Optimal active OPF with FACTS devices by an innovativeload-equivalent approach

In this letter, a load-equivalent model suitable for FACTS devices is proposed for use in optimal active power flow computations. Specified power value or voltage-dependent loads can represent a FACTS device. The power flow of the power system including FACTS devices can be solved with slight modification of the conventional power flow program to include the effects of the introduced equivalent loads     

A new approach for design of organic electrochromic devices with inter-digitated electrode structure

We present a new approach for design of organic electrochromic devices (ECD) with inter-digitated electrode (IDE) structure and three-electrode dynamic operation. The advantages of the IDE design include the ability to produce fast and homogenous color change over large areas. In addition, it enables fabrication of multi-color devices. Our method involves photolithographic etching of ITO followed by electrophoretic deposition (EPD) and mechanical compression of porous titania to produce finely patterned electrodes with high surface area. The titania layer is chemically modified by new stable and reversible electrochromic viologen derivatives involving phenylphosphonic acid anchoring moiety. The new device demonstrates reversible and strong color change from colorless to deep blue and yellow.     

Impact of FACTS devices on exercising market power in deregulated electricity market

In power system studies, congestion in transmission lines and utilization of flexible alternating current transmission system (FACTS) devices are closely associated. These devices are very important due to their role in power delivery system enhancement. It is to be noted that the generation companies can exercise their market power which depends on the line flows, line constraints, generators’ location and its share to the individual loads. This issue cannot be overlooked as it creates monopoliness which is against the deregulated market policy. The objective of this paper is to study the impact of market power when FACTS devices like thyristor controlled switching capacitor (TCSC) and thyristor controlled phase angle regulator (TCPAR) are used under steady state operation. The market power is determined using nodal must-run share (NMRS) index for the standard IEEE 14-bus system with and without the above FACTS devices and the results obtained are compared. All the above simulations are conducted in a MATLAB 7.9-R2009b environment.     

A new hybrid approach for nonconvex economic dispatch problem with valve-point effect

In literature, economic dispatch problems are generally categorized as convex and nonconvex optimization problems. In this study, a solution is proposed for economic dispatch problem with valve point effect, which is one of the nonconvex optimization problems. For this reason the hybrid approach used for solution of this problem is formed as a combination of modified subgradient (MSG) and harmony search (HS) algorithms. This approach (MSG-HS) is applied in three different lossy test systems (Three machines 6-bus, IEEE 5-machines 14-bus, IEEE 6-machines 30-bus systems) solved with different methods in the literature. System losses are calculated by using B loss matrix. The resulting optimal solution values are compared with the solution values in the literature and the results are discussed.     

Energy storage devices for future hybrid electric vehicles

Powertrain hybridization as well as electrical energy management are imposing new requirements on electrical storage systems in vehicles. This paper characterizes the associated vehicle attributes and, in particular, the various levels of hybrids. New requirements for the electrical storage system are derived, including: shallow-cycle life, high dynamic charge acceptance particularly for regenerative braking and robust service life in sustained partial-state-of-charge usage. Lead/acid, either with liquid or absorptive glass-fibre mat electrolyte, is expected to remain the predominant battery technology for 14 V systems, including micro-hybrids, and with a cost-effective battery monitoring system for demanding applications. Advanced AGM batteries may be considered for mild or even medium hybrids once they have proven robustness under real-world conditions, particularly with respect to cycle life at partial-states-of-charge and dynamic charge acceptance. For the foreseeable future, NiMH and Li-ion are the dominating current and potential battery technologies for higher-functionality HEVs. Li-ion, currently at development and demonstration stages, offers attractive opportunities for improvements in performance and cost. Supercapacitors may be considered for pulse power applications. Aside from cell technologies, attention to the issue of system integration of the battery into the powertrain and vehicle is growing. Opportunities and challenges for potential “battery pack” system suppliers are discussed.     

