Solar-heat Conversion Research Articles

Photothermal catalytic conversion of water and inert nitriles to amide activated by in-situ formed transition-metal-complex nanodots

Photothermal catalytic N-acetylation of aniline has been a promising strategy to synthesize amides, which combined the advantages of thermal catalysis and photocatalysis. Herein, we demonstrate a high-performance strategy to synthesize amides catalyzed by the in-situ formed first-row transition-metal (Fe, Co, Ni, Mn et al.) complexes nanodots (TMC NDs) under solar light excitation without using noble metals or strong acids. The dual-functional nitriles substrates acted as the ligands to coordinate with transition-metal salts affording photosensitive TMC NDs with high solar-to-thermal energy conversion efficiency. Intramolecular charge transitions reduced the energy barrier of nitriles activation by weakening CN bond and triggered near-field temperature rise via the electron–phonon scattering non-radiative pathway. The reaction system exhibited good tolerance to different functional groups, affording a series of amide derivatives. Such a dynamic coordination reaction mode and the in-situ formed TMC NDs opens new avenues toward solar-heat conversion via photon–phonon coupling in the field of chemical synthesis.

Portable solar array technology in remote operation of electric-based vehicles for TNI vehicles

Indonesia’s geographical expanse, spanning from Sabang to Merauke, ensures a consistent and predictable supply of solar energy due to its perpetual shining period. This presents a significant opportunity for the country to embrace sustainable and renewable energy sources, with solar power being particularly advantageous given Indonesia’s tropical climate. However, the conversion of solar heat into electrical energy offers a compelling solution, enabling the utilization of portable solar arrays to meet the electricity requirements of military vehicle operations while simultaneously reducing reliance on fossil fuels. Solar thermal energy to electrical energy conversion requires efficient energy storage devices. Sodium batteries are more robust and eco-friendly. Moreover, portable solar panels can serve as an energy source for various military tasks, including powering tents and charging communication equipment. By incorporating solar energy into their operations, the Indonesian army can enhance their operational capabilities while reducing their dependence on conventional energy sources. In conclusion, capitalizing on Indonesia’s abundant sunlight and tropical climate through the deployment of portable solar arrays and sodium-based batteries presents a sustainable and reliable solution for meeting the energy needs of military operations. This approach enables the Indonesian army to effectively conduct their missions while simultaneously minimizing their environmental impact.

Magnetically Assembled Ultrablack Surface with Omnidirectional and Broadband Light Absorption

Ultrablack surfaces with stable and omnidirectional light absorption over a wide spectral range are fundamentally crucial for applications concerning strict optical requirements from high-end optical to solar-heat conversion devices. Inspired by nature, we report a needle-like array structure (NAS) prepared by spraying and self-assembling the magnetic composite ink under an external magnetic field. With high structure regularity and small feature size, the NAS presents extremely low hemispherical reflectance (≤0.3%) over a wide spectral range of 300-2000 nm and stable omnidirectional absorption (incident angle insensitivity up to 70°), which could be one of the darkest surfaces ever reported. The exciting light absorption performance can be attributed to the synergistic effects of (1) structural absorption caused by multiple scattering between array units and (2) strong forward scattering and high light absorptivity of magnetic particles. The NAS exhibits outstanding photothermal conversion for solar harvesting, self-cleaning performance, good flexibility, and thermal-aging resistance, offering an appealing alternative to construct ultrablack surfaces for practical applications.

High-Performance Organic Photothermal Material Based on Fusion of the Donor–Acceptor Structure for Water Evaporation and Thermoelectric Power Generation

