High Solar-thermal Conversion Efficiency Research Articles

Comparative Numerical Energy and Performance Analysis of Solar Photovoltaic and Solar Thermal Power Generation

This study analyses fixed and tracking solar photovoltaics and, solar thermal power. Performance in different locations was analysed for each configuration and technology using simulations based on a Typical Meteorological Year data. The study analysed a 25MWp solar photovoltaic and solar thermal power plants in each of the eleven selected locations in Zimbabwe. The performance of the solar photovoltaic and solar thermal power plants under different meteorological variables were assessed for all the selected locations. It was shown that different configurations together with different technologies have different conversion efficiencies. A high solar thermal conversion efficiency was found to be 18.718% in Gweru while it was 15.502% for solar photovoltaics in Mutare. The study also showed that highest insolation and clearness index values were found in Gweru. The average energy generated by the fixed photovoltaic collectors, tracking photovoltaic collectors and the Concentrating Solar Power plant were respectively 47.38GWh, 68.18GWh and 192.86GWh. There was a maximum percentage difference in the LCoE generated of 32.03% between the fixed PV collectors and the Concentrating Solar Power plant and a difference of 4.74% was realised between the tracking photovoltaics and Concentration Solar Power.

Phase change materials encapsulated in a novel hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage

Phase change materials (PCMs) with high energy density and stationary transition temperature are now considered promising solar energy storage mediums. However, their intrinsic poor light absorption, thermal conductivity and stability severely impede their potential applications. In this study, a novel carbonized hybrid aerogel (CHA) structure was firstly constructed by incorporating MXene and carbon nanofibers (CNFs) into a continuous phase polyamic acid salt (PAAS) aqueous solution, followed by directional freezing, vacuum drying, imidization, and carbonization processes. Finally, the composite PCMs (CPCMs) were fabricated by vacuum impregnation of PCMs into the CHAs. The CPCM, of which CHA consists of 20 wt% MXene and 10 wt% CNF@PDA, demonstrates high solar-thermal conversion efficiency (>91 %), improved thermal conductivity of 0.40 W·m−1·K−1, great thermal stability (enthalpy loss < 0.19 % after 100 cycling tests with no obvious leakage). The introduction of MXene and CNFs endows PCM with broader light absorption spectrum range. The skeleton matrix embedded with bonded MXene sheets and CNFs provides more thermal pathways, light absorption sites and carrying capacity, improves the thermal conductivity, solar-thermal conversion property and stability of PCM. In addition, CPCM also exhibits outstanding EMI SE (95 dB). The multifunctional and high-performance CPCMs shows potential to realize the effective capture and utilization of solar energy. This work provides a new strategy to construct stable and multifunctional hybrid carbon skeleton for high-efficiency solar-thermal conversion and energy storage.

Anisotropic and hierarchical porous boron nitride/graphene aerogels supported phase change materials for efficient solar-thermal energy conversion

The formation of shape-stabilized composite phase change materials (CPCMs) with special structure is an efficient strategy to prevent the leakage of phase change materials (PCMs) and improve the solar-thermal conversion ability. In this work, graphene and boron nitride nanosheets (BBNS) were prepared by the magnesiothermic reduction SHS method in CO2 and N2 atmosphere, respectively. Then, an anisotropic and hierarchical porous boron nitride/graphene aerogel with three-dimensional network was constructed by directional ice-freezing method using carboxymethyl cellulose as supporting framework and adhesive, and polyethylene glycol (PEG) was impregnated to prepare novel CPCMs. The CPCMs had enthalpies of 150∼160 J/g, and a highest thermal conductivity of 0.390 W/(m·K), which was around 47% higher than that of pure PEG. The ability of the CPCMs to convert solar energy to thermal energy was significantly enhanced. Under a simulated light intensity of sunlight (100 mW/cm2), its solar-thermal conversion efficiency reaches 94.92%, and after 20 min of irradiation, the surface temperature can reach 72 °C. These CPCMs are promising for the efficient use of renewable solar energy due to their high solar-thermal conversion efficiency and thermal storage capabilities.

