Browsing by Author "Ortega, Alfonso"

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    A bidirectional solar thermoelectric generator combining heat storage for daytime and nighttime power generation
    (2023) Montero, Francisco J.; Lamba, Ravita; Ortega, Alfonso; Jahn, Wolfram; Chen, Wei-Hsin; Guzman, Amador M.
    A solar thermoelectric generator (STEG) is a promising technology for harvesting solar energy for standalone applications. However, the STEG cannot generate electricity during nighttime due to unavailability of solar energy. The efficiency of thermoelectric generator (TEG) is also low that limits its application areas. This low efficiency can be improved by partially utilizing the waste heat from its cold side using phase change materials (PCMs). Further, the STEG systems operating during day and nighttime are not proposed so far. Therefore, an experimental test rig of a bidirectional (operative in day and night both) STEG coupled with latent heat storage and cooling system (LHSCS) has been developed in this paper. The LHSCS acts as a sink by storing waste heat from the TEG cold side in a phase change material during the daytime and regulates its temperature effectively. During nighttime, LHSCS acts as a heat source for TEG power generation. This proposed bidirectional model aims to provide non-intermittent electricity generation for 24 h. An experimental setup was tested under laboratory conditions and adjusted using a numerical model previously developed in COMSOL Multiphysics software. Once both models are mutually adjusted and verified, the proven numerical model is used to simulate the prototype in the environmental conditions of the Atacama Desert in Chile. The transient effects of solar radiation, ambient temperature and wind speed of the selected location on the hot and cold side temperatures, voltage, power output and efficiency of STEG have been analyzed. A maximum temperature difference of 120 degrees C is obtained between the TEG hot and cold sides. The experimental results showed TEG efficiency of 5%. The system generated average annual electricity of 5735 Wh. The STEG generated around 0.6 % of the total electricity during the night in the Atacama Desert location. The levelized cost of energy and storage have also been calculated for the proposed system and compared with PV and STEG systems. The LCOE and LCOS of the proposed system are 8850 and 566 USD/MWh respectively. The proposed configuration may provide a reference study for design and development of an efficient and cost-effective STEG coupled LHSCS system.
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    A novel 24-h day-night operational solar thermoelectric generator using phase change materials
    (2021) Montero, Francisco J.; Lamba, Ravita; Ortega, Alfonso; Jahn, Wolfram; Guzman, Amador M.
    To improve the energy matrix using solar energy, the intermittency and variation of the solar resource must be resolved for effective implementation of solar operated electricity generation systems. Solar thermoelectric generators (STEG) can be used for electricity generation in non-grid and grid connected applications. However, to use the STEG systems extensively, the limitations of lower conversion efficiency of around 7%, effective passive thermal management of the thermoelectric generator (TEG) and storage of residual heat of the thermoelectric generator need to be solved. In this study, a conceptual theoretical model of latent heat storage and cooling system (LHSCS) is proposed for the effective thermal management and enhanced electricity generation from the solar thermoelectric generator. The numerical model of the proposed system has been developed in COMSOL Multiphysics software for the climatic conditions of the Atacama Desert, Chile. The effect of phase change material (PCM) volume, heat sink and container geometry on the performance of the system has been studied. It is found that the desert locations are the best geographical locations for operating the solar thermoelectric generator coupled latent heat storage and cooling system due to higher solar radiation resource and favorable environmental conditions. The results showed that with 6 kg of phase change material, a temperature difference of 120 degrees C has been achieved between the hot and cold sides of the thermoelectric generator without using an active cooling system and the stored residual heat in phase change material generated 0.6% more electricity during the off-sunshine hours. Further, it has been found that the natural convection has a relevant impact on the melting of the phase change material and must be considered in the designing of a latent heat container. This proposed numerical model can be used to demonstrate the solar thermoelectric generator coupled latent heat storage and cooling system for any geographical location. (c) 2021 Elsevier Ltd. All rights reserved.