Recently, organic photothermal materials have shown great application potential for solar-driven water–electricity co-generation. However, their extended application is limited by low solar-heat conversion efficiency. This study designed a planarized donor–acceptor (D–A)-type organic photothermal material 5,18-dibutyl-5,18-dihydrodiquinoxaline[2,3-a:2′,3′-c]phenazine (DDHT) by fusing a strongly electron-donating arylamine unit and strongly electron-withdrawing quinoxalino[2,3-a]phenazine unit. The fused-ring D–A structure not only endowed the material with broad absorption spectra through low-energy intramolecular charge–transfer transition, but also allowed for intense intermolecular π–π interactions, which improve non-radiative transition probability and, correspondingly, the photothermal conversion efficiency (58.58% under laser irradiation at 655 nm). Under a solar intensity of 1 kW m–2, the water evaporation rate was 1.13 kg m–2 h–1 with a solar-to-vapor efficiency of 78.40% for the DDHT-based interfacial evaporation devices. Finally, a solar-driven steam and electricity co-generation device was prepared with the DDHT/wood composite as the solar-evaporator material, demonstrating electricity generation performances and excellent water purification capabilities. Our research found that fused-ring D–A structures are promising organic photothermal systems for efficient solar-heat conversion.

Interface Engineering of a Ti4O7 Nanofibrous Membrane for Efficient Solar-Driven Evaporation.

Solar-driven interfacial evaporation provides a feasible and sustainable way to solve the fresh water shortage using abundant solar energy and has recently attracted considerable attention. However, it has been limited by the evaporation rate and solar-heat conversion efficiency of the current materials. Herein, a novel Ti4O7 membrane with synergetic photothermal and electrothermal effects was developed using a straightforward in situ approach. Based on interface engineering, the interface between the surface of the membrane and water was hydrophobically modified, and a thermal insulation layer was added to the bottom of the membrane. The optimized self-floating membrane with excellent sunlight absorbability and conductivity achieved a remarkably high evaporation rate of 7.51 kg m-2 h-1 with a voltage of 3 V as compensation under one-sun irradiation (1 kW m-2). Moreover, the bilayered membrane displayed efficient salt ion rejection, and the collected water can meet the World Health Organization (WHO) standard required for potable water.

Nature-inspired poly(N-phenylglycine)/wood solar evaporation system for high-efficiency desalination and water purification

The development of low-cost, scalable wood-based photothermal systems that utilize renewable solar energy for energy conservation and desalination has received extensive attention. Although some materials such as precious metals, semiconductor materials and carbon nanomaterials have been used as light absorbers, the issues of low evaporation rate and efficiency, as well as the high energy consumption and cost of photothermal layer design need to be addressed. In this work, inspired by the transpiration process of trees, a poly(N-phenylglycine) (PNPG)-wood solar evaporator was developed. The coating of PNPG, a conjugated polymer with good light absorption, greatly cover the shortage of weak light absorbance of wood, and effectively improved the solar-heat conversion efficiency. Moreover, benefited from the low thermal conductivity and special microstructure of the wood, the relationship among water transport, solar energy conversion, and heat regulation was better adjusted. As a result, the PNPG-wood system can effectively and quickly generate steam, the evaporation rate and efficiency can be 1.64 kg m–2 h–1 and 90.4% under 1 sun, which are higher than most reported wood-based solar evaporators. Hence, such a well-designed, cost-effective, durable, and high-efficiency solar evaporation system has the potential to be applied to solve the practical problem of seawater desalination and water purification.

The analysis of Polish patent applications in the solar energy technology with the use of text mining methodology

Purpose: Knowledge management belongs to the most important elements of organisational management, including manufacturing enterprises. Patent information plays an increasingly important role in this area. Identification of the main directions of invention activity may inspire new product and process ideas, and can help to improve existing solutions. The above is particularly important in the energy sector, which is currently struggling with increasing problems. In this context, solar energy is the subject of interest to inventive communities. The paper discusses patent applications related to solar energy, taking up the task of discovering the main tendencies of technological solutions in this area. Design/methodology/approach: In the work, a pilot study of the research aimed to indicate the directions of technological development in the field in Poland was undertaken. Shortened descriptions of selected patent documents from the Polish Patent Office (PPO) were the subject of the investigation. The descriptions were reduced to the form of a vector space model by using text mining tools. The exploration of such prepared data was done applying unsupervised text mining techniques. Hierarchical cluster analysis enabled the identification of groups of similar inventions. An algorithm to detect outliers within individual patent groups was also developed and applied. Findings: Five patent clusters were identified covering the following thematic areas: PV panel designs, PV panel component designs, the improvement of solar-heat conversion device performance, and solar collector designs. Six patent applications stood out thematically in four of the five clusters. Research limitations/implications: The research is limited to a selected number of patent documents form PPO. However, the presented method and research area are promising. It is planned to extend the analyses to a larger set of patent documents and solve the problem related to the language uniformity of patent applications along with merging data from various sources. In this aspect, a full patent description will be consider as well. Keywords: solar energy patent analysis, patent documents processing, patent clustering, outliers detection, Polish Patent Office. Originality/value: In relation to solar energy issues, main patent areas and patent outliers that may be indicators of special interests of inventors were identified. In relation to methodology issues, new solutions within consecutive research steps were proposed.

