Low-grade Solar Thermal Energy Research Articles

Comprehensive Investigation of Cooling, Heating, and Power Generation Performance in Adsorption Systems Using Compound Adsorbents: Experimental and Computational Analysis

The extensive utilization of petrochemical energy sources has led to greenhouse gas emissions, the greenhouse effect, the frequent occurrence of extreme weather events, and the severe degradation of Earth’s ecosystems. The development of renewable energy technologies has become an inevitable trend. This paper investigates an adsorption-based cooling/heating/power generation technology driven by low-grade solar thermal energy. The research results demonstrate that the adsorption performance of vermiculite compound adsorbents impregnated with LiCl solution is superior to those impregnated with CaCl2 solution, with the former exhibiting adsorption at lower p/po partial pressure ratios. Furthermore, at an adsorption bed temperature of 25 °C and a p/po partial pressure of 0.8, the adsorption cooling performance of Comp. 2 compound adsorbent impregnated with LiCl solution reaches 5760.7 kJ/kg, with a coefficient of performance (COP) of 0.75, heating performance of 9920.8 kJ/kg, COPh of 1.51, and power generation capacity of 10.6 kJ/kg. This research contributes to the advancement of sustainable energy technologies and the mitigation of environmental impacts associated with petrochemical energy sources.

Thermodynamic analysis of mechanical booster pump-assisted sorption thermochemical heat transformer driven by low-grade heat for building applications

Thermochemical heat transformers (THT) can offer the potential for efficient energy storage and upgrade based on a reversible solid-gas reaction. A mechanical booster pump (MBP)-assisted water-based sorption thermochemical heat transformer driven by low-grade solar thermal energy is proposed to handle variations in the heat demand of buildings. The MBP operates during the discharging process to adjust the magnitudes of temperature lift by compression ratio depending on the user’s demands. The performances of the proposed cycle employing three different reactive salts are investigated and compared with the conventional THT cycle under various operating conditions. Results indicate that compared to the conventional THT cycle, the proposed cycle achieves a maximum temperature lift of 15–17°C, 17–19°C, and 23–26°C for SrBr2, LiOH, and CaCl2 in the evaporating temperature range of 20–40°C, respectively. In the same operating conditions, SrBr2 demonstrates the highest energy and exergy efficiencies, while CaCl2 is inferior to the others due to its greater sensible heat consumption and lower reaction heat under the studied conditions. A suggestion is put forth for enhancing the temperature lift by employing a two-stage MBP-assisted cycle that utilizes the reactive salt SrBr2. Compared to the single-stage MBP-assisted cycle, the heat output temperature can be further increased by up to 3–16°C at the expense of a maximum decrease of 6.6%, 84.4%, and 9.0% in coefficient of performance (COP) based on total energy input, COP based on electricity input, and exergy efficiency, respectively, at 30°C evaporating temperature. The economic and environmental analysis indicates that the proposed system is economically and environmentally feasible and could be a promising alternative to residential water heaters.

Thermo-economic assessment of salt hydrate-based thermochemical heat transformer system: Heat upgrade for matching domestic hot water production

Efficient energy storage technology is a crucial step in achieving the broad deployment of renewable energies. Thermochemical heat transformer (THT), which rely on reversible gas–solid reactions, can provide an option for efficient energy storage and heat upgrade. In this article, a pressurisation-assisted sorption THT system driven by low-grade solar thermal energy is proposed to meet the heat demand of domestic hot water (DHW) production, and different temperature rises can be realised by regulating the water vapour pressure. The thermodynamic and economic performances of the THT systems employing ten kinds of salt hydrates are investigated under various operating conditions. The results indicate that most salts-based THT systems enable output temperatures higher than 60 °C. Two-stage pressurisation systems can further elevate the temperature lift but at the cost of thermodynamic performance. SrBr2·6H2O, K2CO3·1.5H2O, and LiOH·H2O are more promising hydrates for the THT system by taking energy density, temperature lift, and thermo-economic performance into account. Compared to the classical TCES cycle, the temperature lifts attained by the above salts-based single-stage and two-stage pressurisation THT systems are 17.6–19.9 °C and 32.2–37.8 °C, respectively. Multi-objective optimisation results suggest that the optimum exergy efficiency for the SrBr2-, K2CO3-, and LiOH-based systems are 82.47%, 55.08%, and 63.97%, and the corresponding levelized energy costs (LECs) are 0.3549, 0.7132, and 0.5721 $/kWh, respectively. The results of this study demonstrate the significant potential of developing such pressurisation-assisted THT system for heat upgradation targeting DHW production.

