Output Power Variation Research Articles

Application of Titanium Dioxide Self-Cleaning Coatings on Photovoltaic Modules for Soiling Related Losses Reduction

Several studies have assessed the influence of soiling deposition on Photovoltaic (PV) modules front-cover with regards to performance losses over time. In fact, soiling phenomena in PV systems are ascribed as responsible for medium and long-term yield reduction up to 16% over the first-year of outdoor exposure. Provided that PV technology is a low yield energy production source, maintaining module initial power output declared values is of the outmost importance to ensure that the return time of investment matches project calculations. The scope of this work was a detailed investigation on self-cleaning coating application as a viable retrofit option on already installed modules, or on newly built PV systems, to avoid soiling build-up on front-covers and guarantee threshold performance level in time. The aim is to provide system designers with a consistent alternative to manual cleaning, without losing effectiveness in terms of yield maintenance. The use of self-cleaning coating instead of acting on panels on a regular basis is more convenient in terms of operation and cost. These issues were analyzed through a set of experiments performed both on commercial size modules and laboratory assembled samples. Results prove product compatibility with PV components and its effectiveness in preventing soiling and dust deposition. Outcomes are presented in terms of maximum power output (Pmax) variation according to measurements performed in Standard Test Conditions (STC) at different time steps. In addition, a parallel comparison with uncoated modules exposed to the same outdoor conditions is also proposed to allow for Pmax variation monitoring performed on a reference sample.

Organic Rankine Cycle Based Geothermal Energy for Power Generation in Egypt

Low temperature geothermal resources are located in many areas and represent a high potential energy resource. One of the most common technologies, efficient and to exploit this type of resource is the binary cycle technology. Organic Rankine Cycle (ORC) is one of the main types of binary cycles. Electricity generation from low enthalpy geothermal energy using ORC is a talented technology. This paper addresses the design of binary cycle power plant utilizing one of the low temperature geothermal resource of temperature 92°C using four alternative working fluids: Butane, Isobutane, Pentane and 1,1,1,3,3-Pentafluoropropan (R245fa). Bir Nabi is the well under consideration which located in the Eastern desert, Egypt. Three operation parameters: geothermal temperature, reinjection temperature and geothermal flow rate are taken into consideration to analyze the performance of the power plant for different fluids. A performance analysis is conducted on ORC binary power plant using MATLAB programming to study the variation of output power and efficiency with the operation parameters. Also, the effect of these parameters on the area of ORC binary cycle power plant components; preheater, evaporator and condenser is presented. The geothermal resources temperatures are in the range of 90°C to130°C, the mass flow rate of the geothermal fluid ranges between 10 kg/s and 50 kg/s and reinjection temperature ranges from 30°C to 70°C. The results indicate that, the highest output power and plant efficiency are obtained with Pentane.

Multi-objective control of direct-driven wind power generation system with frequency separation

Variable-speed wind power generation system usually adopts maximum power point tracking (MPPT) below the rated wind speed or constant power control above the rated wind speed. However, single objective control has large dynamic loads on transmission systems. This paper presents a multi-objective control scheme for wind turbine in low wind speed, which achieves not only high power capture efficiency but also low fatigue load on mechanical parts. Input wind speed is separated into two components: a slowly varying seasonal component and a rapidly varying turbulent component. Correspondingly, the machine-side converter controller is divided into low frequency loop and high frequency loops. The low frequency loop implements MPPT control, the high frequency loop reduces the fluctuations of torque, and both loops together suppress the variations of output power. Simulation was conducted in Matlab/Simulink and FAST code was used to further verify the correctness of the multi-objective control strategy.

Performance Analysis of Flower Pollination Algorithm Optimized PID Controller for Wind-PV-SMES-BESS-Diesel Autonomous Hybrid Power System

Integration of the wind and solar power in an autonomous hybrid power system poses significant impacts on the system frequency affecting relay operation, consequence load disconnections, generation outage etc. leading to system collapse. An appropriate control strategy needs to be developed to maintain the system frequency within the permissible limit thus maintaining the stability of the power system. This paper presents a coordinated control strategy among the generating units in an autonomous hybrid power system comprising of wind turbine generator (WTG), the photovoltaic system (PV), diesel engine generator (DEG), battery energy storage system (BESS) and superconducting magnetic energy storage (SMES). Proportional-Integral (PI) and Proportional-Integral-Derivative (PID) are employed with DEG, BESS, and SMES so as to adjust the output power in response to the change in loading and or output power variation of renewable sources. The parameters of the controllers are optimized using Flower Pollination Algorithm (FPA). The system dynamic responses obtained the PI and PID controllers are compared. Simulation results revealed that FPA optimized PID controller outperform PI controller. Further, to check the robustness of the controllers, sensitivity analysis has been carried out.

