Emerging Next Generation Solar Cells Route to High Efficiency and Low Cost

Generation of clean energy is one of the main challenges of the 21st century. Solar energy is the most abundantly available renewable energy source which would be supplying more than 50 of the global electricity demand in 2100. Solar cells are used to convert light energy into electrical energy directly with an appeal that it does not generate any harmful bi products, like greenhouse gasses. The manufacturing of solar cells is actually based on the types of semiconducting or non semiconducting materials used and commercial maturity. From the very beginning of the terrestrial use of Solar Cells, efficiency and costs are the main focusing areas of research. The definition of so called emerging technologies sometimes described as including any technology capable of overcoming the Shockley-Queisser limit of power conversion efficiency 33.7 percent for a single junction device. In this paper, few promising materials for solar cells are discussed including their structural morphology, electrical and optical properties. The excellent state of the art technology, advantages and potential research issues yet to be explored are also pointed out. Md. Samiul Islam Sadek | Dr. M Junaebur Rashid | Dr. Zahid Hasan Mahmood "Emerging Next Generation Solar Cells: Route to High Efficiency and Low Cost" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-1 | Issue-4 , June 201

Numerical and Experimental Analysis of a CPV/T Receiver Suitable for Low Solar Concentration Factors

AbstractSolar energy conversion is one promising technology to provide the building required energy. Generally, the main used technologies are the PV and thermal flat panels, but this situation provides separately electricity and thermal energy. Electrical and Thermal power combined production is available for the concentrating solar but, usually, this technology is applied to devices working at high concentration factor (over 100), which are large and, therefore, are not suitable for roof installations. At lower concentrating factors (less of 50 suns) small linear, mono-axial, roof integrated devices can be designed and built. The solar receiver plays a key role in the performance of energy generation because it houses the solar cells and itis used to recover the thermal solar power: actually, this is the device where solar energy is converted in electrical and thermal power. The radiation flux distribution on the receiver affects the efficiency of the linear solar concentrator system, because in a mono-axial sunrays are not perpendicular to the receiver. This paper describes the numerical and experimental investigation useful to evaluate the performance of a linear low (20 suns) CPV device and to understand the thermal working condition of the solar receiver. The experimental study focuses to a quantitative analysis of the energy transfer from sun to the water. The numerical activity is a CFD conjugate analysis where the solid volume and the fluids are investigated together; the scope is to individuate how the energy flux cross the device

A methodology for the construction of efficient PLC based low-power photovoltaic generation plants

The research of the operation of low-power photovoltaic generation plants used for self-contained electric power supply in Siberian climatic conditions is performed in this paper. It provides an analysis of the operation of individual units of an automated control system, and gives recommendations for the selection of hardware components. The article describes the operational principles, developed based on functional modules of the programmable logic controller, ensuring maximum possible use of solar energy in this continuous power supply system. The results of plant operation have been obtained, in the form of a power counter log, as well as data on the volume of solar energy produced in both overcast and in sunny weather, throughout the observation period. The article provides visual illustration of generated energy, which could be used to assess the efficiency and economic viability of the low-power photovoltaic plant. Authors would like to point out that examples of the proposed methodology for the construction of self-contained power supply systems can be found in existing industrial facilities, on which further scientific research can be based

Off-design performance of concentrated solar heat and coal double-source boiler power generation with thermocline energy storage

