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High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection

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A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Energy Science and Technology".

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 56139

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Dr. Kenji Araki

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Faculty of Engineering, University of Miyazaki, 889-2192 Miyazaki, Japan
Interests: automobile and transportation by renewable energy; solar energy; solar cell; CPV; standardization
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Special Issue Information

Dear Colleagues,

The R&D for renewable energy will accelerate the reduction of greenhouse gas emissions. High-efficiency power or energy conversion is the typical research target. However, it is also known through field experience that the system that wins the efficiency-race does not always perform the best in the real world. We may find that there are several reasons for this. Some are strong scientific reasons, and others are constrained by realistic compromise. In any case, positive or negative, it is worthwhile to collect arguments about the myths, scientific analyses, and field experience of the efficiency-oriented renewable energy technologies. This Special Issue was intended to collect such articles, as well as editorials and reviews of renewable energy technologies, in order to spark up debate. We welcome both positive and negative contributions, however they should be based on science.

In this Special Issue, we are interested in a wide range of discussions about the conversion efficiency of renewable energy from theoretical analyses, simulations, economic calculations, system demonstrations, and field experience. We welcome every kind of renewable energy as well as the application of renewable energy, such as the energy source of vehicles and digital commerce in renewable energy.

Dr. Kenji Araki
Guest Editor

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Published Papers (12 papers)

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Research

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13 pages, 7840 KiB

Open AccessArticle

Synthesis of Amorphous Conjugated Copolymers Based on Dithienosilole-Benzothiadiazole Dicarboxylic Imide with Tuned Optical Band Gaps and High Thermal Stability

by Ary R. Murad, Elham M. A. Dannoun, Shujahadeen B. Aziz, Ahmed Iraqi, Sozan N. Abdullah, Muaffaq M. Nofal and Ranjdar M. Abdullah

Appl. Sci. 2021, 11(11), 4866; https://doi.org/10.3390/app11114866 - 25 May 2021

Cited by 2 | Viewed by 2145

Abstract

Two alternating copolymers of dithienosilole (DTS) were designed and synthesized with small optical band gaps, flanked by thienyl units as electron-donor moieties and benzothiadiazole dicarboxylic imide (BTDI) as electron-acceptor moieties. The BTDI moieties were anchored to two different solubilizing side chains, namely 3,7-dimethyloctyl and n-octyl chains. An analysis of the effect of the electrochemical, optical, thermal, and structural characteristics of the resulting polymers along with their solubility and molecular weight is the subject of this paper. The Stille polymerization was used to synthesize PDTSDTBTDI-DMO and PDTSDTBTDI-8. The average molecular weight of PDTSDTBTDI-DMO and PDTSDTBTDI-8 is 14,600 and 5700 g mol⁻¹, respectively. Both polymers have shown equivalent optical band gaps around 1.4 eV. The highest occupied molecular orbital (HOMO) levels of the polymers were comparable, around −5.2 eV. The lowest unoccupied molecular orbital (LUMO) values were −3.56 and −3.45 eV for PDTSDTBTDI-DMO and PDTSDTBTDI-8, respectively. At decomposition temperatures above 350 °C, both copolymers showed strong thermal stability. The studies of powder X-ray diffraction (XRD) have shown that they are amorphous in a solid-state. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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12 pages, 4490 KiB

Open AccessArticle

Optimal Coordination of PV Active Power Curtailment and EVs Charging among Aggregators

by Andrés Felipe Cortés Borray, Julia Merino, Esther Torres and Javier Mazón

Appl. Sci. 2020, 10(20), 7176; https://doi.org/10.3390/app10207176 - 15 Oct 2020

Cited by 1 | Viewed by 2093

Abstract

With the growing adoption of electric vehicles (EVs) and residential photovoltaic (PV) systems around the world, the distribution system operators (DSOs) are facing several technical challenges on their network planning and operation, particularly on low-voltage grids. As the aggregators are intermediary actors at that system level, they are a promising figure to coordinate these devices in an aggregated manner to help to mitigate adverse effects like overloading of network assets. However, to do so, proper coordination techniques among these entities and the DSO should be developed to avoid further investments in new network assets. In this context, a centralised coordination strategy among aggregators at the DSO level is proposed. By employing a linear programming model, the optimal export limit of PV and charging profile for each aggregator is dictated by the DSO, maintaining the operational limits of the network assets. A case study on two aggregators with moderate and critical penetration levels was carried out. Results show that, by controlling the aggregated export limit of PV power and the aggregated charging rate of EVs, high penetration levels can be integrated into current networks with minor or no need for reinforcing network infrastructure. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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9 pages, 2143 KiB

