Solar Photothermal Conversion Research Articles

Hydrothermal synthesis of nanostructured CuS for broadband efficient optical absorption and high-performance photo-thermal conversion

Solar photo-thermal conversion is the simplest way to utilize solar energy by using nanofluid as the working medium. In this paper, we aim to investigate the broadband optical absorption and high-performance photo-thermal conversion via CuS nanofluids to realize the efficient solar energy utilization. Nanostructured CuS nanospheres and nanotubes were successfully synthesized by using simple hydrothermal reaction. The crystal structures, element compositions and surface properties of the obtained CuS nanostructures were characterized. And the formation mechanisms of the nanostructured CuS were discussed. The optical absorption and photo-thermal conversion performances of the CuS nanofluids based on water were studied. The UV/Vis/NIR absorption spectra tests show that the CuS nanofluids prepared have strong optical absorption in both visible light and near infrared light regions. The photo-thermal conversion results indicate that the CuS nanofluids possess good photo-thermal conversion performances, and the maximum temperature of the nanofluid reaches about 72.15 ℃ only with the volume fraction of 0.02% related to the nanotube nanofluid. Moreover, at the same volume fractions, the nanotube nanofluids show better photo-thermal conversion performances than those of the nanosphere nanofluids. This implies a simple approach to enhance photo-thermal conversion for efficient solar energy utilization.

Bionic structure mimicking frog eggs as working fluid for solar thermal collection

The structure of frog eggs in the nature has inspiration for the designing of working fluids for solar thermal collection. This work explore the application of bionic structure mimicking frog eggs (BSMFE) as working fluid for solar photo-thermal conversion. According to the comparative experiments with Cu, CuO and carbon black nanofluids, it is found that the sustainability of suspension and photo-thermal conversion performance of BSMFE are better than those of other nanofluids, and BSMFE can achieve a higher heating rate in a short time. The performance of BSMFE-2 prepared from collagen protein and carbon black nanoparticles is better than that of BSMFE-1 prepared from bone glue and carbon black nanoparticles. This work provides an efficient but economical approach for industrial solar thermal collection.

Plasmonic Graphene Polyurethane Nanocomposites for Efficient Solar Water Desalination

Solar energy is the cleanest and most abundant renewable natural resource available. Materials for solar photothermal energy conversion are highly sought after for their cost savings, clean environment, and broad utility in providing water heating and/or steam for many applications including domestic water heating and solar-driven desalination. Water desalination via solar steam generation is considered one of the most important technologies to address the increasing pressing global water scarcity. The current solar thermal systems rely on the use of copper or aluminum for absorbers which have limited utility because of their inflexibility for tailored applications, high cost, and limited availability. These bulk metals are not very efficient in absorbing the solar spectrum. Therefore, the current solar thermal desalination devices have low efficiency and low water productivity due to the ineffectiveness of solar collectors to convert most of the sun energy into heat. Herein, we report the development of ...

Hydrothermal synthesis of highly stable copper sulfide nanorods for efficient photo-thermal conversion

Copper sulfide (CuS) nanostructures have an important application prospect in the field of solar photo-thermal conversion because of their excellent photo-thermal stability. In this paper, nanostructured CuS nanorods were successfully prepared via hydrothermal reaction method. The crystal structure and surface morphology of the as-prepared CuS nanorods were characterized. The optical absorption and photo-thermal conversion performance of the CuS emulsions based on water were studied. The ultraviolet/visible/near infrared (UV/Vis/NIR) absorption spectra tests show that the prepared CuS emulsions have strong optical absorption in both visible light and near infrared light bands. And the photo-thermal conversion results indicate that the CuS emulsions possess good photo-thermal conversion performance, and the maximum temperature of the emulsion reaches about 74.44 °C with the mass fraction of 0.10%. Moreover, in a certain concentration range, the photo-thermal conversion performance will be effectively enhanced with increasing the mass fractions of the emulsions.

Chinese ink: High performance nanofluids for solar energy

Nanofluids have shown competitive performance on solar thermal collection. This work proposes the application of Chinese ink as nanofluid in solar photo-thermal conversion. The dispersion stability of the nanofluid was characterized by spectrophotometer. Compared with reported Cu, CuO nanofluids, that of Chinese ink has shown more satisfied stability of dispersion. The obtained results reveal that the nanofluid of Chinese ink has surprisingly higher efficiency of photo-thermal conversion than that of Cu and CuO nanoparticles. Carbon black is determined for Chinese ink nanofluid to convert solar photo to heat. Bone glue coated on the surface of Chinese ink nanoparticle also plays a significant role that it prevents the carbon black nanoparticles from aggregation and deposition. The preparation process of Chinese ink is pretty simple and the raw materials are cheap and widely available, which promises the large-scale industrial applications of Chinese ink for solar thermal collections.

