In this paper, we present a theoretical analysis and experimental results of a pyrometric temperature measurement method based on a two-color pyroreflectometer (working wavelengths of 1.3μm and 1.55μm) equipped with an optical fiber probe. By measuring simultaneously the radiance temperature and the normal reflectivity, the true temperature of the measurement target can be determined without the previous knowledge of the optical properties of the sample. The method is based on the introduction and the definition of the diffusivity factor ηd and the assumption that it is equal for the two wavelengths. Besides the experimental results, the sources of errors and their impact on the method accuracy and the performance of the setup are discussed. The quality of the measurement results demonstrates the utility of the pyroreflectometry in a domain where fundamental parameters, such as the temperature and radiative properties, present the major measurement difficulties. The diffusivity factor appears not only a step to determine the true temperature but also as a parameter very useful to evaluate the diffusing behavior of opaque materials.

Linear Fresnel collectors have the potential to reduce levelized electricity costs (LEC) of solar thermal power plants and thus accelerate sustainable market penetration of solar thermal power plants. So far no reliable information is available on the operation and performance characteristic of linear Fresnel collectors. To overcome this lack of information a German consortium was formed and led by MAN-Ferrostaal Power Industry with the Solar Power Group GmbH (SPG) aiming at the design, construction, operation and assessment of a linear Fresnel collector operated in direct steam generation mode. To test the collector prototype under real solar conditions, it is connected to the so called DISS test facility of the Plataforma Solar de Almeria (PSA). The DISS test facility is a parabolic trough collector loop used for the in depth investigation of the direct solar steam generation. The test set-up is designed in a way that the linear Fresnel collector can be fed with pre-heated water, a two-phase water-steam flow and a pure steam flow. The linear Fresnel test collector is used to investigate its performance characteristic under real solar conditions.

The temperature distribution on solar trough absorber tubes determines thermal losses and hotspots can lead to material stress and limit absorber tube lifetime. The concentrated solar radiation, however, makes it difficult to determine the temperature on solar absorbers. Temperature sensors that require contact to the measurement object are not appropriate and even pyrometry fails, when external light sources interfere. Only solar-blind pyrometry offers reliable temperature readings without perturbation through reflected solar radiation. This paper presents two concepts for a pyrometric solar-blind measurement on solar trough absorber tubes. One solar-blind approach is a spectral measurement range in regions, where the solar spectrum shows gaps due to the discrete absorption of the atmosphere. Another possibility for a solar-blind pyrometric temperature measurement results from the optical behavior, i.e. the distinct angle dependence of the directional reflectance and emittance of a typical selective trough absorber coating. First experimental results are shown and the accuracy and performance advantages and disadvantages of the setups are reported and discussed.

In order to optimize the solar field output of parabolic trough collectors (PTC) it is essential to study the influence of collector and absorber geometry on the optical performance. The optical ray-tracing model of PTC conceived for this purpose uses photogrammetrically measured concentrator geometry in commercial Monte Carlo ray tracing software. The model has been validated with measurements of a scanning flux measurement system, measuring the solar flux density distribution close to the focal line of the PTC. The tool uses fiber optics and a CCD-camera to scan the focal area of a PTC module. Since it is able to quantitatively detect spilled light with good spatial resolution it provides an evaluation of the optical efficiency of the PTC. For comparison of ray tracing predictions with measurements, both flux maps and collector geometry have been measured under identical conditions on the Eurotrough prototype collector at PSA. The validation of the model is provided by three methods: the comparison of measured intercept factors with corresponding simulations; comparison of measured flux density distributions with corresponding ray tracing predictions; and comparison of thermographically measured temperature distribution on the absorber surface with flux density distribution predicted for this surface. Examples of sensitivity studies performed with the validated model are shown.

An experimental approach with a solar blind infrared camera with a highly spectral selective filter gives temperature maps of absorber tubes of the EuroTrough collector. In addition to the temperature measurements raytracing models are used to predict flux distribution on the absorber tube. The calculations are based on photogrammetrically measured reflector geometry. The results confirm the assumptions of inhomogeneous flux and temperature profiles on the absorber surface and deliver data for appropriate stress analysis.

The operation of solar thermal high temperature receivers requires an accurate knowledge of the temperature distribution on critical parts of the receiver. However, concentrated solar radiation makes it difficult to determine the temperature on irradiated surfaces. Contact thermometry is not appropriate for the use under concentrated solar radiation and also pyrometry fails when external light sources interfere significantly. To avoid distortion of the temperature reading, the measurement has to be performed in a spectral range where the emitted thermal radiation exceeds the reflected solar radiation by a multiple. The measurement in solar blind spectral regions of atmospheric absorption bands offers one possible solution of filtering the solar radiance from the measurement signal. Along with the intensity of the incoming solar radiation and the absorber emittance, the bidirectional reflection properties and the temperature of the object determine the required selectivity of the spectral filter. In atmospheric absorption bands, the influence of the atmospheric absorption on the measurement signal cannot be neglected even for small path length. The paper describes the methods of solar blind pyrometric temperature measurement on solar thermal high temperature receivers and shows the possibilities and limitations of accounting for the atmospheric absorption with models based on radiation transfer calculations. Finally, experimental results recorded with an infrared mirror scanner especially designed for the measurement on a pressurized volumetric receiver are presented and compared to thermocouple readings and results of a thermodynamic model of the receiver.

