Series-parallel Configuration Research Articles

Graphic Transfer Matrix Method for Kinetostatic and Dynamic Analyses of Compliant Mechanisms

Abstract Kinetostatic and dynamic analyses of compliant mechanisms with complex configurations continue to be an attractive issue for obtaining a process-concise and result-accurate solution. In this paper, the transfer matrix method (TMM) is improved for a unified linear kinetostatics and dynamic modeling of compliant mechanisms with complex serial-parallel configurations in an oriented graphic way. In detail, the transfer matrices of typical building blocks commonly used in compliant mechanisms are summarized and derived. Then, a graphic transfer matrix modeling procedure capturing both the kinetostatics and dynamics of general compliant mechanisms is introduced. The displacement amplification ratio, input/output stiffness, parasitic error, natural frequencies, and frequency response of a typical compliant microgripper and a planar parallel three-degrees-of-freedom (3DOF) nanopositioner are calculated with such a graphic transfer matrix method. The advantages of the proposed modeling method lie in its convenience and uniformity in formulating both the kinetostatic and dynamic behaviors of a class of compliant mechanisms with distributed and lumped compliances in a transfer matrix manner, which has minimal DOF and is easily programmed.

An analysis on comprehensive influences of thermoelectric power generation based on waste heat recovery

The thermoelectric characteristics of the thermoelectric power generation based on waste heat recovery, including the influence factors of cooling water flow rate, the overlapping value between load resistance and internal resistance and pressing block weight, were experimentally discussed. In addition to the experimental analyses of simple series-parallel configuration, the thermoelectric characteristics of complex series-parallel configurations were numerically simulated. The fast locating method was proposed to achieve the optimal thermoelectric characteristic. The results showed that the cooling water flow rate makes slight impact on total pressing block weight. All the thermoelectric characteristics increase with increasing pressing block weight. The overlapping value between internal resistance and load resistance is an core index, which determines the optimum thermoelectric efficiency. The changing law of thermoelectric characteristics of numerical simulations are identical with testing data, but the smoothness of simulation curves are better. Three complex series-parallel configurations perform identical total output power characteristic, which increases with increasing thermoelectric modules. However, the output power of a single thermoelectric module exhibits unique characteristic. The inflection points and peak value points in DSIP, ISDP and ISIP configurations are used to examine the output power characteristics of thermoelectric power generation and a single thermoelectric module.

Novel cell balancing applied near-field coupling and Serial–Parallel Circuit configuration

This paper proposes a near-field cell balancing method to be applied to batteries of higher capacity and power. This method involves a wireless power transfer to balance battery cells, which produces higher efficiency than conventional passive approaches, and faster equalization than active approaches. Cell balancing is a crucial function of the battery management system (BMS) that maintains the balance of charge and discharge between cells of individual batteries. Furthermore, this method is designed to meet the increasing demand for faster cell balancing associated with high-capacity and high-power batteries. We selected a serial–parallel configuration to minimize the technical concern for isolation, or energy transfer to unselected cells. Experiments were conducted with two battery cells, and voltage equalization accelerated by 51% when the proposed cell balancing approach was applied.

Impact of Individual Cell Parameter Difference on the Performance of Series-Parallel Battery Packs.

Lithium-ion power batteries are used in groups of series-parallel configurations. There are Ohmic resistance discrepancies, capacity disparities, and polarization differences between individual cells during discharge, preventing a single cell from reaching the lower limit of the terminal voltage simultaneously, resulting in low capacity and energy utilization. The effect of the parameter difference (difference in parameters) of individual cells on the performance of the series-parallel battery pack is simulated and analyzed by grouping cells with different parameters. The findings reveal that when cells are connected in series, the capacity difference is a significant factor impacting the battery pack's energy index, and the capacity difference and Ohmic resistance difference are significant variables affecting the battery pack's power index. When cells are connected in parallel, the difference in Ohmic internal resistance between them causes branch current imbalance, low energy utilization in some individual cells, and a sharp expansion of unbalanced current at the end of discharge, which is prone to overdischarge and shortens battery life. Interestingly, we found that when there is an aging cell in a series-parallel battery pack, the terminal voltage of the single battery module containing the aging single cell will decrease sharply at the end of discharge. Evaluating the change rate of battery module terminal voltage at the end of discharge can be used as a method to evaluate the aging degree of the battery module. The research results provide a reference for connecting batteries to battery packs, particularly the screening of retired power battery packs and the way to reconnect into battery packs.