Preparation of Au–Ag bimetallic nanoparticles for enhanced solar photothermal conversion

In this study, the solar photothermal conversion performance of bimetallic Au–Ag nanoparticles (NPs) was investigated experimentally. NPs were prepared using a sodium citrate thermal reduction method, using the same procedure and materials to maintain the same particle surface properties. NPs with a tunable plasmon resonance wavelength and demonstrating a high intensity in the visible region were obtained by adjusting the molar ratio of Ag to Au precursors. Experimental results show that blended Au–Ag NPs exhibit a solar photothermal conversion efficiency of 31.41%, which lies between the values of pure Au and Ag NPs under the same NP volume fraction due to the independently scatter light of the Au and Ag NPs in this composite system. Bimetallic Au–Ag NPs demonstrated the highest solar photothermal conversion efficiency of 41.37%, a 31.7% increase over that of blended Au–Ag NPs. The efficiency of the bimetallic Au–Ag NP system was also higher than that of the pure Au NPs (37.81%) with a 40% decrease in Au consumption.

Design and fabrication of bifunctional microcapsules for solar thermal energy storage and solar photocatalysis by encapsulating paraffin phase change material into cuprous oxide

This article reported the design and fabrication of bifunctional microcapsules for solar photocatalysis and solar thermal energy storage by using cuprous oxide (Cu2O) as an inorganic shell to encapsulate a paraffin-type phase change material (PCM), n-eicosane. Such a new type of microcapsules was synthesized successfully by using an emulsion templating self-assembly method along with in-situ precipitation. The chemical structures of the resultant microcapsules were determined by Fourier-transform infrared spectroscopy, and the elemental distributions of microcapsule shell were confirmed by X–ray photoelectron spectroscopy and energy-dispersive X–ray spectroscopy. The scanning and transmission electronic microscopic observations demonstrated that the microstructures and morphologies of microcapsules were influenced significantly by the surfactant and alkali concentrations as well as the portion of cupper source for the synthesis. After the synthetic condition was optimized, the obtained microcapsules exhibited an interesting octahedral morphology and a typical core-shell structure. The thermal analysis results suggested that the microcapsules synthesized at the optimum condition not only obtained high encapsulation and energy-storage efficiencies but also presented a high thermal stability and phase-change reliability. Most of all, the microcapsules obtained a solar thermal energy-storage capability through solar photothermal conversion and also exhibited a high solar photocatalytic activity to organic dyes under the sunlight illumination. In addition, the microcapsules showed a gas-sensitive feature to some harmful organic gases in the presence of Cu2O shell. The microcapsules developed by this work indeed reveal a bifunctional feature derived from both the core and the shell materials and thus show a great potential for industrial and domestic applications due to their extended functions.

Investigation into Au nanofluids for solar photothermal conversion

We herein investigate the solar photothermal conversion performances of Au nanofluids both experimentally and theoretically. In the experiments, the Au nanofluids are loaded into a beaker and are exposed to solar radiation. The solar photothermal conversion efficiency performances of the Au nanofluids using different nanoparticle (NP) volume fractions and solar intensities are discussed. Experimental results show that the equilibrium temperature increases as the NP volume fraction and solar intensity increase, although the extent of variation in the photothermal conversion efficiency declines under these conditions. Furthermore, a theoretical analysis based on the Rayleigh scattering approximation and the Beer-Lambert Law to predict the solar absorption efficiency is discussed. A good agreement between the calculated absorption efficiency and the experimental solar photothermal conversion efficiency is reported. The absorption efficiency increases exponentially with increasing collector height and NP volume fraction. Moreover, the optimization of NP selection and collector design for direct absorption solar collectors without consideration of the temperature field is of particular scientific importance.

Synthesis and solar photo-thermal conversion of Au, Ag, and Au-Ag blended plasmonic nanoparticles

An experimental investigation was performed on the solar photo-thermal conversion performance of Au, Ag and Au-Ag blended Nanoparticles (NPs). The experimental results showed that both the temperature and photo-thermal conversion efficiency increased as the Au NP volume fraction increased. However, nanofluids with lower NP volume fractions showed a higher Specific Absorption Rate (SAR) since the photon-absorption of each NP was limited. Plasmonic Au and Ag nanofluids showed a better photo-thermal conversion performance than semiconductor ZnO and TiO2 nanofluids. The photo-thermal conversion efficiency of Au-Ag blended NPs (1.75–0.15ppm) was 30.97%. This is almost equal to the arithmetic sum (30.91%) of the photo-thermal conversion efficiencies of Au NPs (1.75ppm) and Ag NPs (0.15ppm) separately because of the separate absorption of different wavebands by the Au and Ag NPs. Our work provides a promising method for preparing working fluids for solar photo-thermal conversion by mixing different NPs to match the solar spectral intensity instead of increasing the volume fraction of the same NP.