A Flexible Polymer Nanofiber-Gold Nanoparticle Composite Film for Solar-Thermal Seawater Desalination.

Interfacial solar-thermal conversion has broad application prospects in solar driven steam generation, seawater desalination, sewage purification, and other fields. For a wide range of applications, high-efficiency interfacial solar-thermal conversion materials with the feature of being lightweight, flexible, and easy to scale up at the same time are significantly valued. Herein, a strategy for the preparation of solar-thermal poly (4-vinylpyridine) (P4VP) nanofiber-gold nanoparticle (Au NP) composite film (PGCF) is reported. Combining with the flexible and lightweight P4VP nanofibers, these absorbed Au NPs enable better solar-thermal conversion efficiency. Accordingly, the PGCF provides high-performance interfacial solar-driven steam generation, with 77% solar-heat conversion efficiency under the power density of 3.4kW m-2 , which shows stable output (3.4kg m-2 h-1 ) in the application of solar-driven seawater desalination. In addition, PGCF is light in weight, flexible, and suitable for scalable commercial production, enabling PGCF broad application prospects in the field of light-to-heat conversion.

Cellulose nanofibril/polypyrrole hybrid aerogel supported form-stable phase change composites with superior energy storage density and improved photothermal conversion efficiency

The development of phase change materials (PCMs) with high energy storage density, enhanced photothermal conversion efficiency and good form-stability is essential for practical application in utilization of solar energy. Herein, novel PCM composites (CPPCMs) with extremely high energy storage density and superb solar-thermal conversion performance were fabricated by introducing n-octacosane into three-dimensional (3D) porous cellulose nanofibril (CNF)/polypyrrole (PPy) hybrid aerogels. Due to the strong encapsulation capability of CNF/PPy hybrid aerogels (CPAs), the synthesized PCM composites maintained perfect shape stability above the melting point of n-octacosane. Further investigation showed CPPCMs exhibited extremely high latent heat in the range of 239.4–258.4 J/g and high loading rate of n-octacosane (up to 96%). The melting/cooling cycling test and thermogravimetric analysis indicated the composite PCMs possessed excellent cyclic stability and thermal stability. Moreover, simulated sunlight test showed that the photothermal conversion efficiency of CPPCMs significantly improved with the increased content of polypyrrole in the PCM composites. In conclusion, the obtained PCM composites, which exhibited excellent shape stability, superior solar-heat conversion capability and extremely high energy storage density, showed considerable potential for practical utilization and storage of solar energy.

Evaporation Kinetics of Nano Water Droplets using Coarse-Grained Molecular Dynamic Simulations

