Showing papers on "Solar energy published in 2017"

Photoelectrochemical devices for solar water splitting – materials and challenges

Abstract: It is widely accepted within the community that to achieve a sustainable society with an energy mix primarily based on solar energy we need an efficient strategy to convert and store sunlight into chemical fuels. A photoelectrochemical (PEC) device would therefore play a key role in offering the possibility of carbon-neutral solar fuel production through artificial photosynthesis. The past five years have seen a surge in the development of promising semiconductor materials. In addition, low-cost earth-abundant co-catalysts are ubiquitous in their employment in water splitting cells due to the sluggish kinetics of the oxygen evolution reaction (OER). This review commences with a fundamental understanding of semiconductor properties and charge transfer processes in a PEC device. We then describe various configurations of PEC devices, including single light-absorber cells and multi light-absorber devices (PEC, PV-PEC and PV/electrolyser tandem cell). Recent progress on both photoelectrode materials (light absorbers) and electrocatalysts is summarized, and important factors which dominate photoelectrode performance, including light absorption, charge separation and transport, surface chemical reaction rate and the stability of the photoanode, are discussed. Controlling semiconductor properties is the primary concern in developing materials for solar water splitting. Accordingly, strategies to address the challenges for materials development in this area, such as the adoption of smart architectures, innovative device configuration design, co-catalyst loading, and surface protection layer deposition, are outlined throughout the text, to deliver a highly efficient and stable PEC device for water splitting.

Vertically Aligned Graphene Sheets Membrane for Highly Efficient Solar Thermal Generation of Clean Water

Abstract: Efficient utilization of solar energy for clean water is an attractive, renewable, and environment friendly way to solve the long-standing water crisis. For this task, we prepared the long-range vertically aligned graphene sheets membrane (VA-GSM) as the highly efficient solar thermal converter for generation of clean water. The VA-GSM was prepared by the antifreeze-assisted freezing technique we developed, which possessed the run-through channels facilitating the water transport, high light absorption capacity for excellent photothermal transduction, and the extraordinary stability in rigorous conditions. As a result, VA-GSM has achieved average water evaporation rates of 1.62 and 6.25 kg m–2 h–1 under 1 and 4 sun illumination with a superb solar thermal conversion efficiency of up to 86.5% and 94.2%, respectively, better than that of most carbon materials reported previously, which can efficiently produce the clean water from seawater, common wastewater, and even concentrated acid and/or alkali solutions.

Mushrooms as Efficient Solar Steam-Generation Devices

Abstract: Solar steam generation is emerging as a promising technology, for its potential in harvesting solar energy for various applications such as desalination and sterilization. Recent studies have reported a variety of artificial structures that are designed and fabricated to improve energy conversion efficiencies by enhancing solar absorption, heat localization, water supply, and vapor transportation. Mushrooms, as a kind of living organism, are surprisingly found to be efficient solar steam-generation devices for the first time. Natural and carbonized mushrooms can achieve ≈62% and ≈78% conversion efficiencies under 1 sun illumination, respectively. It is found that this capability of high solar steam generation is attributed to the unique natural structure of mushroom, umbrella-shaped black pileus, porous context, and fibrous stipe with a small cross section. These features not only provide efficient light absorption, water supply, and vapor escape, but also suppress three components of heat losses at the same time. These findings not only reveal the hidden talent of mushrooms as low-cost materials for solar steam generation, but also provide inspiration for the future development of high-performance solar thermal conversion devices.

