Showing papers on "Photovoltaic system published in 2011"

Electrical Energy Storage for the Grid: A Battery of Choices

Abstract: The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.

Handbook of photovoltaic science and engineering

Abstract: About the Editors. List of Contributors. Preface to the 2nd Edition. 1 Achievements and Challenges of Solar Electricity from Photovoltaics (Steven Hegedus and Antonio Luque). 1.1 The Big Picture. 1.2 What is Photovoltaics? 1.3 Photovoltaics Today. 1.4 The Great Challenge. 1.5 Trends in Technology. 1.6 Conclusions. 2 The Role of Policy in PV Industry Growth: Past, Present and Future (John Byrne and Lado Kurdgelashvili). 2.1 Introduction. 2.2 Policy Review of Selected Countries. 2.3 Policy Impact on PV Market Development. 2.4 Future PV Market Growth Scenarios. 2.5 Toward a Sustainable Future. 3 The Physics of the Solar Cell (Jeffery L. Gray). 3.1 Introduction. 3.2 Fundamental Properties of Semiconductors. 3.3 Solar Cell Fundamentals. 3.4 Additional Topics. 3.5 Summary. 4 Theoretical Limits of Photovoltaic Conversion and New-generation Solar Cells (Antonio Luque and Antonio Marti). 4.1 Introduction. 4.2 Thermodynamic Background. 4.3 Photovoltaic Converters. 4.4 The Technical Efficiency Limit for Solar Converters. 4.5 Very-high-efficiency Concepts. 4.6 Conclusions. 5 Solar Grade Silicon Feedstock (Bruno Ceccaroli and Otto Lohne). 5.1 Introduction. 5.2 Silicon. 5.3 Production of Silicon Metal/Metallurgical Grade Silicon. 5.4 Production of Polysilicon/Silicon of Electronic and Photovoltaic Grade. 5.5 Current Silicon Feedstock to Solar Cells. 5.6 Requirements of Silicon for Crystalline Solar Cells. 5.7 Routes to Solar Grade Silicon. 5.8 Conclusions. 6 Bulk Crystal Growth and Wafering for PV (Hugo Rodriguez, Ismael Guerrero, Wolfgang Koch, Arthur L. Endros, Dieter Franke, Christian Hassler, Juris P. Kalejs and H. J. Moller). 6.1 Introduction. 6.2 Bulk Monocrystalline Material. 6.3 Bulk Multicrystalline Silicon. 6.4 Wafering. 6.5 Silicon Ribbon and Foil Production. 6.6 Numerical Simulations of Crystal Growth Techniques. 6.7 Conclusions. 7 Crystalline Silicon Solar Cells and Modules (Ignacio Tobias, Carlos del Ca"nizo and Jesus Alonso). 7.1 Introduction. 7.2 Crystalline Silicon as a Photovoltaic Material. 7.3 Crystalline Silicon Solar Cells. 7.4 Manufacturing Process. 7.5 Variations to the Basic Process. 7.6 Other Industrial Approaches. 7.7 Crystalline Silicon Photovoltaic Modules. 7.8 Electrical and Optical Performance of Modules. 7.9 Field Performance of Modules. 7.10 Conclusions. 8 High-efficiency III-V Multijunction Solar Cells (D. J. Friedman, J. M. Olson and Sarah Kurtz). 8.1 Introduction. 8.2 Applications. 8.3 Physics of III-V Multijunction and Single-junction Solar Cells. 8.4 Cell Configuration. 8.5 Computation of Series-connected Device Performance. 8.6 Materials Issues Related to GaInP/GaAs/Ge Solar Cells. 8.7 Epilayer Characterization and Other Diagnostic Techniques. 8.8 Reliability and Degradation. 8.9 Future-generation Solar Cells. 8.10 Summary. 9 Space Solar Cells and Arrays (Sheila Bailey and Ryne Raffaelle). 9.1 The History of Space Solar Cells. 9.2 The Challenge for Space Solar Cells. 9.3 Silicon Solar Cells. 9.4 III-V Solar Cells. 9.5 Space Solar Arrays. 9.6 Future Cell and Array Possibilities. 9.7 Power System Figures of Merit. 9.8 Summary. 10 Photovoltaic Concentrators (Gabriel Sala and Ignacio Anton). 10.1 What is the Aim of Photovoltaic Concentration and What Does it Do? 10.2 Objectives, Limitations and Opportunities. 10.3 Typical Concentrators: an Attempt at Classification. 10.4 Concentration Optics: Thermodynamic Limits. 10.5 Factors of Merit for Concentrators in Relation to the Optics. 10.6 Photovoltaic Concentration Modules and Assemblies. 10.7 Tracking for Concentrator Systems. 10.8 Measurements of Cells, Modules and Photovoltaic Systems in Concentration. 10.9 Summary. 11 Crystalline Silicon Thin-Film Solar Cells via High-temperature and Intermediate-temperature Approaches (Armin G. Aberle and Per I. Widenborg). 11.1 Introduction. 11.2 Modelling. 11.4 Crystalline Silicon Thin-Film Solar Cells on Intermediate-T Foreign Supporting Materials. 11.5 Conclusions. 12 Amorphous Silicon-based Solar Cells (Eric A. Schiff, Steven Hegedus and Xunming Deng). 12.1 Overview. 12.2 Atomic and Electronic Structure of Hydrogenated Amorphous Silicon. 