Solar-driven Cycle Research Articles

Efficient in situ conversion of captured CO2 into fuels enabled by direct solar driven multifunctional calcium looping

Carbon neutrality requires credible action to reduce greenhouse gas emissions and develop clean and renewable energy. The solar driven multifunctional calcium looping (CaL), which integrates CO2 capture, CO2 conversion into fuels, and thermochemical energy storage into a solar driven cycle, tends to be one of the most promising pathways to establish a zero-carbon energy system. However, the progress of this concept remains in the proof-of-principle stage and the research into its magnified operations and underlying fundamental scientific problems is seldom reported. In fact, the thermodynamic and kinetic features of this integrated cycle are intertwined during the solar harvesting, CO2 capture, calcination, and CO2 reduction processes, so that the synergetic manipulation of the reactions becomes vital and challenging. Here, attempts are made to develop the design and regulation scheme for implementing full-scale application according to the research into a preliminarily enlarged operation carried out in a stirred bed reaction system. The kinetic matching relationships between different chemical reactions involving intense heat and mass transfer across the entire solar energy conversion chain are investigated. The average solar absorption of CaCO3 based composite particle material is promoted to 90.9% through doping catalysts into CaCO3. The solar-to-chemical conversion efficiency reaches up to 51.6%. More than 88.2% of the CO2 is converted into syngas in-situ. The high energy conversion efficiency indicates the bright prospect of such a direct solar driven multifunctional CaL system, and the proposed design and enhancement methods are expected to provide theoretical and practical references for its industrialization process.

Energetic and exergetic performance of a novel polygeneration energy system driven by geothermal energy and solar energy for power, hydrogen and domestic hot water

The present study develops a novel energy system comprising a double-flash based geothermal cycle, a solar-driven cycle, a polymer electrolyte membrane (PEM) system and a waste heat recovery system. The proposed system can be used to generate electricity, produce hydrogen, space heating and prepare domestic hot water, and the solar-driven cycle can be turned off as a double-flash geothermal system when there is no solar radiation and the storage is empty. The unique aspect of the proposed system lies in the coupling relationship between the three turbine units in clear weather. Energy and exergy analyses are carried out to determine the irreversibilities, show the performance of the system and compare it with sole geothermal system. The results show that the proposed system has satisfactory thermodynamic properties. Under the reference conditions, the proposed energy system has a 148.3% (from 6171 kW to 15321 kW) increase in power generation compared with a sole double-flash geothermal system; under the optimal working conditions, the energy efficiency and exergy efficiency of the system can reach 29.6% and 29.2%, respectively. Furthermore, the effect of changing various system parameters on the energy and exergy efficiencies of the entire system and its subsystems were also studied.