The utilization of nanocompounds can significantly enhance the production efficiency for solar steam generation, and much research and development efforts have been dedicated to designing their surface and structure to optimize the solar-heat conversion as well as evaporation performance. In particular, computational modeling studies using molecular dynamic (MD) simulations had been extensively performed for this objective. However, those studies typically assumed constant vacuum evaporation, thus yielding unrealistically high evaporation fluxes compared to laboratory and field measurements reported in the literature. To address this issue, we capture the transient thermodynamic properties of a nano water droplet that undergoes evaporation in a vapor medium under a closed periodic system with vapor pressures, using non-equilibrium MD simulations with the ELBA coarse-grain model. The changes of the nanodroplet and the localized vapor pressures inside the system from vacuum to saturation are monitored quantitatively. In addition, the varying radial extent of the Knudsen layer around the droplet is determined spatially through the transient pressure and energy distribution. The results illustrate the dynamical changes in the evaporation behavior from the diffusive-dominant to the kinetically limited transport mechanism. They also explain why the Kelvin equation can still apply in nanometer-scale systems, due to the fact that the density profiles are independent of the changes in pressure gradients. The Hertz-Knudsen Schrage equation, which is commonly used to compute the evaporation flux in the literature, is found unable to accurately predict the transient evaporative behavior observed. Thus, the results from this study illustrate that future molecular dynamic evaporation studies need to identify the location of the Knudsen layer in the simulations when calculating bulk evaporation fluxes in realistic vapor ambient conditions, due to its predominance in nanoscale interfacial processes.

Combined optics and heat transfer numerical model of a solar conical receiver with built-in helical pipe

The performance of a solar conical receiver greatly influences the concentrated solar power (CSP) system. It is worthy to devote efforts on performance optimization for a solar conical receiver with a built-in helical pipe. A comprehensive investigation on the whole solar-heat conversion process is significant. Using a combined optics and heat transfer model, this study simulated the influence of the conical angle, loop number, and insulation thickness on cavity receiver performances. The combination consists of two parts: an optical simulation using the optics software TracePro 7.3.4 and a heat-transfer simulation using the CFD software ANSYS 17.0. Model validation is performed by comparing the simulation results to the published experiment data. Good agreement is achieved. The results indicate that the optimal value of conical angle is 5°, the overall efficiency in this case is 63.6%. From 4 to 15, both thermal efficiency and overall efficiency increase as the loop number increases; however, optical efficiency shows a different trend. The optimal value of insulation thickness ranging from 25 mm to 200 mm is 175 mm, achieving 70.4% overall efficiency. This study provides an effective method of performance optimization for a conical cavity receiver.

Thermo-economic analysis of a novel cascade integrated solar combined cycle system

Integrated solar combined cycle (ISCC) systems have been demonstrated to be more promising than solar-only power generation systems in terms of higher solar heat conversion efficiency and lower cost. In most ISCC projects, concentrating solar fields (e.g., parabolic trough solar fields with heat transfer (HTF) technology or direct steam generation (DSG) technology) are integrated for solar heat production with a temperature up to 400 °C to substitute for water preheating, evaporation or steam superheating in heat recovery steam generator (HRSG) for conventional combined cycle (CC) power systems. Although the ISCC scheme is effective for solar thermal energy utilization, the intermittent nature of solar energy usually causes this kind of systems to run inefficiently at part-load conditions when no or low solar radiation is available because most of the state-of-art ISCC systems are not equipped with costly thermal storage. To improve ISCC system performance, a new solution is proposed and investigated. This paper presents a novel cascade integrated solar combined cycle system, in which parabolic troughs solar collectors with DSG technology and non-concentrating solar collectors (e.g. evacuated tubes) are simultaneously integrated into the combined cycle power system. Thermodynamic and preliminary economic analysis for the new system are conducted to look into its feasibility and advantages. The results show that higher solar-to-electricity conversion efficiency and lower levelized electricity cost for the proposed system are achieved than for a reference ISCC system coupled with only DSG technology. Integration of both concentrating and non-concentrating solar collectors into an ISCC system in a temperature cascade way is viable and more efficient than the use of parabolic trough solar collectors alone.