12.3 Depositing Amorphous Silicon. 12.4 Understanding a-Si pin Cells. 12.5 Multijunction Solar Cells. 12.6 Module Manufacturing. 12.7 Conclusions and Future Projections. 13 Cu(InGa)Se2 Solar Cells (William N. Shafarman, Susanne Siebentritt and Lars Stolt). 13.1 Introduction. 13.2 Material Properties. 13.3 Deposition Methods. 13.4 Junction and Device Formation. 13.5 Device Operation. 13.6 Manufacturing Issues. 13.7 The Cu(InGa)Se2 Outlook. 14 Cadmium Telluride Solar Cells (Brian E. McCandless and James R. Sites). 14.1 Introduction. 14.2 Historical Development. 14.3 CdTe Properties. 14.4 CdTe Film Deposition. 14.5 CdTe Thin Film Solar Cells. 14.6 CdTe Modules. 14.7 Future of CdTe-based Solar Cells. 15 Dye-sensitized Solar Cells (Kohjiro Hara and Shogo Mori). 15.1 Introduction. 15.2 Operating Mechanism of DSSC. 15.3 Materials. 15.4 Performance of Highly Efficient DSSCs. 15.5 Electron-transfer Processes. 15.6 New Materials. 15.7 Stability. 15.8 Approach to Commercialization. 15.9 Summary and Prospects. 16 Sunlight Energy Conversion Via Organics (Sam-Shajing Sun and Hugh O'Neill). 16.1 Principles of Organic and Polymeric Photovoltaics. 16.2 Evolution and Types of Organic and Polymeric Solar Cells. 16.3 Organic and Polymeric Solar Cell Fabrication and Characterization. 16.4 Natural Photosynthetic Sunlight Energy Conversion Systems. 16.5 Artificial Photosynthetic Systems. 16.6 Artificial Reaction Centers. 16.7 Towards Device Architectures. 16.8 Summary and Future Perspectives. 17 Transparent Conducting Oxides for Photovoltaics (Alan E. Delahoy and Sheyu Guo). 17.1 Introduction. 17.2 Survey of Materials. 17.3 Deposition Methods. 17.4 TCO Theory and Modeling: Electrical and Optical Properties and their Impact on Module Performance. 17.5 Principal Materials and Issues for Thin Film and Wafer-based PV. 17.6 Textured Films. 17.7 Measurements and Characterization Methods. 17.8 TCO Stability. 17.9 Recent Developments and Prospects. 18 Measurement and Characterization of Solar Cells and Modules (Keith Emery). 18.1 Introduction. 18.2 Rating PV Performance. 18.3 Current-Voltage Measurements. 18.4 Spectral Responsivity Measurements. 18.5 Module Qualification and Certification. 18.6 Summary. 19 PV Systems (Charles M. Whitaker, Timothy U. Townsend, Anat Razon, Raymond M. Hudson and Xavier Vallve). 19.1 Introduction: There is gold at the end of the rainbow. 19.2 System Types. 19.3 Exemplary PV Systems. 19.4 Ratings. 19.5 Key System Components. 19.6 System Design Considerations. 19.7 System Design. 19.8 Installation. 19.9 Operation and Maintenance/Monitoring. 19.10 Removal, Recycling and Remediation. 19.11 Examples. 20 Electrochemical Storage for Photovoltaics (Dirk Uwe Sauer). 20.1 Introduction. 20.2 General Concept of Electrochemical Batteries. 20.3 Typical Operation Conditions of Batteries in PV Applications. 20.4 Secondary Electrochemical Accumulators with Internal Storage. 20.5 Secondary Electrochemical Battery Systems with External Storage. 20.6 Investment and Lifetime Cost Considerations. 20.7 Conclusion. 21 Power Conditioning for Photovoltaic Power Systems (Heribert Schmidt, Bruno Burger and Jurgen Schmid). 21.1 Charge Controllers and Monitoring Systems for Batteries in PV Power Systems. 21.2 Inverters. 22 Energy Collected and Delivered by PV Modules (Eduardo Lorenzo). 22.1 Introduction. 22.2 Movement between Sun and Earth. 22.3 Solar Radiation Components. 22.4 Solar Radiation Data and Uncertainty. 22.5 Radiation on Inclined Surfaces. 22.6 Diurnal Variations of the Ambient Temperature. 22.7 Effects of the Angle of Incidence and of Dirt. 22.8 Some Calculation Tools. 22.9 Irradiation on Most Widely Studied Surfaces. 22.10 PV Generator Behaviour Under Real Operation Conditions. 22.11 Reliability and Sizing of Stand-alone PV Systems. 22.12 The Case of Solar Home Systems. 22.13 Energy Yield of Grid-connected PV Systems. 22.14 Conclusions. 23 PV in Architecture (Tjerk H. Reijenga and Henk F. Kaan). 23.1 Introduction. 23.2 PV in Architecture. 23.3 BIPV Basics. 23.4 Steps in the Design Process with PV. 23.5 Concluding Remarks. 24 Photovoltaics and Development (Jorge M. Huacuz, Jaime Agredano and Lalith Gunaratne). 24.1 Electricity and Development. 24.2 Breaking the Chains of Underdevelopment. 24.3 The PV Alternative. 24.4 Examples of PV Rural Electrification. 24.5 Toward a New Paradigm for Rural Electrification. References. Index.