Integration of solar thermal energy into a coal-fired power station is a promising technology for many coal-dependent countries. This work investigated the off-design performance of such a dual heat source boiler power generation from a system-level modelling approach. As an example study, heat from a solar power tower (SPT) was integrated into a 660 MW supercritical coal-fired power unit, and two integration schemes were considered. A system level analytical model was established that coupled the transient process of heliostat field with one-tank thermocline thermal energy storage. The off-design performance of such a hybrid system in one typical year was analyzed accordingly. The results revealed the importance of the seasonal variation of direct normal insolation (DNI), thermal energy storage scheme and integration methodology. Both the quality of sunshine and the amount of sun flux could influence the solar power efficiency; while an increase in the storage volume could decrease the discharging efficiency. Under the maximum capacity of DNI, increasing the storage capacity by 1 h could improve the efficiency by 0.5–0.8%. For either integration scheme, the coal consumption could be economized at least 9 × 103 ton per year. The maximum of solar efficiency for Scheme I, where solar energy was used to heat the superheat steam, could reach 20.42%, which also came with a penalty of reduced efficiency of thermal receiver. Under the minimum storage capacity, the solar efficiency for Scheme I was changed from 16.7% to 19.6%, while for Scheme II the change was from 14.7% to 17.3%

Mathematical modelling of a system for solar PV efficiency improvement using compressed air for panel cleaning and cooling

The efficiency of solar photovoltaic (PV) panels is greatly reduced by panel soiling and high temperatures. A mechanism for eliminating both of these sources of inefficiencies is presented by integrating solar PV generation with a compressed air system. High-pressure air can be stored and used to blow over the surface of PV panels, removing present dust and cooling the panels, increasing output power. A full-system mathematical model of the proposed system is presented, comprised of compressed air generation and storage, panel temperature, panel cleaning, and PV power generation. Simulation results indicate the benefit of employing compressed air for cleaning and cooling solar PV panels. For a fixed volume of compressed air, it is advantageous to blow air over the panels early in the day if the panel is soiled or when solar radiation is most abundant with the highest achievable flow rate if the panel is clean. These strategies have been shown to achieve the greatest energy captures for a single PV panel. When comparing the energy for air compression to the energy gain from cleaning a single PV over a two-week period, an energy ROI of 23.8 is determined. The system has the potential to eliminate the requirement for additional manual cleaning of solar PV panels

Radiant Energy Spectrum Converters for Solar Energy Harvesting

Solar energy is a particularly attractive form of renewable energy because it is widely available and the amount of solar energy received on Earth each year is ~3.5 x 10^6 EJ, which is more than 7000 times greater than the annual global energy consumption. However, solar energy remains largely untapped because it is a broadband, intermittent and sparse resource, making it difficult to harness. Herein, the implementation of newly designed optical cavities, referred to as Radiant Energy Spectrum Convertors (RESC), in the form of ellipsoids, spheroids and/or paraboloids is presented for broadband solar energy harvesting and conversion applications. In this thesis RESC structures are designed and their application in four broadband solar energy harvesting applications is numerically analyzed: 1) photobioreactors, 2) agri-voltaics, 3) hybrid solar lighting, and 4) Solar Thermophotovoltaics (STPV). 1) The RESC structure in the photobioreactor is a luminescent solar spectrum splitter that partitions the solar irradiance into photosynthetically active radiation (PAR) and photosynthetically inactive radiation (non-PAR) to simultaneously power algae cultivation systems and PV cells, respectively. Results show that a RESC structure enables 0.25 MJ of electric power generation in a photobioreactor with a projected area of and volume of 0.2 m^2 and 0.2 m^3, respectively. 2) The RESC structure implemented in agri-voltaics is an elliptic array luminescent solar concentrator for combined power generation and microalgae growth with the similar concept of partitioning solar irradiance into its PAR and non-PAR components. Considering the combined effects of emission, transmission and surface scattering losses, numerical results show the optical efficiency of the elliptic array luminescent solar concentrator (LSC) is 63%, whereas in comparison the optical efficiency for a conventional planar LSC of the same size is 47.2%. 3) The RESC structures used in hybrid solar lighting applications are based on luminescent solar spectrum splitters that partition the incoming solar irradiance into its visible and non-visible components to simultaneously power fibre optic lighting system and PV cells, respectively. Numerical analysis shows that the non-visible portion of the solar irradiance can be converted to electricity with an efficiency of 13.4% using a double-junction PV cell within a RESC structure. 4) RESC structures implemented into STPV systems are based on highly specular IR reflective optical cavities in the form of oblate and prolate spheroid structures to enhance the power density and photoconversion efficiency of the STPV systems. The optical cavity partially encloses a solar receiver that is located at the focal point of an ellipsoid/paraboloid. Concentrated solar radiation is absorbed by the receiver, which functions as both an absorber and an emitter. Radiation is emitted from the emitter, and the internal surface of the cavity is able to reflect a large portion of this emitted radiation either back to the emitter or to a PV cell. Emitted radiation that is returned to the emitter is referred to as "photon recycling". A high degree of photon recycling can be used to achieve high emitter temperatures, which enhances the performance of STPV systems. The results presented in this thesis show that optical structures in the form of spheroids and paraboloids can be used to partition, control and harness broadband solar energy to simultaneously provide for multiple applications, which ultimately increases overall solar energy conversion efficiencies