Open AccessArticle

Optical Properties of CaF₂ Thin Film Deposited on Borosilicate Glass and Its Electrical Performance in PV Module Applications

by Muhammad Aleem Zahid, Shahzada Qamar Hussain, Young Hyun Cho and Junsin Yi

Appl. Sci. 2020, 10(16), 5647; https://doi.org/10.3390/app10165647 - 14 Aug 2020

Cited by 9 | Viewed by 3117

Abstract

Calcium fluoride (CaF₂) is deposited via vacuum thermal evaporation on borosilicate glass to produce an anti-reflection coating for use in solar modules. Macleod’s essential simulation is used to optimize the thickness of the CaF₂ coating on the glass. Experimentally, a 120 ± 4 nm-thin CaF₂ film on glass shows an average increase of ~4% in transmittance and a decrease of ~3.2% in reflectance, respectively, when compared to that of uncoated glass (Un CG), within the wavelength spectrum of approximately 350 to 1100 nm. The electrical PV performance of CaF₂-coated glass (CaF₂-CG) was analyzed for conventional and lightweight photovoltaic module applications. An improvement in the short-circuit current (J_sc) from 38.13 to 39.07 mA/cm² and an increase of 2.40% in the efficiency (η) was obtained when CaF₂-CG glass was used instead of Un CG in a conventional module. Furthermore, J_sc enhancement from 35.63 to 36.44 mA/cm² and η improvement of 2.32% was observed when a very thin CaF₂-CG was placed between the polymethyl methacrylate (PMMA) and solar cell in a lightweight module. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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12 pages, 2981 KiB

Open AccessFeature PaperArticle

Evaluation of a Sabatier Reaction Utilizing Hydrogen Produced by Concentrator Photovoltaic Modules under Outdoor Conditions

by SoeHtet Wai, Yasuyuki Ota, Masakazu Sugiyama and Kensuke Nishioka

Appl. Sci. 2020, 10(9), 3144; https://doi.org/10.3390/app10093144 - 30 Apr 2020

Cited by 7 | Viewed by 6635

Abstract

Power to gas (P2G) process chains have tremendous potential to enhance energy systems because of the capability of solar energy to convert solar radiation into electrical energy as well as the increasing use of specific gases as a means to store the resulting energy. Utilizing sunlight, photovoltaic systems are capable of producing useful gases such as hydrogen (H₂) and methane (CH₄). These gases are utilized in gas grids, transportation, and heavy industry. In employing a sunlight-derived gas, H₂ production, by water disbanding, needs to be cost-effective with tremendous adaptability. New powerful solar to gas conversion system modules have been successfully carried out in the University of Miyazaki, Japan. These systems contain DC/DC converters and electrolyzer sets linked in parallel with efficient three concentrator photovoltaics (CPV). The performance of the solar to methane conversion process and power consumption analysis will be the focus of the current research. Efficiencies of 97.6% of CO₂ to CH₄ conversion and 13.8% for solar to methane on a clear sunny day were obtained by utilizing highly efficient CPV modules connected with multiple converters, electrochemical cells, and reactors fixed with Ni-based catalysts. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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17 pages, 4177 KiB

Open AccessArticle

The Outdoor Field Test and Energy Yield Model of the Four-Terminal on Si Tandem PV Module

by Kenji Araki, Hiroki Tawa, Hiromu Saiki, Yasuyuki Ota, Kensuke Nishioka and Masafumi Yamaguchi

Appl. Sci. 2020, 10(7), 2529; https://doi.org/10.3390/app10072529 - 07 Apr 2020

Cited by 7 | Viewed by 3309

Abstract

The outdoor field test of the 4-terminal on Si tandem photovoltaic module (specifically, InGaP/GaAs on Si) was investigated and a performance model, considering spectrum change affected by fluctuation of atmospheric parameters, was developed and validated. The 4-terminal on Si tandem photovoltaic module had about 40% advantage in seasonal performance loss compared with standard InGaP/GaAs/InGaAs 2-terminal tandem photovoltaic module. This advantage increases (subarctic zone < temperate zone < subtropical zone). The developed and validated model used an all-climate spectrum model and considered fluctuation of atmospheric parameters. It can be applied every type of on-Si tandem solar cells. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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26 pages, 6745 KiB

Open AccessFeature PaperArticle

Measurement and Modeling of 3D Solar Irradiance for Vehicle-Integrated Photovoltaic

by Kenji Araki, Yasuyuki Ota and Masafumi Yamaguchi

Appl. Sci. 2020, 10(3), 872; https://doi.org/10.3390/app10030872 - 27 Jan 2020

Cited by 46 | Viewed by 8528

Abstract

The energy yield of vehicle-integrated photovoltaics (VIPV) differs from that of standard photovoltaics (PV). It is mainly by the difference of the solar irradiance onto the car roof and car bodies as well as its curved shape. Both meaningful and practical modeling and measurement of solar irradiance for VIPV need to be established, rather than the extension of the current technologies. The solar irradiance is modeled by a random distribution of shading objects and car orientation with the correction of the curved surface of the PV modules. The measurement of the solar irradiance onto the car roof and car body is done using five pyranometers in five local axes on the car for one year. The measured dynamic solar irradiance onto the car body and car roof is used for validation of the solar irradiance model in the car. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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17 pages, 6724 KiB