Wireless Solar Water Splitting Using Silicon-Based Semiconductors and Earth-Abundant Catalysts

Abstract: We describe the development of solar water-splitting cells comprising earth-abundant elements that operate in near-neutral pH conditions, both with and without connecting wires. The cells consist of a triple junction, amorphous silicon photovoltaic interfaced to hydrogen- and oxygen-evolving catalysts made from an alloy of earth-abundant metals and a cobalt|borate catalyst, respectively. The devices described here carry out the solar-driven water-splitting reaction at efficiencies of 4.7% for a wired configuration and 2.5% for a wireless configuration when illuminated with 1 sun (100 milliwatts per square centimeter) of air mass 1.5 simulated sunlight. Fuel-forming catalysts interfaced with light-harvesting semiconductors afford a pathway to direct solar-to-fuels conversion that captures many of the basic functional elements of a leaf.

A review of solar photovoltaic technologies

Abstract: Global environmental concerns and the escalating demand for energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till date. The power from sun intercepted by the earth is about 1.8 × 1011 MW, which is many times larger than the present rate of all the energy consumption. Photovoltaic technology is one of the finest ways to harness the solar power. This paper reviews the photovoltaic technology, its power generating capability, the different existing light absorbing materials used, its environmental aspect coupled with a variety of its applications. The different existing performance and reliability evaluation models, sizing and control, grid connection and distribution have also been discussed. © 2011 Published by Elsevier Ltd.

Comparing photosynthetic and photovoltaic efficiencies and recognizing the potential for improvement.

