An electrodialysis sea water desalination system powered by photovoltaic cells

An electrodialysis sea water desalination system powered by photovoltaic cells

Photovoltaics literature survey (No. 181)

A Hybrid Electric and Thermal Solar Receiver

Synergistic Tandem Solar Electricity-Water Generators

A Photovoltaic (PV) cell is a device that converts sunlight or incident light into direct current (DC) based electricity. Among other forms of renewable energy, PV-based power sources are considered a cleaner form of energy generation. Due to lower prices and increased efficiency, they have become much more popular than any other renewable energy source. In a PV module, PV cells are connected in a series and parallel configuration, depending on the voltage and current rating, respectively. Hence, PV modules tend to have a fixed topology. However, in the case of partial shading, mismatching or failure of a single PV cell can lead to many anomalies in a PV module’s functioning. If proper attention is not given, it can lead to the forward biasing of healthy PV cells in the module, causing them to consume the electricity instead of producing it, hence reducing the PV module’s overall efficiency. Hence, to further the PV module research, it is essential to have an approximate way to model them. Doing so allows for understanding the design’s pros and cons before deploying the PV module-based power system in the field. In the last decade, many mathematical models for PV cell simulation and modeling techniques have been proposed. The most popular among all the techniques are diode based PV modeling. In this book chapter, the author will present a double diode based PV cell modeling. Later, the PV module modeling will be presented using these techniques that incorporate mismatch, partial shading, and open/short fault. The partial shading and mismatch are reduced by incorporating a bypass diode along with a group of four PV cells. The mathematical model for showing the effectiveness of bypass diode with PV cells in reducing partial shading effect will also be presented. Additionally, in recent times besides fixed topology of series–parallel, Total Cross-Tied (TCT), Bridge Link (BL), and Honey-Comb (H-C) have shown a better capability in dealing with partial shading and mismatch. The book chapter will also cover PV module modeling using TCT, BL, and H-C in detail.

Photovoltaics literature survey (no. 149)

Currently, photovoltaic energy conversion has developed tremendously in the global energy industry. The enormous capacity of solar power plants generates electricity all over the world. Hundreds of gigawatts of electrical energy are supplied to the networks of various countries around the globe. In addition, up to hundreds of gigawatts of installed capacity of solar power plants are commissioned every year in all countries of the world. And this has been the trend for the past few decades. The main problem of solar photovoltaic conversion is the instability of the solar radiation flux associated with the climatic conditions in the regions where photovoltaic plants are operated. This problem can be solved by using highly efficient methods to control the generation of solar power plants, in particular, such as the use of information control systems for a particular PV system to increase the final generation of electrical energy supplied to the consumer. The photovoltaic (PV) conversion of solar radiation flux is an important renewable energy source. Due to the varying intensity of the sun, the electricity generated by PV directly from the radiation flux is not constant. The photovoltaic system currently uses maximum power point (PMP) tracking in perturbation and observation (P&O) mode to increase the final output power of the photovoltaic panels. A step-down DC-DC converter allows PMP to change the PV operating voltage and determine the maximum power output of the PV panel. This study proposes a fuzzy logic implementation. The magnitude of the perturbed voltage is determined by the change in power dq and the change in power relative to the change in voltage dq/dv is fuzzy. The performance of fuzzy logic is investigated in this work in order to optimize MPM. Fuzzy logic can simplify maximum power tracking and reduce voltage instability. According to the simulation results, the MPM method based on fuzzy computation performs better than the traditional P&O method. By using the proposed methods, we can significantly improve electric power generation and increase the efficiency of photovoltaic conversion.

Photovoltaic (PV) cell powered base stations (BSs) have been widely considered for reducing the cellular network's environmental footprint in the future. An inherent challenge is to match the energy generation profile with the energy consumption profile. In this paper, we develop a Markov chain based algorithm to determine the optimal orientation angle of the PV cell for matching the two profiles, given the energy generation profile of the geo-location, the load profile of the BS and the battery capacity. We investigate the effects of different battery capacities on the optimized PV cell orientation angle for BSs located in a business district in London in summer. Our results show that the optimal orientation angle for a small battery capacity (10000 Joules at a small BS) is in the range from 35° to 60°, whereas a wider range from −50° to 60° could be chosen for a large battery capacity (50000 Joules at a small BS). This reveals that PV cell orientation angle optimization is more important for PV cell powered BSs with small battery capacities than for large battery capacities.