A genetic evolving ant direction DE for OPF with non-smooth cost functions and statistical analysis

This paper proposes an evolving ant direction differential evolution (EADDE) algorithm for solving the optimal power flow problem with non-smooth and non-convex generator fuel cost characteristics. The EADDE employs ant colony search to find a suitable mutation operator for differential evolution (DE) whereas the ant colony parameters are evolved using genetic algorithm approach. The Newton–Raphson method solves the power flow problem. The feasibility of the proposed approach was tested on IEEE 30-bus system with three different cost characteristics. Several cases were investigated to test and validate the robustness of the proposed method in finding the optimal solution. Simulation results demonstrate that the EADDE provides superior results compared to a classical DE and other methods recently reported in the literature. An innovative statistical analysis based on central tendency measures and dispersion measures was carried out on the bus voltage profiles and voltage stability indices.     

A new approach in tracking maximum power under partially shaded conditions with consideration of converter losses

The fact that photovoltaic panels are very sensitive to non-uniform insolation conditions, which can occur several times a day, causes a decrease of efficiency and so increases time for return on investment. This work presents a maximum power point tracking algorithm (MPPT) operating on the load characteristic in order to take the converters losses into account. In addition, the proposed MPPT deals with the problems of shadowing for which the power-load characteristic can present two or more local maximums close to each other. Considering the converters losses it can be shown that the maximum output power of the photovoltaic panels does not necessarily coincide with the maximum output power of the converters. The proposed MPPT algorithm tracks the maximum power with the intention of reducing the total losses including those of converters. Its performance is verified by simulation and confirmed by experimental results.     

A novel approach to the data center hybrid cooling design with containment

Hybrid cooling solutions, which consist of the installation of heat exchangers near IT equipment, aim to eliminate hot spots in data centers containing high-density computer cabinets. In addition, cold aisle containment is often used to reduce hot air recirculation to improve energy efficiency. However, the viability and efficiency of each hybrid cooling strategy with or without containment depend on the IT load and equipment arrangement, and no formal procedure exists for selecting the most efficient strategy for a given application. Therefore, this study provides a computational approach for ranking the performance of different cooling strategies based on their capacity and cooling efficiency. The results of analyses indicate that applying containment is beneficial in (1) lowering the maximum temperature of the air entering the racks as airflow rates are increased, and (2) increasing the uniformity of rack inlet temperatures. However, applying containment also requires additional mechanical work by the computer room air handler (CRAH) fan, which may raise the data center power usage effectiveness (PUE). Application of the computational approach discussed here highlights the use of hybrid cooling to lower PUE by reducing the CRAH fan power.     

A new technique for solving the multi-objective optimization problem using hybrid approach

Energy efficiency, which consists of using less energy or improving the level of service to energy consumers, refers to an effective way to provide overall energy. But its increasing pressure on the energy sector to control greenhouse gases and to reduce CO₂ emissions forced the power system operators to consider the emission problem as a consequential matter besides the economic problems. The economic power dispatch problem has, therefore, become a multi-objective optimization problem. Fuel cost, pollutant emissions, and system loss should be minimized simultaneously while satisfying certain system constraints. To achieve a good design with different solutions in a multi-objective optimization problem, fuel cost and pollutant emissions are converted into single optimization problem by introducing penalty factor. Now the power dispatch is formulated into a bi-objective optimization problem, two objectives with two algorithms, firefly algorithm for optimization the fuel cost, pollutant emissions and the real genetic algorithm for minimization of the transmission losses. In this paper the new approach (firefly algorithm-real genetic algorithm, FFA-RGA) has been applied to the standard IEEE 30-bus 6-generator. The effectiveness of the proposed approach is demonstrated by comparing its performance with other evolutionary multi-objective optimization algorithms. Simulation results show the validity and feasibility of the proposed method.     