Bioinspired Au–CuS coupled photothermal materials: enhanced infrared absorption and photothermal conversion from butterfly wings

A macro centimeter-scale Au–CuS combination nanoparticle system integrated with a sub-micrometer antireflection quasi-photonic structure (SAPS) was synthesized for the first time by utilizing T. helena forewings (T_FW) as a biomimetic template (Au–CuS_T_FW). As-fabricated Au–CuS_T_FW exhibits enhanced broadband infrared absorption and lowered reflectance performance. Such an improvement is attributed to the plasmon-to-exciton/plasmon coupling effect among the Au and CuS nanoparticles as well as the coherent coupling between adjacent resonant systems integrated with the SAPS of the T_FW. Moreover, the Au–CuS_T_FW not only possesses a predominant infrared photothermal conversion performance (30.56%), but also is effective for solar photothermal conversion, for low-temperature applications (T<60°C). Furthermore, the plasmon coupling effect integrates with the SAPS to enhance broadband infrared absorption, and the coherent coupling between adjacent resonant systems enhances the hot power yield, both of which were demonstrated by numerical simulation. Our results offer a new research direction for absorbing and utilizing infrared light and open a novel pathway for improving the absorber of the solar thermal collectors for sunlight photothermal and photoelectric conversion, especially over the infrared range.

Chromium-based thin sputtered composite coatings for solar thermal collectors

One of the fundamental components of a solar thermal collector is the absorber surface that should be spectrally selective for solar radiation. Efficient solar photothermal conversion benefits from spectrally selective absorber surfaces. Most solar selective coatings use metal-dielectric composites, known as cermets, as the absorber of solar energy. In this study we will present a numerical model that allow us to correlate the selectivity of the produced absorbers to the collector efficiency. The cathodic magnetron sputtering being a promising method to produce thin solar selective films, a study of some cermet Cr–Cr 2O 3–CrO 3 coatings obtained by this technique in reactive atmosphere and using a DC power unit will be presented. The multilayered composites produced were based in metallic chromium in a matrix of a chromium oxide with a gradient in oxygen composition. The selective graded films were produced by a reactive DC magnetron sputtering of pure chromium target in a plasma of argon–oxygen at different sputtering pressures and substrate temperatures. The microstructure, surface roughness, crystallographic phases, composition and chemical analysis by X-ray photoelectron spectroscopy and reflectivity spectra in vis-NIR were analysed.

Spectrally selective composite coatings of Cr–Cr 2O 3 and Mo–Al 2O 3 for solar energy applications

Efficient solar photothermal conversion benefits from spectrally selective absorber surfaces. In this paper, a numerical model that allows correlation of the selectivity of the absorbers produced to the collector efficiency is presented. Since magnetron sputtering is a promising method to produce thin, solar selective films, a study of cermet Cr–Cr 2O 3 and Mo–Al 2O 3 coatings obtained by this technique in a reactive atmosphere is presented. The multilayered cermets produced have a thickness of approximately 300 nm and were based on metallic chromium (molybdenum) in a matrix of a chromium oxide (aluminium oxide) with a gradient in oxygen composition. The selective cermet graded films were produced by a reactive DC magnetron sputtering of pure chromium (aluminium with molybdenum) target in a plasma of argon–oxygen at different sputtering pressures (ranging from 5×10 −3 to 1.2×10 −2 mbar) and substrate temperatures (150 and 250°C). The microstructure, surface roughness, crystallographic phases, composition and chemical analysis were determined by X-ray photoelectron spectroscopy, reflectivity spectra in the vis/NIR region were analysed, and thermal emissivity was measured with an emissometer. The coatings have high spectral selectivity, with solar absorption ranging from 0.88 to 0.94 and thermal emissivity ranging from 0.15 to 0.04, depending on the coating materials and sputtering conditions.

5472986 Methanol production process using a high nitrogen content synthesis gas with a hydrogen recycle

This chapter deals with the description and the current state of the existing technological options for powering reverse osmosis (RO) desalination with solar energy (thermal and photovoltaic). With respect to solar thermal-powered RO, before giving information about particular options, general concepts about solar photothermal conversion and power cycles are provided in order to aid understanding of the importance of solar radiation concentration in proposed system designs. Description of different designs and experimental solar thermal-powered RO systems are reported, and these systems are grouped in three categories: low-scale, medium-scale and large-scale. In the case of medium-scale systems, a preliminary design of a system with a 2500 m3/day output capacity RO plant is presented. For photovoltaic-driven RO, a general overview and several experiences, including a list of the worldwide installed system, of this solar desalination mature technology are discussed. Finally, a case study about a system working with constant production capacity (using batteries) vs. variable (battery-less) is presented.