Effects of high intensity unltrasound on structural and physicochemical properties of myosin from silver carp

Myosin from silver carp was sonicated with varying power output (100, 150, 200 and 250W) for 3, 6, 9, and 12min. The changes in the structure and physicochemical properties of myosin were evaluated by dynamic light scattering, SDS-PAGE and some physicochemical indexes. The ultrasound treatments induced a significant conversion of myosin aggregates to smaller ones with a more uniform distribution, and obvious enhancement in solubility. The structure of myosin was also notably changed by sonication, with a decrease in Ca2+-ATPase activity and SH content, and an increase in surface hydrophobicity. Furthermore, SH groups were oxidized, leading to a decrease in reactive SH and total SH contents. SDS-PAGE analysis revealed that ultrasound could induce the degradation of myosin heavy chain and change the protein fraction of myosin. Collectively, the ultrasonic treatment of 100W for 3min showed slight influence on the SH content, S0-ANS, and electrophoretic patterns, and the extent of changes in myosin structure and physicochemical properties tended to increase with ultrasonic power and time. The integrated data indicate that ultrasonic treatment can facilitate the improvement of the solubility and dispersion of myosin, but the choice of a suitable ultrasonic condition to avoid oxidation and degradation of myosin is very important.

Measurement of unsteady loading and power output variability in a micro wind farm model in a wind tunnel

Unsteady loading and spatiotemporal characteristics of power output are measured in a wind tunnel experiment of a microscale wind farm model with 100 porous disk models. The model wind farm is placed in a scaled turbulent boundary layer, and six different layouts, varied from aligned to staggered, are considered. The measurements are done by making use of a specially designed small-scale porous disk model, instrumented with strain gages. The frequency response of the measurements goes up to the natural frequency of the model, which corresponds to a reduced frequency of 0.6 when normalized by the diameter and the mean hub height velocity. The equivalent range of timescales, scaled to field-scale values, is 15 s and longer. The accuracy and limitations of the acquisition technique are documented and verified with hot-wire measurements. The spatiotemporal measurement capabilities of the experimental setup are used to study the cross-correlation in the power output of various porous disk models of wind turbines. A significant correlation is confirmed between streamwise aligned models, while staggered models show an anti-correlation.

Impact of Renewable Based Microgrid Supply/Demand Profiles on Low Voltage Distribution Networks

Abstract Integration of distributed generation (DG) from renewables into power systems has been one of the major challenges for operators. Impact of bidirectional power flow on the bus voltages and on the power losses is more severe in low voltage networks, due to high R/X ratio of the lines. Operators generally evaluate capacity additions considering the extreme cases. However, extreme cases occur rarely in a long-term operation or their impact is generally less than expected. This study presents daily operation analysis of a low voltage network including a renewable supported microgrid. Using a field-data based virtual test bed, daily variations in DG output power, residential demand and network voltages are simulated. The analysis reveals the occurrence rate of extreme cases in daily operation and changes in the line losses of low voltage networks with microgrids.

Assessing the European offshore wind and wave energy resource for combined exploitation

The main concern when utilizing renewable energy resources is their intermittency and variability. One way to deal with this shortcoming is to harvest energy from complementary sources. In this study, wind and wave energy were selected as such and further analyzed in terms of availability, variability, coherence, correlation and potential impact from extreme values. This resource characterization was performed in different timescales, during a 10-year period, using high resolution numerical modeling systems. Based on the results of this analysis, the most suitable areas for combined exploitation were identified and the possible merits from this synergy were pin-pointed and discussed. It was indicated that the most suitable areas for combined use are the western offshore areas of Europe. The wind and wave fields in these open sea areas reveal the lowest correlation in the examined field in contrast to those located in semi-enclosed and enclosed basins that exhibit the highest ones. The joint exploitation in the former regions gives a less variable power output with considerable fewer hours of zero production. Moreover, the suitable energy conversion system for a specific area is strongly dependent on the local characteristics of the available resource.

