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Abstract The transient cooling process of an underground water pit thermal storage with inclined sidewalls is investigated in this paper. An experimental device was designed in order to validate the mathematical model proposed. Materials properties have been assumed constant with temperature, except for the water’s density that has been treated using the Boussinesq approximation. The simulations of temperature distributions are proved well by comparison with the experimental results. Results show that the water temperature decreasing next to the tank walls by the heat losses from the top and sidewalls of the tank, which creates a downward flow along the tank wall. At the center of the tank, a slight upward flow is generated, which lifts the warmer water at the bulk of the tank to a higher level. In this way, the buoyancy-driven flow gradually builds up the thermal stratification in the tank. The Nusselt number values show that comparing with the upper surface of the storage tank, there is more radical heat exchange at the bottom and inclined sidewalls. The maximum velocity appears near the top part of the inclined sidewalls, and its value decreases as the cooling continues.

AbstractThis paper describes a new2nd generation linear focus solar simulator test bench. The test bench is used for the non-destructive calorimetric measurement of relative optical efficiency of parabolic trough receivers. Compared to the predecessor, the test bench has been optimized for faster measurement, better long term stability and easier operation. The test bench optics is an elliptical shaped glass mirror trough with flat end mirrors. The receiver and six solar simulator lamps, metal halide lamps with 2.5 kWeeach are located in their respective focal lines. Absorbed power is measured via temperature increase of the water flowing through the receiver and the mass flow rate. By comparison to the absorbed power of a reference receiver, the optical efficiency of a sample can be determined relative to the optical efficiency of the reference receiver.

Abstract The complete cycle of specific processes related to the geological storage of CO 2 is investigated in detail at Ketzin since 2004. The scientific monitoring program targets different depths of the involved area and addresses the safety and reliability of the storage. The surface monitoring comprises long-term soil CO 2 flux measurements and soil gas analyses. Annual mean values of soil CO 2 fluxes ranged from 2.4 to 3.4 µmol m -2 s -1 before the injection started (2005-2008) and from 2.3 to 3.5 µmol m -2 s -1 during and after CO 2 injection (2009-2016) and thus do not indicate an upward migration of the injected CO 2 .

AbstractEven though the integration of renewable energies in new buildings is technically easy, the rise of solar thermal systems in the French market of energy renovation is limited by recurring constraints of implementation related to the installation of the storage tank. This is the reason why the Integrated Solar Collector (ISC) constitutes a very promising concept to develop. For both new buildings and renovation of the existing buildings, the ISC gives the opportunity to reduce the cost of installation and operation comparatively to a conventional Solar Domestic Hot Water System, because of their simplicity and passive operating process (without pump, nor controller). This second advantage is extremely important for the development prospects of the solar thermal market which is currently slowed down by the level of investment. The third advantage of our new ISC is the possibility of successful architectural integration, contrary to the currently available solutions with the storage installed on the roof.We developed a new concept of ISC adapted to the energy renovation with a multidisciplinary approach. Its design took into account various aspects: architectural integration (storage bellow the collector), energy performance (solar heat transfer at the bottom of the storage, fully insulated storage) and technological constraints (freezing risk). The project made it possible to study on the one hand its global performance (stratification, solar fraction) and on the other hand the free convective heat transfers inside the storage cavity. The approach used both numerical (architectural draft and design of the prototype, global modelling, and velocity / temperature fields) and experimental tools (test of heat, PIV on a cavity heated at the bottom, test of the prototype). The first prototype of ISC puts forward very satisfactory energy performances. Improvements are possible by enhancing thermal stratification in the storage system. Concerning the heat pipes operation against gravity, the project highlighted the current lack of technological solution adapted to our needs. The study of the building integration showed the architectural opportunities given during the renovation (new volumes) and the technical constraints which were solved (weight, storage insulation, freezing).

Abstract Copper is a common impurity in photovoltaic silicon. While reported to precipitate instantly in n-type Si, copper causes light-induced degradation (Cu-LID) in p-type Si. Recently, partial recovery of Cu-LID was observed after only few minutes of dark annealing at 200 °C. In this contribution, we investigate the effects of the dark anneal on Cu-LID-limited minority carrier lifetime both experimentally and by simulations. Surprisingly, after initial recovery, the dark anneal results in further degradation corresponding to a many-fold increase in recombination activity compared to the degraded state after illumination. This anneal-induced degradation can potentially cause additional losses in accidentally Cu-contaminated devices when exposed to elevated temperatures, for example during recovery and regeneration treatments of solar cells. Transient ion drift measurements confirmed that the anneal-induced degradation cannot be attributed to residual interstitial Cu after illumination. After hundreds of hours of annealing, the samples showed another recovery. To analyze these experimental results, a comparison to simulations is performed at the end of the paper.

Oil shale, as an unconventional fossil fuel, exhibits unique properties compared with coal and other petroleum. Due to the nature of sedimentary rock, large amounts of inorganic mineral impurities in rock matrix reduce the grade of oil shale, whilst increase the grinding resistance. This investigation presents the effects of microwave-enhanced pretreatment on the nature of oil shale and compared with conventional preheating process. Two Chinese oil shale from Fushun and Xingsheng Deposits were grounded and sieved into a size fraction (1-1.18mm) and were cut into eighteen cube-shaped specimens respectively. The prepared samples were processed accordingly to investigate how the grindability changed, in comparison to that of raw samples, and how the fundamental chemical properties of oil shale were altered after pretreatment. Quantitive data were used to assess the effects of different pretreatment methods on oil shale milling performance in a lab-scale pulverizer along with the impacts on moisture content, chemical properties. The uniaxial compressive strength (σmax) of Fushun oil shale was reduced 63.1% and the breakage rate increased 44.9% by short exposure to microwave irradiation. In conclusion, microwave-enhanced pretreatment presents significant improvement in oil shale milling performance compared to conventional preheating process in terms of breakage rate (Si) and uniaxial compressive strength (σmax) which showed negligible alterations. © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 - The 10th International Conference on Applied Energy.

AbstractThe paper presents the concept, implementation and results of the hardware-in-the-loop test bench (HiL) established for a medium-scale parabolic trough collector system under construction. The 122.4m2 plant heats the make-up water of a fossil-fired steam boiler in a meat factory in Austria. The test bench consists of a plant model implemented in a Real-Time machine, which is electrically connected to the plant control hardware (PLC) through several I/O terminals. Within the test bench, it is possible to run different test cycles and emulate critical operation scenarios like collector loop overheating. The control strategy of the solar plant can be checked with minimal risk. The test bench also enables to improve the control ability to cope with weather and sensor disturbances. A suitable fault detection strategy is prepared, which minimizes the risk of component damage and enhances the plant availability.