Engineering of hybrid interfaces in organic photovoltaic devices

In this study, we engineer and investigate the interface structure and chemistry at the indium tin oxide (ITO) anode (front-side electrode) as well as at the Mg−Ag cathode (back-side electrode) in metal phthalocyanine (MePc)/C₆₀ organic solar cells (OSCs).For the front-side electrode, Zn-phthalocyaninetetraphosphonic acid (Zn-PTPA) and Sn-phthalocyanine axially substituted with tartaric acid (Sn-PTA) have been used for the surface termination of ITO coated glass substrates. Both terminations yielded OSCs with higher fill factors and open circuit voltages, thus increasing the power conversion efficiency by 33% and 67%, respectively. A possible influence of a chemisorbed Zn-PTPA on the film growth of the adjacent ZnPc absorber in the vicinity of the hybrid interface is discussed using X-ray reflectivity and near edge X-ray absorption fine structure data. Distinct effects of the Zn-PTPA and Sn-PTA terminations on the electronic properties of the ITO surface were found by X-ray photoelectron spectroscopy (XPS) measurements at the valence band edge. We demonstrate the possibility to engineer the hybrid interface without additional buffer.For the back-side electrode we report the formation of buffer-free charge carrier selective Mg−Ag cathodes, which are applied for bulk heterojunction organic absorbers consisting of copper phthalocyanine (CuPc) donor and fullerene C₆₀ acceptor materials. The chemical and structural properties of the CuPc:C₆₀/Mg−Ag interface are investigated by element depth profiling using secondary ion mass spectrometry (SIMS), grazing incidence X-ray diffraction analysis (GI-XRD) and XPS.We demonstrate that an optimum charge carrier selectivity is achieved with Mg:Ag/Ag cathode structures, where the Mg:Ag alloy layer has a composition close to that of Ag₃Mg. In addition, Mg diffusion into CuPc:C₆₀ layer is observed. As a result, an interaction between Mg and Cu²⁺ with a concurrent change in oxidation state of both metals takes place. However, no formation of MgPc is observed.The findings of this work are discussed against the background of the performance and electrical properties of the corresponding MePc/C₆₀-based organic solar cells.     

A corrected hybrid approach for wind speed prediction in Hexi Corridor of China

Wind energy has been well recognized as a renewable resource in electricity generation, which is environmentally friendly, socially beneficial and economically competitive. For proper and efficient evaluation of wind energy, a hybrid Seasonal Auto-Regression Integrated Moving Average and Least Square Support Vector Machine (SARIMA-LSSVM) model is significantly developed to predict the mean monthly wind speed in Hexi Corridor. The design concept of combining the Seasonal Auto-Regression Integrated Moving Average (SARIMA) method with the Least Square Support Vector Machine (LSSVM) algorithm shows more powerful forecasting capacity for monthly wind speed prediction at wind parks, when compared with the single Auto-Regression Integrated Moving Average (ARIMA), SARIMA, LSSVM models and the hybrid Auto-Regression Integrated Moving Average and Support Vector Machine (ARIMA-SVM) model. To verify the developed approach, the monthly data from January 2001 to December 2006 in Mazong Mountain and Jiuquan are used for model construction and model testing. The simulation and hypothesis test results show that the developed method is simple and quite efficient.     

POSS based ionic liquid as an electrolyte for hybrid electrochromic devices

The main objective of this study was to broaden the assortment of I⁻/I₃⁻ redox ionic liquids using polyhedral oligomeric silsesquioxanes (POSS) acting as nanobuilding blocks for the construction of functionalized 1,3-alkylimidazolium iodide solid (melting temperature 150-200 °C) and room temperature (RT) ionic liquids.The structural characteristics of the synthesised final ionic liquids and the corresponding intermediates were determined using ¹H, ²⁹Si NMR and infrared spectroscopic measurements. Raman spectra were next reported, in order to demonstrate the presence of polyiodides formed after the addition of iodine and the formation of redox electrolytes. Ionic conductivity values obtained from the impedance (EIS) spectra were determined in the temperature interval from room temperature up to 100 °C. Finally, a hybrid electrochromic cell was constructed from room temperature MePrIm⁺I_x⁻ IO₇ T₈ POSS (x=1, 1.2, 3 and 5) ionic liquids encapsulated between a lithiated WO₃ working and Pt counter-electrode, and colouring-bleaching changes assessed for cells cycled up to 1000 repetitive cycles.     