The collocation feasibility index – A method for selecting sites for co-located wave and wind farms

Marine energy is one of the most promising solutions to attempt the ambitious renewable energy target of 20% by 2020 due to its very substantial energy resource. However, it is often considered uneconomical and difficult, and this may hinder its development. Combined energy systems, such as co-located offshore wind turbines and wave energy converters, have recently emerged as a solution to increase the competitiveness of marine energy by taking advantage of the synergies between renewables; which would lead to reductions in the energy cost and improvements in the power output variability and security. On this basis, finding viable locations for combined offshore renewable energies is fundamental to boosting their development. The objective of this paper is to determine suitable locations for deploying a co-located wind and wave energy farm in the North Sea - an area with several characteristics that make large-scale integration of renewable energy sources attractive. In this assessment we investigate not only the existing resource but also other parameters such as its variability and the correlation between waves and winds by means of the CLF index. In addition, inter- and intra-national user conflicts are considered, while balancing environmental conservation and economic development.

Optimization of SMES-FCL for Augmenting FRT Performance and Smoothing Output Power of Grid-Connected DFIG Wind Turbine

Fault-ride-through (FRT) performance and output power variation are crucial issues of the grid-connected wind turbine with the doubly fed induction generator (DFIG). To overcome these problems, the optimal parameters tuning of the superconducting magnetic energy storage and the fault-current limiter (SMES-FCL) with the common part of the superconducting coil (SC) is proposed. In addition to the alleviation of the DFIG output power, the SC behaves as the short-circuit current limiter to enhance the FRT capability. The tuning of the SC inductance and the controller parameters of converters is optimally conducted, so that the DFIG terminal voltage deviation and the power fluctuation during faults are at their minimum. By simulation study, the utilized power and energy of the SC for the grid stabilization are curtailed, whereas the dynamic performance of the SMES-FCL is higher than a single SMES unit.

Performance and dynamic characteristics of a multi stages vertical axis wind turbine

Vertical axis wind turbines (VAWTs) are used to convert wind energy to mechanical output or electricity. Vertical axis wind turbines are favorable at buildings as it can receive wind from any direction, have a design that can be integrated simply with building architecture and they have better response in turbulent wind flow which is common in urban areas. Using a calculation code based on the Double Multiple Stream Tube theory, symmetrical straight-bladed NACA0012 wind turbine performance was evaluated. The induction factor for both upwind and downwind zone is determined with the aid of a root-finding algorithm. This numerical analysis highlighted how turbine performance is strongly influenced by the wind speed (Reynolds number) and rotor solidity (turbine radius and blade chord length). Also a dimensional analysis is introduced and is to be considered in such a way to generalize the design for different turbine specifications. One of the qualities provided by dimensional analysis is that geometrically similar turbines will produce the same non-dimensional results. This allows one to make comparison between different sizes wind turbines in terms of power output and other related variables. One of the main problems affecting the turbine performance and dynamics is the torque ripple phenomena. So in this paper a turbine design configuration is introduced in order to decrease the turbine torque fluctuation. This design is carried out by constructing more similar turbine units (stages) on the vertical axis on top of each other with different orientation phase angles. The results showed that using even number of turbine assembly is better than odd number to avoid torque fluctuation and mechanical vibrations acting on the turbine. Also it is preferred to use four turbine stages as the eight stages will have no sensible effect on decreasing the torque fluctuation.

Probabilistic evaluation of available load supply capability of distribution networks as an index for wind turbines allocation

This study deals with placement of wind turbines in distribution networks for maximising the probabilistic index of load supply capability (LSC). To calculate this index, one of the most accurate and efficient probabilistic simulation methods known as Latin hypercube sampling is used. Variations of load and output power of wind turbines are considered in the probabilistic evaluation of LSC. Moreover, the constraints of maximum voltage drop and current carrying capacity of conductors are considered as the limiting factors of the network LSC. Since there is a correlation between the network load and the output power of wind turbines, considering this correlation in simulations will push the results closer to reality. Therefore, the Cholesky decomposition approach is used to take into account the correlation between the input variables of the problem. Casestudiesare carried out on the 33-bus IEEE distribution network. The results of case studies demonstrate the effectiveness of the proposed methodology.