Abstract: Comparing photosynthetic and photovoltaic efficiencies is not a simple issue. Although both processes harvest the energy in sunlight, they operate in distinctly different ways and produce different types of products: biomass or chemical fuels in the case of natural photosynthesis and nonstored electrical current in the case of photovoltaics. In order to find common ground for evaluating energy-conversion efficiency, we compare natural photosynthesis with present technologies for photovoltaic-driven electrolysis of water to produce hydrogen. Photovoltaic-driven electrolysis is the more efficient process when measured on an annual basis, yet short-term yields for photosynthetic conversion under optimal conditions come within a factor of 2 or 3 of the photovoltaic benchmark. We consider opportunities in which the frontiers of synthetic biology might be used to enhance natural photosynthesis for improved solar energy conversion efficiency.

Review of Nonisolated High-Step-Up DC/DC Converters in Photovoltaic Grid-Connected Applications

Abstract: The photovoltaic (PV) grid-connected power system in the residential applications is becoming a fast growing segment in the PV market due to the shortage of the fossil fuel energy and the great environmental pollution. A new research trend in the residential generation system is to employ the PV parallel-connected configuration rather than the series-connected configuration to satisfy the safety requirements and to make full use of the PV generated power. How to achieve high-step-up, low-cost, and high-efficiency dc/dc conversion is the major consideration due to the low PV output voltage with the parallel-connected structure. The limitations of the conventional boost converters in these applications are analyzed. Then, most of the topologies with high-step-up, low-cost, and high-efficiency performance are covered and classified into several categories. The advantages and disadvantages of these converters are discussed. Furthermore, a general conceptual circuit for high-step-up, low-cost, and high-efficiency dc/dc conversion is proposed to derive the next-generation topologies for the PV grid-connected power system. Finally, the major challenges of high-step-up, low-cost, and high-efficiency dc/dc converters are summarized. This paper would like to make a clear picture on the general law and framework for the next-generation nonisolated high-step-up dc/dc converters.

A Hybrid AC/DC Microgrid and Its Coordination Control

Abstract: This paper proposes a hybrid ac/dc micro grid to reduce the processes of multiple dc-ac-dc or ac-dc-ac conversions in an individual ac or dc grid. The hybrid grid consists of both ac and dc networks connected together by multi-bidirectional converters. AC sources and loads are connected to the ac network whereas dc sources and loads are tied to the dc network. Energy storage systems can be connected to dc or ac links. The proposed hybrid grid can operate in a grid-tied or autonomous mode. The coordination control algorithms are proposed for smooth power transfer between ac and dc links and for stable system operation under various generation and load conditions. Uncertainty and intermittent characteristics of wind speed, solar irradiation level, ambient temperature, and load are also considered in system control and operation. A small hybrid grid has been modeled and simulated using the Simulink in the MATLAB. The simulation results show that the system can maintain stable operation under the proposed coordination control schemes when the grid is switched from one operating condition to another.

A review of solar photovoltaic levelized cost of electricity

Abstract: As the solar photovoltaic (PV) matures, the economic feasibility of PV projects are increasingly being evaluated using the levelized cost of electricity (LCOE) generation in order to be compared to other electricity generation technologies. Unfortunately, there is lack of clarity of reporting assumptions, justifications and degree of completeness in LCOE calculations, which produces widely varying and contradictory results. This paper reviews the methodology of properly calculating the LCOE for solar PV, correcting the misconceptions made in the assumptions found throughout the literature. Then a template is provided for better reporting of LCOE results for PV needed to influence policy mandates or make invest decisions. A numerical example is provided with variable ranges to test sensitivity, allowing for conclusions to be drawn on the most important variables. Grid parity is considered when the LCOE of solar PV is comparable with grid electrical prices of conventional technologies and is the industry target for cost-effectiveness. Given the state of the art in the technology and favorable financing terms it is clear that PV has already obtained grid parity in specific locations and as installed costs continue to decline, grid electricity prices continue to escalate, and industry experience increases, PV will become an increasingly economically advantageous source of electricity over expanding geographical regions.