Thermodynamic Assessment of a Solar-Driven Integrated Membrane Reactor for Ethanol Steam Reforming.

To efficiently convert and utilize intermittent solar energy, a novel solar-driven ethanol steam reforming (ESR) system integrated with a membrane reactor is proposed. It has the potential to convert low-grade solar thermal energy into high energy level chemical energy. Driven by chemical potential, hydrogen permeation membranes (HPM) can separate the generated hydrogen and shift the ESR equilibrium forward to increase conversion and thermodynamic efficiency. The thermodynamic and environmental performances are analyzed via numerical simulation under a reaction temperature range of 100–400 °C with permeate pressures of 0.01–0.75 bar. The highest theoretical conversion rate is 98.3% at 100 °C and 0.01 bar, while the highest first-law efficiency, solar-to-fuel efficiency, and exergy efficiency are 82.3%, 45.3%, and 70.4% at 215 °C and 0.20 bar. The standard coal saving rate (SCSR) and carbon dioxide reduction rate (CDRR) are maximums of 101 g·m−2·h−1 and 247 g·m−2·h−1 at 200 °C and 0.20 bar with a hydrogen generation rate of 22.4 mol·m−2·h−1. This study illustrates the feasibility of solar-driven ESR integrated with a membrane reactor and distinguishes a novel approach for distributed hydrogen generation and solar energy utilization and upgradation.

Performance evaluation of a variable geometry ejector applied in a multi-effect thermal vapor compression desalination system

Nowadays, desalination is the primary alternative to increase water supply for domestic, agriculture and industrial use. Energy demanding desalination could be a sustainable solution in places where renewable energy resources are abundant. Multi-effect thermal vapour compression desalination is widely applied; however, its integration with solar energy requires more research effort. One of the key components of these systems is the steam ejector. The present study focuses on the geometry modification of an ejector, designed for a small-scale multi-effect thermal vapour compression unit, by means of computational fluid dynamics simulations. Its performance is evaluated considering a range of operating temperatures of the primary flow (i.e. 120 °C–180 °C) that would be suitable for running the system using low-grade solar thermal energy. Results show that for relatively high primary inlet temperatures, the primary jet undergoes a considerable expansion after leaving the nozzle. Consequently, the effective area for the secondary fluid becomes reduced, leading to a poor ejector performance and the entrainment ratio decreases from 1.2 to 0.3. In order to improve the ejector performance, variable geometry features are tested by allowing two geometry components to vary: the nozzle exit position and the area ratio (rA). The results show that nozzle exit position influences the ejector performance only about 16% within the considered range. The influence of the area ratio on the entrainment ratio is however very significant. The results indicate that the improvement of the entrainment ratio for high primary inlet temperatures could be as high as 400% when compared to a fixed geometry design.

Thermodynamic Performance Investigation of a Small-Scale Solar Compression-Assisted Multi-Ejector Indoor Air Conditioning System for Hot Climate Conditions

In year-round hot climatic conditions, conventional air conditioning systems consume significant amounts of electricity primarily generated by conventional power plants. A compression-assisted, multi-ejector space cooling system driven by low-grade solar thermal energy is investigated in terms of energy and exergy performance, using a real gas property-based ejector model for a 36 kW-scale air conditioning application, exposed to annually high outdoor temperatures (i.e., up to 42 °C), for four working fluids (R11, R141b, R245fa, R600a). Using R245fa, the multi-ejector system effectively triples the operating condenser temperature range of a single ejector system to cover the range of annual outdoor conditions, while compression boosting reduces the generator heat input requirement and improves the overall refrigeration coefficient of performance (COP) by factors of ~3–8 at medium- to high-bound condenser temperatures, relative to simple ejector cycles. The system solar fraction varies from ~0.2 to 0.9 in summer and winter, respectively, with annual average mechanical and overall COPs of 24.5 and 0.21, respectively. Exergy destruction primarily takes place in the ejector assembly, but ejector exergy efficiency improves with compression boosting. The system could reduce annual electric cooling loads by over 40% compared with a conventional local split air conditioner, with corresponding savings in electricity expenditure and GHG emissions.