Flexible photothermal-triggered MOF-composite nanofibers textures for freshwater harvesting with high efficiency and stability

Vast freshwater reserves in the atmosphere have been investigated as a sustainable source of water for the alleviation of the water crisis with suitable sorbent-based atmospheric water harvesting (AWH) materials. In this work, we design a flexible photothermal-triggered MOF-composite nanofiber texture (PMNT), which is fabricated by combining nanofibers to be optimally integrated with UiO-66-NH2, carbon black and lithium chloride. PMNT achieves not only efficient water molecule uptake but also high solar thermal conversion efficiency. The PMNT effectively harvests atmospheric water to ∼ 1.44 g g−1 under 60 % RH in 80 min and quickly releases water over 30 min under 1 sun. In particular, PMNT outdoors collects water of ∼ 1.16 g g−1, even if the light intensity is ∼ 1.16 kW m−2 and the temperature is ∼ 34 °C, the RH is only 23 %. PMNT outdoors can achieve a total water yield of ∼ 4.61 g g−1 through 5 uptake-release cycles per day, along with stability and low energy consumption for AWH. It has been demonstrated that the as-harvesting water via PMNT meets the WHO standard. This study provides insight into the design of novel materials for AWH performance, which can be extended to practical applications, e.g., water engineering in arid regions, water harvesting devices and systems in industry.

Biomass-Based Shape-Stabilized Composite Phase-Change Materials with High Solar-Thermal Conversion Efficiency for Thermal Energy Storage.

To alleviate the increasing energy crisis and achieve energy saving and consumption reduction in building materials, preparing shape-stabilized phase-change materials using bio-porous carbon materials from renewable organic waste to building envelope materials is an effective strategy. In this work, pine cone porous biomass carbon (PCC) was prepared via a chemical activation method using renewable biomaterial pine cone as a precursor and potassium hydroxide (KOH) as an activator. Polyethylene glycol (PEG) and octadecane (OD) were loaded into PCC using the vacuum impregnation method to prepare polyethylene glycol/pine cone porous biomass carbon (PEG/PCC) and octadecane/pine cone porous biomass carbon (OD/PCC) shape-stabilized phase-change materials. PCCs with a high specific surface area and pore volume were obtained by adjusting the calcination temperature and amount of KOH, which was shown as a caterpillar-like and block morphology. The shape-stabilized PEG/PCC and OD/PCC composites showed high phase-change enthalpies of 144.3 J/g and 162.3 J/g, and the solar-thermal energy conversion efficiencies of the PEG/PCC and OD/PCC reached 79.9% and 84.8%, respectively. The effects of the contents of PEG/PCC and OD/PCC on the temperature-controlling capability of rigid polyurethane foam composites were further investigated. The results showed that the temperature-regulating and temperature-controlling capabilities of the energy-storing rigid polyurethane foam composites were gradually enhanced with an increase in the phase-change material content, and there was a significant thermostatic plateau in energy absorption at 25 °C and energy release at 10 °C, which decreased the energy consumption.

Donor-Acceptor molecule with TICT character: a new design strategy for organic photothermal material in solar energy

Organic photothermal materials, particular the donor–acceptor (D-A) type ones, have attracted increased attention because they could efficiently transform solar energy to heat in an environmentally friendly manner. So far, there are many strategies to improve the fluorescence of D-A type molecules, while how to quench the fluorescence via non-radiative decay process and thus maximize the solar-thermal conversion efficiency is rarely investigated. Herein, a new design strategy is proposed to overcome this bottleneck, that is, formatting a unique twisted intramolecular charge-transfer (TICT) excitation state for the D-A type molecule. To demonstrate this new design strategy, three D-A molecules TPA-BTO, TPA-BTO-Py+ and GTPA-BTO-Py+ are synthesized with the consideration of employing stronger donor/acceptor moieties. The photophysical measurements and theoretical calculations reveal that these molecules display strong tendency to form TICT state, and the stronger donor/acceptor would significantly promote the TICT-based non-radiative decay process. Consequently, the target molecule GTPA-BTO-Py+ is totally non-fluorescent and could efficiently transform the absorbed solar energy to heat. Further combined with the wide absorption up to 1300 nm, GTPA-BTO-Py+ solid displays a high solar-thermal conversion efficiency of 20.5%. Finally, the utility of GTPA-BTO-Py+ as highly efficient photothermal material in solar energy is highlighted by water evaporation and thermoelectric generation.

