Full-spectrum Solar Energy Utilization Research Articles

A spectral splitting CPV/T hybrid system based on wave-selecting filter coated compound parabolic concentrator and linear Fresnel reflector concentrator

Efficient full-spectrum solar energy utilization shows great potential to improve solar energy conversion efficiency. In this paper, a spectral splitting concentrated photovoltaic/thermal hybrid system based on a wave-selecting filter-coated compound parabolic concentrator and linear Fresnel reflector mirror field is developed. Optical models to simulate the linear Fresnel reflector have been developed and validated. With the wave-selecting filter coated compound parabolic concentrator, the visible and near infrared spectra transmit onto the photovoltaic cells, while the rest are reflected to the receiver tube. Furthermore, a simplified receiver indoor test prototype is designed to investigate the characteristic of solar photovoltaic module with the spectral filter in the context of the compound parabolic concentrator. The measured I–V curves are compared with the modeled results. Additionally, the thermodynamic performance of the system is analyzed. Parametric studies are performed to investigate the effect of key design parameters including the mirror width, focal length and the radius of the receiver tube on the solar flux density and the exergy efficiency. An exergy efficiency of 35.51% and an optical efficiency of 94.78% are achieved. With a preliminary techno-economic analysis, the levelized cost of the electricity of the system is $0.209/kWh with a payback period of 10 years.

Modeling of the synergistic anti-reflection effect in gradient refractive index films integrated with subwavelength structures for photothermal conversion.

Photothermal materials generally suffer from challenges such as low photothermal conversion efficiency and inefficient full-spectrum utilization of solar energy. This paper proposes gradient refractive index transparent ceramics (GRITCs) integrated with subwavelength nanostructure arrays and simulates the synergistic anti-reflection effect by an admittance recursive model. An innovative subwavelength structure, possessing a superior light-trapping capability, is initially crafted based on this model. Subsequently, various intelligent optimization algorithms including genetic algorithm, particle swarm optimization, and simulated annealing are employed to optimize the structure of gradient refractive index films respectively. Finally, the photothermal conversion efficiencies of devices based on different photothermal materials are calculated. The simulations and finite-difference time-domain calculations demonstrate that the three-layer GRITCs integrated with an optimal SNA exhibit outstanding full-spectrum and omnidirectional anti-reflection performance. The solar transmittance of the devices can exceed 97% for light wavelengths ranging from 300 to 2500 nm over the full angle of incidence. Our results reveal that the synergistic anti-reflection effect in the SNAs and GRITCs can enhance the photothermal conversion efficiency by more than 20%.

Tandem solar cells based on quantum dots

We provide a comprehensive review of the latest research progress and challenges associated with various tandem solar cells based on lead chalcogenide (PbX, X = S, Se) quantum dot (QD) materials (including QD/QD, organic/QD, and perovskite/QD).

Thermodynamic evaluation of a combined cooling, heating, hydrogen, and power multi-generation system for full-spectrum solar energy utilization

Solar photovoltaic/thermal (PV/T) hybrid systems are considered energy-efficient and eco-friendly. However, conventional PV/T systems generate electricity with high power fluctuations and low-grade thermal energy. In this paper, dry reforming of methane (DRM) is introduced to convert low-grade thermal energy through chemical reaction and enhance the dispatchability of the PV/T system. A combined cooling, heating, hydrogen and power (CCHHP) multi-generation system that integrates the PV/T, DRM and CCHP (combined cooling, heating and power) is proposed to use the full-spectrum solar energy. Energy and exergy analysis under design and variable working conditions are conducted to analyze the system performance. The results reveal that the proposed system can achieve a high energy conversion efficiency of 61.34 % and 18.8 % energy storage ratio at direct normal irradiance (DNI) of 800 W·m−2. In addition, the system can save up to 81.78 % primary energy when compared with the reference system. This study can facilitate the better design and performance evaluation of PV/T hybrid systems.

Energy and exergy analyses of a solar PV/T driving hybrid reverse osmosis-thermal distillation system

Solar desalination holds significant promise for providing freshwater to remote and off-grid areas, which includes solar thermal distillation (STD) and solar photovoltaic reverse osmosis (PV-RO). To achieve higher efficiency via full-spectrum utilization of solar energy, this paper proposes a hybrid reverse osmosis-thermal distillation system driven by a solar photovoltaic-thermal collector (PV/T-RO-TD). To evaluate the conversion of solar energy, electrical energy, thermal energy and chemical energy in these three systems, both the first-law and second-law based analyses are adopted. Results show that while PV/T-RO-TD systems only have moderate energy and exergy efficiencies in the desalination process, it achieves better utilization of solar energy. Meanwhile, the energy and exergy efficiencies are 83%, 81%, 13%, and the exergy efficiencies are 20%, 3%, 13% in the solar harvesting process of PV/T-RO-TD, STD, and PV-RO, respectively. In addition, the specific water productivity under one-sun of 26.94–73.92 L/m2 h in the PV/T-RO-TD system surpasses it in STD and PV-RO systems, which are 3.79–9.89 L/m2 h and 22.74–69.63 L/m2 h, respectively. With better performance, the PV/T-RO-TD system can be regarded as an effective choice for boosting the water productivity of solar desalination.