Potential application of a novel integrated adsorption–absorption refrigeration system powered with solar energy in Australia

• Thermal performance study of a solar integrated AD–AB cooling system is performed. • Two solar system layouts with and without storage tank are investigated. • A considerable high cooling energy produces at low-grade solar thermal energy. • An economic analysis is performed to evaluate the feasibility of the solar system. • A stable system energy performance is obtained under different climate conditions. This article presents a new effective utilization way of low-grade solar energy to produce cooling power with a novel integrated adsorption - absorption cooling system under climate conditions in Australia. In the integrated cooling system, the solution generation happens in the intermediate pressure, which is associated with the heat source temperature and can be adjusted according to the solution concentration and generation temperature. Two different solar system layouts with and without hot water storage tank are investigated. In the system without storage tank no cooling energy is generated at the beginning and ending cycle time and it reaches the maximum value of 16 kW around noon. While the maximum cooling capacity, 15 kW, is produced in the late afternoon between 14 h and 16 h along with higher cooling capacity at the beginning and ending cycle time in the system with storage tank. It is found that the average daily cooling capacity improve by 15% with better coefficient of performance by installing storage tank for a wide range of collecting area. Furthermore, the average daily coefficient of performance remains slightly stable at around 0.37 with expanding the solar collecting area. Results obtained from the economic analysis disclose that the lifecycle cost is minimised for the financially viable collector area of 34 m 2 . Moreover, the payback period of 10.46 years for the optimum collecting area indicates the high profitability of the solar energy application in the proposed cooling system in a 25-year project investment lifetime. The performance comparison among various solar systems indicates that the average daily specific cooling powers are as high as 106 and 121 Wkg −1 in the 1st and 2nd layouts respectively, which are achieved considerably greater than other systems operating at low driving hot water temperature of 60 °C. The low heat temperature required to run the proposed cooling system and the advantage of high solar radiation availability in Australia proves the high potentiality for operating the proposed system in most warm months.

Low-priced stable SrCl2@SG composite sorbents for low-grade solar heat storage application in open sorption systems

The combination of thermal energy storage (TES) unit and solar air heater is one of the most efficient methods for long-term utilization of solar energy. In this study, a series of stable SrCl 2 @SG composite sorbents were prepared based on silica gel (SG) pellets and strontium chloride hexahydrate (SrCl 2 ·6H 2 O) to store low-grade solar thermal energy for space heating application. Composite characteristics, kinetic hydration/dehydration performance of SG and SrCl 2 @SG sorbents were thoroughly studied. Results demonstrated that the SrCl 2 @SG_10 sorbent has the largest sorption capacity of 0.34 g/g at the temperature of 25 °C and relative humidity (RH) of 90% without any liquid leakage. Additionally, kinetic hydration experiments showed that RH has a great impact on the water sorption performance of the TES materials, while the temperature effect is relatively insignificant. The TES performance of sorbents was further investigated in a laboratory prototype reactor with a multilayer structure, which was designed following an open sorption system concept. 800 g of sorbent pellets were evenly distributed on each layer of the sieve. Maximum instant output power and energy storage density of the SrCl 2 @SG_10 sorbent at 70% RH are 19.7 W and 100 kWh/m 3 respectively. Furthermore, the open TES system still maintains a comparatively high TES performance after fifteen charging/discharging cycles. • Preparation of stabilized SrCl 2 @SG composite sorbent for low-grade thermal energy storage. • Kinetic hydration/dehydration behavior of reversible SrCl 2 ⸱6H 2 O are investigated. • Sorption mechanism of SrCl 2 @SG composite sorbents is proposed. • Thermal energy storage performance of SrCl 2 @SG_10 sorbent is tested in an open sorption system. • SrCl 2 @SG_10 sorbent has discharging efficiency of 58.5% and can be recycled stably.