Performance analysis of a novel low CO2-emission solar hybrid combined cycle power system

This paper is a proposal and analysis of a novel low-CO2 emission solar hybrid combined cycle power system, which is based on solar-driven methane reforming. Nearly full methane conversion is achieved at a mild temperature (∼550 °C) using a methane reforming reactor integrated with a hydrogen separation membrane, enabling the solar thermal energy collected at middle temperature to be applied as the reaction heat in methane reforming, thereby converting the solar heat to chemical energy of the produced syngas. The membrane reactor also offers the advantage of continuously withdrawing hydrogen from the reaction zone, which is then burned at high temperature for power generation in the proposed advanced combined cycle system. The CO2-enriched gas concentrated at the end of the reaction zone is processed through pre-combustion decarbonization. It is shown that system thermal efficiency of 51.6% can be obtained, which is 2.2%-points higher than that of a referenced gas-steam combined cycle system with post-combustion decarbonization (CC-Post) at an equal CO2 removal ratio and no solar assistance. Fossil fuel saving ratio of 31.2% is achieved with a solar thermal share of 28.2%. Exergy analysis indicates that the main contributors for efficiency improvements are the reduced exergy destructions in the combustion and CO2 separation processes. The hybrid system has an exergy efficiency of 58% with 91% CO2 capture, which is 10%-points higher than that of a comparable CC-Post system. A preliminary economic analysis predicts that levelized electricity cost and payback period for the system are found to be 0.062 $/kWh and 10 years, respectively, and cost of CO2 avoided is 81 $/(ton CO2), which is 42.5% lower than that for a CC-Post system. The proposed system hybridization approach simultaneously achieves the dual-purpose of high-efficiency solar heat conversion and low-energy penalty CO2 capture.

Performance comparison of two low-CO 2 emission solar/methanol hybrid combined cycle power systems

Abstract Two novel hybrid combined cycle power systems that use solar heat and methanol, and integrate CO2 capture, are proposed and analyzed, one based on solar-driven methanol decomposition and the other on solar-driven methanol reforming. The high methanol conversion rates at relatively low temperatures offer the advantage of using the solar heat at only 200–300 °C to drive the syngas production by endothermic methanol conversions and its conversion to chemical energy. Pre-combustion decarbonization is employed to produce CO2-free fuel from the fully converted syngas, which is then burned to produce heat at the high temperature for power generation in the proposed advanced combined cycle systems. To improve efficiency, the systems’ configurations were based on the principle of cascade use of multiple heat sources of different temperatures. The thermodynamic performance of the hybrid power systems at its design point is simulated and evaluated. The results show that the hybrid systems can attain an exergy efficiency of about 55%, and specific CO2 emissions as low as 34 g/kW h. Compared to a gas/steam combined cycle with flue gas CO2 capture, the proposed solar-assisted system CO2 emissions are 36.8% lower, and a fossil fuel saving ratio of ∼30% is achievable with a solar thermal share of ∼20%. The system integration predicts high efficiency conversion of solar heat and low-energy-penalty CO2 capture, with the additional advantage that solar heat is at relatively low temperature where its collection is cheaper and simpler. The systems’ components are robust and in common use, and the proposed hybridization approach can be also used with similar benefits by replacing the solar heat input with other low heat sources, and the system integration achieves the dual-purpose of clean use of fossil fuel and high-efficiency conversion of solar heat at the same time.

A Solar Thermoelectric Conversion Material Based on Bi2Te3 and Carbon Nanotube Composites

Carbon nanotubes (CNTs) have been proved to possess a very high light absorption coefficient in a very broad spectrum, showing very good potential for solar–thermal conversion. Bi2Te3 is a typical thermoelectric material with high thermoelectric conversion efficiencies. In this study, we fabricated Bi2Te3 and CNT composites, which combined the solar–heat conversion advantage of CNT sheets and the thermoelectric power generation advantage of Bi2Te3. Property measurements indicate that the simple composites are very promising in converting sunlight into electricity. The efficiency of converting solar energy to electricity reaches up to 1% in natural sunlight without using any kind of optical concentrator or thermal concentrator. This work may provide a simple and convenient approach to prepare solar-energy conversion devices for large-scale applications in the future.