Open AccessArticle

Influencing Factors of Motion Responses for Large-Diameter Tripod Bucket Foundation

by Xianqing Liu, Puyang Zhang, Mingjie Zhao, Hongyan Ding and Conghuan Le

Appl. Sci. 2019, 9(22), 4957; https://doi.org/10.3390/app9224957 - 18 Nov 2019

Cited by 12 | Viewed by 2662

Abstract

Large-diameter multi-bucket foundation is well suited for offshore wind turbines at deeper water than 20 m. Air floating transportation is one of the key technologies for the cost-effective development of bucket foundation. To predict the dynamic behavior of large-diameter tripod bucket foundation (LDTBF) supported by an air cushion and a water plug inside every bucket in waves, three 1/25-scale physical model tests with different bucket spacing were conducted in waves; detailed prototype foundation models were established using a hydrodynamic software MOSES with a draft of 4.0 m, 4.5 m, and 5.0 m and with a water depth of 10.0 m, 11.25 m, and 12.5 m. The numerical and experimental results are consistent for heaving motion, while exhibiting favorable agreement for pitching motion. The results show that the resonant periods for heaving motion increased with increasing draft and water depth. The maximum amplitude for heaving motion first decreased and then increased with the increase of water depth and spacing between the buckets. The maximum amplitude for pitching motion first decreased and then increased with increasing water depth but decreased with increasing spacing between the buckets. The wider the spacing between the bucket foundations, the larger the heave response amplitude operators (RAOs). Simply improving the pitch RAOs by increasing the spacing between bucket foundations is limited and negatively affects motion performance during the transportation of LDTBF. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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21 pages, 4712 KiB

Open AccessFeature PaperArticle

Super-Multi-Junction Solar Cells—Device Configuration with the Potential for More Than 50% Annual Energy Conversion Efficiency (Non-Concentration)

by Kenji Araki, Yasuyuki Ota, Hiromu Saiki, Hiroki Tawa, Kensuke Nishioka and Masafumi Yamaguchi

Appl. Sci. 2019, 9(21), 4598; https://doi.org/10.3390/app9214598 - 29 Oct 2019

Cited by 13 | Viewed by 8123

Abstract

The highest-efficiency solar cell in the efficiency race does not always give the best annual energy yield in real world solar conditions because the spectrum is always changing. The study of radiative coupling of concentrator solar cells implies that efficiency could increase by recycling the radiative recombination generated by the surplus current in the upper junction. Such a configuration is called a super-multi-junction cell. We expand the model in the concentrator solar cell to a non-concentrating installation. It is shown that this super-multi-junction cell configuration is robust and can keep maximum potential efficiency (50% in realistic spectrum fluctuation) for up to 10 junctions. The super-multi-junction cell is also robust in the bandgap engineering of each junction. Therefore, a future multi-junction may not be required for tuning the bandgap to match the standard solar spectrum, as well as relying upon artificial technologies such as epitaxial lift-off (ELO), wafer-bonding, mechanical-stacking, and reverse-growth, but merely uses upright and lattice-matching growth technologies. We present two challenging techniques; one is the optical cap layer that may be the directional photon coupling layer in the application of the photonics technologies, and another is the high-quality epitaxial growth with almost 100% radiative efficiency. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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17 pages, 3457 KiB

Open AccessFeature PaperArticle

Repair Process Analysis for Wind Turbines Equipped with Hydraulic Pitch Mechanism on the U.S. Market in Focus of Cost Optimization

by Gergely Kocsis and George Xydis

Appl. Sci. 2019, 9(16), 3230; https://doi.org/10.3390/app9163230 - 07 Aug 2019

Cited by 15 | Viewed by 3133

Abstract

In recent years both the demand and supply for upgrade solutions and repair services are growing. The majority of the American turbine owners are motivated to be able to operate their various fleets of wind turbines on their own and gain sufficient knowledge to do so in a professional manner. With this goal in mind, the learning curve includes optimizing operation cost, fine-tuning practices, and building a network with suppliers. This work focused on hydraulic pitch system designed for a modern wind turbine, technology overview, and economic loss due to leakage. Furthermore, the work covers the drivers of the customers, performance requirements, and evaluation the current solutions that are available on the market. The possible solutions are listed for each scenario and follow up actions are suggested on how to control future processes. The paper describes how to optimize the long-term running costs and discuss on the changes that could maximize the availability percentage. The findings can be also applied to both other platforms in the product line and even other Original equipment manufacturers’ (OEM) turbines to a certain extent. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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16 pages, 3829 KiB