Geothermal trigeneration systems with Organic Rankine Cycles: Evaluation of different plant configurations considering part load behaviour

Due to the increasing importance of cooling applications, geothermal trigeneration systems might be of high interest in the future. This work aims at evaluating different plant layouts against the background of more advanced plant configurations and part load behaviour. Five different plant configurations are analysed for geothermal heat source temperatures between 110 and 150 °C. The highest net power output is achieved by an advanced serial-parallel configuration (ASPC), but in case of high heating and cooling demand, a standard serial-parallel configuration is more favourable. For the considered base demand scenario of 130 °C, the ASPC results in an annual net power generation of 20.94 GWh, which is 6.9% higher than the second favourable configuration. The application of a recuperator within the ORC system has a significant impact on the serial concepts, but only marginally increases the power output of the parallel layouts. Comparing two exergetic efficiencies highlights that the assumed definition can result in a different ranking of the plant layouts. Considering the exergy that is transferred from the brine to the trigeneration system reveals the highest exergetic efficiency for a serial configuration, while the focus on the available exergy flow reveals the highest efficiency for the ASPC layout. Considering a brine temperature of 130 °C results in a maximal achievable second law efficiency of 34.1% if evaluating the available exergy flow. The evaluation of the pay-back period reveals that the ASPC results in the shortest pay-back period of 13.8 years.

Generalized modelling of PV module and different PV array configurations under partial shading condition

This paper proposes generalized modelling of photovoltaic(PV) module and different PV array configurations - (i) conventional configurations: Series, Parallel, Series-Parallel, Total-Cross-Tied, Bridge-Linked, Honey-Comb and (ii) hybrid configurations: SeriesParallel-TotalCrossTied, BridgeLinked-TotalCrossTied, HoneyComb-TotalCrossTied, BridgeLinked-HoneyComb under partialshadingcondition. The projected modelling is fully efficient in determining the detailed output graphs of PV module and different PV array configurations of whichever rating, synthesized of any class of PV cell or module, and for every probable real-time partially shaded situation. The presented modelling can accomplish this objective by merely exploiting the information given in the catalogue released by manufacturers. The results obtained by the execution of MATLAB codes of the proposed equations for the module and the aforesaid array configurations under uniformirradiancecondition and partialshadingcondition in presence and absence of bypass diodes have been investigated on the basis of their maximumpower, fill-factor, thermalvoltage, and relativepowerloss and authenticated by MATLAB simulation. The proposed modelling has also been practically verified on the ZONHAN PV module and array made of four WS-330 PV modules.

Impact of environmental factors on night-time electricity generation using thermoelectric generator

Nighttime electricity generation (NTEG) using thermoelectric generators (TEGs) and radiative cooling concept is a widely known phenomenon. However, the NTEGs are challenged by low voltage generation. The factors influencing the performance of the NTEGs comprise environmental conditions, such as ambient temperature, wind velocity and relative humidity. However, the effect of these parameters has not been explored. Therefore, the present study aims to experimentally investigate the influence of these variables on the generated power resulting from the temperature difference created between different entities of the NTEG setup by using an in-house designed facility. The experimental setup consisted of multiple TEGs sandwiched between a radiative plate at the top and an aluminium block attached to a hot plate at the bottom. The tests were performed on various nights to analyse the effect of these parameters. The night with a higher ambient temperature triggered higher temperature difference between the top and bottom surface of the TEGs, resulting in the higher voltage production. Moreover, the same trend was observed for the wind velocity. By contrast, the largest temperature gap between an emitter plate and the surrounding air was recorded on a night with the lowest relative humidity, thereby providing a higher voltage. Furthermore, with various series, parallel and series–parallel configurations, we finally found a combination of commercially available TEGs for NTEG, which can be effectively used for lighting up a three-watt bulb.

