Maximization Of Conversion Efficiency Research Articles

A multi-junction-based near-field solar thermophotovoltaic system with a graphite intermediate structure

A solar thermophotovoltaic (STPV) system can transform incident concentrated solar energy into electrical energy with an efficiency that could be higher than the Shockley–Queisser limit. Near-field thermophotovoltaic (NF-TPV) devices can generate larger electrical power output than traditional far-field TPV devices with the aid of photon tunneling. Moreover, multi-junction PV cells can boost the performance of TPV devices by effectively distributing the absorbed photon energy inside the PV cell. In this work, we design a multi-junction-based near-field STPV system with a practical and high-temperature stable graphite intermediate structure. To optimize the system configuration, we employ a genetic algorithm and a surrogate model based on an artificial neural network, which enables us to suggest a better design approach for the multi-junction-based NF-STPV system between the power output density and power conversion efficiency maximization scenarios. When the concentration factor of the incident solar energy is 5000 and the absorber-to-emitter area ratio is 3, we can achieve a system efficiency of 23%. By introducing a material whose emissivity is as high as a blackbody on the solar absorber, the system efficiency can be further enhanced up to 35%.

A five-target innovation discussion on low-speed wind turbine system optimization

ABSTRACT A couple of decades ago it was about photovoltaics, when their investment cost was at 6–7 €/kW, while today is less than 0.5 €/kW. In the wind energy field, since sites with high wind speeds disappear, a discussion on decision parameters and decision-making under various uncertainties related to the turbine and the low-speed environment is on the table outlining the most important growth limitations on wind power development (mainly) in the U.S. But, which one is easier? Wait and improve the technology to increase the efficiency of a wind turbine and then proceed in long-term and serious investments or proactively move on to mass deployment and exploit the resources capabilities today widening (perhaps) the application areas and opportunities? That question has been in the air for many decades in various fields. Ultimately, the U.S. is now in a position where exploiting a mature and well tested technology can convince the American people that if energy security is to be established soon, the power available from the abundance of low wind speed (LWS) sites (avoiding the price volatility witnessed from multiple energy crises in the past) should be also harnessed. A five-target innovation analysis focused on increased rotor diameter, taller towers, maximization of conversion efficiency of generation equipment, advanced blade design, and efficient logistical management pointed out the need for developers to improving these areas for viable investments in LWS. A worthy cost of energy (COE) on LWS sites is more important compared to high wind sites for the investability of the projects. In a case of a 2.6 MW wind turbine in a LWS, the COE was calculated at 12.4 ₵/kWh, which gives space in terms of sustainability.

Investigation of Photovoltaic Grid System under Non-Uniform Irradiance Conditions

Photovoltaic (PV) systems have recently been recognized as a leading way in the production of renewable electricity. Due to the unpredictable changes in environmental patterns, the amount of solar irradiation and cell operating temperature affect the power generated by the PV system. This paper, therefore, discusses the grid-integrated PV system to extract maximum power from the PV array to supply load requirements and the supply surplus power to the AC grid. The primary design is to have maximum power point tracking (MPPT) of the non-uniformly irradiated PV array, conversion efficiency maximization, and grid synchronization. This paper investigates various MPPT control algorithms using incremental conductance method, which effectively increased the performance and reduced error, hence helped to extract solar array’s power more efficiently. Additionally, other issues of PV grid-connected system such as network stability, power quality, and grid synchronization functions were implemented. The control of the voltage source converter is designed in such a way that PV power generated is synchronous to the grid. This paper also includes a comparative analysis of two MPPT techniques such as incremental conductance (INC) and perturb-and-observe (P&O). Extensive simulation of various controllers has been conducted to achieve enhanced efficient power extraction, grid synchronization and minimal performance loss due to dynamic tracking errors, particularly under fast-changing irradiation in Matlab/Simulink. The overall results favour INC algorithm and meet the required standards.