Synthesis of porous flower-like Ni-Co-Mo-S nanostructures on Ni foam for battery-supercapacitor hybrid devices

The synergistic effects of multiple components and unique nanostructures were contributed to prepare the high-performance battery-type electrode materials. In this work, Mo element was introduced to form the ternary transition metal oxides/hydroxides of Ni-Co to improve conductivity, and then charge transfer was accelerated to enhance the capacity storage. After sulfidation, the electrical conductivity was further improved, and a porous flower-like nanostructure was formed. Except for that, the composites of transition metal oxides/hydroxides and sulfides were formed via sulfidation. With the help of the synergistic effects of multiple components and a porous flower-like nanostructure, more Faradic redox reactions occurred. Therefore, the as-prepared porous flower-like Ni-Co-Mo-S nanostructures on Ni foam exhibited an excellent areal capacitance of 7.22 C·cm⁻² at 5 mA·cm⁻² and long-cycle stability (96.9% retention after 5000 cycles). Furthermore, a coin-type battery-supercapacitor hybrid (BSH) device was assembled, which achieved 54.54 Wh·kg⁻¹ at 540 W·kg⁻¹ and displayed 74.8% capacitance retention after 3500 cycles. All mentioned above demonstrated that ternary transition metal oxides/hydroxides precursors via sulfidation can form special structures and the composites of transition metal oxides/hydroxides and sulfides to prepare high-performance battery-type electrodes for energy storage.     

A hybrid modelling approach to develop scenarios for China's carbon dioxide emissions to 2050

This paper describes a hybrid modelling approach to assess the future development of China's energy system, for both a “hypothetical counterfactual baseline” (HCB) scenario and low carbon (“abatement”) scenarios. The approach combines a technology-rich integrated assessment model (MESSAGE) of China's energy system with a set of sector-specific, bottom-up, energy demand models for the transport, buildings and industrial sectors developed by the Grantham Institute for Climate Change at Imperial College London. By exploring technology-specific solutions in all major sectors of the Chinese economy, we find that a combination of measures, underpinned by low-carbon power options based on a mix of renewables, nuclear and carbon capture and storage, would fundamentally transform the Chinese energy system, when combined with increasing electrification of demand-side sectors. Energy efficiency options in these demand sectors are also important.     

A cost-effective approach for optimal energy management of a hybrid CCHP microgrid with different hydrogen production considering load growth analysis

An optimum design and energy management of various distributed energy resources is investigated in a hybrid microgrid system with the examination of electrical, heating, and cooling demand. This paper suggested an optimal approach to design and operate a microgrid incorporating with battery energy storage, thermal energy storage, photovoltaic arrays, fuel cell, and boiler with minimization of the total operational cost of the hybrid microgrid. Two different hydrogen production methods are considered to assure the advantage of the developed proposed methodology. Furthermore, besides natural gas, residential and municipal wastes are collected and are utilized to produce electricity in fuel cell units. Load growth for different type of loads is also considered. The new number of households are added to the proposed system in different years and the proposed program is determined the optimum size of each employed resources to add each year for satisfying the total demand. To find out the optimum energy management and the optimum capacity of each employed distributed energy resources, a meta-heuristic Particle Swarm Optimization Algorithm is utilized. It is concluded from the results that by utilizing residential waste, the amount of natural gas consumption by fuel cells is reduced about 6.2%, and by utilizing residential plus municipal waste, the reduction is about 26.7%. It is also observed that the amount of CO₂ emission is reduced significantly (46.8%) in the case of utilization of produced heat by fuel cells. Finally, the results confirmed the efficacy of the suggested optimal energy management of the hybrid microgrid.     