Open AccessArticle

Algorithmically Optimized Hemispherical Dome as a Secondary Optical Element for the Fresnel Lens Solar Concentrator

by Hassan Qandil, Shuping Wang and Weihuan Zhao

Appl. Sci. 2019, 9(13), 2757; https://doi.org/10.3390/app9132757 - 08 Jul 2019

Cited by 1 | Viewed by 3951

Abstract

The significance of this work lies in the development of a novel code-based, detailed, and deterministic geometrical approach that couples the optimization of the Fresnel lens primary optical element (POE) and the dome-shaped secondary optical element (SOE). The objective was to maximize the concentration acceptance product (CAP), while using the minimum SOE and receiver geometry at a given f-number and incidence angle (also referred to as the tracking error angle). The laws of polychromatic light refraction along with trigonometry and spherical geometry were utilized to optimize the POE grooves, SOE radius, receiver size, and SOE–receiver spacing. Two literature case studies were analyzed to verify this work’s optimization, both with a spot Fresnel lens POE and a spherical dome SOE. Case 1 had a 625 cm² POE at an f-number of 1.5, and Case 2 had a 314.2 cm² POE at an f-number of 1.34. The equivalent POE designed by this work, with optimized SOE radiuses of 13.6 and 11.4 mm, respectively, enhanced the CAP value of Case 1 by 52% to 0.426 and that of Case 2 by 32.4% to 0.45. The SOE’s analytical optimization of Case 1 was checked by a simulated comparative analysis to ensure the validity of the results. Fine-tuning this design for thermal applications and concentrated photovoltaics is also discussed in this paper. The algorithm can be further improved for more optimization parameters and other SOE shapes. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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14 pages, 4149 KiB

Open AccessArticle

Study of Dynamic Response Characteristics of the Wind Turbine Based on Measured Power Spectrum in the Eyewall Region of Typhoons

by Ran Han, Long Wang, Tongguang Wang, Zhiteng Gao and Jianghai Wu

Appl. Sci. 2019, 9(12), 2392; https://doi.org/10.3390/app9122392 - 12 Jun 2019

Cited by 6 | Viewed by 3212

Abstract

The present research envisages a method for calculating the dynamic responses of the wind turbines under typhoon. The measured power spectrum and inverse Fourier transform are used to generate the fluctuating wind field in the eyewall of the typhoon. Based on the beam theory, the unsteady aerodynamic model and the wind turbine dynamic model are coupled to calculate the dynamic response. Furthermore, using this method, the aeroelastic responses of a 6 MW wind turbine at different yaw angles are studied, and a 2 MW wind turbine are also calculated to verify the applicability of the results for different sizes of wind turbines. The results show that the turbulence characteristics of the fluctuating wind simulated by the proposed method is in good agreement with the actual measurement. Compared with the results simulated by the recommended power spectrum like the Kaimal spectrum, the energy distribution and variation characteristics simulated by the proposed method represent the real typhoon in a superior manner. It is found that the blade vibrates most violently at the inflow yaw angle of 30 degrees under the coupled effect of the aerodynamic, inertial and structural loads. In addition, the load on the tower exceeds the design limit values at the yaw angles of both 30 degrees and 120 degrees. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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Review

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29 pages, 5005 KiB

Open AccessReview

Virtual Inertia-Based Inverters for Mitigating Frequency Instability in Grid-Connected Renewable Energy System: A Review

by Kah Yung Yap, Charles R. Sarimuthu and Joanne Mun-Yee Lim

Appl. Sci. 2019, 9(24), 5300; https://doi.org/10.3390/app9245300 - 05 Dec 2019

Cited by 83 | Viewed by 8180

Abstract

This study paper presents a comprehensive review of virtual inertia (VI)-based inverters in modern power systems. The transition from the synchronous generator (SG)-based conventional power generation to converter-based renewable energy sources (RES) deteriorates the frequency stability of the power system due to the intermittency of wind and photovoltaic (PV) generation. Unlike conventional power generation, the lack of rotational inertia becomes the main challenge to interface RES with the electrical grid via power electronic converters. In the past several years, researchers have addressed this issue by emulating the behavior of SG mathematically via pulse width modulation (PWM) controller linked to conventional inverter systems. These systems are technically known as VI-based inverters, which consist of virtual synchronous machine (VSM), virtual synchronous generator (VSG), and synchronverter. This paper provides an extensive insight into the latest development, application, challenges, and prospect of VI application, which is crucial for the transition to low-carbon power system. Full article

(This article belongs to the Special Issue High-Efficiency Conversion in Renewable Energy, Challenge, or Reflection)

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