Highly Flexible and Efficient Solar Steam Generation Device

Abstract: Solar steam generation with subsequent steam recondensation has been regarded as one of the most promising techniques to utilize the abundant solar energy and sea water or other unpurified water through water purification, desalination, and distillation. Although tremendous efforts have been dedicated to developing high-efficiency solar steam generation devices, challenges remain in terms of the relatively low efficiency, complicated fabrications, high cost, and inability to scale up. Here, inspired by the water transpiration behavior of trees, the use of carbon nanotube (CNT)-modified flexible wood membrane (F-Wood/CNTs) is demonstrated as a flexible, portable, recyclable, and efficient solar steam generation device for low-cost and scalable solar steam generation applications. Benefitting from the unique structural merits of the F-Wood/CNTs membrane-a black CNT-coated hair-like surface with excellent light absorbability, wood matrix with low thermal conductivity, hierarchical micro- and nanochannels for water pumping and escaping, solar steam generation device based on the F-Wood/CNTs membrane demonstrates a high efficiency of 81% at 10 kW cm-2 , representing one of the highest values ever-reported. The nature-inspired design concept in this study is straightforward and easily scalable, representing one of the most promising solutions for renewable and portable solar energy generation and other related phase-change applications.

Hierarchical Graphene Foam for Efficient Omnidirectional Solar-Thermal Energy Conversion.

Abstract: Efficient solar-thermal energy conversion is essential for the harvesting and transformation of abundant solar energy, leading to the exploration and design of efficient solar-thermal materials. Carbon-based materials, especially graphene, have the advantages of broadband absorption and excellent photothermal properties, and hold promise for solar-thermal energy conversion. However, to date, graphene-based solar-thermal materials with superior omnidirectional light harvesting performances remain elusive. Herein, hierarchical graphene foam (h-G foam) with continuous porosity grown via plasma-enhanced chemical vapor deposition is reported, showing dramatic enhancement of broadband and omnidirectional absorption of sunlight, which thereby can enable a considerable elevation of temperature. Used as a heating material, the external solar-thermal energy conversion efficiency of the h-G foam impressively reaches up to ≈93.4%, and the solar-vapor conversion efficiency exceeds 90% for seawater desalination with high endurance.

Thermal energy storage materials and systems for solar energy applications

Abstract: Usage of renewable and clean solar energy is expanding at a rapid pace Applications of thermal energy storage (TES) facility in solar energy field enable dispatchability in generation of electricity and home space heating requirements It helps mitigate the intermittence issue with an energy source like solar energy TES also helps in smoothing out fluctuations in energy demand during different time periods of the day In this paper, a summary of various solar thermal energy storage materials and thermal energy storage systems that are currently in use is presented The properties of solar thermal energy storage materials are discussed and analyzed The dynamic performances of solar thermal energy storage systems in recent investigations are also presented and summarized

Photocatalytic Water Splitting: Quantitative Approaches toward Photocatalyst by Design

Abstract: A widely used term, “photocatalysis”, generally addresses photocatalytic (energetically downhill) and photosynthetic (energetically uphill) reactions and refers to the use of photonic energy as a driving force for chemical transformations, i.e., electron reorganization to form/break chemical bonds. Although there are many such important reactions, this contribution focuses on the fundamental aspects of photocatalytic water splitting into hydrogen and oxygen by using light from the solar spectrum, which is one of the most investigated photosynthetic reactions. Photocatalytic water splitting using solar energy is considered to be artificial photosynthesis that produces a solar fuel because the reaction mimics nature’s photosynthesis not only in its redox reaction type but also in its thermodynamics (water splitting: 1.23 eV vs glucose formation: 1.24 eV). To achieve efficient photocatalytic water splitting, all of the parameters, though involved at different time scales and spatial resolutions, should be op...

Recent Progress in Energy-Driven Water Splitting

Abstract: Hydrogen is readily obtained from renewable and non-renewable resources via water splitting by using thermal, electrical, photonic and biochemical energy. The major hydrogen production is generated from thermal energy through steam reforming/gasification of fossil fuel. As the commonly used non-renewable resources will be depleted in the long run, there is great demand to utilize renewable energy resources for hydrogen production. Most of the renewable resources may be used to produce electricity for driving water splitting while challenges remain to improve cost-effectiveness. As the most abundant energy resource, the direct conversion of solar energy to hydrogen is considered the most sustainable energy production method without causing pollutions to the environment. In overall, this review briefly summarizes thermolytic, electrolytic, photolytic and biolytic water splitting. It highlights photonic and electrical driven water splitting together with photovoltaic-integrated solar-driven water electrolysis.