Flower pollination global peak search algorithm for partially shaded solar photovoltaic system

Photovoltaic (PV) systems are required to function at their maximum power point (MPP) to fully utilize solar energy. Solar PV panels are configured with maximum power point tracking (MPPT) systems to enhance the generation and supply of the maximum available power. However, owing to external environmental factors and partial shading conditions (PSCs), the tracking process becomes complex. Conventional MPPT methods cannot always achieve the global MPP. Thus, an advanced metaheuristic MPPT scheme for PV systems, the flower pollination algorithm (FPA), is implemented in this study to find the best global duty cycle to obtain the maximum power output, and a Levy flight is utilized to enhance FPA convergence. The FPA MPPT model was established, and its performance was compared with the conventional, and some meta-heuristic-based MPPT techniques; perturb and observe (PO), incremental conductance (INC), particle swarm optimization (PSO), cuckoo search (CS), grey wolf optimization (GWO), genetic algorithm (GA), double integral sliding mode control (DISMC), and hill-climbing (HC). Different scenarios were considered for the simulation: partial shading, complex partial shading, long-width, and long-length partial shading, and different temperature conditions employing series and series-parallel PV array configurations. In addition, real-world field atmospheric irradiance data for Daejeon city is used for the study. In terms of efficiency, the FPA attains at most 83%–96% of the expected GMP from the PV array as compared with the other MPPT techniques in all scenarios considered. The adopted FPA obtained the following root mean square error (RMSE), mean relative error (MRE), and mean absolute error (MAE) values respectively for each Scenario as follows: Scenario I: RMSE: 0.0061, MRE: 0.0463, MAE: 6.0745e-06, Scenario II: RMSE: 0.0116, MRE: 0.0430, MAE: 1.0738e-05, Scenario III: RMSE: 0.0640, MRE: 0.206, MAE: 4.8239e-05, Scenario IV (varying temperature conditions): RMSE: 0.0062–0.0074, MRE: 0.0460–0.0548, MAE: 6.1333e-06 – 7.4922e-06. A unique sensitivity performance comparison analysis is done employing the power spectral analysis to validate the effectiveness of the adopted FPA to the other MPPT techniques. The FPA performs better than all the techniques in all scenarios in comparing their maximum power tracked, convergence speed and accuracy, system efficiency, and optimum statistical results attained.

Elektrikli Araçlarda Kullanılan Paralel ve Seri Kanallı Soğutma Plakalarının Performanslarının HAD Yöntemi ile Karşılaştırılması

In a cold plate low thermal resistance thus high heat transfer rate and also low pressure drop is desired. In this study, performances of three liquid cold plates with different configurations are investigated for the thermal regulation of li-ion battery cells in electric vehicle applications. The outer dimensions of the cold plates are kept identical in order to use the cold plates in the same battery module under series, parallel and series-parallel configurations. The performances of the cold plates are investigated by using Computational Fluid Dynamic (CFD) tools. ANSYS Fluent commercial software is used to calculate the flowfield and the thermal field inside the cold plates for various flowrates. The performances of the cold plates are obtained by 3D simulations that solve Navier-Stokes, energy and continuity equations in a steady manner. The flow is assumed to be laminar for all the cases since calculated Reynolds number stay in laminar flow limits. The results show that the pressure drop of the coolant liquid of parallel flow arrangement is significantly lower than the serial arrangement. However, high thermal resistance and low uniformity of the temperature through the cold plate is observed compared to the serial case, as expected. As a result, series-parallel configuration results show that the trade-off between pressure drop and heat transfer rate can be optimized by applying a serpentine shape while keeping the flow arrangement as parallel as possible and increasing the length of the cross channels.

Modified transfer matrix method for vibration analysis of beam structures including branches and rigid bodies

Beam frames can be found in many application scenarios, ranging from big-scale structure engineering of buildings, bridges to small systems of micromachines, sensors, robotics and metamaterials. However, several challenging issues, e.g. serial-parallel configurations, beam and rigid body coupling along with inconsistent dimension of state variables, often lead to a complicated dynamic modeling. In this paper, we show that the free vibration analysis of a class of beam structures with serial-parallel branches and rigid bodies can be significantly streamlined by modifying the transfer matrix method in a graphic manner. Treating general beam structures as a topological graph with standard building blocks enables a modular modeling process and hence offers a new way to divide the complex modeling issue into much easier steps. The transfer matrix of typical building blocks, such as a beam connected to rigid bodies, tree branches and parallel clamped sub-chains, are derived and standardized providing new perspectives and distinct forms in contrast to previous studies. The transfer matrix method exhibits several advantages of easy programming, accurate solution and small degrees-of-freedom for serial structures. The presented approach extends these characteristics to a range of multi-body systems consisting of rigid bodies and beams. Comparative validation with four application case studies confirms these advantages.