Photovoltaic (PV) cells can absorb up to 80% of the incident solar radiation of the solar spectrum, however, only certain percentage of the absorbed incident energy is converted into electricity depending on the conversion efficiency of the PV cell technology used, while the remainder energy is dissipated as heat accumulating on the surface of the cells causing elevated temperatures. Temperature rise at the PV cell level is addressed as one of the most critical issues influencing the performance of the cells causing serious degradations and shortens the life-time of the PV cells, hence cooling of the PV module during operation is essential. Hybrid PV designs which are able to simultaneously generate electrical energy and utilize the waste heat have been proven to be the most promising solution. In this study, analytical investigation of a hybrid system comprising of a Heat Pipe-based Photovoltaic-Thermoelectric Generator (HP-PV/TEG) for further enhanced performance is presented. The system presented incorporates a PV panel for direct electricity generation, a heat pipe to absorb excessive heat from the PV cells and assist uniform temperature distribution on the surface of the panel, and a thermoelectric generator (TEG) to perform direct heat-to-electricity conversion. A mathematical model based on the heat transfer process within the system is developed to evaluate the cooling capability and predict the overall thermal and electrical performances of the hybrid system. Results are presented in terms electrical efficiencies of the system. It was observed that the integration of TEG modules with PV cells aid improving the performance of the PV cells through utilizing the waste-heat available, leading to higher output power. The system presented can be applied in regions with hot desert climates where electricity demand is higher than thermal energy.

Worldwide rapid growth of photovoltaics requires not only high-efficiency but also high-reliability and long-lifetime photovoltaic cells and modules. Reliability of photovoltaic modules is determined by module materials such as encapsulant, backsheet, etc. and, of course, also by photovoltaic cells themselves. There are some complicated phenomena concerning degradation of photovoltaic properties. Those physical and chemical degradation phenomena should be microscopically analyzed in detail in order to clarify degradation mechanism and also realize highly reliable photovoltaic cells and modules. Although such degradation phenomena are complicated and often related each other, degradation mechanism is classified into only three categories; 1) less incident light into solar cells, 2) less collection of photogenerated carriers, and 3) less photovoltaic ability itself. Less incident light often originates from soiling of cover glass; however, in some cases originates from browning of encapsulant or reduction of transparent conductive oxide electrode. Less correction of carriers originates from damage of electrodes on the cell or damage of interconnector ribbons between the cells. Less photovoltaic ability originates from surface or bulk recombination or shunting. These three categories are schematically shown in the attached figure. There are various degradation factors, for example, thermal or mechanical stress, high temperature, high humidity, UV irradiation, and potential difference. In particular, hygrothermal stress, UV irradiation, potential difference, and also their combination are considerable factors. For example, UV irradiation accelerates degradation by hygrothermal stress [1], on the other hand, delays degradation by potential difference [2].Both development of indoor acceleration test method and estimation of acceleration factor are also important for predicting the lifetime of photovoltaic modules. As mentioned above, although UV light irradiation much influences degradation phenomena, test method with UV light irradiation is not popular. The reason is that it is quite difficult to keep the module temperature under irradiation during test duration and also to realize uniform irradiation for large-size photovoltaic modules over 1.5 m. However, using acetic acid concentration in the encapsulant as the mediator between outdoor exposure and indoor acceleration test, it was elucidated that damp heat test at 85°C and 85% relative humidity for 4000 h corresponds to outdoor exposure at Japan for 30 years [3].Based on degradation mechanism clarified, highly reliable photovoltaic cells and modules should be developed. It is clarified that the most important key material is electrode of solar cells. Even when photocarriers are generated, if damage or degradation occurs in the electrodes, such carriers are not collected and photovoltaic performance is lowered. Problems in photocarrier collection occupy majority of origins for degradation observed outdoors. Degradation by potential difference has also attracted much attention in the last 10 years especially in mega-watt scale photovoltaic plant with high system voltage. Encapsulant materials and anti-reflection coating of solar cells are key materials for suppressing such kinds of degradation.There are some remaining issues on photovoltaic cells and modules for improving reliability and increasing lifetime. First, interaction between module materials and cells should be completely clarified. Photovoltaic modules are composed of various materials including polymers, metals, ceramics, and, of course, semiconductors. Complicated reactions should occur both at the interface and in the bulk of those materials by many stressors such as high temperature, high humidity, thermal cycle, UV irradiation, and potential difference. Many observations and knowledges have been obtained so far, however, we do not reach the complete understanding, and essential point is that materials with less change and less interaction with other materials should be employed. Second, acceleration test results should be always analyzed considering outdoor exposure results. Especially, climate conditions such as desert, tropical zone, etc. for outdoor exposure also should be employed for acceleration test conditions. Photovoltaic cells and modules appropriate to specific climate conditions should be developed. Third, high efficiency photovoltaic cells and modules should be developed always considering high reliability and long lifetime. Those are inseparable issues for development of photovoltaic cells and modules. Especially, reliability issues on high-efficiency perovskite cells and modules should be intensively studied and urgently solved for realizing high-efficiency and high-stable perovskite/silicon tandem solar cells and modules.The author is grateful to Professors Keisuke Ohdaira, Sachiko Jonai, Yasuaki Ishikawa, Yasushi Sobajima, Fumitaka Ohashi, Kentaro Iwami, Dr. Seira Yamaguchi, Mr. Yasushi Tachibana, and Ms. Yukiko Hara for their collaboration and fruitful discussion. This study was in part supported by the New Energy and Industrial Technology Development Organization.