Development and Characterization of Novel III-V Materials for High Efficiency Photovoltaics

Photovoltaics (PV) are an enabling technology in the field of aerospace, allowing satellites to operate far beyond the technological limitations of chemical batteries by providing a constant power source. However, launch costs and payload volume constraints result in a demand for the highest possible mass and volume specific power generation capability, a proxy for which is device power conversion efficiency. Enhancing the efficiency of III-V PV devices beyond the single-junction Shockley Queisser (SQ) limit has been a driving goal in PV development. Two competing loss mechanisms are thermalization, where photon energy in excess of the absorbing material’s bandgap is lost to heat, and transmission or non-absorption, where a photon has too little energy to generate an electron-hole pair in the semiconductor. A further complication regarding the longevity of PV on satellites is damage due to exposure of high energy particle radiation limiting the operational life of the satellite via gradual degradation in efficiency. In this work, two approaches to achieving higher power conversion efficiency are explored. The first, for devices at beginning of life, is towards the development of a prototype intermediate band solar cell (IBSC) where the spectrum is split into three optical transitions via the formation of an intermediate band between the conduction and valence bands of a wide bandgap host material. Towards this goal, an InAs/AlAsSb quantum dot solar cell (QDSC) capable of enabling sequential absorption is demonstrated via a two-step photon absorption measurement and photoreflectance is used to demonstrate the presence of intraband optical transitions. The second approach, focusing on power generation at end of life, utilizes multijunction photovoltaics where successively higher bandgap materials are stacked in series to optically split the solar spectrum to reduce both thermalization and transmission loss. The addition of InAs/GaAs QDs to a GaAs subcell and InGaAs strain balanced quantum well superlattices to inverted metamorphic multijunction (IMM) devices are explored in order to improve device current retention as material is damaged due to knock-on events displacing atoms from the crystalline lattice. A third section of this work focuses on reducing costs by demonstrating a model for performance of III-V devices grown on polycrystalline virtual substrates considering two primary extended defects: the effects of crystal grain boundaries and the effects of antiphase boundaries induced by growing polar III-V materials on nonpolar Ge substrates

A Steady State Thermodynamic Model of Concentrating Solar Power with Thermochemical Energy Storage