Architecting the Water State of Polypyrrole/Polyvinyl Alochol‐Wood Evaporator to Enhance Water Yield in Multistage Solar Stiller

Solar desalination is one of the most promising ways to produce freshwater. Interfacial solar steam generation system is especially studied for its high solar–thermal conversion efficiency. However, the phase transition process of water evaporation is energy intensive and a salt cluster is easily accumulated at the surface of the evaporator, which limits the water yield and stability of the distiller. Herein, a hybrid design involving tuning the water state, recycling latent heat, and spatial localizing low‐concentration zone to distill for stable and efficient solar‐water harvesting is demonstrated. In a two‐stage distiller, the water yield can reach 1.62 kg m−2 h−1 under one sun irradiation, corresponding to the solar‐to‐vapor conversion efficiency of 110%. The scale‐up device can also steadily operate for 1 week outdoors. This work provides an effective strategy for high‐efficiency solar distillation, holding the promise of application in seawater desalination and domestic water supply.

Polydopamine modified ZIF-L/sodium alginate composites as the highly efficient photothermal membrane for solar steam generation

Interfacial solar steam generation (ISSG) technology is considered to be one of the most promising approaches to alleviating the global shortage of clean water due to its high solar thermal conversion efficiency. However, achieving stable evaporation in high salinity solutions and preventing the occurrence of salt deposition phenomena remains a challenge. Here, an efficient and stable photothermal membrane-based evaporator has been developed, which consists of polydopamine (PDA) modified leaf-like zeolitic imidazolate framework (ZIF-L) implanted in sodium alginate (SA) membrane supported on a melamine sponge (S-ZIF-L/PDA sponge), providing more advantages for boosting the photothermal conversion performance and preventing salt deposition. This S-ZIF-L/PDA sponge displays an excellent light absorption (>95 %), and remarkable evaporation rate of 1.66 kg·m−2·h−1 with a solar-thermal efficiency of 91.06 % under 1.0 sun (1 kW·m−2) illumination. Benefiting from the super hydrophilic feature of the melamine sponge and the rejection properties of the SA membrane structure, the obtained sponge effectively prevents salt and contaminants from depositing on the surface. Particularly, the S-ZIF-L/PDA sponge achieves an evaporation efficiency of 86.17 % in 20 wt% NaCl solution, along with excellent resistance to salt deposition and marvelous stability in cycling tests. The salt ion concentration of the obtained fresh water is much lower than the World Health Organization (WHO) drinking water standard, and the organic removal rate exceeds 99 %. This work provides a competitive solution for high-salinity desalination and wastewater treatment.

Ni@rGO into nickel foam for composite polyethylene glycol and erythritol phase change materials

The exploitation of shape-stabilized composite phase change materials (CPCMs) with high solar-thermal conversion efficiency, thermal storage capacity and thermal conductivity has attractive prospects for solar energy utilization. In this work, reduced graphene oxide (rGO) nanosheets decorated with Ni nanoparticles (Ni@rGO) are successfully filled into the nickel foam (NF) skeletons by acidic graphene oxide solution impregnation and subsequent thermal reduction methods. The obtained NF/Ni@rGO supports with controllable Ni@rGO content are used as the carrier for loading polyethylene glycol (PEG) and erythritol (ET) to prepare CPCMs. The Ni@rGO hybridization enhances the interaction of the carrier framework with the PCM, which can effectively increase the PCM loading and prevent its leakage. As compared with bare NF supported CPCMs, the NF/Ni@rGO supported CPCMs have better shape stability, far higher thermal storage density, and better recyclability. The optimized CPCMs with PEG and ET show high latent enthalpies of 125.30 J·g−1 and 280.66 J·g−1, respectively. It is also found that the thermal conductivity of CPCMs is significantly improved to 0.9199 W·m−1K−1 for NF/Ni@rGO-10/PEG and 0.9146 W·m−1K−1 for NF/Ni@rGO-10/ET, which is 344 % and 35 % higher than that of PEG and ET, respectively. In addition, the decoration of Ni nanoparticles on the rGO support (i.e., NF/Ni@rGO-10) could further improve the thermal conductivity, solar-thermal conversion efficiency (95.74 %) and electro-thermal conversion efficiency (71.39 %) of CPCMs. This research furnishes the basis for the development of high performance CPCMs. Moreover, it has great potential and broad application prospects in the efficient utilization of solar energy and thermal management of electronic devices.