3D-Printed, All-in-One Evaporator for High-Efficiency Solar Steam Generation under 1 Sun Illumination.

Abstract: Using solar energy to generate steam is a clean and sustainable approach to addressing the issue of water shortage. The current challenge for solar steam generation is to develop easy-to-manufacture and scalable methods which can convert solar irradiation into exploitable thermal energy with high efficiency. Although various material and structure designs have been reported, high efficiency in solar steam generation usually can be achieved only at concentrated solar illumination. For the first time, 3D printing to construct an all-in-one evaporator with a concave structure for high-efficiency solar steam generation under 1 sun illumination is used. The solar-steam-generation device has a high porosity (97.3%) and efficient broadband solar absorption (>97%). The 3D-printed porous evaporator with intrinsic low thermal conductivity enables heat localization and effectively alleviates thermal dissipation to the bulk water. As a result, the 3D-printed evaporator has a high solar steam efficiency of 85.6% under 1 sun illumination (1 kW m-2 ), which is among the best compared with other reported evaporators. The all-in-one structure design using the advanced 3D printing fabrication technique offers a new approach to solar energy harvesting for high-efficiency steam generation.

Wood–Graphene Oxide Composite for Highly Efficient Solar Steam Generation and Desalination

Abstract: Solar steam generation is a highly promising technology for harvesting solar energy, desalination and water purification. We introduce a novel bilayered structure composed of wood and graphene oxide (GO) for highly efficient solar steam generation. The GO layer deposited on the microporous wood provides broad optical absorption and high photothermal conversion resulting in rapid increase in the temperature at the liquid surface. On the other hand, wood serves as a thermal insulator to confine the photothermal heat to the evaporative surface and to facilitate the efficient transport of water from the bulk to the photothermally active space. Owing to the tailored bilayer structure and the optimal thermo-optical properties of the individual components, the wood–GO composite structure exhibited a solar thermal efficiency of ∼83% under simulated solar excitation at a power density of 12 kW/m2. The novel composite structure demonstrated here is highly scalable and cost-efficient, making it an attractive materia...

Emergence of highly transparent photovoltaics for distributed applications

Abstract: Solar energy offers a viable solution to our growing energy need. While adoption of conventional photovoltaics on rooftops and in solar farms has grown rapidly in the last decade, there is still plenty of opportunity for expansion. See-through solar technologies with partial light transmission developed over the past 30 years have initiated methods of integration not possible with conventional modules. The large-scale deployment necessary to offset global energy consumption could be further accelerated by developing fully invisible solar cells that selectively absorb ultraviolet and near-infrared light, allowing many of the surfaces of our built environment to be turned into solar harvesting arrays without impacting the function or aesthetics. Here, we review recent advances in photovoltaics with varying degrees of visible light transparency. We discuss the figures of merit necessary to characterize transparent photovoltaics, and outline the requirements to enable their widespread adoption in buildings, windows, electronic device displays, and automobiles. Transparency offers integration routes unavailable to opaque photovoltaics. Here, Lunt and co-workers review recent progress in transparent solar technologies, highlight technical challenges and measurement considerations, and review performance requirements for various applications.

Raising the one-sun conversion efficiency of III-V/Si solar cells to 32.8% for two junctions and 35.9% for three junctions

Abstract: To improve the efficiency of photovoltaic devices while keeping the same spatial footprint, solar cells can be stacked on top of each other. Here, Essig et al. fabricate very efficient dual-junction and triple-junction solar cells by placing one or two III–V solar cells on top of a silicon solar cell.

