforming method is proposed using a microphone array to detect leak locations and visualize them (acoustic camera). The objective of this investigation is to identify the potential of this technique for application to building envelopes. A pair of omnidirectional speakers is placed as a sound generator inside a room, and the microphone ring array with 48 microphones outside. As an experimental setup, cable ties are wedged in a window frame to simulate a damaged window gasket and to create reproducible leaks of different sizes at the same place. Overlay of an optical picture with the acoustic image obtained from beamforming enables the visualization of leaks of sound through the building envelope. All experiments were conducted using white noise with an analyzed frequency range of 1-25 kHz. The sound sources are evaluated at multiple third-octave bands within this frequency range, enabling a distinction between these leaks at different frequencies

Second Generation Linear Focus Sun Simulator to Test Optical Performance of Parabolic Trough Receivers - OptiRec

This paper presents results from a characterization of DLR’s second generation sun simulator test facility (OptiRec) for determining the optical performance of parabolic trough receivers. The configuration of the test bench is an elliptical mirror trough with flat end mirrors. Solar simulator lamps are situated in one focal line, the receiver in the other focal line. Water at ambient temperature flows through the receiver and allows for a calorimetric measurement of the absorbed power. Compared to the first generation test bench (ElliRec) the mirror material is changed from aluminum to glass, the ellipse size is changed and the handling is improved. Based on 34 measurements of the absorbed power the repeatability for OptiRec measurements is measured to 0.13% (1σ), compared to 0.2% in the ElliRec. Seven receivers from different manufacturers are measured in both test benches yielding agreeing relative optical efficiency with <1.1% deviation. Particular differences are larger than the repeatability, which are attributed to differences in spectra and incidence angles between both test benches

Determination of loads and boundary conditions causing deformations of concentrating solar mirrors using non-derivative optimization methods and finite element analysis

Mirror shape optimization is a major part of improving the performance of concentrating solar power (CSP) collectors. Loads and boundary conditions of different origin and with varying influence on shape deviation need to be understood and quantified, e.g., in order to give specifications for the design of new collector generations. Finite element analysis (FEA) has proven to be a suitable method for evaluating mirror shape. An optimization process is presented that utilizes finite element models (FEM) of mirrors and a subsequent evaluation of the slope deviation to approximate a reference, e.g., a measured mirror shape, and determine the load values causing the mirror panel to deform. In this paper, the suggested approach is proven to be feasible: Two optimization algorithms are implemented: BOBYQA and CMA-ES. A simulated reference created in ANSYS Workbench and a reference from a deflectometry measurement are investigated. The determined geometrical parameters are compared to the reference values. For BOBYQA an absolute minimum and maximum deviation of 0.02 % and 0.3 %, and for CMA-ES of 0.0001 % and 0.004 % relative to the reference values is found. With the measured mirror shape as reference, the optimization algorithm was again capable of reproducing the mirror shape in FEA. However, the geometrical load parameters found were only partially in agreement with the measured values. Yet, it is concluded that the proposed method for reproducing mirror shape works

SOLAR TROUGH MIRROR SHAPE SPECIFICATIONS

The performance of concentrating solar collectors depends to a significant amount on the shape accuracy of the mirrors reflecting the sunlight onto the absorber. For the case of parabolic trough mirrors and on the basis of previous work on shape measurements and ray-tracing, a quality parameter has been defined, that quantifies the average deviation of the reflected beam from the design focal line. It could be demonstrated that application of standard distribution (Gauss distribution) is sufficiently related to derive the performance relevant intercept factor from it. As objective for the glass reflector for high performance trough collectors a typical value for the focus deviation RMS in transversal direction is about 15% of the absorber diameter