Full spectrum photon management of photonic crystal-based aerogels to achieve the multiscale multiphysics regulations and optimizations of PV-TE/T systems

Multicomponent coupling is an effective way to achieve full-spectrum solar energy utilization. However, conventional multicomponent coupled PV systems are deficient in the rational distribution of full-spectrum sunlight. In this study, a photovoltaic-thermoelectric/thermal (PV-TE/T) system with photonic crystal-based aerogels (PCA) is proposed based on a novel strategy for efficient full-spectrum solar energy utilization. Then, a multiscale multiphysics theoretical model is developed to study the effects of full-spectrum selectivity characteristics of PCA on the performance of the PCA-based PV-TE/T system. Comparative analyses between stand-alone PV system, tandem PV-TE system, normal PV-TE/T system and PCA-based PV-TE/T system are performed. The full-spectrum selectivity characteristics of PCA allows the PCA-based PV-TE/T system to not only increase the maximum achievable photon current density of PV component by 2.39%–3.00%, but also to increase the heat source (light absorption) for TE component by at least 2609.84%. When the concentration increases to 20, the electrical efficiency of the stand-alone PV system is already 0%, and the electrical efficiency of the tandem PV-TE starts to decrease to 27.01%. As for the PCA-based PV-TE/T system, the maximum electrical efficiency of the PCA-based PV-TE/T system is 32.64% at the concentration of 93. Meanwhile, the thermal collector of the PCA-based PV-TE/T system absorbs 6277.5 W/m2 of thermal energy. Therefore, the PCA-based PV-TE/T system not only has a high efficiency of full-spectrum solar energy utilization, but also is applicable to higher concentrations, which offers the system the potential for further cost reductions.

Boosting solar-driven thermal-assisted photocatalytic hydrogen production through device thermal management

To achieve full-spectrum utilization of solar energy, photo-thermal synergistic catalysis for hydrogen production provided an efficient route. However, most of the studies only focused on how to realize the conversion of solar energy to thermal energy, and neglected the dissipation of thermal energy to environment. Here, we designed a device with vacuum insulation layer (DVIL), which can achieve heat transfer optimization to accelerate photocatalytic hydrogen evolution. Compared to conventional device which is in contact with ambient air directly (DCAD), DVIL exhibited faster heating response, and the final equilibrium temperature was raised by ∼20 °C, leading to enhancement of 47.3% and 28.7% on the hydrogen production rate from organic and inorganic reaction system, respectively. Further analysis on the heat transfer process proved that the vacuum layer serves as a thermal resistance that blocks the direct convective heat transfer between the reaction system and ambient air. Such thermal management through simple device designing holds great potential toward practical solar-to-hydrogen conversion and can be extended to other fields of photothermal catalysis.

Analysis of cascade and hybrid processes for hydrogen production by full spectrum solar energy utilization

Hydrogen energy is a clean energy that is expected to replace fossil energy. However, current hydrogen production methods still have some drawbacks, including environmental pollution and low efficiency of photovoltaic (PV) cells at high temperature, etc., thus the current task is to explore a green and efficient hydrogen production approach. Based on spectral splitting technology, this paper proposes a hydrogen production system that combines a two-step thermochemical cycle (TC) with photovoltaic power generation electrolysis water for the first time, achieving full spectrum and efficient utilization of solar energy. The input of this system only includes solar energy and water. The high-temperature steam that is not reacted in the TC is further electrolyzed in solid oxide electrolytic cells (SOEC) directly, achieving zero carbon hydrogen production and cascade utilization of energy. A hydrogen production model for the new system is established, and the thermodynamic performance of the proposed system is evaluated. The performance of the system under different splitting wavelengths and temperatures is given and analyzed. The results show that although there is no heat recovery, the exergy efficiency of the proposed system can reach approximately 32%, and the solar-to-hydrogen (STH) efficiency can reach nearly 40% (TH=1500 °C, TL = 900 °C). Compared to TC and photovoltaic electrolysis under the same conditions, the energy utilization efficiency of the proposed system has been greatly improved, thus providing a new concept for green and efficient hydrogen production.