Selective materials for solar energy photothermal conversion

The interest in selective surfaces for the photothermal conversion of solar energy is demonstrated. The various physical phenomena which lead to the spectral selectivity are briefly investigated. The different criteria which may be considered at the time of choosing a selective surface are described. Finally some of the results obtained with materials like black chrome and amorphous carbon are described and discussed.

A study of two binary eutectic aluminium alloys as selective absorbers for solar photothermal conversion

The fine microstructure found in two eutectic aluminium alloys, Al-6%Ni and Al-33% Cu is used to study their probable application as textured selective surfaces. A solar calorimeter has been used to determine bulk absorptivity and emissivity of sample surfaces. For the studied samples the figure of merit α/ϵ is 2.08 for the AlCu alloy and 1.38 for the AlNi alloy. It is found that solidification rate and etching time are the two important parameters controlling the optical properties, i.e. the α/ϵ ratio of the surface.

High absorptivity AlPbS selective surfaces for solar photothermal conversion

Low cost two layer AlPbS selective coatings for solar photothermal conversion have been produced by a chemical deposition process. The AlPbS coatings are stable at room temperature and have good adhesive properties. When cycled between room temperature and 120°C, the coatings suffer no change in their spectral absorptance. The coatings have high absorptivity in solar spectral region (0.93) and low emittance in the infrared region (0.21). The selective coatings gave a stagnation temperature of 120°C. The ultraviolet irradiation in air caused oxidation of the sulfide to sulfate. No such effect was seen on uv treatment in vacuum. The chemically sprayed two layer AlPbS provides a low cost selective coating for solar photothermal conversion. An apparatus for measuring normal emittance of solar selective coatings and low emittance metallic substrates over the temperature range 25 to 250°C to an accuracy of ±0.01 has been described.

A new approach to low cost large area selective surfaces for photothermal conversion

In the present study, selective black paint coatings have been prepared by coating reflective metal particles with a layer of selective black material. the coated particles were mixed in a binder and applied easily as a thin layer onto aluminium or galvanized iron (G.I.) sheet. Three selective black materials, namely CuO, CuS and PbS + CuS have been deposited on zinc metal powder, the solar absorptance of the coatings is ±0.95 and the emittance is ±0.4. the thickness of the coatings was about 20 to 30 μm. the emissivity decreases as the thickness increases, while the solar absorptivity does not change appreciably. the improvement in the collector efficiency, which is the ratio of the temperature increase above the temperature of the standard panel to the temperature increase of the standard panel above the ambient temperature, is estimated to be around 11 per cent. the process is potentially a low cost one for large scale application in solar photothermal conversion.

Selective surfaces for high temperature solar photothermal conversion

High performance, low cost, selective surfaces which are chemically and thermally stable are a key limiting problem in the development of the thermal applications of solar energy. This review deals with selective coatings that withstand high temperatures. After indicating the comparative advantages of selective over black-body absorbers, the different ways of generating selectivity are briefly investigated. The physicochemical requirements that must be met, in addition to the specific optical properties that are needed, are established, and criteria for the choice of materials are given. Finally several examples of selective surfaces are described and some trends for further research in the field are discussed.

High temperature; stable, spectrally selective solar absorbers for thermochemical hydrogen production

The thermochemical reduction of water by reactions similar to the Mark I process requires a processing temperature of 730°C. The efficient utilization of solar photothermal energy conversion, in distributed collector systems, to attain this temperature will require the use of suitable spectrally selective surfaces which are stable at the operating temperature. A coating system with demonstrated high temperature capability has been developed at the Optical Sciences Center under NSF/RANN sponsorship. A silicon thin film absorber is deposited by chemical vapor deposition (CVD) on a silver thin film reflector. This optical stack is fabricated at temperatures in excess of 800°C, and the CVD technology is amenable to large scale production in a flow-through system. At 500°C the present Si-Ag system has typical solar absorptance and total normal emittance values of 0.75 and 0.06, respectively. Samples were fabricated which maintained their high spectral selectivity after 2000 thermal cycles between 150°C and 450°C, and after 100 h at 600°C. Further process studies now underway indicate that the solar absorptance can be improved to better than 0.85 by employing a Si-Ge multilayer absorber and that the operating range of the stacks can potentially be raised to the 800–900°C range by employing a refractory metal thin film reflector.