Irradiance-Adaptive PV Module Integrated Converter for High Efficiency and Power Quality in Standalone and DC Microgrid Applications

The strive for efficient and cost-effective photovoltaic (PV) systems motivated the power electronic design developed here. The work resulted in a dc-dc converter for module integration and distributed maximum power point tracking (MPPT) with a novel adaptive control scheme. The latter is essential for the combined features of high energy efficiency and high power quality over a wide range of operating conditions. The switching frequency is optimally modulated as a function of solar irradiance for power conversion efficiency maximization. With the rise of irradiance, the frequency is reduced to reach the conversion efficiency target. A search algorithm is developed to determine the optimal switching frequency step. Reducing the switching frequency may, however, compromise MPPT efficiency. Furthermore, it leads to increased ripple content. Therefore, to achieve a uniform high power quality under all conditions, interleaved converter cells are adaptively activated. The overall cost is kept low by selecting components that allow for implementing the functions at low cost. Simulation results show the high value of the module integrated converter for dc standalone and microgrid applications. A 400-W prototype was implemented at 0.14 Euro/W. Testing showed efficiencies above 95 %, taking into account all losses from power conversion, MPPT, and measurement and control circuitry.

Maximization of conversion efficiency based on global normal irradiance using hybrid concentrator photovoltaic architecture

AbstractMaximization of module conversion efficiency based on global normal irradiance (GNI) rather than direct normal irradiance (DNI) was experimentally demonstrated using a hybrid concentrator photovoltaic (CPV) architecture in which a low‐cost solar cell (a bifacial crystalline silicon cell) was integrated with a high‐efficiency concentrator solar cell (III–V triple‐junction cell) to harvest diffuse sunlight. The results of outdoor experiments showed that the low‐cost cell enhanced the generated power by factors of 1.39 and 1.63 for high‐DNI and midrange‐DNI conditions, respectively, and that the resultant GNI‐based module efficiencies were 32.7% and 25.6%, respectively. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

Suppression of Inter-channel Higher Order Four Wave Mixing in Four-Mode Phase-Sensitive Parametric Wavelength Multicasting

Phase manipulation of four-mode phase-sensitive (4MPS) process was developed as a means for suppression of high-order four wave mixing (HoFWM) terms in dual-pump driven parametric wavelength multicasting and, consequently, for reduction of inter-channel crosstalk and inter-channel interference. In contrast to the previous studies that focused on power stabilization and conversion efficiency maximization, the investigation in this paper focuses on the evolution of the inter-channel HoFWM tones, whose suppression can be accomplished by arranging the phases of signals in a complementary manner. In addition, broadband 4MPS multicasting with suppressed HoFWM effects over 100-nm bandwidth, reaching up to 12-dB suppression ratio was demonstrated.

Influence of thermal environment on optimal working conditions of thermoelectric generators

Optimization analysis of thermoelectric generators operation is of importance both for practical applications and theoretical considerations. Depending on the desired goal, two different strategies are possible to achieve high performance: through optimization one may seek either power output maximization or conversion efficiency maximization. Recent literature reveals the persistent flawed notion that these two optimal working conditions may be achieved simultaneously. In this article, we lift all source of confusion by correctly posing the problem and solving it. We assume and discuss two possibilities for the environment of the generator to govern its operation: constant incoming heat flux, and constant temperature difference between the heat reservoirs. We demonstrate that, while power and efficiency are maximized simultaneously if the first assumption is considered, this is not possible with the second assumption. This latter corresponds to the seminal analyses of Ioffe who put forth and stressed the importance of the thermoelectric figure of merit ZT. We also provide a simple procedure to determine the different optimal design parameters of a thermoelectric generator connected to heat reservoirs through thermal contacts with a finite and fixed thermal conductance.

Optimal Design of Solar Assisted Hydrothermal Gasification for Microalgae to Synthetic Natural Gas Conversion

Catalytic hydrothermal gasification is a promising technology which allows the conversion of wet biomass into methane rich syngas. It consists of three major steps, in which thermal energy has to be supplied at different temperature levels, leading to multiple products, such as clean water, nutrients/salts and methane rich syngas. Microalgae have an important potential as a new source of biomass, principally due to the fact that they can grow much faster than others biomass feedstock available in nature. Considering the energy balance of the algae cultivation step, the gasification process and thecrude product upgrading step, part of the converted syngas has to be used to close the energy balance. In this context, solar heat can be considered as an alternative to replace the heat that has to be generated from product or crude product burning. This would lead to higher fuel production, higher carbon conversion efficiency and in general a better sustainable use of energy sources. In this paper, the goal is to show the integration potential of solar thermal energy use in the catalytic hydrothermal gasification of microalgae. In order to maximize the fuel production, thermal energy requirements of the gasification and SNG upgrading process can be generated in concentrating solar systems, coupled with thermal energy storage. This allows to continuously provide heat for the process at different temperature levels. A superstructure of design models will permit the estimation of the optimal size and integration of the solar utility for different process configurations. The optimal design configurations are evaluated by solving a multi objective optimization problem which aims at the maximization of conversion efficiency and the minimization of operating and total production costs. Copyright © 2013, AIDIC Servizi S.r.l.