High-performance flat-panel solar thermoelectric generators with high thermal concentration

Abstract: The conversion of sunlight into electricity has been dominated by photovoltaic and solar thermal power generation. A highly efficient solar to electric energy conversion device based on nanostructured thermoelectric materials and high solar concentration is now demonstrated. The results show potential for cost effective solar thermoelectric generation.

A Review of Solar Photovoltaic Levelized Cost of Electricity

Abstract: As the solar photovoltaic (PV) matures, the economic feasibility of PV projects are increasingly being evaluated using the levelized cost of electricity (LCOE) generation in order to be compared to other electricity generation technologies. Unfortunately, there is lack of clarity of reporting assumptions, justifications and degree of completeness in LCOE calculations, which produces widely varying and contradictory results. This paper reviews the methodology of properly calculating the LCOE for solar PV, correcting the misconceptions made in the assumptions found throughout the literature. Then a template is provided for better reporting of LCOE results for PV needed to influence policy mandates or make invest decisions. A numerical example is provided with variable ranges to test sensitivity, allowing for conclusions to be drawn on the most important variables. Grid parity is considered when the LCOE of solar PV is comparable with grid electrical prices of conventional technologies and is the industry target for cost-effectiveness. Given the state of the art in the technology and favorable financing terms it is clear that PV has already obtained grid parity in specific locations and as installed costs continue to decline, grid electricity prices continue to escalate, and industry experience increases, PV will become an increasingly economically advantageous source of electricity over expanding geographical regions.

Simulation and Hardware Implementation of Incremental Conductance MPPT With Direct Control Method Using Cuk Converter

Abstract: This paper presents simulation and hardware implementation of incremental conductance (IncCond) maximum power point tracking (MPPT) used in solar array power systems with direct control method. The main difference of the proposed system to existing MPPT systems includes elimination of the proportional-integral control loop and investigation of the effect of simplifying the control circuit. Contributions are made in several aspects of the whole system, including converter design, system simulation, controller programming, and experimental setup. The resultant system is capable of tracking MPPs accurately and rapidly without steady-state oscillation, and also, its dynamic performance is satisfactory. The IncCond algorithm is used to track MPPs because it performs precise control under rapidly changing atmospheric conditions. MATLAB and Simulink were employed for simulation studies, and Code Composer Studio v3.1 was used to program a TMS320F2812 digital signal processor. The proposed system was developed and tested successfully on a photovoltaic solar panel in the laboratory. Experimental results indicate the feasibility and improved functionality of the system.

Energy Management and Operational Planning of a Microgrid With a PV-Based Active Generator for Smart Grid Applications

Abstract: The development of energy management tools for next-generation PhotoVoltaic (PV) installations, including storage units, provides flexibility to distribution system operators. In this paper, the aggregation and implementation of these determinist energy management methods for business customers in a microgrid power system are presented. This paper proposes a determinist energy management system for a microgrid, including advanced PV generators with embedded storage units and a gas microturbine. The system is organized according to different functions and is implemented in two parts: a central energy management of the microgrid and a local power management at the customer side. The power planning is designed according to the prediction for PV power production and the load forecasting. The central and local management systems exchange data and order through a communication network. According to received grid power references, additional functions are also designed to manage locally the power flows between the various sources. Application to the case of a hybrid supercapacitor battery-based PV active generator is presented.

Optimal Power Flow Management for Grid Connected PV Systems With Batteries

Abstract: This paper presents an optimal power management mechanism for grid connected photovoltaic (PV) systems with storage. The objective is to help intensive penetration of PV production into the grid by proposing peak shaving service at the lowest cost. The structure of a power supervisor based on an optimal predictive power scheduling algorithm is proposed. Optimization is performed using Dynamic Programming and is compared with a simple ruled-based management. The particularity of this study remains first in the consideration of batteries ageing into the optimization process and second in the “day-ahead” approach of power management. Simulations and real conditions application are carried out over one exemplary day. In simulation, it points out that peak shaving is realized with the minimal cost, but especially that power fluctuations on the grid are reduced which matches with the initial objective of helping PV penetration into the grid. In real conditions, efficiency of the predictive schedule depends on accuracy of the forecasts, which leads to future works about optimal reactive power management.

