Johannes Pernpeintner

A Transient Thermography Method to Separate Heat Loss Mechanisms in Parabolic Trough Receivers

This paper describes a transient thermography method to measure the heat loss of parabolic trough receivers and separate their heat loss mechanisms. This method is complementary to existing stationary techniques, which use either energy balances or glass envelope temperature measurements to derive overall heat losses. It is shown that the receiver heat loss can be calculated by applying a thermal excitation on the absorber tube and measuring both absorber tube and glass envelope temperature signals. Additionally, the emittance of the absorber selective coating and the vacuum quality of the annulus can be derived. The benefits and the limits of the transient method are presented and compared to the established stationary method based on glass envelope temperature measurements. Simulation studies and first validation experiments are described. A simulation based uncertainty analysis indicates that an uncertainty level of approximately 5% could be achieved on heat loss measurements for the transient method introduced in this paper, whereas for a conventional stationary field measurement technique, the uncertainty is estimated to 17–19%.

New methods and instruments for performance and durability assessment

This chapter describes new methods and instruments for performance and durability assessment of concentrating solar power (CSP) systems. It comprises point and line focusing systems, and presents new methods on both the component level (heliostats, thermal receivers, and rotation and expansion performing assemblies) and the system level.

Steady state calorimetric measurement of total hemispherical emittance of cylindrical absorber samples at operating temperature

At DLR’s QUARZ Center a test bench has been established to measure, using steady state calorimetric method, the total hemispherical emittance of cylindrical solar thermal absorber samples at temperatures up to 450 °C. Emittance measurement of solar absorber surfaces is commonly performed by direct-hemispherical reflectance measurements with spectrophotometers. However, the measurement of cylindrical samples with spectrophotometers can be considered still a challenge as integrating spheres, reference samples and calibration services by national metrology institutions are optimized for flat sample measurement. Additionally samples are typically measured at room temperature. The steady state calorimetric method does not rely on reference samples and the measurement is performed at operating temperature. In the steady state calorimetric method electrical power input used to heat the sample is equated to the radiative heat loss from a heated sample to the environment. The total emittance can be calculated usin...

Parabolic trough receiver heat loss and optical efficiency round robin 2015/2016

A round robin for parabolic trough receiver heat loss and optical efficiency in the laboratory was performed between five institutions using five receivers in 2015/2016. Heat loss testing was performed at three cartridge heater test benches and one Joule heating test bench in the temperature range between 100 °C and 550 °C. Optical efficiency testing was performed with two spectrometric test bench and one calorimetric test bench. Heat loss testing results showed standard deviations at the order of 6% to 12 % for most temperatures and receivers and a standard deviation of 17 % for one receiver at 100 °C. Optical efficiency is presented normalized for laboratories showing standard deviations of 0.3 % to 1.3 % depending on the receiver.