Spinel Cu-Mn-Cr Oxide Nanoparticle-Pigmented Solar Selective Coatings Maintaining >94% Efficiency at 750 °C.

High-temperature concentrating solar power (CSP) system is capable of harvesting and storing solar energy as heat toward cost-effective dispatchable solar electricity. Solar selective coating is a critical component to boost its efficiency by maximizing solar absorptance and minimizing thermal emittance losses. However, maintaining a high solar-thermal conversion efficiency >90% for long-term operation at ≥750 °C remains a significant challenge. Herein, we report spray-coated spinel Cu-Mn-Cr oxide nanoparticle-pigmented solar selective coatings on Inconel tube sections maintaining ≥94% efficiency at 750 °C and ≥92.5% at 800 °C under 1000× solar concentration after 60 simulated day-night thermal cycles in air, each cycle comprising 12 h at 750 °C/800 °C and 12 h cooling to 25 °C. The solar spectral selectivity is intrinsic to the band-to-band and d-d transitions of nonstoichiometric spinel Cu-Mn-Cr oxide nanoparticles. This feature offers a large fabrication tolerance in nanoparticle volume fraction and coating thickness, facilitating low-cost and scalable spray-coated high-efficiency solar selective absorbers for high-temperature CSP systems.

Selective absorber and emitter boost water evaporation and condensation toward water collection

Solar evaporation has attracted much attention for water collection. However, previous studies on the traditional interface evaporation pay little attention to the selective spectral properties of solar absorbers, leading to mid-infrared radiative heat loss. Besides, during the vapor condensation, the scatter and absorption of the droplets reduce the incident solar intensity on the evaporation interface below. In this work, a freshwater collection strategy combining solar selective absorber and daytime passive radiative cooling techniques is proposed. The solar selective absorber achieves a high solar thermal conversion efficiency (ηevap = 0.894 at 1 sun) to enhance solar evaporation. The passive daytime radiative cooling coating achieves a high solar reflectance R¯solar = 0.927 and thermal emittance ε¯LWIR = 0.929 in the atmospheric transmission window to cool the condensation surface and enhance vapor condensation. In addition, the contact angle is optimized to be 79° by manipulating the hydrophilicity of the condensation surface to ensure the droplet nucleation and shedding. Indoor experiments show that the water collection rate reaches 0.43 kg m−2 h−1. This work provides a promising water collection strategy through solar heating and radiative cooling.

Metal-organic framework derived magnetic phase change nanocage for fast-charging solar-thermal energy conversion

Efficient capture, conversion and storage of solar energy has been a long-term pursuit facing the green and low-carbon strategic goal. Nevertheless, fast-charging solar-thermal conversion and sustainable stable energy output are the key challenges in current solar-thermal energy storage systems. Herein, we rationally designed a sustainable stable and fast-charging solar-driven energy storage system that can simultaneously supply electricity and heat by integrating phase change materials (PCMs) and metal-organic framework (MOF) derived magnetic Co-decorated hybrid graphitic carbon and N-doped carbon (Co-GC@NC) nanocage. Benefiting from the synergistic effect between magnetic Co nanoparticles and GC@NC carbon hybrid, the resultant magnetic carbon nanocage demonstrates superior full-spectrum absorption and Co-GC@NC-based composite PCMs exhibit a high solar-thermal conversion efficiency of 90.7%. More attractively, the solar-thermal energy conversion and storage efficiency of Co-GC@NC-based composite PCMs is significantly enhanced by 115.8% due to the excellent magnetic manipulation ability of nanocage when a magnetic field was applied. Meanwhile, the designed solar-thermal energy conversion and storage system achieves a maximum output voltage of 290 mV and current of 92.6 mA. This magnetic nanocage-accelerated strategy provides constructive insights into the targeted construction of sustainable and stable fast-charging solar-driven energy storage systems.