Determination of loss coefficients for high-temperature flow devices: An entropy-based approach

Thermodynamic analysis of a high-temperature confined turbulent gas-jet is presented in this paper. The numerical model is two dimensional, steady, and includes the effect of gravity in the governing equations. Computations are carried out with a commercial CFD code and the local exergy losses are determined as post processed quantities. The analysis takes into account the second law effects of viscous dissipation, heat conduction and convection, and radiative heat transfer. The study is extended by conducting a parametric investigation to determine the effects of Reynolds number, inlet fluid temperature, optical thickness, and Planck number on the exergy loss coefficient, which is defined as the total exergy destroyed per unit mechanical energy input. The results show that exergy loss trough radiation entropy production is higher than that due to heat conduction and convection when the inlet gas temperature is high. It has also been found that in contrast to the conventional head loss coefficient, the exergy loss coefficient increases with inlet gas temperature, optical thickness, and Planck number.     

A novel approach for reactive power compensation in hybrid wind-battery system using distribution static compensator

This paper proposes a novel algorithmic approach to compensate the reactive power using distribution static compensator (DSTATCOM) for wind energy conversion system (WECS). Three phase bidirectional converter is utilized to exchange real and reactive power in both directions. The plug-in hybrid electric vehicle (PHEV) is enabled to consume during excess power availability. The battery is connected through a separate bidirectional DC-DC converter to adjust the power at the desired range. The compensated reference current is being generated based on the load requirement, wind power generations and state of charge (SOC) status. The proposed algorithmic approach helps to stabilize the grid by injecting accurate compensating current at the point of common coupling (PCC). Thereby, the proposed approach ensures the grid at balanced states under all operating cases. In order to validate the proposed approach, different case studies have been considered and validated through simulation results using PSCAD/EMDTC software.     

A biofuel supply chain equilibrium analysis with subsidy consideration

We consider a biofuel supply chain problem in which a farmer supplies two downstream refineries with nonidentical crops (corn and energy crop). The problem has been modeled as a multi leader single follower game to derive the farmer's decisions on land use as well as refineries' proposed prices to the farmer. We consider subsidizing the farmer and the refinery that uses the energy crop to study whether a subsidy plan can enhance the advanced biofuel production and meet the mandate of the Environmental Protection Agency (EPA). This mandate requires the production of 36 billion gallons of biofuel, out of which 21 billion gallons should be noncorn‐based biofuel. We solve the problem under four cases based on the willingness of the farmer to sell corn to the food market as well as the availability of land expansion for her. The Nash equilibrium is derived for all cases, and parametric analyses are used to study the effect of subsidies on the profit of the players and the total social welfare of the supply chain. We observe that a government's expenditure can be offset by the increase of the social welfare under certain circumstances. We find the minimum budget requirement to meet the EPA's mandate and show that a specific budget can be distributed in different ways while obtaining the same results.     

Solid hybrid polyelectrolyte with high performance in electrochromic devices: Electrochemical stability and optical study

This paper presents a high-stability, single-phase hybrid polyelectrolyte (SPHP) applied in a large EC device (5×10 cm²) using WO₃ (electrochromic) and CeO₂–TiO₂ (counter-electrode–ion storage) electrodes, both produced by Leibniz—Institut of New Materials (Leibniz—INM, Germany). The electrochromic device exhibited excellent color and bleach reversibility, high coloration efficiency (>35 cm²/C) from the first cycle up to more than 60,000 CA cycles, and a maximum constant rate of deintercalation/intercalation (O_out/Q_in=1). Its remarkable behavior and high stability render this material an excellent candidate for application in electrochromic devices.     

A consideration of possible receiver designs for solar tower plants

The 500-kW Solar Tower Plant in Almeria, Spain, will be provided with a sodium primary circuit. In the present paper detailed information is given on the basic investigations and on the design of the solar receiver of this circuit. Considerations concerning the optimum geometry as well as thermodynamic behaviour are described. Different design possibilities and the respective behaviour of the receiver with respect to short term transients due to cloud passage, heliostat field or mass flow failure, as well as with respect to optimum operational conditions are discussed. Special stress is placed upon a comparison between receivers with or without a large thermal mass.