Dual closed-loop chemical recycling support sustainable mitigation of plastic pollution

Recently, the Feringa Nobel Prize Scientist Joint Research Center demonstrated a green method to synthesize plastics from natural small thioctic acid (TA) monomers. This novel recycling system provides successful chemical recycling using a dual closed-loop process under mild operating conditions. Here, we discuss the critical environmental sustainability dynamics of these recycling systems and their potential to support a plastic circular economy. Recently, the Feringa Nobel Prize Scientist Joint Research Center demonstrated a green method to synthesize plastics from natural small thioctic acid (TA) monomers. This novel recycling system provides successful chemical recycling using a dual closed-loop process under mild operating conditions. Here, we discuss the critical environmental sustainability dynamics of these recycling systems and their potential to support a plastic circular economy. Plastic pollution is widespread and affects a wide range of ecosystem types including atmospheric, aquatic, and terrestrial environments. Plastic pollution is an important driver of global environmental change due to their cascading effects on ecosystems, including impacts on safe drinking water and crop productivity.1Jia L. Evans S. Linden S.V. Motivating actions to mitigate plastic pollution.Nat. Commun. 2019; 10: 4582Crossref PubMed Scopus (39) Google Scholar, 2Bank M.S. Ok Y.S. Swarzenski P.W. Microplastic’s role in antibiotic resistance.Science. 2020; 369: 1315Crossref PubMed Google Scholar, 3Rillig M.C. Ryo M. Lehmann A. Aguilar-Trigueros C.A. Buchert S. Wulf A. Iwasaki A. Roy J. Yang G. The role of multiple global change factors in driving soil functions and microbial biodiversity.Science. 2019; 366: 886-890Crossref PubMed Scopus (186) Google Scholar By 2015, total global plastic waste was estimated to be4Geyer R. Jambeck J.R. Law K.L. Production, use, and fate of all plastics ever made.Sci. Adv. 2017; 3: e1700782Crossref PubMed Scopus (4364) Google Scholar 6,300 million metric tons (Mt) of which only 21% was incinerated or properly recycled while the remaining was either accumulated in landfills or released into the environment.4Geyer R. Jambeck J.R. Law K.L. Production, use, and fate of all plastics ever made.Sci. Adv. 2017; 3: e1700782Crossref PubMed Scopus (4364) Google Scholar Accordingly, at the current rate of production and management, approximately 12,000 Mt of plastic waste is destined for landfills or will be mismanaged by 2050.4Geyer R. Jambeck J.R. Law K.L. Production, use, and fate of all plastics ever made.Sci. Adv. 2017; 3: e1700782Crossref PubMed Scopus (4364) Google Scholar Primary macroplastic particles (>5 mm) often degrade into secondary microplastic (<5 mm and >100 nm) or nanoplastics (<100 nm) causing negative impacts on a wide array of ecosystem services.2Bank M.S. Ok Y.S. Swarzenski P.W. Microplastic’s role in antibiotic resistance.Science. 2020; 369: 1315Crossref PubMed Google Scholar,3Rillig M.C. Ryo M. Lehmann A. Aguilar-Trigueros C.A. Buchert S. Wulf A. Iwasaki A. Roy J. Yang G. The role of multiple global change factors in driving soil functions and microbial biodiversity.Science. 2019; 366: 886-890Crossref PubMed Scopus (186) Google Scholar Microplastics are widely distributed throughout the world’s ecosystems including remote, high-elevated sites such as Mount Everest.5Napper I.E. Davies B.F.R. Clifford H. Elvin S. Koldewey H.J. Mayewski P.A. Miner K.R. Potocki M. Elmore A.C. Gajurel A.P. et al.Reaching New Heights in Plastic Pollution—Preliminary Findings of Microplastics on Mount Everest.One Earth. 2020; 3: 621-631Abstract Full Text Full Text PDF Scopus (109) Google Scholar Americans unknowingly consume >50,000 microplastic particles per year,6Cox K.D. Covernton G.A. Davies H.L. Dower J.F. Juanes F. Dudas S.E. Human Consumption of Microplastics.Environ. Sci. Technol. 2019; 53: 7068-7074Crossref PubMed Scopus (535) Google Scholar and nanoplastic accumulation is reported in plants (i.e., Arabidopsis thaliana).7Sun X.D. Yuan X.Z. Jia Y. Feng L.J. Zhu F.P. Dong S.S. Liu J. Kong X. Tian H. Duan J.L. et al.Differentially charged nanoplastics demonstrate distinct accumulation in Arabidopsis thaliana.Nat. Nanotechnol. 2020; 15: 755-760Crossref PubMed Scopus (241) Google Scholar This global and ubiquitous distribution of micro and nanoplastics in the environment may accumulate in terrestrial and aquatic food webs, threatening ecosystems and potentially human health.6Cox K.D. Covernton G.A. Davies H.L. Dower J.F. Juanes F. Dudas S.E. Human Consumption of Microplastics.Environ. Sci. Technol. 2019; 53: 7068-7074Crossref PubMed Scopus (535) Google Scholar This biogeochemical cycle of micro and nanoplastics8Bank M.S. Hansson S.V. The Plastic Cycle: A Novel and Holistic Paradigm for the Anthropocene.Environ. Sci. Technol. 2019; 53: 7177-7179Crossref PubMed Scopus (74) Google Scholar implicates plastic pollution as a critical environmental challenge. These findings demonstrate not only the global and ubiquitous nature of plastic pollution but also the declaration of a “Plastic Wars” to mitigate effects on human and ecosystem health. These threats, including access to clean drinking water and food security, call for coordinated global monitoring, recovery, and management programs supported by sustainable investments, international cooperation, and innovation. Plastic pollution is amplified by its long environmental residence time and non-degradable persistence derived from petrochemicals. From a life cycle perspective, biodegradable plastics is a promising candidate for a plastic circular economy that reduces the environmental burdens at the end of the product’s lifetime. Bio-based plastics have recently gained support as a viable alternative to petroleum-based plastics due to their biodegradability and carbon neutral characteristics. However, the effects of depolymerization may negatively affect monomer quality during the recycling process when degradation occurs. Recently, Prof. Ben L. Feringa (awarded the 2016 Nobel Prize in Chemistry) from the East China University of Science and Technology and the University of Groningen in the Netherlands, invented a green method to synthesize two types of easily recyclable plastics using natural small thioctic acid (TA) monomers as precursors (Figure 1).9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar Interestingly, this novel method includes thermoplastic elastomers Poly(TA-M) and mechanically robust ionic films Poly(TA-Na)—both which were successful using a dual closed-loop chemical recycling system under mild operating conditions.