Das Projekt SAPHIR hat zum Ziel, die Konzentratorqualitat von Heliostaten fur Solarturmkraftwerke zu messen, geeignet und kostengunstig zu optimieren und so zu einer signifikanten Ertragssteigerung des Kraftwerks und zu reduzierten Kosten fur die Fertigungskontrolle beizutragen. Dafur ist ein Messsystem in Entwicklung, das die Spiegelform von Heliostaten so wirtschaftlich messen kann, dass es fur die Fertigung und die Endkontrolle von Solarfeldern eingesetzt werden kann. Gleichzeitig werden weitere Messverfahren fur die Fernbeobachtung von Flussdichte- und Temperaturverteilung von kommerziellen Solarturmkraftwerken entwickelt und allgemeine Abnahmeverfahren fur Heliostaten und Solarfelder definiert.

This paper describes the test and the results of a first prototype solar powered gas turbine system, installed during 2002 in the CESA-1 tower facility at Plataforma Solar de Almería (PSA) in Spain. The main goals of the project were to develop a solar receiver cluster able to provide pressurized air of 1000°C and solve the problems arising from the coupling of the receivers with a conventional gas turbine to demonstrate the operability of the system. The test set-up consists of the heliostat field of the CESA-1 facility providing the concentrated solar power, a pressurized solar receiver cluster of three modules of 400kWth each which convert the solar power into heat, and a modified helicopter engine (OST3) with a generator coupled to the grid. The first test phase at PSA started in December 2002 with the goal to reach a temperature level of 800°C at the combustor air inlet by the integration of solar energy. This objective was achieved by the end of this test phase in March 2003, and the system could be operated at 230kWe power to grid without major problems. In the second test phase from June 2003 to August 2003 the temperature level was increased to almost 1000°C. The paper describes the system configuration, the component efficiencies and the operation experiences of the first 100h of solar operation of this very successful first test of a solar operated Brayton gas turbine system.

The knowledge of the absorber surface temperature distribution is essential for efficient operation and further development of solar thermal high temperature receivers. However, the concentrated solar radiation makes it difficult to determine the temperature on irradiated surfaces. Contact thermometry is not appropriate and pyrometric measurements are distorted by the reflected solar radiation. The measurement in solar-blind spectral ranges offers a possible solution by eliminating the reflected solar radiation from the measurement signal. The paper shows that besides the incoming solar radiation and the absorber emittance, the bi-directional reflection properties and the temperature of the object are determining for the required selectivity of the spectral filter. Atmospheric absorption affects the solar blind pyrometric measurements in absorption bands of CO2 and water vapor. The deviation of temperature measurement due to atmospheric absorption is quantified and the possibilities and limitations of accounting for the atmospheric absorption with models based on radiation transfer calculations are discussed.

Operation of solar thermal receivers requires an accurate knowledge of the temperature distribution at the absorber. However, concentrated solar radiation makes it difficult to determine the temperature on irradiated surfaces. Contact thermometry is not appropriate for the use under concentrated solar radiation and also pyrometry fails when external light sources interfere significantly. To avoid distortion of the temperature reading the measurement has to be performed in a spectral range where the emitted thermal radiation exceeds the reflected solar radiation by a multiple. The paper describes the methods of solar blind pyrometric temperature measurement on solar thermal high temperature receivers.

The PSA flux density measuring system PROHERMES measures the concentrated solar radiation in the entrance aperture of solar tower receivers with a white rotating bar as target and a CCD-camera taking images. The calibration is done with commercial flux gauges placed in the measurement plane. To im prove the calibration of the system and to reveal systematic errors, measurements are performed with two different types of commercial flux gauges (Thermogage sensors with and without quartz window) and a large custom-made calorimeter used as reference. The comparison shows that the sensors without quartz window measure about 5–8% higher and the sensors with quartz window about 100% higher. This error is explained with the differences in the spectral composition of the radiation and different angles of incidence between the manufacturer calibration and the solar measurements and corrections are proposed. Spectral changes of the sunlight during the day and year can affect the measurements by more than 10%. By selecting a correction filter adapted to the camera sensitivity, this influence can be reduced to less than 2.5%. Due to the reflective properties of the target coating, changes in angle of incidence can affect the measurements. In standard solar field conditions, this error is less than 0.5%, but for special conditions a correction of the systematic error of up to 8% is proposed.

Solar hybrid power plants have a significant potential for cost reduction when the solar energy is introduced into a gas turbine system. The introduction into gas turbine systems could be realized with pressurized volumetric air receivers heating the compressed air of the gas turbine before it enters the combustor. A receiver module, consisting of a secondary concentrator and a volumetric receiver unit, was tested at the Plataforma Solar de Almerı´a, Spain. Air exit temperatures up to 815°C and power levels of 410 kW were achieved. Total solar test time summed up to 400 hours. Receiver efficiencies were in the range of 70%. A new secondary concentrator with improved efficiency was designed and built. Based on an inexpensive manufacturing technology, the secondary concentrator geometry was optimized to reduce the optical losses. Performance tests with this new secondary concentrator and a cold-water calorimeter proved the expected increase in efficiency of about 10%. Maximum operation power was 450 kW at the exit aperture. The dependency of performance on the incidence-angle showed good agreement with the predictions, as well as the results of a special photographic measurement campaign. Several configurations of solar-hybrid gas turbine cycles in the low to medium power range are examined for performance and costs. The results confirm the promising potential of this technology to reach competitiveness in certain power markets; a comparison between a 30 MW solar-hybrid combined cycle plant and an ISCCS power plant are presented. Future developments for system improvement and cost reduction are discussed.