(Invited) Beyond Single Cell Characterization: Impacts of Module Configuration on Lithium-Ion Battery Performance and Degradation

Batteries are commonly connected in series and parallel to form modules that meet the power and energy requirements of specific applications. However, conclusions about battery performance and degradation under different conditions are often based on single cell cycling results. In this study, we evaluate the performance of lithium-ion eight-cell modules in six different series-parallel configurations over the course of hundreds of cycles. Each cell was individually instrumented for voltage, current, and temperature monitoring. Current data were collected using closed-loop Hall effect sensors to provide accurate measurements of parallel branch currents without the influence of in-circuit shunt sensing elements. This cell-level data collection enabled calculation of the underutilization of individual cells and assessment of differences in energy lost to cell balancing for different configurations. We also evaluated current redistribution in parallel cells, which in some cases yielded transients with peak magnitudes more than twice the average expected cell current value. The capacity and energy fade of the full modules was compared to that of individual cells cycled under the same conditions. This module cycling study, one of the broadest reported to date, allows us to systematically evaluate the performance trade-offs and safety implications of different module configurations.Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2022-5209 A

Power Flow Optimization for a Hybrid-Electric Propulsion System

Abstract This study deals with the optimization of performance for a hybrid-electric propulsion system. It focuses on the modeling and power management frameworks, while evaluation is done on a single flight basis. The main objective is to extract the maximum out of the novel powertrain archetype. Two hybridization factors are considered. The pair helps to describe the degree of hybridization at the power supply and power consumption levels. Their revised mathematical definition facilitates a unique method of hybrid-electric propulsion system modeling that maximizes the conveyed amount of information. An in-house computational tool is developed. It employs a genetic algorithm optimizer in the interest of managing power usage during flight. Energy consumption is set as the objective function. The operation of a 19-seater, commuter aircraft is investigated. Turbo-electric, series-hybrid, parallel-hybrid, and series-parallel variants are derived from a generic composition. An analysis on their optimized performance, with different technological readiness levels for 2020 and 2035, is aimed at identifying where each system performs best. Considering 2020 technology, it does not yield a viable hybrid-electric configuration, without suffering significant payload penalties. Architectures relying on mechanical propulsors show promise of 15% reduction to energy consumption, accounting for 2035 readiness levels. The concepts of Boundary Layer Ingestion and Distributed Propulsion display the potential to boost electrified propulsion. The series-hybrid and series-parallel configurations are the primary beneficiaries of these concepts, displaying up to 30% reduction in fuel and 20% reduction in energy consumption.

Impact of Air Mass on PV modules Power Generation in Eastern Indian Climatic Zone

The PV technology has matured to the gigawatt (GW) level of power generation. Thus, many PV modules are connected in a series-parallel configuration to configure a GW level PV array. Now the vital question of the reliability of such a PV system depends mainly on the performance of the constituent modules (setting aside the reliability consideration arising from the BOS component). Therefore, different climatic parameters directly impact the power output of PV modules. In this research paper, the authors have tried to find out the impacts of climatological parameters like air mass (AM) on the power output as well as the overall performances of different technology PV modules. Mainly crystalline (mono-Si), amorphous silicon (a-Si), and poly-Si photovoltaic (PV) modules are examined thoroughly for different times of three seasons during the year in the eastern Indian climatic zone. Now, for determining the reliability of any PV array or module, mainly the important parameters considered are regression analysis, Fill Factor variation with changing solar irradiation and temperature. After that, the performance ratio and Fill Factor parameters will be evaluated thoroughly under different climatic conditions. Finally, after the exhaustive evaluations of other reliable PV parameters like FF and PR under naturally outdoor conditions, it is established that the poly-Si module shows the best performance in the Eastern Indian climatic zone with varying AM.