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar This work could ostensibly pave the way for efficient synthesizing of recyclable polymers in a simple, mild, organic solvent-free, and low-cost way that supports environmental sustainability and a plastic circular economy. These efforts have the potential to mitigate plastic pollution and support several of the relevant UN sustainable development goals (SDGs). Since the production and utilization of TA-based polymers has largely occurred in cities and urban areas, this proposed system will significantly accelerate the mitigation of plastic pollution to achieve the relevant SDGs, namely SDG 11 - Sustainable Cities and Communities and SDG 12 - Responsible Consumption and Production. Furthermore, plastic pollution is an environmental and societal problem that could be effectively mitigated through the application of this dual closed-loop chemical recycling system, which will also aid in achieving SDG 14 - Life below Water and SDG 15 - Life on Land. The TA polymer precursors are natural small-molecule monomers synthesized by plants, animals, and humans. The Poly(TA-M) and Poly(TA-Na) are synthesized using a solvent-free heat-induced ring-opening polymerization (ROP) in the presence of metal salts at 120°C and an evaporation-induced ROP in the presence of NaOH at 80°C, respectively.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar The two-step treatment for chemical recycling of two types of TA-based polymers includes: (1) a ring-closing depolymerization using simple inorganic base as a catalyst and distilled water as a preferred solvent, and (2) a direct acidification separation with slow addition of acid.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar The polymerization and chemical recycling operated at low temperatures, making clean renewable energy such as low-grade solar thermal energy or wind-power as applicable and clean heat sources. In addition, the additives (i.e., metal ions, etc.) could easily be separated in the acidification treatment, which is beneficial for practical applications of the plastic recycling process. Around 87% of the TA monomers are recovered in a pure form for efficient re-polymerization thereby creating fully recyclable plastics. The large-scale 100 g experiment for both polymerization and chemical recycling verify the practical industrial applications and support for a sustainable plastic circular economy. Considering the practical applications of these polymers synthesized in this effort, the performance of both origin and re-polymerized polymers exhibited excellent and consistent recoveries and mechanical function even after completing three cycles of chemical recycling.9Zhang Q. Deng Y. Shi C.-Y. Feringa B.L. Tian H. Qu D.-H. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides).Matter. 2021; 4 (this issue): 1352-1364https://doi.org/10.1016/j.matt.2021.01.014Abstract Full Text Full Text PDF Scopus (29) Google Scholar Compared with the established concept of depolymerization and reprocessing, dual closed-loop chemical recycling is robust and environmentally friendly making the polymers more sustainable based on the simple, natural, and small TA molecule. This innovation is critically important to polymer science and society as it is a cost-effective mitigation strategy to address plastic pollution in a holistic manner. Most importantly, an evaluation of the overall recycling potential of TA-based polymers requires a comprehensive life cycle assessment (LCA) including detailed life cycle inventory (LCI) data. Approximately, 44 relevant LCA investigations, including environmental impacts for both bio-based and petroleum-based plastics published during 2011–2020,10Bishop G. Styles D. Lens P.N.L. Environmental performance comparison of bioplastics and petrochemical plastics: A review of life cycle assessment (LCA) methodological decisions.Resour. Conserv. Recycling. 2021; 168: 105451Crossref Scopus (48) Google Scholar question whether biodegradable plastics can support both sustainable ecosystems and a circular economy. The evaluation of environmental impacts from bio-based polymers requires comprehensive reporting of LCI data including all plastic additives in the LCI. In addition, plastic utilization cycles need to be incorporated using standardized functional unit definitions and system boundaries. Collectively, strategic support for environmental, social, and corporate governance (ESG) in the evaluation of TA-based polymers may encourage industrial mitigation of the unsustainable use of plastics. Dual closed-loop chemical recycling of synthetic polymers by intrinsically reconfigurable poly(disulfides)Zhang et al.MatterFebruary 4, 2021In BriefDeveloping repeatedly recyclable polymers is a timely and urgent task for chemists. An intrinsically reconfigurable polymer made from thioctic acid, a natural small molecule, is found to be a promising candidate for chemically recyclable polymers. Owing to the reversible nature of disulfide bond, the resulting poly(disulfides) can be easily and efficiently recycled by using basic aqueous solution. The reproduced materials exhibit fully recovered properties due to the virgin quality of the recycled monomers, showing the excellent recyclability and great prospects toward future green plastics. Full-Text PDF Open Archive