The study of temperature effect on the performance characteristics of the InGaN-based vertical cavity surface emitting laser (VCSEL) by solving the rate equations

The use of semiconductor lasers is beneficial in long-distance communications. Practical communication systems based on these lasers need high ambient temperature, with temperature changes between [Formula: see text]C and [Formula: see text]C. The study of the temperature-dependent response of these lasers is important to improve them. This study investigates the effect of temperature on InGaN-based vertical cavity surface emitting lasers (VCSEL). The active region in this structure includes a single quantum well (SQW). The rate equations of carriers and densities are numerically solved. The time variations of carrier density, photon density and output power ([Formula: see text], [Formula: see text] and [Formula: see text]) at [Formula: see text]C and the current injection of 0.04 A are obtained. Values obtained for threshold current and output power include 7 mA and 44 mW, respectively. The effect of temperature on the time variations of [Formula: see text], [Formula: see text] and [Formula: see text] from [Formula: see text]C to [Formula: see text]C is studied. Results show that these parameters decrease and the threshold current increases with an increase in temperature. Furthermore, the investigation of the effect of injection current on [Formula: see text], [Formula: see text] and [Formula: see text] shows that raising the injection current can increase these parameters. Moreover, an increase in the injection current reduces the time response.

Analysis of a Switched-Capacitor Converter Above its Resonant Frequency to Overcome Voltage Regulation Issue of Resonant SCCs

A resonant switched-capacitor converter (SCC) has been analyzed above its resonant frequency to realize zero-voltage switching (ZVS) and to overcome voltage regulation issue of SCCs even when wide input voltage and output power variations are applied. ZVS operation under the continuous conduction mode (CCM) conditions improves efficiency due to lower conduction and switching losses. It is more efficient than the widely used zero-current switching (ZCS) approach in recent years under the discontinuous conduction mode (DCM) condition. Because, switching losses dominant components are reduced in MOSFET-based converters under the ZVS not ZCS conditions. Also, it has been demonstrated that output voltage can be well regulated under the CCM operation when wide input voltage and load variations are used. When output voltage regulation is not the major issue, operating at fixed switching frequency higher than, but near to, the resonant frequency results smaller components, higher power density, and lower electromagnetic interference level, as compared to the constant voltage ratio DCM operation mode, widely used in recent years. Also, output voltage ripple has been calculated, in details, by considering parasitic components of the output capacitor. A 110–165 to 200 V SCC has been implemented in 206.6–402.5 kHz frequency range to deliver 100–500 W. Maximum and average efficiency values equal to 96.8% and 94% are achieved, respectively.

Dynamic Gain-Tuning Control (DGTC) Approach for AGC With Effects of Wind Power

Variable wind power output introduces new challenges to power system frequency regulation and control, such as automatic generation control (AGC) which is very important to regulate power system frequency. The existing methods to design control gains for proportional-integral (PI) controllers in AGC are either time consuming or easily affected by the designer's experience. Further, the control gains are usually designed with fixed values for specific scenarios in the studied power system. The desired response may not be achieved when variable wind power is integrated into power systems. To address these challenges, a dynamic gain tuning control (DGTC) method for AGC is proposed in this paper. By the proposed control method, PI control gains can be dynamically adjusted to reach the desired performance. The proposed method is tested in a modified IEEE 39 bus system with actual wind data, and compared with conventional control approach with well-tuned fixed gains in the simulation. The simulation results show that the proposed control method provides better AGC response with less deviation of system frequency and tie-line flow under variable wind power.

Short-term forecasting of solar photovoltaic output power for tropical climate using ground-based measurement data

This paper highlights a new approach using high-quality ground measured data to forecast the hourly power output values for grid-connected photovoltaic (PV) systems located in the tropics. A case study using the 1-year database consisting of PV power output, global irradiance, module temperature, and other relevant variables obtained from Universiti Teknikal Malaysia Melaka is used to develop forecast models for three typical weather conditions—clear, cloudy, and overcast sky conditions. A machine learning method (Support Vector Regression—SVR) and an Artificial Neural Network method (nonlinear autoregressive) are used to produce the models and the results are compared with a benchmark model using the persistence method. Comparison with all the variables suggests that tilted global horizontal irradiance (GHItilt) and module temperature (Tmod) are the essential input variables to forecast the PV power output. It has also been observed that SVR performs well across all types of sky conditions, with the forecasting skill values between 0.65 and 0.79 when compared to the benchmark persistence method.