Full-spectrum utilization of solar energy for simultaneous CO2 reduction and seawater desalination

To address the underutilization of infrared light in photocatalysis, a synergistic CO2 photoreduction and seawater desalination system was developed, which exhibited a good bifunctional performance.

Experimental investigation of full solar spectrum utilization based on nanofluid spectral splitter for greenhouse applications

According to its application, solar spectrum can be divided into plant active spectrum (PAS) (300 ∼ 800 nm) and heat active spectrum (HAS) (800 ∼ 1500 nm). PAS is absorbed by plants for photosynthesis, and HAS will cause indoor high temperature when entering the greenhouse, which is unfavorable to plants. Nanofluid-based spectral splitter (NSS) is an effective way to improve the full-spectrum utilization of solar energy because of its superior performance of high transmittance in PAS and strong absorption in HAS. In this study, ATO-WO3/H2O nanofluids (NFs) are synthesized, in which the nanoparticles (NPs) are composed of 2.4 vol% ATO and 97.6 vol% WO3 (ATO-WO3). Physical property analysis shows that the NPs are well-dispersed in the fluid. The average transmittance of 0.005 vol% ATO-WO3 NFs with 10 mm optical path-length is 79.56% in PAS and 24.22% in HAS. The photothermal efficiency of NSS is related to the thickness and flow rate of NFs. The outdoor experimental results show that the total solar utilization efficiency of NSS is higher than 73% under the condition of 10 mm thick NFs layer and 100 L/h flow rate. Among them, the photothermal conversion efficiency is 34.4%, and the annual output power is 358.9 kWh/m2. Meanwhile, the light use efficiency is 39.2%, and the defined crop growth factor is 93.6%. In addition, the NSS system has a payback period of 0.76 years and a levelized cost of energy of 0.041 $/kWh within a 10-year life cycle. It shows that NSS greenhouse is feasible in technical and economic aspects. This study broadens the application of NFs in greenhouse and is an effective method to improve the full-spectrum utilization of solar energy.

Division methods and selection principles for the ideal optical window of spectral beam splitting photovoltaic/thermal systems

Spectral beam splitting photovoltaic/thermal (SBS-PV/T) system has been attracting a lot of interest in its ability to achieve extremely efficient full-spectrum utilization of solar energy and co-generate electricity and thermal energy flexibly. The ideal optical window (IOW) is an essential concept in the SBS-PV/T system, splitting solar spectrum, and directly determining the ratio of electricity to thermal energy generated. In this work, 5 division methods (1, PV material bandgap division method; 2, Approximations of PV material spectral response method; 3, Spectral short-circuit current density method; 4, Optimal merit function method; 5, Optimal overall exergy efficiency method) for IOW have been reviewed and classified into three categories. Moreover, based on a 3-dimensional numerical model of the SBS-PV/T system, a systematic analysis and comparison of the aforementioned 3 types of methods were implemented under non-concentrated condition. Results showed that division method 2 is the best choice of IOW when considering system performance indicators, while division methods 4 and 5 are more suitable choices of IOW when considering thermal-economics. And, the divided bands of method 4 for Si solar cells show that energy balance model introduced comparatively big errors, the numerical modeling can predict IOW values of better accuracy. The IOW prediction results of the energy balance model introduced a maximum error of even 150 nm width. Substantially, the selection principles of different IOW division methods are provided, which is helpful for further development of SBS-PV/T systems.

Thermodynamic evaluation of a concentrated photochemical–photovoltaic–thermochemical (CP-PV-T) system in the full-spectrum solar energy utilization

In most concentrated photovoltaic–thermal systems, solar energy that cannot be used by photovoltaic cells is recycled for the thermal process. The unutilized energy is converted into thermal energy for driving other processes. This increases irreversible losses and restricts the efficient utilization of high energetic photons. To address these challenges, a concentrated photochemical–photovoltaic–thermochemical system is proposed to use the full spectrum of solar energy more efficiently. Photons with photonic energy significantly higher than Eg (the bandgap of photovoltaic cells) are used in the photochemical process, and the below-Eg loss of photovoltaic cells is recycled to provide heat for the thermochemical process. The proposed system realizes the cascade utilization of the full-spectrum solar radiation and can use high-energy photons more efficiently. The irreversible loss from the proposed system is decreased, resulting in higher solar utilization efficiency. The numerical results clearly show that the proposed system outperforms concentrated photovoltaic systems, concentrated thermochemical systems, and concentrated photovoltaic–thermochemical systems. The solar utilization efficiency of high-energy photons (before 600 nm) is increased from 44.01% (of common concentrated photovoltaic–thermal systems) to 80.68%. The total solar utilization efficiency in the proposed system attains 66.95% under the design condition.