MOORA and TOPSIS based selection of input parameter in solar powered absorption refrigeration system

ABSTRACT Absorption cooling using energy media like low-grade solar thermal energy and many other sources is of utmost importance for energy needs. To enhance the coefficient of performance of system, an experimentation using forced convection, air/water cooled absorber was carried out. The input power from 40 to 70 W is given to the generator with each case of the framework and found improvement in the coefficient of performance from 8.69% to 18.18% in water cooled absorber. To determine optimal input power, optimisation of the refrigeration systems is important. In this work, Multi-Objective Optimisation based on Ratio Analysis (MOORA) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) are used and observed that the best solution for input power is 40 W for water cooled absorber system and the ranking order is 1 > 3>4 > 2, i.e. (40 W > 60 W > 70 W > 50 W).

Solar-assisted pressure-temperature swing adsorption for CO2 capture: Effect of adsorbent materials

Because of the ability to utilize the low-grade solar thermal energy for regeneration, a CO2 capture system characterized by solar-assisted pressure temperature swing adsorption (SOL-PTSA) is studied on the effects of adsorbent materials. A detailed cycle description is firstly presented within the diagram of adsorption isotherm for the energy-efficiency analysis. Typical adsorbent materials, including zeolites and chemical adsorbent, are assessed in terms of sensible heat and latent heat, etc. Then, the energy consumption and the second-law efficiency, which can be considered as lumped indicators from such material parameters, are chosen as performance indicators as well. The influence of separation temperature, desorption temperature, CO2 concentration and CO2 adsorption pressure on system performance are finally obtained. For the chosen three adsorbent materials, the energy consumption of SOL-PTSA system is at the range of 25.96–87.76 kJ/mol, and the corresponding second-law efficiencies are at the range of 9.18–26.89%. The effect of adsorbent materials on the energy-efficiency of SOL-PTSA system mainly depends on specific heat, CO2 working capacity and cycle design. In addition, the integration options of solar energy into PTSA technology are also discussed from the standpoint of the utilization of solar grade heat due to two energy loads required for PTSA's operation.