Optical Characterization and Modeling of Coatings Intended as High Temperature Solar Selective Absorbers

SiCNH thin coatings synthesized by Plasma Enhanced Chemical Vapor Deposition (PECVD) are considered as high temperature ceramic materials for solar selective multilayer absorbers. As indicated by ellipsometry and spectrophotometry measurements, their optical characteristics make them suitable as solar absorbing and antireflective coatings in multilayer stacks and/or ceramic- metal composites (cermets). These measurements gave access to spectral values of complex refractive index N = n + ik, reflectance R and transmittance T of the coatings. R and T were also modeled from N, based on Fresnel equations, and a good agreement was found between simulated and measured reflectance in the visible region. A transfer matrix method was then applied to predict the optical response (R, T) of virtual multilayer stacks including SiCNH materials. W-SiCNH cermets were also considered as absorptive layers in these stacks and their refractive indices were calculated using Bruggeman effective medium approximation theory. Solar absorptance αS and thermal emittance ɛ(T) were estimated from simulated reflectance. Layer thicknesses and cermet composition were optimized using CODE software and a MATLAB in-house code, so as to maximize solar-heat conversion efficiency which relied on high αS (up to 95%) and low ɛ (down to 6% at 500°C). The corresponding global yield which could be attained in typical Fresnel and central tower solar plants using these selective coatings was also calculated and compared to current technology.

A Study on the Solar-Thermal Performance in PV/T System

Based on the thermal equilibrium between the PV panels and the glazing cover of PV/T system, the influence of the spacing between PV panels and glazing cover on the solar-thermal efficiency is discussed. The heat release and solar-heat conversion efficiency of the photovoltaic panels, under different plate spacing, in the PV/T systems in summer are calculated, according to the typical annual meteorological parameters of Tianjin area. The results show that the photo-thermal efficiency of the PV/T system can be improved by appropriate setup of the plate spacing, and the optimal plate spacing is affected by the temperature of photovoltaic panels.

Theoretical investigation of the performance of a novel loop heat pipe solar water heating system for use in Beijing, China

A novel loop heat pipe (LHP) solar water heating system for typical apartment buildings in Beijing was designed to enable effective collection of solar heat, distance transport, and efficient conversion of solar heat into hot water. Taking consideration of the heat balances occurring in various parts of the loop, such as the solar absorber, heat pipe loop, heat exchanger and storage tank, a computer model was developed to investigate the thermal performance of the system. With the specified system structure, the efficiency of the solar system was found to be a function of its operational characteristics - working temperature of the loop heat pipe, water flow rate across the heat exchanger, and external parameters, including ambient temperature, temperature of water across the exchanger and solar radiation. The relationship between the efficiency of the system and these parameters was established, analysed and discussed in detail. The study suggested that the loop heat pipe should be operated at around 72 °C and the water across the heat exchanger should be maintained at 5.1 l/min. Any variation in system structure, i.e., glazing cover and height difference between the absorber and heat exchanger, would lead to different system performance. The glazing covers could be made using either borosilicate or polycarbonate, but borosilicate is to be preferred as it performs better and achieves higher efficiency at higher temperature operation. The height difference between the absorber and heat exchanger in the design was 1.9 m which is an adequate distance causing no constraint to heat pipe heat transfer. These simulation results were validated with the primary testing results.

Conversion of solar heat into work: A supplement to the actual thermodynamic description

The absorption of radiant energy in solar cells is divided into reversible and irreversible processes occurring in parallel. The paper proposes a method for calculating their relative contributions. We also show that photon reemission without work production plays a particular role in the conversion of solar heat into work and the attainment of higher solar cell efficiencies. The comparison of the well-known thermodynamic efficiency limitations of the solar energy conversion with and without entropy production makes it possible to formulate the notion “antenna states of the absorber particles.” The carriers of similar states are known as pigment molecules in the photosynthesis of plants. We show that it is impossible to attain very high efficiencies in the conversion of solar heat into work without the reversible antenna reemission of solar energy.

Utilization of solar radiation by polar animals: an optical model for pelts

A summary of existing passive solar-heat conversion panels provides the basis for a definition of an ideal passive solar-heat converter. Evidence for the existence of a biological greenhouse effect in certain homopolar homeothermic species is reviewed. The thermal and optical properties of homeothermic pelts, in particular those of the polar bear, are described, and a qualitative optical model of the polar bear pelt is proposed. The effectiveness of polar bear and seal pelts as solar-heat converters is discussed, and comparison is made with the ideal converter.