Efficient hydrogen production from solar energy and fossil fuel via water-electrolysis and methane-steam-reforming hybridization

A new concept of efficient and low-carbon hydrogen production via thermochemical and electrochemical hybrid route based on full-spectrum utilization of solar energy is proposed: sunlight with wavelength suitable for PV conversion is assigned to PV cells for electricity production, which drives water electrolysis for hydrogen production; the rest sunlight is assigned to thermal collectors and utilized for thermochemical hydrogen production. Based on this concept, a photovoltaic-electrolysis-methane-steam-reforming (PV-E-MSR) hybrid system for efficient and low-carbon hydrogen production is designed and analyzed. In the hybrid system, middle-wavelength (x-870 nm) sunlight is concentrated onto PV cells to generate electricity for water electrolysis and low-temperature heat (140 °C) for reactant preheating and vaporizing; the shorter- (280-x nm) and longer-wavelength (870–4000 nm) sunlight are concentrated onto MSR reactor to supply heat for MSR reaction. Thermodynamic analysis results show that solar-to-hydrogen efficiency and ratio of fossil-fuel energy in hydrogen of the hybrid system is higher to 54.6% and lower to 65.5%, respectively. Compared with a reference system composed of parallel-arranged solar MSR system and solar PV-E system, the hybrid system can generate 4.2% more hydrogen and save 3.8% fossil fuel, which benefits from full-spectrum optimized utilization of sunlight and complementarity between solar energy and fossil fuel. The concept and system proposed in this study might suggest a promising way for efficient and low-carbon hydrogen production from solar energy and fossil fuel.

A concentrating solar power system integrated photovoltaic and mid-temperature solar thermochemical processes

The approach of cascading solar energy utilization provides access to reliable and ample supplies of energy and has thus attracted widespread attention. Currently, the hybridization of a concentrating solar photovoltaic process and a solar thermochemical process is a promising approach. This paper describes and investigates a concentrating solar power system to harvest solar energy. Co-producing photovoltaic electricity and solar thermal fuel is its attractive distinction. The visible spectrum is cast onto concentrating photovoltaics to generate electricity, and the ultraviolet and infrared spectra are used to drive methanol decomposition at approximately 250 °C. A spectral splitting parabolic trough concentrator is developed in which incident solar radiation is first split and then concentrated. Based on the measured optical data of concentrators, photovoltaics and reactor, the solar-to-electricity performance is evaluated in the proposed system. The results show that a satisfied solar-to-electricity efficiency of approximately 31.8% would be realized if monocrystalline silicon photovoltaics is adopted. In comparison to individual systems, the efficiency enhancements of about 15.3% and 6.3% are obtained. The solar-to-electricity efficiency can reach approximately 35.1% by adopting gallium arsenide. Meanwhile, the improved optical performance proves that the approach of first splitting and then concentrating sunlight is feasible and promising. Finally, the results are anticipated to lead to a new approach for improving full-spectrum solar energy utilization and guiding the establishment of a prototype in the near future.

Synergistic Tandem Solar Electricity-Water Generators

Summary Energy and clean water are two intertwined fundamental elements for human civilization and sustainable development. Here, we devise a monolithic tandem solar electricity-water generator that synergistically produces electricity and clean water by utilizing the full spectrum of solar irradiance. The tandem generator has two components: a top infrared-transparent photovoltaic device using above-band-gap photons, and a bottom solar water purifier using the below-band-gap photons. More strikingly, a well-designed water-proof thermal interconnecting layer (WTIL) makes these two components work synergistically: the bottom purifier serves as an evaporative cooler of the top solar cell to increase its efficiency, whereas the thermalization energy of the top cell is reutilized by the bottom purifier for producing more clean water. We experimentally demonstrate that a prototype hybrid tandem solar device with WTIL can generate electricity with a power output of 204 W m−2 and purify water at a rate of 0.80 kg m−2 h−1 under 1-sun illumination.