Processing wood into a phase change material with high solar-thermal conversion efficiency by introducing stable polyethylene glycol-based energy storage polymer

Wood is widely used in the field of building materials as a green and renewable natural porous material. With the continuous increase of global carbon dioxide emissions and increasingly serious environmental problems, improving the energy storage performance of wood is conducive to reduce carbon dioxide and regulate the temperature of the living environment. In this work, a composite phase change material is prepared by introducing stable polyethylene glycol-based energy storage polymer (PGMA) into the porous structure of delignified wood by high temperature immersion method. The wood structure has a greater influence on the crystallinity of PGMA and the modifier is widely distributed inside the lumen and also the cell wall, with crystallinity of 90% PGMA-Wood up to 8.97% and it exhibits good dimensional stability at high temperature. The thermal conductivity of 90% PGMA-Wood is increased to 0.32W/m·K, which reaches 190% higher than that of original wood for the lattice heat transfer replaces phonon heat transfer. The phase change temperature of 90% PGMA-Wood meets the comfortable indoor temperature for human with the melting enthalpy and solidification enthalpy are 25.12 J/g and 31.59 J/g, respectively. The simulated sunlight experiment shows that under the same lighting conditions, the indoor temperature of the house model made by 90% PGMA-Wood is 3 °C higher than that of the house made of original wood, which also has stronger thermal insulation performance at low temperature. All above indicates thatPGMA-Wood have great potential applications in the field of solar-thermal energy conversion and storage as building insulation board and agricultural greenhouses.

Donor-Acceptor Molecule Based High-Performance Photothermal Organic Material for Efficient Water Purification and Electricity Generation.

In this contribution, a unique donor-acceptor conjugated organic-small-molecule photothermal material, namely GDPA-QCN, is presented. Bulky dendritic triphenylamine (GDPA) was grafted onto quinoxaline-6,7-dicarbonitrile (QCN) with a phenyl ring as a bridge to form an "umbrella" architecture. Benefited from the particular molecular structure, in solid state, GDPA-QCN molecules adopted a loose packing mode due to the steric effect of "umbrella head" dendritic triphenylamine and flexible molecular structure feature, which allows efficient intramolecular motions and consequently elevates energy dissipation by taking the pathway of thermal deactivation within broad absorption range. The GDPA-QCN solid has high solar-thermal conversion efficiency with an absorption range from 300 to 1100 nm, which can promote superior water purification and electricity generation performance.

Flexible MCNTs cross-linked polyimide membranes with high light absorbance and hierarchical pore distribution for photo-thermal conversion in solar water evaporation

Solar water evaporation membranes are considered as one of the most sustainable and cost-effective strategies to realize seawater desalination, sewage treatment and distillation. However, low-cost preparation of photo-thermal conversion membranes with both high light absorbance and efficient water transport remains a longstanding challenge. Herein, versatile and simple phase inversion strategy combined with surface corrosion is applied to fabricate flexible MCNTs cross-linked polyimide membranes (MCNTs/PIMs) with hierarchical pore distribution. The surface corrosion is used to dissolve the surface dense layer formed during the phase inversion process and obtain the adjustable surface pore structure with high sunlight absorption performance. Besides, the microchannel structure is prepared to realize multiple reflection of incident light and optimize water transport by controlling the coagulating bath. The results demonstrate that the MCNTs/CPIMs exhibit high light absorption performance of 94% in the long wavelength range of 200–2500 nm. The MCNTs/CPIMs possess rapid water evaporation rate of 1.26 kg m−2 h−1 and high solar thermal conversion efficiency of 72.7%. The flexible and scalable MCNTs/CPIMs exhibit efficient light/thermal management and rapid water transport performance, which enables them promising application in sustainable, low-cost and high efficient solar water evaporation.

One-step synthesis of graphene-based composite phase change materials with high solar-thermal conversion efficiency