A review on solar energy use in industries

Abstract: Presently, solar energy conversion is widely used to generate heat and produce electricity A comparative study on the world energy consumption released by International Energy Agency (IEA) shows that in 2050, solar array installations will supply around 45% of energy demand in the world It was found that solar thermal is getting remarkable popularity in industrial applications Solar thermal is an alternative to generate electricity, process chemicals or even space heating It can be used in food, non-metallic, textile, building, chemical or even business related industries On the other hand, solar electricity is wildly applied in telecommunication, agricultural, water desalination and building industry to operate lights, pumps, engines, fans, refrigerators and water heaters It is very important to apply solar energy for a wide variety of applications and provide energy solutions by modifying the energy proportion, improving energy stability, increasing energy sustainability, conversion reduction and hence enhance the system efficiency The present work aimed to study the solar energy systems utilization in industrial applications and looked into the industrial applications which are more compatible to be integrated with solar energy systems

High-Performance Adaptive Perturb and Observe MPPT Technique for Photovoltaic-Based Microgrids

Abstract: Solar photovoltaic (PV) energy has witnessed double-digit growth in the past decade. The penetration of PV systems as distributed generators in low-voltage grids has also seen significant attention. In addition, the need for higher overall grid efficiency and reliability has boosted the interest in the microgrid concept. High-efficiency PV-based microgrids require maximum power point tracking (MPPT) controllers to maximize the harvested energy due to the nonlinearity in PV module characteristics. Perturb and observe (PO second, no steady-state oscillations around the MPP; and lastly, no need for predefined system-dependent constants, hence provides a generic design core. A design example is presented by experimental implementation of the proposed technique. Practical results for the implemented setup at different irradiance levels are illustrated to validate the proposed technique.

Coordinated Active Power Curtailment of Grid Connected PV Inverters for Overvoltage Prevention

Abstract: Overvoltages in low voltage (LV) feeders with high penetration of photovoltaics (PV) are usually prevented by limiting the feeder's PV capacity to very conservative values, even if the critical periods rarely occur. This paper discusses the use of droop-based active power curtailment techniques for overvoltage prevention in radial LV feeders as a means for increasing the installed PV capacity and energy yield. Two schemes are proposed and tested in a typical 240-V/75-kVA Canadian suburban distribution feeder with 12 houses with roof-top PV systems. In the first scheme, all PV inverters have the same droop coefficients. In the second, the droop coefficients are different so as to share the total active power curtailed among all PV inverters/houses. Simulation results demonstrate the effectiveness of the proposed schemes and that the option of sharing the power curtailment among all customers comes at the cost of an overall higher amount of power curtailed.

Options for Control of Reactive Power by Distributed Photovoltaic Generators

Abstract: High-penetration levels of distributed photovoltaic (PV) generation on an electrical distribution circuit present several challenges and opportunities for distribution utilities. Rapidly varying irradiance conditions may cause voltage sags and swells that cannot be compensated by slowly responding utility equipment resulting in a degradation of power quality. Although not permitted under current standards for interconnection of distributed generation, fast-reacting, VAR-capable PV inverters may provide the necessary reactive power injection or consumption to maintain voltage regulation under difficult transient conditions. As side benefit, the control of reactive power injection at each PV inverter provides an opportunity and a new tool for distribution utilities to optimize the performance of distribution circuits, e.g., by minimizing thermal losses. We discuss and compare via simulation various design options for control systems to manage the reactive power generated by these inverters. An important design decision that weighs on the speed and quality of communication required is whether the control should be centralized or distributed (i.e., local). In general, we find that local control schemes are able to maintain voltage within acceptable bounds. We consider the benefits of choosing different local variables on which to control and how the control system can be continuously tuned between robust voltage control, suitable for daytime operation when circuit conditions can change rapidly, and loss minimization better suited for nighttime operation.