Full-Spectrum Solar Energy Utilization and Enhanced Solar Energy Harvesting via Photon Anti-Reflection and Scattering Performance Using Nanophotonic Structure

Full-Spectrum Solar Energy Utilization and Enhanced Solar Energy Harvesting via Photon Anti-Reflection and Scattering Performance Using Nanophotonic Structure

Performance investigation of a hybrid photovoltaics and mid-temperature methanol thermochemistry system

This work theoretically and experimentally presents a high-efficiency solar system which integrates photovoltaic cells and methanol thermal decomposition to make full use of the full-spectrum solar energy. In this optimized system, spectral beam splitting technology is used to split the solar spectrum into several wavebands. The spectrum suitable for photovoltaic conversion is directly converted to electricity using photovoltaic cells. The rest of the spectrum is converted into chemical energy of syngas (to be stored and converted to electricity on demand) via a mid-temperature solar-thermochemical process of methanol vapor decomposition reaction. A theoretical model is established and predicts that the electrical efficiency of the hybrid system could surpass 35%. The best system electrical efficiency, that we have experimentally demonstrated, was as high as 31.18% for a concentration ratio as low as 56 and a solar thermal temperature as low as 265 °C. The comparison to existing solar systems indicates that this proposed solar system has a great potential for efficient utilization of solar energy in large scale. This work paves the way to high-efficiency and full-spectrum utilization of solar energy.

Compound nanostructure capable of realizing full-spectrum utilization of solar energy for PV-TE hybrid systems.

The photovoltaic-thermoelectric (PV-TE) hybrid system can achieve full-spectrum utilization of the solar spectrum, but surface reflection has always been an important reason to suppress its power conversion efficiency. Therefore, a novel composite nanostructure (CN) is proposed by the finite-difference time-domain (FDTD) simulation method to reduce the surface reflection in the spectral range of 0.3-2.5μm, which consists of a pyramid and grating structure. For the sake of generality, this paper studies the spectral reflectance of the CN under multiple parameters. The results show that the CN integrated pyramid and grating correspond to excellent anti-reflection performance in the short wavelength range and long wavelength range, respectively, compared to a unitary structure, achieving anti-reflection in the full spectral range. In addition, the CN expresses the insensitivity to the structural parameters, and has lower reflectivity compared with a commercial battery. The mechanism for achieving this full-spectrum anti-reflection is mainly to enhance the path of light in the medium to enhance absorption and achieve high transmission under the action of the waveguide. This paper implements ultra-broadband anti-reflection of a compound nanostructure for full-spectrum utilization of solar energy, and provides a solution to improve the power conversion efficiency of PV-TE hybrid systems.

A spectral splitting solar concentrator for cascading solar energy utilization by integrating photovoltaics and solar thermal fuel

Full-spectrum solar energy utilization has drawn widespread attention for cascading solar energy utilization. The hybrid approach integrating photovoltaic generation and solar thermochemical reaction is attractive to convert full-spectrum solar energy into electricity and chemical energy. This paper proposes a concentrating solar photovoltaic/thermochemical hybrid system. Meanwhile, a spectral splitting concentrator is proposed and designed. The proposed concentrator consists of above-mirror and sub-mirror. The above-mirror enables the visible spectrum to be concentrated onto photovoltaics. The sub-mirror allows the infrared and ultraviolet spectra to be concentrated onto a solar thermochemical reactor. The design methodology based on ray tracing is described. The distribution of solar radiation on the photovoltaics and the thermochemical reactor is made analysis. The results show that solar radiation can be uniformly cast to the photovoltaic surface without using secondary optical element; the common solar flux concentration of thermochemical reactor is also mitigated. The proposed spectral splitting concentrator is introduced in the hybrid system. The total conversion efficiency of the solar energy can exceed 20%. Compared with individual photovoltaic electricity and solar thermal fuel, this hybrid system has the potential to increase the conversion efficiency of solar energy into both electricity and fuel, with greater than 5% absolute enhancement. The design of the spectral splitting concentrator provides the possibility of cascading utilization of full-spectrum solar energy.

Full-spectrum solar energy utilization integrating spectral splitting, photovoltaics and methane reforming

A spectral splitting photovoltaic-methane-steam-reforming hybrid system for heat and power cogeneration has been proposed. In the system, sunlight with wavelengths shorter than 870 nm is assigned to photovoltaic cells for direct power and heat cogeneration, while the rest of the solar spectrum is utilized by a methane-steam-reforming reactor via the route of solar thermal energy – chemical energy – heat and power. Analysis reveals that the hybrid system is characterized by high net solar-to-exergy efficiency (40%), high energy storage capability and low-emission energy supply (63% fossil energy saving and 77% carbon-dioxide emission reduction). Primary reasons underlying the excellent performance are full-spectrum optimized utilization of solar energy and comprehensive utilization among solar energy, thermal energy and chemical energy.