Impact of the operation of non-displaced feedwater heaters on the performance of Solar Aided Power Generation plants

Solar Aided Power Generation is a technology in which low grade solar thermal energy is used to displace the high grade heat of the extraction steam in a regenerative Rankine cycle power plant for feedwater preheating purpose. The displaced extraction steam can then expand further in the steam turbine to generate power. In such a power plant, using the (concentrated) solar thermal energy to displace the extraction steam to high pressure/temperature feedwater heaters (i.e. displaced feedwater heaters) is the most popular arrangement. Namely the extraction steam to low pressure/temperature feedwater heaters (i.e. non-displaced feedwater heaters) is not displaced by the solar thermal energy. In a Solar Aided Power Generation plants, when solar radiation/input changes, the extraction steam to the displaced feedwater heaters requires to be adjusted according to the solar radiation. However, for the extraction steams to the non-displaced feedwater heaters, it can be either adjusted accordingly following so-called constant temperature strategy or unadjusted i.e. following so-called constant mass flow rate strategy, when solar radiation/input changes. The previous studies overlooked the operation of non-displaced feedwater heaters, which has also impact on the whole plant’s performance. This paper aims to understand/reveal the impact of the two different operation strategies for non-displaced feedwater heaters on the plant’s performance. In this paper, a 300MW Rankine cycle power plant, in which the extraction steam to high pressure/temperature feedwater heaters is displaced by the solar thermal energy, is used as study case for this purpose. It was found that plant adopting the constant temperature strategy is generally better than that adopting the constant mass flow rate strategy. However, if rich solar energy is available, adopting the constant mass flow rate strategy can achieve better performance.

Mid and low-temperature solar–coal hybridization mechanism and validation

A higher solar-to-electricity conversion efficiency was one of the major advantages of the solar-fossil hybrid systems, compared to the solar-only power plants. In this paper, a new mechanism to reveal the reasons for the improved solar-to-electricity efficiency in a solar-hybrid power plant was given. A correlation was built to describe the main influencing factors of its thermodynamic performances, including higher collector efficiency, higher turbine internal efficiency and upgraded energy level of the mid and low-temperature solar heat. This proposed mechanism can be used to integrate solar–coal hybridization system effectively. A case study was taken as the typical 200 MW coal-fired power plant hybridized with solar heat at approximately 300 °C, where the solar heat was used to preheat the feed water before entering the boiler. Furthermore, simulation results of this mid and low-temperature solar-hybridization system was conducted to prove the proposed mechanism. It is expected that the theoretical values have a good agreement with the simulation ones. The results obtained indicate that why development of mid and low-temperature solar–coal hybridization technology may provide a promising direction to efficient utilization of low-grade solar thermal energy, and provide the direction to enhance system performances of this kind of solar–coal hybrid power plants.

Proposed Partial Repowering of a Coal-Fired Power Plant Using Low-Grade Solar Thermal Energy

In this paper, a hybrid power-generation system with integration of solar heat at approximately 300 ⁰C was proposed for a coal-fired power plant. The system was investigated with the aid of energy-utilization diagram methodology (EUD methodology). In this research, instead of steam, low-grade solar heat was utilized to heat the feed water, leading to an improvement in the plant thermodynamic performance. The net annual solar-to-electric efficiency was recorded as over 15%. Solar feed-water heaters can operate in line with previously used feed-water heaters during the solar off-design period. A preliminary economic evaluation demonstrated that the increased capital cost of the solar collectors may be approximately $2,007/kWe. The promising results indicated that the proposed thermal cycle offers an approach that integrates mid-temperature solar heat to partially repower existing coal-fired power plants.

Numerical investigation of a two-stage air-cooled absorption refrigeration system for solar cooling: Cycle analysis and absorption cooling performances

Two-stage air-cooled ammonia–water absorption refrigeration system could make good use of low-grade solar thermal energy to produce cooling effect. The system simulation results show that thermal COP is 0.34 and electrical COP is 26 under a typical summer condition with 85°C hot water supplied from solar collector. System performances under variable working conditions are also analyzed. Circular finned tube bundles are selected to build the air-cooled equipment. The condenser should be arranged in the front to get an optimum system performance. The mathematical model of the two-stage air-cooled absorber considering simultaneous heat and mass transfer processes is developed. Low pressure absorber should be arranged in front of middle pressure absorber to minimize the absorption length. Configuration of the air-cooled equipment is suggested for a 5kW cooling capacity system. Temperature and concentration profiles along the finned tube length show that mass transfer resistance mainly exists in liquid phase while heat transfer resistance mainly exists in cooling air side. The impacts on system refrigeration capacities related to absorption behaviors under variable working conditions are also investigated. Both cycle analysis and absorption performances show that two-stage air-cooled ammonia–water absorption chiller is technically feasible in practical solar cooling applications.