Background Hotspot over the surface of the Photo Voltaic (PV) Modules due to partial shading through dust deposition can cause a p-n junction breakdown leading to temperature rise over the surface of the modules. When the PV module operating current exceeds the reduced short circuit current(Isc) of the shaded cell, it cannot produce energy, rather starts to consume power from the other PV cells connected in series. Researchers measured hotspot temperature rise in the range of 150~200Deg.C due to partial shading or illumination distribution imbalance. Also the intensity of rise can reach to the tune of +300Deg.C, when hotspot occurs due to a crack / damage on cell. Level of temperature rise depending on numerous factors such as number of PV cells connected in series to shaded cell, Open Circuit Voltage (Voc) of the PV cell, shunt resistance, band gap of the PV cell material and location of shade etc. Installation of grid connected PV solar farms adjacent to flammable dust environment can deposit over the PV modules creating partial shading leading to rise in surface temperature. Auto Ignition Temperature (AIT) of many of the flammable / explosive substances are well classified and above + 85Deg.C can become a source of ignition. By-pass diodes are employed to minimize or prevent the effect of hotspot on PV cell by forward biasing the diode during faulty conditions. Normal design in commercial PV modules consider to add a by-pass diode for a set of 15~18 PV cells. There are characteristics mismatch between the PV cells and by-pass diode hence prevention of hotspot is not ensured in total in the event of diode failure. Encapsulated PV module can withstand localized temperature to the tune of +95~150Deg.C depending on the material, the temperature rise due to hotspot can rise above these limits. Methods: Flammable dust is a mixture of lowest AIT (+102Deg.C) substance Carbon Disulfide(CS2) liquid with ash and saw dust. Partial shading of PV modules by the flammable dust mixture for the test is to select cell current coincides as closely as possible with module Isc. Objectives: The main objective of this research paper is to study and evaluate the effect of hotspot phenomena of the PV Modules in flammable dust environment with a focus on fire safety. Results & Conclusions: Mono crystalline and polycrystalline PV modules with varying voltage levels and power output are setup for the experimental verification. Flammable dust mixture for shading is prepared for the experimentation with CS2, ash and saw dust materials in equal proportion. Lower temperature rise PV module is more suited for a flammable dust environment and this study is aimed to identify the material. Key outcome this research may recommend for an application specific PV module is recommended with following design configurations for use in flammable atmosphere, 1. By-pass diode across 3 ~ 6 PV cells thereby reducing the power to dissipate across the shaded cell. 2. Materials of PV cell with lower Voc or band-gap engineered semiconducting material to reduce the effect of hotspot.

