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Global industrialization and excessive dependence on nonrenewable energy sources have led to an increase in solid waste and climate change, calling for strategies to implement a circular economy in all sectors to reduce carbon emissions by 45% by 2030, and to achieve carbon neutrality by 2050. Here we review circular economy strategies with focus on waste management, climate change, energy, air and water quality, land use, industry, food production, life cycle assessment, and cost-effective routes. We observed that increasing the use of bio-based materials is a challenge in terms of land use and land cover. Carbon removal technologies are actually prohibitively expensive, ranging from 100 to 1200 dollars per ton of carbon dioxide. Politically, only few companies worldwide have set climate change goals. While circular economy strategies can be implemented in various sectors such as industry, waste, energy, buildings, and transportation, life cycle assessment is required to optimize new systems. Overall, we provide a theoretical foundation for a sustainable industrial, agricultural, and commercial future by constructing cost-effective routes to a circular economy.

A solar-powered biomass steam gasification system was developed, in which heat transfer model, flow model and chemical model were constructed to predict the distributions of temperature, pressure, mole fraction of syngas, and solar incident flux. Several key parameters of gasifier were designed to ensure the fluidization stability. Based on the model validation, gasifier performance simulations in the design working conditions were obtained. The effects of the key variable parameters, including the rim angle of the dish collector, steam-to-biomass mass flow ratio, biomass feeding rate and the solar irradiance in the different operation working conditions on the composition of syngas, lower heating value, and efficiencies were investigated. The results reveal that the coupled system implements the best gasification performance in the design conditions which the rim angle, steam-to-biomass mass flow ratio, and biomass feeding rate are set at 60°, 0.4, and 2.5 g/min, while the LHV, carbon conversion, and gasification energy efficiencies are 11.51 MJ/m3, 78.17%, and 93.01%, respectively. The overall energy efficiency considering solar energy is 30.79%.

The operational flexibility is improved to decouple the thermoelectric limitation of the combined heat and power (CHP) system and meet the dynamic changes of heat and electrical loads in an afforda...

Hybrid natural gas combined cooling, heating, and power (CCHP) systems integrated with solar technologies offer the efficient use of distributed energy resources for reducing the use of fossil fuels and greenhouse gas emissions. This paper proposes a novel CCHP system, using the phosphoric acid fuel cell (PAFC) as the prime mover, integrated with the natural gas reforming with solar energy assistance. Their respective thermodynamic models are constructed for simulation of the system thermodynamic performance. The simulation results demonstrate that the energy efficiencies of the hybrid system with solar energy assistance are 55.12% for the heater mode and 66.77% for the chiller mode, while the exergy efficiencies are 32.87% and 31.59%, respectively. Similarly, when solar energy is not available, its energy efficiencies are 59.24% and 69.18%, while its exergy efficiencies are 40.09% and 39.01%, respectively. In the PAFC–CCHP hybrid system, the exergy efficiencies are key components in the overall efficiency, and the efficiencies with and without solar energy are 29.34% and 36.95%, respectively. Solar energy and exergy share is employed to analyze the solar energy contribution, and they are 36.1% and 35.6%, respectively. Meanwhile, the parametric analysis is also carried out to evaluate the effects of key parameters on the performance. The results show that increasing the reforming temperature, influenced by solar energy, improves the natural gas conversion and boosts the hydrogen concentration of the syngas fed into the PAFC, which increases the overall exergy efficiency. However, the effect of the reforming temperature is reduced when the reforming temperature is higher than 1073.15 K.

Azobenzene (AZO) has attached tremendous attention in the field of photo-isomerization energy storage due to its advantages of absorbing light in ultraviolet-visible range and reversible isomerization. However, the issues of low energy density and short half-lifetime restrict the further development of AZO. Therefore, a method, by preparing hybrid photo-isomerization energy storage materials using nanoscale templates, was proposed to handle the above two issues. In this paper, a summary of hybrid photo-isomerization energy storage materials with AZO and nanoscale templates is conducted from the aspects of templates, preparation methods, derivatives and applications. The performances of template candidates, i.e. carbon nanotubes (CNTs) and graphene (GO) are reviewed and compared based on the analysis of grafting density, energy density, and half-lifetime of hybrid materials. Then, two major preparation methods of AZO hybrid materials including non-covalent and covalent functionalizations are discussed. Furthermore, the studies on AZO derivatives functionalized on nanoscale templates are summarized to further point to the direction of derivatization towards high performance AZO-functionalized materials. Finally, due to the superiority of AZO hybrid solid-state films in large-scale utilization, their current applications are reviewed to find out some promising applications.