Economic research of the transcritical Rankine cycle systems to recover waste heat from the marine medium-speed diesel engine

The aim of this study is to investigate the economic performance of a transcritical Rankine cycle (TRC) system for recovering waste heat from the exhaust gas of a marine medium-speed diesel engine. The variation of net power output, total cost of equipments and exergy destruction are investigated for the TRC system. Furthermore, to evaluate the economic performance of energy utilization, a parameter, net power output index, which is the ratio of net power output to the total cost, is introduced of the TRC system using R125, R143a, R218 and R1234yf as working fluids. The results show that R1234yf performs the highest economic performance, followed by R143a, R125 and R218 of the TRC system. It reveals that R1234yf not only has the smallest high and low pressures of the TRC system for reducing the purchased cost of equipments, but also promotes a larger pressure ratio of the expander for generating power output among these working fluids. The comparisons of optimal pressure ratios obtained from thermodynamic and economic optimizations for these working fluids in the TRC system are also reported. In addition, an evaluation method using thermal efficiency and operating pressure ratio as parameters is proposed to assess the suitability of the working fluids of TRC system in economic analysis for waste heat recovery from the exhaust gas of a diesel engine.

The Effects of Cold Environments on Double-Poling Performance and Economy in Male Cross-Country Skiers Wearing a Standard Racing Suit.

To investigate differences in double-poling (DP) endurance performance, economy, and peak oxygen uptake (V̇O2peak) at low (-15°C) and moderate (6°C) ambient temperatures (TA) in cross-country skiers wearing standard racing suits. Thirteen well-trained male cross-country skiers performed a standardized warm-up followed by a 5-min submaximal test (Sub1), a 20-min self-paced performance test, a 2nd 5-min submaximal test (Sub2), and an incremental test to exhaustion while DP on an ergometer at either low or moderate TA, randomized on 2 different days. Skin and rectal temperatures, as well as power output and respiratory variables, were measured continuously during all tests. Skin and rectal temperatures were more reduced at low TA than moderate TA (both P < .05). There was a 5% (P < .05) lower average power output during the 20-min performance test at low TA than at moderate TA, which primarily occurred in the first 8 min of the test (P < .05). Although DP economy decreased from Sub1 to Sub2 for both TAs (both P < .01), a 3.7% (P < .01) larger decrease in DP economy from Sub1 to Sub2 emerged for the low TA. Across the sample, V̇O2peak was independent of TA. These results demonstrate a lower body temperature and reduced performance for cross-country skiers when DP at low than at moderate TA while wearing standard cross-country-skiing racing suits. Lower DP performance at the low TA was mainly due to lower power production during the first part of the test and coincided with reduced DP economy.

A Conservation Voltage Reduction Scheme for a Distribution Systems with Intermittent Distributed Generators

In this paper, a conservation voltage reduction (CVR) scheme is proposed for a distribution system with intermittent distributed generators (DGs), such as photovoltaics and wind turbines. The CVR is a scheme designed to reduce energy consumption by lowering the voltages supplied to customers. Therefore, an unexpected under-voltage violation can occur due to the variation of active power output from the intermittent DGs. In order to prevent the under-voltage violation and improve the CVR effect, a new reactive power controller which complies with the IEEE Std. 1547TM, and a parameter determination method for the controller are proposed. In addition, an optimal power flow (OPF) problem to determine references for the resources of CVR is formulated with consideration of the intermittent DGs. The proposed method is validated using a modified IEEE 123-node test feeder. With the proposed method, the voltages of the test system are maintained to be greater than the lower bound, even though the active power outputs of the DGs are varied. Moreover, the CVR effect is improved compared to that used with the conventional reactive power control methods.

The benefits of flexibility: The value of wind energy with hydropower

Several studies have shown that the revenue of wind power generators on spot markets (“market value”) diminishes with increasing deployment. This “value drop” is mostly observed in power markets that are dominated by thermal power plants, such as in Germany. This paper assesses the wind market value in power systems where hydroelectric stations with large reservoirs prevail, such as in Sweden. Due to their dispatch flexibility, such hydropower compensates for wind power output variability and thereby mitigates the wind power value drop. The market value of electricity from wind declines with penetration in both types of power systems, but it tends to decline at a slower rate if hydropower is present. This paper presents empirical evidence on the relevance of this effect derived from market data and numerical model results. Our results indicate that when moving from 0% to 30% wind penetration, hydropower mitigates the value drop by a third. As a result, 1 MWh of wind energy is worth 18% more in Sweden than in Germany. Sensitivity analyses indicate high robustness despite large parameter uncertainty: in 80% of all sensitivities, wind energy is valuable 12–29% more in Sweden than in Germany. The benefits of hydropower seem to level off at around 20% wind penetration. This suggests that the hydro flexibility is “exhausted” at this level. Low wind speed wind turbines, carbon pricing, and upgrades of hydropower generation capacity can lever the added value of hydro flexibility further. Not only is wind energy more valuable in the presence of hydropower, hydroelectricity also becomes more valuable if paired with wind power.