Despite the increasing interest in photovoltaic (PV) cell powered small-cell base stations (SBSs), it has not been sufficiently studied yet how different PV cell angles can be utilized to achieve a good match between the energy arrival and consumption at the SBS. This is especially important in an urban environment where cellular network operators often struggle to apply optimal angles to the PV cells due to implementation constraints or shadowing effects of surrounding buildings. We develop an energy generation, storage and consumption model of a PV cell powered SBS, which includes the effects of PV cell orientations. A linear optimization problem is derived to optimize the energy performance of the SBS throughout the day. The effects of different PV cell orientations on the green energy utilization are evaluated assuming deployment in London in summer and winter. Our results show that west orientated PV cells (45° misalignment to the southern direction) are preferred in London during summer, whereas south orientated ones are preferred during winter. This reveals that the PV cell orientation needs to be optimized for not only the location and weather of the SBS deployment site but also the network traffic distribution in time (or energy consumption profile) of the deployment location.

Manage the environmental risks of perovskites

The goal of the current project was to help make the US solar industry a world leader in the manufacture of thin film photovoltaics. The overall approach was to leverage ORNL’s unique characterization and processing technologies to gain a better understanding of the fundamental challenges for solar cell processing and apply that knowledge to targeted projects with industry members. ORNL has the capabilities in place and the expertise required to understand how basic material properties including defects, impurities, and grain boundaries affect the solar cell performance. ORNL also has unique processing capabilities to optimize the manufacturing process for fabrication of high efficiency and low cost solar cells. ORNL recently established the Center for Advanced Thin-film Systems (CATS), which contains a suite of optical and electrical characterization equipment specifically focused on solar cell research. Under this project, ORNL made these facilities available to industrial partners who were interested in pursuing collaborative research toward the improvement of their product or manufacturing process. Four specific projects were pursued with industrial partners: Global Solar Energy is a solar industry leader in full scale production manufacturing highly-efficient Copper Indium Gallium diSelenide (CIGS) thin film solar material, cells and products. ORNL worked with GSE to develop a scalable, non-vacuum, solution technique to deposit amorphous or nanocrystalline conducting barrier layers on untextured stainless steel substrates for fabricating high efficiency flexible CIGS PV. Ferro Corporation’s Electronic, Color and Glass Materials (“ECGM”) business unit is currently the world’s largest supplier of metallic contact materials in the crystalline solar cell marketplace. Ferro’s ECGM business unit has been the world's leading supplier of thick film metal pastes to the crystalline silicon PV industry for more than 30 years, and has had operational cells and modules in the field for 25 years. Under this project, Ferro leveraged world leading analytical capabilities at ORNL to characterize the paste-to-silicon interface microstructure and develop high efficiency next generation contact pastes. Ampulse Corporation is developing a revolutionary crystalline-silicon (c-Si) thin-film solar photovoltaic (PV) technology. Utilizing uniquely-textured substrates and buffer materials from the Oak Ridge National Laboratory (ORNL), and breakthroughs in Hot-Wire Chemical Vapor Deposition (HW-CVD) techniques in epitaxial silicon developed at the National Renewable Energy Laboratory (NREL), Ampulse is creating a solar technology that is tunable in silicon thickness, and hence in efficiency and economics, to meet the specific requirements of multiple solar PV applications. This project focused on the development of a high rate deposition process to deposit Si, Ge, and Si1-xGex films as an alternate to hot-wire CVD. Mossey Creek Solar is a start-up company with great expertise in the solar field. The primary interest is to create and preserve jobs in the solar sector by developing high-yield, low-cost, high-efficiency solar cells using MSC-patented and -proprietary technologies. The specific goal of this project was to produce large grain formation in thin, net-shape-thickness mc-Si wafers processed with high-purity silicon powder and ORNL's plasma arc lamp melting without introducing impurities that compromise absorption coefficient and carrier lifetime. As part of this project, ORNL also added specific pieces of equipment to enhance our ability to provide unique insight for the solar industry. These capabilities include a moisture barrier measurement system, a combined physical vapor deposition and sputtering system dedicated to cadmium-containing deposits, adeep level transient spectroscopy system useful for identifying defects, an integrating sphere photoluminescence system, and a high-speed ink jet printing system. These tools were combined with others to study the effect of defects on the performance of crystalline silicon and thin film solar cells, to explore non-vacuum ink-based approaches to solar cell production, as well as large-scale and low-cost deposition and processing of thin film CdTe material.