abstract: Fluids such as steam, oils, and molten salts are commonly used to store and transfer heat in a concentrating solar power (CSP) system. Metal oxide materials have received increasing attention for their reversible reduction-oxidation (redox) reaction that permits receiving, storing, and releasing energy through sensible and chemical potential. This study investigates the performance of a 111.7 MWe CSP system coupled with a thermochemical energy storage system (TCES) that uses a redox active metal oxide acting as the heat transfer fluid. A one-dimensional thermodynamic model is introduced for the novel CSP system design, with detailed designs of the underlying nine components developed from first principles and empirical data of the heat transfer media. The model is used to (a) size components, (b) examine intraday operational behaviors of the system against varying solar insolation, (c) calculate annual productivity and performance characteristics over a simulated year, and (d) evaluate factors that affect system performance using sensitivity analysis. Time series simulations use hourly direct normal irradiance (DNI) data for Barstow, California, USA. The nominal system design uses a solar multiple of 1.8 with a storage capacity of six hours for off-sun power generation. The mass of particles to achieve six hours of storage weighs 5,140 metric tonnes. Capacity factor increases by 3.55% for an increase in storage capacity to eight hours which requires an increase in storage volume by 33% or 737 m3, or plant design can be improved by decreasing solar multiple to 1.6 to increase the ratio of annual capacity factor to solar multiple. The solar reduction receiver is the focal point for the concentrated solar energy for inducing an endothermic reaction in the particles under low partial pressure of oxygen, and the reoxidation reactor induces the opposite exothermic reaction by mixing the particles with air to power an air Brayton engine. Stream flow data indicate the solar receiver experiences the largest thermal loss of any component, excluding the solar field. Design and sensitivity analysis of thermal insulation layers for the solar receiver show that additional RSLE-57 insulation material achieves the greatest increase in energetic efficiency of the five materials investigated.Dissertation/ThesisMasters Thesis Civil and Environmental Engineering 201

EVALUATION AND ENHANCEMENT OF CLEAN ENERGY SYSTEMS: ANALYTICAL, COMPUTATIONAL AND EXPERIMENTAL STUDY OF SOLAR AND NUCLEAR CYCLES

Clean (and specifically renewable) energy is steadily improving its global share. However, finite availability of fossil fuels and the growing effects of climate change make it an urgent priority to convince the industry and governments to incentivize investment in the renewable energy field and to make it more attractive by decreasing the capital cost. Until recently, uncertainties in funding limited renewable energy development, especially in the US. That limitation has been one of the barriers to progress. Another limitation of many renewable energy systems is the variability in their output, which makes them unsuitable for baseline power production. Therefore, fossil fuels are still the dominant source of energy globally. The estimated US energy consumption in 2015 relied heavily on fossil fuels which generated about 82% of US primary energy. The share of solar energy in 2015 US energy consumption was just 0.43%. This is a disappointingly small share for a zero carbon source of energy. Nuclear energy as another clean energy source has a small share as 8% of the total US energy consumption. Although it is one of the most reliable/stable and low carbon sources of energy, the nuclear power industry is currently facing several challenges. First, nuclear generated electricity is not cost-competitive with other types of generation. Second, there is a diminished availability of cooling water to reject heat from large power plants. Third, the penetration of solar and wind generation systems into the electrical power market is producing significant fluctuations in the demand for nuclear generation. Open Air-Brayton systems are one of the solutions here since the ultimate heat sink for nuclear supplied power is the atmosphere, so a more direct method of dumping this heat would be useful. An open Air-Brayton system can also provide a great deal of flexibility in adjusting power plant electrical output without significantly ramping reactor power output. This dissertation develops a common framework for understating and improving the solar and nuclear clean energy system components which are based on Brayton cycles. For this purpose, experimental and numerical studies of solar and nuclear systems are conducted. The open air Brayton cycle of a solar chimney power plant is studied in this investigation in different cases as a solar power cycle. Additionally, the air Brayton cycle of a nuclear power plant is considered for several different cases, including a combined nuclear-solar cycle. Air flow is driven by buoyancy in the open air Brayton cycle of a solar chimney power plant system (SCCPS). In SCPPS, the energy of buoyant hot air is converted to electrical energy. SCPPS includes a collector at ground level, covered with a transparent roof that collects the solar radiation, which heats the air inside and the ground underneath. This dissertation proposes and studies new modifications and optimizations to increase the thermal efficiency of the SCCPS, as well as combining SCCPS cycles with other clean sustainable cycles. The nuclear-combined air Brayton cycles are studied with the focus on producing low-carbon energy and combining pressurized water reactor and small modular reactor cycles with another thermal cycle, leading to increased combined efficiency. In this manuscript, chapters are organized with respect to the type of their thermal cycle. Part I, includes three chapters focusing on simple/single Brayton cycle. Part II contains two chapters regarding combined Brayton cycles. Each chapter in this investigation is based on at least one published or accepted/ready to publish article, and which have undergone peer review. The citation for each original source manuscript is included as a footnote on the bottom of the first page of each chapter. Therefore, each chapter is in the format of a journal article, including: an introduction, motivation and background, theory, numerical approach, experimental approach, results and dissections, future work and conclusion. The references and acknowledgments associated with each article are provided at the end of each chapter. All achievements of this work are listed in Appendix A. Part I, chapter one describes non-deterministic computational fluid dynamics (CFD) and conjugate heat transfer (CHT) study of a solar chimney power plant. The initial CFD analyses were validated against the data from the only available large-scale prototype (Manzanares solar tower). To evaluate our CFD analysis beside code verification, an analytical model was developed based on Navier-Stokes equations coupled with the equation of state and using the Boussinesq approximation. The second chapter of this research focuses on evaluating the patented idea of having a double-inlet collector in SCPPS. In this chapter, efforts are made to achieve quantitative accuracy assessment of the modeling and simulation of SCPPS for a conventional collector. The experimental exploration is based on particle image velocimetry (PIV) to provide experimental values for our finite volume based CFD/CHT results. The results of verification and validation of the CFD/CHT analysis are reported. The third chapter of this research addresses the second patented idea regarding applying inflatable towers on solar collectors. Mathematical and computational analyses were conducted. Also, an experimental apparatus was designed and fabricated in 2014 at the University of New Mexico for different testing and evaluation approaches. The results of this validation and the prototype are available in Appendix B. As mentioned before, Part II focuses on combined air Brayton cycles. Chapter 4 reports the study and modeling of our third patented idea, applying surplus heat from a nuclear power plant to the SCPPS. In the proposed combined cycle, we replaced the power plant cooling tower with SCPPS. Therefore, SCCPS serves the function of a dry cooling tower, and also produces additional electrical power in this novel combined nuclear-solar cycle. By applying this idea, it is possible to increase the thermal efficiency of a typical 1000 MW nuclear power plant (35.5%) to 41.4%. The last chapter is focused on a combined nuclear air Brayton cycle to increase the output power of a 50 MW small modular liquid metal/molten salt reactor. Since the major cost of nuclear electricity is the capital cost of plant construction, the concept of small modular reactors has won favor as a method of improving cash flow and minimizing the time required to bring new generation on line, reducing interest expenses. Considerable power increases are predicted for nuclear air-Brayton systems by Co-Firing with hydrogen before the power turbine