Equivalent Dynamic Analysis of a Cable-Driven Snake Arm Maintainer

In this paper, we investigate a design method for a cable-driven snake arm maintainer (SAM) and its dynamics modelling. A SAM can provide redundant degrees of freedom and high structural stiffness, as well as high load capacity and a simplified structure ideal for various narrow and extreme working environments, such as nuclear power plants. However, their serial-parallel configuration and cable drive system make the dynamics of a SAM strongly coupled, which is not conducive to accurate control. In this paper, we propose an equivalent dynamics modelling method for the strongly coupled dynamic characteristics of each joint cable. The cable traction dynamics are forcibly decoupled using force analysis and joint torque equivalent transformation. Then, the forcibly equivalent dynamic model is obtained based on traditional series robot dynamic modelling methods (Lagrangian method, etc.). To verify the correctness of the equivalent dynamics, a simple model-based controller is established. In addition, a SAM prototype is produced to collect joint angles and cable forces at different trajectories. Finally, the results of the equivalent dynamics control simulation and the prototype tests demonstrate the validity of the SAM structural design and the equivalent dynamics model.

Monitoring State-of-Charge of Lithium-Ion Battery with Diverse Series-Parallel Configuration Using Particle Filter

Lithium-ion battery packs are typically assembled into modules. These modules can be equipped with various series-parallel configurations. In this work a feasible method for monitoring SoC is demonstrated by designing a circuit model in Simulink of three different configurations 3s2p (three in series and two in parallel), 3s3p (three in series and three in parallel), and 4s2p (four in series and two in parallel) using Particle Filter. Initially, lithium-ion cells are connected in 3s2p configuration and then we compared our results by adding one cells in parallel and then in series with the estimated SoC of 3s2p configuration, a complex current pattern is used in simulation to verify PF's performance. As lithium-ion batteries have a great importance and are widely used in electrical vehicles because of their power efficiency, high charging rate, and more lifetime, proper monitoring of SoC plays a vital role in BMS.

Redundancy allocation problem of a Multi-State system with Binary-State continuous performance level components

This paper presents a new single-objective redundancy allocation problem (RAP) for a system with subsystems in a series–parallel configuration. Different types of binary-state components are available for each subsystem, without the choice of component mixing, but the allocated components must be identical. Moreover, the components have a continuous performance level, i.e., their performance level is between zero and their maximum performance level. The presented model aims to maximize the system’s availability by determining the optimum number and type of the allocated components to each subsystem in some constraints, such as the system’s cost and weight. Since the components have continuous performance levels, the performance levels of the subsystems and the system are also continuous. First, the real-time and instantaneous availability of components, subsystems, and systems is modeled and calculated by adopting a modified universal generating function. Then, the mathematical model for the above-mentioned RAP is presented and solved using a Genetic Algorithm (GA), a Particle Swarm Optimization (PSO), and a Teaching-Learning-Based Optimization (TLBO) meta-heuristics. Next, a full enumeration technique is used to validate the performance of the adopted meta-heuristics as well as to validate the presented mathematical model. The results show the superiority of the adopted GA to solve the presented RAP. Finally, sensitivity analyses of the model’s input parameters are conducted using a GA, and the effects of changing the model’s parameters on the system’s availability are investigated.

Multi-objective reliability redundancy allocation using MOPSO under hesitant fuzziness

Enhancing reliability in complex systems often leads to allocating redundant elements and identifying the system configuration by connecting various stages. Most of the redundancy allocation problems depend on critical decisions taken on various uncertainties present in the system. This study presents the modeling of the redundancy allocation under hesitant fuzzy environment as a multi-objective problem. The multi-objective mathematical framework of series–parallel configuration has been proposed for identifying the system performance to obtain optimal cost against enhanced reliability of the power station coal feeding system incorporating the system’s weight and volume restrictions. A sequence of algorithms is presented involving the hesitant alternative of hesitant fuzzy situation based multi-objective particle swarm optimization to illustrate the optimal solutions to improve the system performance in crisp and hesitant fuzzy environments.