A novel cooling, heating, and power system integrated with a solid oxide fuel cell and biomass gasification was proposed and analyzed. The thermodynamic models of components and evaluation indicators were established to present energetic and exergetic analysis. After the validations of thermodynamic models, the system performances under design work conditions were evaluated. The proposed system’s electrical, energy, and exergy efficiencies reached up to 52.6%, 68.0%, and 43.9%, respectively. The gasifier and fuel cell stack were the most significant components of exergy destruction in this system, accounting for 41.0% and 15.1%, respectively, which were primarily caused by the gasification and electrochemical reactions’ irreversibility. The influences of the key parameters of the ratio of steam to biomass mass flow rate (S/B), the biomass flow rate (Mbio), and the temperature and pressure of the fuel cell (Top and Psofc) on system energy performances were analyzed: doubling S/B (from 0.5 to 1.0) reduced the energy efficiency by 5.3%, while increasing the electrical efficiency by 4.6% (from 52.6% to 55.0%) and raising the biomass mass flow rate by 40% increased the energy and exergy efficiencies by 2.4% and 2.1%, respectively. When raising the SOFC operating temperature by 31.3%, the energy and exergy efficiencies rose by 61.2% (from 50.0% to 80.6%) and 45.1% (from 32.8% to 47.6%), respectively, but this likely would result in a higher operating cost. Increasing the SOFC pressure from 2 to 7 bar increased the electrical efficiency by 10.6%, but additional energy for pumping and compression was consumed.

The objective of this paper is to propose and analyze the performance of a novel hybrid combined cooling heating and power (CCHP) system coupled with compound parabolic concentrator-photovoltaic thermal (CPC-PVT) collectors. The electricity and hot water from CPC-PVT are integrated with the electricity and waste heat carried by exhaust gas and jacket water from the internal combustion engine to improve the energy performance. The thermodynamic models were constructed and validated by comparing the simulation results to those from existing studies. The thermodynamic performances were analyzed and the impacts of key parameters on the performances were discussed at the off-design condition. The levelized primary energy saving ratio (PESR) and carbon dioxide emission reduction ratio (CDERR) of the hybrid CCHP system in comparison to the CCHP system without solar energy were employed to evaluate the contribution of solar energy. The results indicated that the energy and exergy efficiencies at the design condition are 63.3% and 21.8% in summer, respectively, and 61.8% and 27.1% in winter, respectively. Compared to the CCHP system without solar energy, the hybrid system has more flexible ability to adjust the heating to electricity ratio and achieves the maximum levelized PESR of 28.6% and CDERR of 36.7%, respectively.

This paper proposes a solar-assisted hybrid combined cooling, heating and power (CCHP) system that consists of an internal combustion engine, solar heat collectors, an absorption heat pump, a heat exchanger, and a thermal storage tank. On the basis of thermodynamic modelling and validation, the hybrid system was investigated from its energy, exergy, exergo-economic and exergo-environmental performances. The heat storage ratio and supplemental heat ratio were defined to consider the dynamic off-design operations and evaluate the contributions of thermal storage and supplement under the static design conditions, whose impacts on system efficiency and unit cost of products were discussed. For a specific case study, the energy and exergy analyses with the Sankey diagrams indicated that the hybrid system achieves annual energy efficiency of 76.3% and exergy efficiency of 22.4%. The unit costs of products were determined using exergo-economic analysis based on energy level, and the costs of products including and excluding carbon dioxide emission cost were compared. Compared to the conventional CCHP system without solar energy, the hybrid system saves 11.3% of natural gas to reduce carbon dioxide emission and shortens the capital payback period by 1 year.