Progress in concentrated solar power technology with parabolic trough collector system: A comprehensive review

Abstract: Advanced solar energy utilization technology requires high-grade energy to achieve the most efficient application with compact size and least capital investment recovery period Concentrated solar power (CSP) technology has the capability to meet thermal energy and electrical demands Benefits of using CSP technology with parabolic trough collector (PTC) system include promising cost-effective investment, mature technology, and ease of combining with fossil fuels or other renewable energy sources This review first covered the theoretical framework of CSP technology with PTC system Next, the detailed derivation process of the maximum theoretical concentration ratio of the PTC was initially given Multiple types of heat transfer fluids in tube receivers were reviewed to present the capability of application Moreover, recent developments on heat transfer enhancement methods for CSP technology with PTC system were highlighted As the rupture of glass covers was frequently observed during application, methods of thermal deformation restrain for tube receivers were reviewed as well Commercial CSP plants worldwide with PTC system were presented, including those that are in operation, under construction, and announced Finally, possible further developments of CSP plants with PTC system were outlined Besides, suggestions for future research and application guidance were also illustrated

Emerging renewable and sustainable energy technologies: State of the art

Abstract: In this paper, five most emerging renewable energy sources are analyzed. These emerging renewables are either special or advanced forms of the mainstream energy sources (solar, wind, geothermal, biofuels, biomass, and hydro) or brand new technologies. The five emerging renewable technologies discussed in this paper include marine energy, concentrated solar photovoltaics (CSP), enhanced geothermal energy (EGE), cellulosic ethanol, and artificial photosynthesis. Marine energy is divided into wave energy, tidal energy, tidal/ocean currents, salinity gradient, and ocean thermal energy conversion. CSP technologies are divided into parabolic troughs, linear Fresnel reflectors, parabolic dishes, and solar towers. The process for developing EGE reservoirs is also explained in detail. Cellulosic ethanol energy extraction is explained for both cellulolysis and gasification. Artificial photosynthesis is explained by considering semiconductor particles, electrolyzers, artificial leaves, and dye-synthesized solar cells. Each emerging renewable source's explanation is followed by its market share, challenges, implications for increased adoption, future prospects, and drawbacks.

Photoelectrochemical water splitting in separate oxygen and hydrogen cells

Abstract: Solar water splitting provides a promising path for sustainable hydrogen production and solar energy storage. One of the greatest challenges towards large-scale utilization of this technology is reducing the hydrogen production cost. The conventional electrolyser architecture, where hydrogen and oxygen are co-produced in the same cell, gives rise to critical challenges in photoelectrochemical water splitting cells that directly convert solar energy and water to hydrogen. Here we overcome these challenges by separating the hydrogen and oxygen cells. The ion exchange in our cells is mediated by auxiliary electrodes, and the cells are connected to each other only by metal wires, enabling centralized hydrogen production. We demonstrate hydrogen generation in separate cells with solar-to-hydrogen conversion efficiency of 7.5%, which can readily surpass 10% using standard commercial components. A basic cost comparison shows that our approach is competitive with conventional photoelectrochemical systems, enabling safe and potentially affordable solar hydrogen production.

A comprehensive review on solar PV maximum power point tracking techniques

Abstract: In recent years solar energy has received worldwide attention in the field of renewable energy systems Among the various research thrusts in solar PV, the most proverbial area is extracting maximum power from solar PV system Application dof Maximum Power Point Tracking (MPPT) for extracting maximum power is very much appreciated and holds the key in developing efficient solar PV system In this paper, a state of the art review on various maximum power point techniques for solar PV systems covering timeworn conventional methods and latest soft computing algorithms is presented To date critical analysis on each of the method in terms of (1) tracking speed, (2) algorithm complexity, (3) Dynamic tracking under partial shading and (4) hardware implementation is not been carried out In this regard the authors have attempted to compile a comprehensive review on various solar PV MPPT techniques based on the above criteria Further, it is envisaged that the information presented in this review paper will be a valuable gathering of information for practicing engineers as well as for new researchers