Energy harvesting and stability analysis of centralized TEG system under non-uniform temperature distribution

Thermoelectric generator (TEG) systems are gaining much attraction due to utility in heat recovery, surface cooling, concentrated solar thermal, and sensor applications. In series–parallel configurations, TEG modules due to Heterogeneous temperature difference (HeTD) show the non-linear behavior. Due to non-uniform temperature distribution (NUTD), multiple maximum power points (MPP) appears on the P-V curve. It is crucial to drive the system at true global maximum power point (GMPP) among multiple MPP’s. Existing classical techniques exhibit slow tracking, low efficiency, and undesired fluctuation in output voltage transients. To address these shortcomings our control technique based on improved Moth Flame Optimization (IMFO) is employed for the maximum power point tracking (MPPT) control under dynamic operating conditions. Comparison of the proposed technique is made with other well-known meta-heuristic techniques including particle swarm optimization (PSO), cuckoo search (CS), Artificial Bee Colony (ABC), and recently developed Dragon Fly Optimization (DFO). The comprehensive case studies with statistical and quantitative analysis are performed to confirm the superior performance of IMFO for NUTD condition, fast varying temperature condition, and stochastic operations. To experimentally validate the performance of the IMFO algorithm a low-cost TEG emulator setup is designed. The IMFO based control is implemented on a low-cost microcontroller achieving effective real-time control application in hardware. The proposed IMFO algorithm attains up to 6 W more power and takes 59% less time to track and settle at GMPP with minimum fluctuation. Results also validate that IMFO extracts 5.2% more electrical energy in comparison to competing techniques. In light of comprehensive analysis, it is safe to conclude that the proposed IMFO performs excellently for TEG MPPT control.

Performance Enhancement of Partial Shaded Photovoltaic System With the Novel Screw Pattern Array Configuration Scheme

The performance of the solar photovoltaic system is affected by the unpredictable phenomenon of partial shading. This causes the mismatch losses that suppress the power generation of healthy PV modules in it. The objective of the proposed work in this paper is to bring out the maximum power from each PV module in the PV array by reducing the mismatch losses. A new array configuration method is proposed in this paper, which follows the screw pattern in the row formation. Each PV row is created with distinct PV modules from the rows of the conventional array configuration. This proposed work allows the PV system to operate with minimum mismatch losses by even shade dispersion over the PV array. The proper mathematical expression with all necessary constraints was derived for the array formation of the proposed work. The output analysis is been validated in the simulation of the <inline-formula> <tex-math notation="LaTeX">$9\times 9$ </tex-math></inline-formula> PV array in MATLAB/Simulink &#x24C7;. The mismatch loss generation and output power enhancement are measured and compared with the various conventional array configuration methods under six kinds of partial shading patterns. The proposed array configuration is 40&#x0025; more efficient than the conventional series-parallel array configuration and also performs better than the total cross-tied and sudoku puzzle pattern methods. The shade dispersion rate of the proposed array configuration has highly reduced the mismatch losses in the PV system and hence, it improves the power output.

Performa Konfigurasi Modul Surya Seri dan Seri Paralel pada Kondisi Mismatch Karakteristik Arus-Tegangan (I-V) terhadap Daya Output

The installation of a Solar Power System (PLTS) within the ideal conditions still uses the type of solar module with the same current and voltage characteristics. However, these ideal conditions can be different if the commonly used modules are no longer available on the market. Once there is damage or interference in the operating system, such as cracks in the module plate, it will take a significantly long time to replace. This particular condition can obstruct electrical power distribution to its intended loads in the other end. Therefore, creating a robust solar panel system that operates at its maximum capacity requires an alternative or approach to find such a similar module replacement. It is expected that the replacement module will have the I-V characteristics, which relatively resemble that of the earlier module and can help to maintain the energy availability of the solar panel system. This study aims to analyze which factors affect the characteristic irregularity of currents and voltages in a solar panel installation towards the output of a solar panel under certain conditions. The solar panel system is designed using 20 solar modules with each capacity is 250 WP power that is simulated with Simulink. The method creates the mismatch condition of the current and voltage on the solar module in a specific panel configuration. These mismatch conditions are created by combining solar modules with different currents and voltages in the Series (S) and Series-Parallel (SP) configurations. The simulation is carried out by replacing the main solar module with a 5% to 100% replacement solar module. The selection of the replacement module is based on Isc, which is close to the same because the current flowing in the series circuit is the same. The simulation results showed that the solar panel system still functioned properly and produced maximum power under mismatch conditions. Of all three configurations with mismatch conditions, it is found that the best performing configuration works with the Series-Parallel (SP) configuration of the STC conditions. The maximum power which can be sustained with Series-Parallel (SP) configuration reaches up to 40% of the original modules.