The objectives of this paper are to propose a novel combined cooling heating and power (CCHP) system based on solar thermal biomass gasification, and to present thermodynamic analyses to effectively improve the utilization of distributed renewable energy sources. By adopting the Engineering Equation Solver software, the thermodynamic models of components were constructed, and the simulation procedures, mainly including the heat transfer of the solar cavity receiver and the biomass gasification, were presented. Based on a 100 kW electricity capacity, the design parameters of the CCHP system were obtained to simulate and discuss the thermodynamic performances and the energy and exergy flow diagrams in the cooling and heating operation modes. The influences of the key variable parameters, including the electric load ratio and the solar direct normal irradiance in the off-design work conditions on the thermodynamic performances, were analyzed and discussed. The simulation results indicate that the CCHP system achieves average energy and exergy efficiencies of 56% and 28%, respectively, and the energy ratio of solar to biomass is approximately 0.19 in the full load operating mode. Compared to the conventional biomass gasification CCHP system without solar energy, the increasing ratio of heating value of product gas based on the solar thermal biomass gasification reaches 55.09%, and the biomass saving ratios are approximately 9.22% and 2.02% in the cooling and heating modes respectively, which indicate that the proposed hybrid system is an effective and feasible method to improve the utilization efficiency of biomass energy.

The aim of this work is to optimize and minimize the thermo-ecological cost (TEC) of a novel hybrid combined cooling heating and power (CCHP) system integrated with solar energy. A basic natural gas CCHP system based on internal combustion engine (ICE) is coupled with compound parabolic concentrated-photovoltaic thermal (CPC-PVT) collectors to construct a novel hybrid CCHP system. To minimize the TEC, an optimization methodology was proposed to optimize the configurations and installations of ICE and CPC-PVT, as well as the operation strategies. The TECs of multi-products of the CCHP system were assessed and compared in the following electrical load (FEL) and following thermal load (FTL) modes. The impacts of key parameters on TEC were analyzed and discussed. The results of a case study indicated that the system integrated with 100% photovoltaic covered ratio and 400 kW ICE gets the lowest TEC of 2.36 J/J in the FTL mode. The TECs of electricity decline 28.8% and 17.0% in the FEL and FTL modes, respectively when the photovoltaic covered ratio increases from 0 to 1.0. The increasing heat storage ratio leads to the increase of TEC of heat exergy carried by water due to the heat loss.

This paper describes the design and energy, exergy, exergoeconomic and environmental (4E) performance analysis of a distributed-generation solar-assisted CCHP (combined cooling, heating and power) gas turbine system. The solar energy is used by the integration of solar parabolic trough collectors (SPTC) that are used to preheat compressed air before its introduction into the Brayton cycle combustor. An absorption chiller/heater and a heat storage tank are incorporated for producing chilled/hot water for space cooling or heating and domestic hot water, respectively. The results indicated that the energy and exergy efficiencies are 83.6% and 24.9% in the cooling operation mode, and 66.0% and 25.7%% in the heating mode, respectively. Compared to the system without solar energy, the carbon emission reduction ratio per unit energy generation of the proposed hybrid system is approximately 41.0%. The off-design analysis demonstrated that the evaluation using only energy and exergy efficiencies cannot describe the contribution of solar energy in the hybrid system. Adapting the exergoeconomic method based on energy level, the unit exergy costs of electricity, chilled water in the cooling mode (or hot water in the heating mode) and domestic hot water in the market pricing strategy are 2.1, 7.8 and 8.3 times than the natural gas's cost respectively.

This paper proposes a distributed solar-assisted biomass gasification power generation system based on internal combustion engine and analyzes the complementary properties of solar energy and biomass. The heat demand of biomass steam gasification is provided by solar energy, which reduces the consumption of biomass fuel, and then the product gas drives the internal combustion engine to generate electricity. Under the design conditions, the thermodynamic performances influenced by the two main parameters including power load and solar radiation intensity (DNI) are studied. The results show that the energy efficiency and exergy efficiency are 17.33% and 16.82% respectively. The increase in the share of solar energy leads to a reduction in energy efficiency and exergy efficiency, and the increase in the share of biomass is conducive to improving efficiency.

Based on the principle of "temperature counterpart and energy cascade utilization" a solar-hybird distributed system driven by natural gas is designed. In this paper, the thermal performance and environmental performance of the system are calculated. The results show that the thermal efficiency of gas turbine is significantly increased with the increase of heat collector area, and when the collector area reaches 1949m2 the thermal efficiency of the gas turbine run up to 44.43% and the fuel consumption reduce by 43.5%. Meanwhile, the introduction of solar subsystem makes the system’s environmental performance greatly improved, and when the collector area reaches 1949m2, the CO2 emission reduction reaches 257.5kg/h. The simulation results show that the supplementary way of solar energy and natural gas is an effective method in distributed energy systems.