Review of recent trends in photoelectrocatalytic conversion of solar energy to electricity and hydrogen

Abstract: This work is a review of the recent trends in the photoelectrocatalytic conversion of solar energy into electricity or hydrogen. It focuses on photocatalytic fuel cells and photoelectrocatalytic water splitting systems and presents both the basic principles and the design of devices. It includes a broad review of materials employed for the construction of photoanodes, photocathodes and tandem cells and highlights the related research fields which are expected to be of interest in the near future. The review is intended to become a basic manual for new adepts to the field and at the same time a handy reference to experienced researchers.

Nanophotonics-enabled solar membrane distillation for off-grid water purification

Abstract: With more than a billion people lacking accessible drinking water, there is a critical need to convert nonpotable sources such as seawater to water suitable for human use. However, energy requirements of desalination plants account for half their operating costs, so alternative, lower energy approaches are equally critical. Membrane distillation (MD) has shown potential due to its low operating temperature and pressure requirements, but the requirement of heating the input water makes it energy intensive. Here, we demonstrate nanophotonics-enabled solar membrane distillation (NESMD), where highly localized photothermal heating induced by solar illumination alone drives the distillation process, entirely eliminating the requirement of heating the input water. Unlike MD, NESMD can be scaled to larger systems and shows increased efficiencies with decreased input flow velocities. Along with its increased efficiency at higher ambient temperatures, these properties all point to NESMD as a promising solution for household- or community-scale desalination.

Direct solar-to-hydrogen conversion via inverted metamorphic multi-junction semiconductor architectures

Abstract: Solar water splitting via multi-junction semiconductor photoelectrochemical cells provides direct conversion of solar energy to stored chemical energy as hydrogen bonds. Economical hydrogen production demands high conversion efficiency to reduce balance-of-systems costs. For sufficient photovoltage, water-splitting efficiency is proportional to the device photocurrent, which can be tuned by judicious selection and integration of optimal semiconductor bandgaps. Here, we demonstrate highly efficient, immersed water-splitting electrodes enabled by inverted metamorphic epitaxy and a transparent graded buffer that allows the bandgap of each junction to be independently varied. Voltage losses at the electrolyte interface are reduced by 0.55 V over traditional, uniformly p-doped photocathodes by using a buried p–n junction. Advanced on-sun benchmarking, spectrally corrected and validated with incident photon-to-current efficiency, yields over 16% solar-to-hydrogen efficiency with GaInP/GaInAs tandem absorbers, representing a 60% improvement over the classical, high-efficiency tandem III–V device. Solar water-splitting efficiency can be enhanced by careful bandgap selection in multi-junction semiconductor structures. Young et al. demonstrate a route that allows independent bandgap tuning of each junction in an immersed water-splitting device, enabling a solar-to-hydrogen efficiency of over 16%.

Photovoltaic/Thermal (PV/T) systems: Status and future prospects

Abstract: In the last four decades, greater attention has been paid to PV/T systems due to their advantages compared with PV or solar thermal systems alone. This paper aims to study various aspects of PV/T systems through the existing literature in order to highlight key points as future work in this field as well as illustrate different techniques used for such systems. In addition, PV/T systems are reviewed in terms of thermal and electrical side views. Furthermore, the analysis of solar thermal systems, various system applications such as air, water, air/water, phase change material PCM and Nanofluid systems are summarized. In light of most attempts to improve the PV/T system, more focus has been paid to the thermal rather than the electrical side. Furthermore, comparisons between PV/T systems in terms of performance parameters and efficiencies are presented. A critical review of many findings of previously conducted research is also discussed. It is found that the PV/T air heater system is promising for future preheating air applications. Moreover, it is suggested that the use of nanoparticles and water as base fluid improves the overall system efficiency. Furthermore, the PV side views require more attention in technical and cost terms. However, more research is essential to reduce the cost and, improve the effectiveness and technical design of such systems.