Composite Energy Storage System Involving Battery and Ultracapacitor With Dynamic Energy Management in Microgrid Applications

Abstract: Renewable-energy-based microgrids are a better way of utilizing renewable power and reduce the usage of fossil fuels. Usage of energy storage becomes mandatory when such microgrids are used to supply quality power to the loads. Microgrids have two modes of operation, namely, grid-connected and islanding modes. During islanding mode, the main responsibility of the storage is to perform energy balance. During grid-connected mode, the goal is to prevent propagation of the renewable source intermittency and load fluctuations to the grid. Energy storage of a single type cannot perform all these jobs efficiently in a renewable powered microgrid. The intermittent nature of renewable energy sources like photovoltaic (PV) demands usage of storage with high energy density. At the same time, quick fluctuation of load demands storage with high power density. This paper proposes a composite energy storage system (CESS) that contains both high energy density storage battery and high power density storage ultracapacitor to meet the aforementioned requirements. The proposed power converter configuration and the energy management scheme can actively distribute the power demand among the different energy storages. Results are presented to show the feasibility of the proposed scheme.

Nanowire Solar Cells

Abstract: The nanowire geometry provides potential advantages over planar waferbased or thin-film solar cells in every step of the photoconversion process. These advantages include reduced reflection, extreme light trapping, improved band gap tuning, facile strain relaxation, and increased defect tolerance. These benefits are not expected to increase the maximum efficiency above standard limits; instead, they reduce the quantity and quality of material necessary to approach those limits, allowing for substantial cost reductions. Additionally, nanowires provide opportunities to fabricate complex single-crystalline semiconductor devices directly on low-cost substrates and electrodes such as aluminum foil, stainless steel, and conductive glass, addressing another major cost in current photovoltaic technology. This review describes nanowire solar cell synthesis and fabrication, important characterization techniques unique to nanowire systems, and advantages of the nanowire geometry.

A Novel Improved Variable Step-Size Incremental-Resistance MPPT Method for PV Systems

Abstract: Maximum power point (MPP) tracking (MPPT) techniques are widely applied in photovoltaic (PV) systems to make PV array generate peak power which depends on solar irradiation. Among all the MPPT strategies, the incremental-conductance (INC) algorithm is widely employed due to easy implementation and high tracking accuracy. In this paper, a novel variable step-size incremental-resistance MPPT algorithm is introduced, which not only has the merits of INC but also automatically adjusts the step size to track the PV array MPP. Compared with the variable step-size INC method, the proposed scheme can greatly improve the MPPT response speed and accuracy at steady state simultaneously. Moreover, it is more suitable for practical operating conditions due to a wider operating range. This paper provides the theoretical analysis and the design principle of the proposed MPPT strategy. Simulation and experimental results verify its feasibility.

A Distributed Control Strategy Based on DC Bus Signaling for Modular Photovoltaic Generation Systems With Battery Energy Storage

Abstract: Modular generation system, which consists of modular power conditioning converters, is an effective solution to integrate renewable energy sources with conventional utility grid to improve reliability and efficiency, especially for photovoltaic generation. A distributed control strategy based on improved dc bus signaling is proposed for a modular photovoltaic (PV) generation system with battery energy storage elements. In this paper, the modular PV generation system is composed of three modular dc/dc converters for PV arrays, two grid-connected dc/ac converters, and one dc/dc converter for battery charging/discharging and local loads, which is available of either grid-connected operation or islanding operation. By using the proposed control strategy, the operations of a modular PV generation system are categorized into four modes: islanding with battery discharging, grid-connected rectification, grid-connected inversion, and islanding with constant voltage (CV) generation. The power balance of the system under extreme conditions such as the islanding operation with a full-charged battery is taken into account in this control strategy. The dc bus voltage level is employed as an information carrier to distinguish different modes and determine mode switching. Control methods of modular dc/dc converters, battery converter, and grid-connected converter are addressed. An autonomous control method for modular dc/dc converters is proposed to realize smooth switching between CV operation and maximum power point tracking operation, which enables the dc bus voltage regulation capability of modular dc/dc converters. Seamless switching of a battery converter between charging and discharging and that of a grid-connected converter between rectification and inversion are ensured by the proposed control methods. Experiments verify the practical feasibility and the effectiveness of the proposed control strategies.