<p indent=0mm>Solar energy is a clean and renewable source of energy. Various solar photovoltaic (PV) cell technologies have been developed, out of which perovskite PV cell technology is growing rapidly. Using organometal halide perovskite as an optical absorption component, the power conversion efficiency (PCE) of heterojunction solar PV cells increased from 3.8% in 2009 to 25.5% recently. Nonetheless, the bottleneck for CH₃NH₃PbI₃-based solar cells entering into commercial market is their poor stabilities relating to environmental, thermal, and ultraviolet light influence. In contrast, transition metal oxide perovskites are thermodynamically and chemically stable enough for solar cells' commercialization, with more advantages such as bandgap (<italic>E</italic>_g) adjustability from <sc>0 to 6 eV,</sc> processing being compatible with transparent conducting oxides, and ferroelectric bulk PV effect. Owing to a wide <italic>E</italic>_g, traditional ferroelectric perovskite oxides exhibit poor visible optical absorption, low electrical conductivity, and thus extremely low PCE. As an alternative to p-n junction PV effect, ferroelectric bulk PV effect provides a new separation mechanism for photo-excited carriers, which is closely related to spatial inversion symmetry breaking and its resulting spontaneous electric polarization. Different from p-n junction, the active space for photo-excited carrier separation spans the whole ferroelectric body, and thus an above-<italic>E</italic>_g open-circuit voltage is produced. By narrowing <italic>E</italic>_g while maintaining ferroelectricity of oxide perovskites, ferroelectric semiconductors become available to monolithically integrate the p-n junction and ferroelectric bulk PV effects, which could, in principle, go beyond the Shockley-Queisser theoretical PCE limit of conventional<italic> </italic>p-n junction solar cells. Bismuth ferrite (BiFeO₃) has been experimentally demonstrated to exhibit ferroelectric PV effect. Meanwhile, it has a high ferroelectric Curie temperature (<italic>T</italic>_C) of 830°C and an intermediate <italic>E</italic>_g of <sc>~2.2 eV,</sc> providing a large chemical space for solid solution perovskite oxides to trade off both target properties of narrow <italic>E</italic>_g and <italic>T</italic>_C><sc>400 K.</sc> In this report, 0.50BiFeO₃-0.25A₁MnO₃-0.25A₂TiO₃ (A₁ = Ca, Sr, Ba, A₂ = Sr, Ba, Pb) and 0.49BiFeO₃-0.26BaTiO₃-0.25(Sr₁₋_{<italic>x</italic>}Ba_{<italic>x</italic>})(Co_1/3Nb_2/3)O₃ (<italic>x </italic>= 0 and 0.4) ferroelectric semiconductors with <italic>E</italic>_g of <sc>~0.9 eV</sc> were created by substituting Fe³⁺ with Mn⁴⁺ or Co²⁺ in BiFeO₃-based solid solution perovskites. Ceramic samples were prepared using a refined solid-state reaction electroceramic processing. X-ray diffraction measurements showed them crystallized in a single pseudo-cubic perovskite phase, while Raman scattering characterizations illustrated a breaking of spatial inversion symmetry at room temperature. Optical absorbance measurements found that these Mn⁴⁺- or Co²⁺-substituted BiFeO₃-based solid solution perovskites have a direct bandgap in a range of <sc>0.75–1.0 eV.</sc> Compared with CH₃NH₃PbI₃ perovskites, their optical absorption reaches near-infrared band of solar spectra. Temperature-dependent resistance measurements showed their resistivity on the magnitude of order of <sc>~10⁶ Ω cm</sc> with thermal excitation energy (<italic>E</italic>_a) of <sc>~0.5 eV.</sc> Combined with observation of frequency-dependent dielectric properties, A-site vacancies were proposed responsible for electrical conduction and dielectric relaxation. Through data-mining causal relationships between <italic>E</italic>_g and the filling number of d electron of B-site cations, <italic>μ</italic>×<italic>r</italic>_A/<italic>r</italic>_B ensemble descriptor of oxide perovskites (<italic>μ</italic>, <italic>r</italic>_A, and <italic>r</italic>_B are the reduced mass of primitive cell, A-site cation radius, and B-site cation radius, respectively), a physical model was proposed to predictively design chemical compositions of ferroelectric semiconducting oxide perovskites with <italic>E</italic>_g<sc>~0.9 eV</sc> for applications of solar PV cells. This essay provides an opportunity for developing novel solar PV cells to integrate monolithically p-n junction and ferroelectric bulk PV effects, with PCE beyond the Shockley-Queisser theoretical limit.