Solar Fuels and Solar Chemicals Industry.

Abstract: Two decades of solar energy research, since the “Holy Grails” Account on Artificial Photosynthesis, has delivered astounding discovery that sets the stage for a paradigm shift from a fuels and chemicals industry powered by fossil fuels to one powered by the sun.

Visible/solar light active photocatalysts for organic effluent treatment: Fundamentals, mechanisms and parametric review

Abstract: Intensive research work is being undertaken globally to effectively use the process of photocatalysis for the degradation of organic pollutants from industrial effluents. For the same, TiO2 has been extensively explored, which however, has a limitation of being able to utilise the UV spectrum only, due to its high band gap property. Since a substantial percentage of the solar spectrum is visible light, it is imperative that for an effective and versatile utilisation of the incident solar energy, visible light active photocatalysts, having a relatively smaller band gap are developed. Smaller band gap, however, often results in rapid recombination and conversion of photonic energy into non-usable heat. This article is a review of the science behind the performance of visible/solar light active photocatalysts. The first part includes the fundamentals of photocatalysis, including thermodynamics, reaction kinetics and recombination. The second part reviews the visible/solar light active photocatalytic materials as well as the significant research efforts made so far in the exploration of possible mechanisms of photoexcitation and remedies for minimization of recombination. Finally, an operational overview is provided which is helpful in assessing the influence of key parameters on the photocatalytic activity. This review presents a single point reference for a comparative study and ready assimilation of the basics and new directions in photocatalysis, thus making it more conducive to further research and active commercialisation.

Low-bandgap conjugated polymers enabling solution-processable tandem solar cells

Abstract: The technology of polymer-based organic photovoltaic (OPV) cells has made great progress in the past decade, with the power conversion efficiency increasing from just a few per cent to around 12%, and the stability increasing from hours to years. One of the important milestones in this progress has been the invention of infrared-absorbing low-bandgap polymers, which allows the OPV cells to form effective tandem structures for harvesting near-infrared energy from the solar spectrum. In this Review, we focus on the progress in low-bandgap conjugated polymers and several tandem OPV cells enabled by these low-bandgap polymers. Specifically, we cover polymer-based tandem solar cells; hybrid tandem solar cells combining polymers with hydrogenated amorphous silicon; and unconventional solar cells. For each of these technologies, we address the challenges and offer our perspectives for future development. Low-bandgap (<1.6 eV) polymers enable polymer solar cells to form effective tandem structures for harvesting near-infrared solar energy as well as reducing thermal loss. This Review summarizes recent progress and provides a perspective on various low-bandgap polymer-containing tandem solar cells; namely, pure polymer–polymer tandem, hybrid polymer–amorphous silicon tandem and unconventional perovskite–polymer tandem solar cells.

Water desalination system using solar heat: A review

Abstract: Most of the desalination systems are energy intensive, which consume high grade energy like gas, electricity, oil and fossil fuels These processes lead to carbon footprints, which causes depletion of ozone layer as well as health hazards on mankind It is also lead to global warming which is the burning topic and becomes threat to life sustainability The potential of harnessing solar energy is most efficient and effective for heat to heat conversion The thermal desalination is a low temperature application processes with one time investment for life time water production up to 10 to 15 years In this paper, various solar thermal desalination methods such as direct and indirect methods have been discussed The indirect methods are preferable for medium and large scale desalination systems, whereas the direct methods employing the solar stills are more suitable for small scale systems The performance of the low cost solar stills can be improved with simple modification by using various locally available materials These low cost stills can be easily and economically fabricated for meeting daily need of the fresh drinking water These low cost solar stills are sufficient for the small households and communities living in islands, coastal areas It can also be uses for distillation of brackish water for the population residing near river banks Such a system also suitable for the fluoride affected area to remove fluoride from the water The low cost solar stills are sufficient for removal of arsenic, mercury, cadmium, coliform, virus and bacteria