Experimental Study of an Open-Cycle Solar Collector/Regenerator Using Liquid Desiccant For Air Conditioning

Liquid desiccant has been widely used in various solar energy applications, such as air conditioning and food drying. Especially, in the emerging solar desiccant air conditioning system, the regenerator, where the diluted solution is concentrated, plays an important role. Using the open-cycle solar collectors/regenerators (C/R) to concentrate the dilute solution is an effective way to utilize low-grade solar thermal energy to regenerate desiccant solution for air conditioning. The desiccant solution itself is a heat-collecting fluid and the regeneration process could be enhanced in this arrangement. To evaluate its thermal performance, a lab-scale experiment has been conducted using lithium bromide (LiBr) solution. The effects of ambient weather variables (solar radiation, air temperature, relative humidity) and operation conditions (air mass flow rate, solution flow rate, air inlet temperature, solution inlet temperature, and solution concentration) on the solar regeneration parallel flow configurations have been experimentally investigated. To further investigate the heat- and mass-transfer phenomenon inside the solar C/R, the heat- and mass-transfer coefficients are calculated based on the experimental data using multi-dimensional optimization method. Unlike those traditional correlations available in the literature, the effects of inlet conditions of the air and solution on the heat- and mass-transfer coefficients are clearly identified. Applying these correlations to the simulation model of the solar C/R and comparing the predicted values with the experimental values, the accuracy is satisfactory and can be applied to the further investigation for the thermodynamic performance of the solar desiccant air conditioning system.

Fundamental study of novel mid- and low-temperature solar thermochemical energy conversion

A new approach to application of mid- and low-temperature solar thermochemical technology was introduced and investigated. Concentrated solar thermal energy in the range of 150―300℃ can be efficiently converted into high-grade solar fuel by integrating this technique with the endothermic reaction of hydrocarbons. The conversion mechanism of upgrading the low-grade solar thermal energy to high-grade chemical energy was examined based on the energy level. The new mechanism was used to integrate two novel solar thermal power systems: A solar/methanol fuel hybrid thermal power plant and a solar-hybrid combined cycle with inherent CO2 separation using chemical-looping combustion, for developing highly efficient solar energy use to generate electricity. An innovative prototype of a 5-kW solar receiver/reactor, as the key process for realizing the proposed system, was designed and manufactured. Furthermore, experimental validation of energy conversion of the mid- and low-temperature solar thermochemical processes were conducted. In addition, a second practical and viable approach to the production of hydrogen, in combination with the novel mid- and low-temperature solar thermochemical process, was proposed and demonstrated experimentally in the manufactured solar receiver/reactor prototype through methanol steam reforming. The results obtained here indicate that the development of mid- and low-temperature solar thermochemical technology may provide a promising and new direction to efficient utilization of low-grade solar thermal energy, and may enable step-wise approaches to cost-effective, globally scalable solar energy systems.

Mechanism of Upgrading Low-Grade Solar Thermal Energy and Experimental Validation

Solar thermochemical processes inherently included the conversion of solar thermal energy into chemical energy. In this paper, a new mechanism of upgrading the energy level of solar thermal energy at around 200°C was revealed based on the second law thermodynamics and was then experimentally proven. An expression was derived to describe the upgrading of the energy level from low-grade solar thermal energy to high-grade chemical energy. The resulting equation explicitly reveals the interrelations of energy levels between middle-temperature solar thermal energy and methanol fuel, and identifies the interactions of mean solar flux and the reactivity of methanol decomposition. The proposed mechanism was experimentally verified by using the fabricated 5kW prototype of the receiver∕reactor. The agreement between the theoretical and the experimental results proves the validity of the mechanism for upgrading the energy level of low-grade solar thermal energy by integrating clean synthetic fuel. Moreover, the application of this new middle-temperature solar∕methanol hybrid thermochemical process into a combined cycle is expected to have a net solar-to-electric efficiency of about 27.8%, which is competitive with other solar-hybrid thermal power plants using high-temperature solar thermal energy. The results obtained here indicate the possibility of utilizing solar thermal energy at around 200°C for electricity generation with high efficiency by upgrading the energy level of solar thermal energy, and provide an enhancement to solar thermal power plants with the development of this low-grade solar thermochemical technology in the near future.