Online Short-term Solar Power Forecasting

Abstract: This paper describes a new approach to online forecasting of power production from PV systems. The method is suited to online forecasting in many applications and in this paper it is used to predict hourly values of solar power for horizons of up to 36 h. The data used is 15-min observations of solar power from 21 PV systems located on rooftops in a small village in Denmark. The suggested method is a two-stage method where first a statistical normalization of the solar power is obtained using a clear sky model. The clear sky model is found using statistical smoothing techniques. Then forecasts of the normalized solar power are calculated using adaptive linear time series models. Both autoregressive (AR) and AR with exogenous input (ARX) models are evaluated, where the latter takes numerical weather predictions (NWPs) as input. The results indicate that for forecasts up to 2 h ahead the most important input is the available observations of solar power, while for longer horizons NWPs are the most important input. A root mean square error improvement of around 35% is achieved by the ARX model compared to a proposed reference model.

Silicon Nanowires for Photovoltaic Solar Energy Conversion

Abstract: Semiconductor nanowires are attracting intense interest as a promising material for solar energy conversion for the new-generation photovoltaic (PV) technology. In particular, silicon nanowires (SiNWs) are under active investigation for PV applications because they offer novel approaches for solar-to-electric energy conversion leading to high-efficiency devices via simple manufacturing. This article reviews the recent developments in the utilization of SiNWs for PV applications, the relationship between SiNW-based PV device structure and performance, and the challenges to obtaining high-performance cost-effective solar cells.

Fuzzy-Logic-Control Approach of a Modified Hill-Climbing Method for Maximum Power Point in Microgrid Standalone Photovoltaic System

Abstract: A new fuzzy-logic controller for maximum power point tracking of photovoltaic (PV) systems is proposed. PV modeling is discussed. Conventional hill-climbing maximum power-point tracker structures and features are investigated. The new controller improves the hill-climbing search method by fuzzifying the rules of such techniques and eliminates their drawbacks. Fuzzy-logic-based hill climbing offers fast and accurate converging to the maximum operating point during steady-state and varying weather conditions compared to conventional hill climbing. Simulation and experimentation results are provided to demonstrate the validity of the proposed fuzzy-logic-based controller.

Modeling and Control of $N$ -Paralleled Grid-Connected Inverters With LCL Filter Coupled Due to Grid Impedance in PV Plants

Abstract: Designing adequate control laws for grid-connected inverters with LCL filters is complicated. The power quality standards and the system resonances burden the task. In order to deal with resonances, system damping has to be implemented. Active damping is preferred to passive damping so as to improve the efficiency of the conversion. In addition, paralleled grid-connected inverters in photovoltaic (PV) plants are coupled due to grid impedance. Generally, this coupling is not taken into account when designing the control laws. In consequence, depending on the number of paralleled grid-connected inverters and the grid impedance, the inverters installed in PV plants do not behave as expected. In this paper, the inverters of a PV plant are modeled as a multivariable system. The analysis carried out enables to obtain an equivalent inverter that describes the totality of inverters of a PV plant. The study is validated through simulation and field experiments. The coupling effect is described and the control law design of paralleled grid-connected inverters with LCL filters in PV plants is clarified.

Maximum Power Point Tracking of Multiple Photovoltaic Arrays: A PSO Approach

Abstract: Multiple photovoltaic (PV) modules feeding a common load is the most common form of power distribution used in solar PV systems. In such systems, providing individual maximum power point tracking (MPPT) schemes for each of the PV modules increases the cost. Furthermore, its v-i characteristic exhibits multiple local maximum power points (MPPs) during partial shading, making it difficult to find the global MPP using conventional single-stage (CSS) tracking. To overcome this difficulty, the authors propose a novel MPPT algorithm by introducing a particle swarm optimization (PSO) technique. The proposed algorithm uses only one pair of sensors to control multiple PV arrays, thereby resulting in lower cost, higher overall efficiency, and simplicity with respect to its implementation. The validity of the proposed algorithm is demonstrated through experimental studies. In addition, a detailed performance comparison with conventional fixed voltage, hill climbing, and Fibonacci search MPPT schemes are presented. Algorithm robustness was verified for several complicated partial shading conditions, and in all cases this method took about 2 s to find the global MPP.