Gain scheduling control of variable-speed wind energy conversion systems using quasi-LPV models

The paper deals with the control of variable-speed wind energy conversion systems (WECS) in the context of linear parameter varying (LPV) systems, a recent formulation of the classic gain scheduling technique. The LPV approach is specially useful in variable-speed WECS control, which is characterized by nonlinear dynamic behavior and opposite objectives. In particular, the following objectives are considered: conversion efficiency maximization, safe operation, resonant modes damping, and robust stability. The proposed LPV controller is compared with a fixed controller that also takes into account the nonlinear behavior of the wind turbine.

Sliding mode control of wind energy systems with DOIG-power efficiency and torsional dynamics optimization

Wind turbines with double output induction generators can operate at variable speed permitting conversion efficiency maximization over a wide range of wind velocities. However, random wind fluctuations, wind shear and tower shadow, may excite the oscillation mode of the mechanical system, producing large torque ripple. Consequently, damage to drive train components and power quality problems may occur. In this paper, a sliding mode control is developed which provides a suitable compromise between conversion efficiency and torque oscillation smoothing. The resultant sliding dynamics is completely robust to uncertainties in the electrical variables and parameters. In addition, to prevent windup problems due to saturation, a combined sliding surface that incorporates such limitations is proposed.

Territory Selection in a Desert Grasshopper: The Maximization of Conversion Efficiency on a Chemically Defended Shrub

SUMMARY (1) Ligurotettix coquilletti is an oligophagous grasshopper found mostly on creosotebush, Larrea tridentata, in the deserts of south-western North America. Adult males defend individual host-plants as mating territories. Preferred shrubs, used as territories each year, are distinguished by low concentrations of the phenolic compound nordihydroguaiaretic acid (NDGA). (2) Long-term growth experiments conducted in situ showed that adult males suffered high mortality on 'avoided' shrubs due to starvation and consequent desiccation. (3) Mortality of females did not differ between preferred and 'avoided' shrubs, but between 7 and 14 days post-eclosion females grew at significantly slower rates on avoided shrubs.

Radiation transport effects in heavy-ion beam–target interaction studies: Measurement of target opacity and beam conversion efficiency

In this paper detailed simulations are presented of radiation-hydrodynamic response of gaseous cylindrical targets irradiated with heavy-ion beams that will be produced at the Gesellschaft für Schwerionenforschung, Darmstadt, using a heavy-ion synchrotron (SIS) [Heavy Ion Fusion, AIP Conference Proceedings No. 152 (AIP, New York, 1986), p. 23]. The purpose of this work is to explore material conditions for which the thermal radiation effects can be maximized. This is desirable in order to study a number of interesting and important effects including maximization of conversion efficiency of the ion beam energy to thermal radiation and measurement of the target opacity in the SIS experiments. It is expected that the SIS beams will produce a specific deposition power of 10 TW/g. The simulations in this paper show that a temperature of the order of 10 eV could be achieved by the SIS beams using homogeneous, cylindrical Xe targets. It has been shown that with the help of these computer simulations one should be able to measure the target opacity in these experiments within a factor of 3. Also these calculations show that in the SIS experiments one should be able to have a 50% conversion efficiency using a Xe target under optimum conditions. It has been found that the radiation effects will be optimized in the SIS experiments if the initial target density is of the order of 10−3 g/cm3. If the initial density is too high (of the order of 10−1 g/cm3 or more), hydrodynamic effects will dominate, while, on the other hand, if the initial density is too low (of the order of 10−4 g/cm3 or less), the electron thermal conductivity will take over.