Low-carbon Operation of Combined Heat and Power Integrated Plants Based on Solar-assisted Carbon Capture

Accelerating the development of renewable energy and reducing CO_(2)emissions have become a general consensus and concerted action of all countries in the world. The electric power industry, especially thermal power industry, is the main source for fossil energy consumption and CO_(2)emissions. Since solvent-based post-combustion carbon capture technology would bring massive extra energy consumption, the application of solar-assisted carbon capture technology has attracted extensive attention. Due to the important role of coal-fired combined heat and power plants for serving residential and industrial heating districts, in this paper, the low-carbon operation benefits of combined heat and power integrated plants based on solar-assisted carbon capture(CHPIP-SACC) are fully evaluated in heat and power integrated energy system with a high proportion of wind power. Based on the selected integration scheme, a linear operation model of CHPIP-SACC is developed considering energy flow characteristics and thermal coupling interaction of its internal modules. From the perspective of system-level operation optimization, the day-ahead economic dispatch problem based on a mix-integer linear programming model is presented to evaluate the low-carbon benefits of CHPIP-SACC during annual operation simulation. The numerical simulations on a modified IEEE 39-bus system demonstrate the effectiveness of CHPIP-SACC for reducing CO_(2)emissions as well as increasing the downward flexibility. The impact of different solar field areas and unit prices of coal on the low-carbon operation benefits of CHPIP-SACC is studied in the section of sensitivity analysis.

Photovoltaic-thermal solar-assisted heat pump systems for building applications:Integration and design methods

The photovoltaic-thermal collector is one of the most interesting technology for solar energy conversion,com-bining electric and thermal energy production in a single device.Vapour-compression heat pump is already considered the most suitable clean technology for buildings thermal energy needs.The combination of these two technologies in an integrated“photovoltaic-thermal solar-assisted heat pump”(PVT-SAHP)system allows reaching a high fraction of the building thermal needs covered by renewable energy sources and to improve the performances of both the photovoltaic-thermal collector and the heat pump.The first is cooled down increasing its energy conversion efficiency,while providing low-temperature thermal energy to the second,which benefits from a higher evaporation temperature.The review study presents the state-of-art of photovoltaic-thermal solar-assisted heat pump systems intended to cover thermal energy needs in buildings,with a particular focus on the integration methodologies,the possible configurations,the use of different sources and the design of sub-system components.These issues are addressed by much scientific research,to improve the reliability and applicability of this technology,as an option for the building decarbonization.This study aims to present PVT-SAHP systems in an organic and critical way to propose a useful tool for future research developments.More in detail,the work highlights the fact that the integration of photovoltaic-thermal collectors as evaporator of the heat pump in direct-expansion systems allows the highest heat recovery and performances.However,the distinction of the two circuits lead to more reliable,flexible and robust systems,especially when combined with a second heat source,being able to cover both heating and cooling needs.The implementation of real-time control strategy,as well as the continuous development of the compressor and refrigerant industries is positively influencing this technology,which is receiving more and more attention from scientific research as a suitable solution for nearly zero energy buildings.

Experiment and numerical simulation on flow and heat transfer in all-glass evacuated tube solar collectors

The experimental study of natural convection in allglass evacuated tube solar collectors is performed through the experimental platform of the solar-assisted fuel cell system.The experimental facility includes solar collectors with different length and diameter tubes, different coating materials, and with / without guide plates, respectively. Threedimensional mathematical models on natural and forced convections in the solar collectors are established and the experimental data is validated by field synergy and entransy principles. The results of natural convection show that the water temperature increases and thermal efficiency decreases gradually with the evacuated tube length. The thermal efficiency increases when absorption rates increase from 0. 95 to 1. 0 and emission rates decrease from 0. 16 to 0. 06. The thermal efficiency of solar collectors is increased after being equipped with the guide plate, which is attributed to the disappearance of the mixed flowand the enhancement of the heat transfer at the bottom of the evacuated tube. The results of forced convertion indicate that the Reynolds, Nusselt and entransy increments of the horizontal double collectors are higher than those of the vertical single collector while the entransy dissipation is lower than that of the vertical single collector. It is concluded that the solar collectors with guide plates are suitable for natural convection while the double horizontal collectors are suitable for forced convection in the thermal field of solar-assisted fuel cell systems with lowand medium temperatures.

Recent trends on energy-efficient solar dryers for food and agricultural products drying:a review

The energy efficiency enhancement of solar dryers has attracted the attention of researchers worldwide because of the need for energy storage in solar drying applications,which arises primarily from the irregular nature of solar energy that leads to improper drying which will reduce the quality of the products being dried.This work comprehensively reviews the state-of-the-art research carried out on solar dryers for energy efficiency enhancement using various alternative strategies,including hybrid solar dryers that use auxiliary heating sources,such as electric heaters or biomass heaters,solar-assisted heat pump dryer,use of desiccant materials,and heat storage systems that use both sensible and latent heat storage.The advent of phase change materials(PCM),such as thermally and chemically stable PCMs,for long-term storage,bio-degradable and bio-compatible PCM materials to alleviate the negative environmental impact of conventional PCMs is also presented.The performance parameters considered for evaluating dryers include the maximum temperature attained inside the drying chamber,drying time and efficiency,specific moisture extraction rate(SMER),energy and exergy efficiency and CO_(2) mitigation effect.The factors considered to analyze the PCMs application in solar dryers include cost and sustainability of PCMs,and both energy and exergy analyses of dryers using PCMs.The gaps in current knowledge and future scope for further improvement of solar dryers are also elucidated.