Graphene-based composite phase change materials (PCMs) exhibit great potential applications in the field of solar-thermal energy conversion and storage, recently, due to their attracting capability of endowing the PCMs with superior light absorption ability and preventing the liquid phase leakage during the transition process. However, current synthesis methods of graphene-based composite PCMs usually involve complicated multi‐step procedures, greatly hindering its large-scale preparation for the practical application of the solar-thermal energy utilization technique. Herein, we report a facile and straightforward one-step strategy of constructing graphene-based shape-stable composite PCMs with polyethylene glycol (PEG) in situ filled into a graphene oxide (GO) network structure hydrogel. Using this one-step strategy, we achieve a high PEG loading capacity up to 95 wt% in the graphene-based composite PCMs. The composite PCMs also have a relatively constant phase change enthalpy of 162.8 J/g even after 1000 heating–cooling cycles. Most importantly, the composites exhibit a superior solar-thermal conversion ability with the conversion efficiency as high as 93.7%. Compared with the currently reported synthetic routes, the complicated processing steps are greatly reduced in this one-step synthesis strategy. This work proposes a simple and efficient method of synthesizing graphene-based composite PCMs with superior solar-thermal conversion efficiency, which may have great potential applications in the field of solar-thermal energy conversion and storage.

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Self-Healing Hydrophilic Porous Photothermal Membranes for Durable and Highly Efficient Solar-Driven Interfacial Water Evaporation

Fabrication of Ag nanoparticles doped hypercrosslinked polymers monoliths for solar desalination

Interfacial solar steam generation is one of the most promising strategies to harvest sunlight for desalination and production of fresh water. Herein, we demonstrate the synthesis of hypercrosslinked polymers (HCPs) via a one-step Friedel-Crafts reaction. The HCPs have abundant porosity, high thermal stability and large specific surface area (＞1219 m2 g−1). After modification with polyvinyl alcohol (PVA), and coated by polypyrrole (PPy) and silver nanoparticles as sunlight absorbing layer, the resulting samples Ag/PPy-PVA-HCPs exhibit excellent surface wettability, low thermal conductivity (ca. 0.27 W m−1 k−1) and high optical absorption (ca. 91%), which well satisfied the features for configuration of a desired interfacial steam generator. As expected, the Ag/PPy-PVA-HCPs show a high solar thermal conversion efficiency of about 87% under 1 sun. Additionally, the Ag/PPy-PVA-HCPs with hydrophilic porous structure exhibit favorable salt-resistant ability in the brine solution, e.g. the evaporation efficiency of Ag/PPy-PVA-HCP-2 is found to be 83.25% in 20 wt% NaCl solution under 1 sun. The as-prepared Ag/PPy-PVA-HCPs may hold great potentials as excellent solar steam generators for desalination due to their simple manufacturing process, inexpensive raw materials, high solar conversion efficiency, super stability and highly recyclability.

Ultra-broadband metamaterial absorber for high solar thermal energy conversion efficiency

In this paper, a titanium cross-shaped based-metamaterial absorber in the visible and near-infrared regions is presented. The proposed solar thermal absorber consists of a cross-shaped titanium/SiO2 spacer/TiN ground film structure enabling high broadband absorption and solar-thermal conversion efficiency. The broadband near-perfect absorption spectra with the proposed structure reach 97% for both TE and TM-polarization in the wavelength ranges of (from 386 to 1178 nm) and (from 300 to 1140 nm), respectively. Furthermore, the proposed structure exhibits a high solar thermal conversion efficiency of 96% under continuously variable of C from 1 to 1000, maintained over the wide operating temperature range 373–779 K. Remarkably, the performance of the structure has been promising for the enhancement of the solar thermal energy harvesting devices at middle to high temperatures.

Molecular engineering of narrow bandgap porphyrin derivatives for highly efficient photothermal conversion

Organic dyes based on porphyrin derivatives have been widely reported to show promising application in dye-sensitized solar cells and organic solar cells due to their desired power conversion efficiency and extinction coefficient while their photothermal conversion performance is rarely reported, to date. Considering the design guideline of photothermal materials with wide near-infrared region absorption and large extinction coefficient, we designed and prepared a narrow bandgap donor-acceptor small molecule P(DPP)4 based on porphyrin and diketopyrrolopyrrole, which showed a photothermal efficiency of 73.2% under irradiation of 808 nm laser, due to its aggregation-induced radical and distinct nonradiative decay. Furthermore, in an interfacial-heating water evaporation system, P(DPP)4 exhibited an evaporation rate of 1.304 kg m−2 h−1 under 1 sun irradiation with a solar-energy-to-vapor efficiency of 90.6%, higher than most of the pure organic photothermal materials. This work provides a promising way for organic small molecules as solar absorbers with high solar-thermal conversion efficiency and reveals the great potential of organic semiconductors with aggregation-induced radical in photothermal materials.