Technical feasibility of storage on large dish stirling systems

Dish-Stirling systems have been demonstrated to provide high-efficiency solar-only electrical generation, holding the world record at 31.25%. This high efficiency results in a system with a high possibility of meeting the DOE SunShot goal of $0.06/kWh. Current dish-Stirling systems do not incorporate thermal storage. For the next generation of non-intermittent and cost-competitive solar power plants, we propose a thermal energy storage system that combines latent (phase-change) energy transport and latent energy storage in order to match the isothermal input requirements of Stirling engines while also maximizing the exergetic efficiency of the entire system. This report takes an initial look at the technical advantages of dish Stirling with storage as well as the technical challenges, in order to make a preliminary estimate as to the technical feasibility of such a system. We find that a storage system using metallic eutectic phase change storage results in a feasible physical embodiment, with mass, volume, and complexity suitable for 25kWe dish Stirling systems. The results indicate a system with 6 hours of storage and a solar multiple of 1.25 provides the optimum impact to LCOE and profit. Further, for no negative impact on LCOE, the optimal storage system may cost as much as$82/kWhth or $33k/dish, a substantial departure from the SunShot goals for tower systems. The storage system also is shown to have substantial structural benefits to the dish design. In addition, there may be benefits in terms of capacity payments or failure-to-deliver penalties. A dish storage system design must take into account the value placed on storage by the PUC or utility