Research

23 pages, 7657 KiB

Open AccessArticle

Wind Turbine Blade Optimal Design Considering Multi-Parameters and Response Surface Method

by Sang-Lae Lee and SangJoon Shin

Energies 2020, 13(7), 1639; https://doi.org/10.3390/en13071639 - 02 Apr 2020

Cited by 19 | Viewed by 6058

Within the framework of blade aerodynamic design, the maximum aerodynamic efficiency, power production, and minimum thrust force are the targets to obtain. This paper describes an improved optimization framework for blade aerodynamic design under realistic conditions, while considering multiple design parameters. The relationship [...] Read more.

Within the framework of blade aerodynamic design, the maximum aerodynamic efficiency, power production, and minimum thrust force are the targets to obtain. This paper describes an improved optimization framework for blade aerodynamic design under realistic conditions, while considering multiple design parameters. The relationship between the objective function and the design parameters, such as the chord length, maximum chord, and twist angle, were obtained by using the second-order response surface methodology (RSM). Moreover, the identified parameters were organized to optimize the aerodynamic design of the blades. Furthermore, the initial and optimized blade geometries were compared and showed that the performance of the optimized blade improved significantly. In fact, the efficiency was increased by approximately 10%, although its thrust was not varied. In addition, to demonstrate the improvement in the resulting optimized blades, the annual energy production (AEP) was estimated when installed in a specific regional location. The result showed a significant improvement when compared to the baseline blades. This result will be extended to a new perspective approach for a more robust optimal design of a wind turbine blade. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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12 pages, 1278 KiB

Open AccessArticle

Reutealis Trisperma Oil Esterification: Optimization and Kinetic Study

by Riky Lim, Deog-Keun Kim and Jin-Suk Lee

Energies 2020, 13(6), 1513; https://doi.org/10.3390/en13061513 - 23 Mar 2020

Cited by 2 | Viewed by 2051

Abstract

Reutealis trisperma, due to its high kernel-oil yield (±50%) and long productivity (±70 years), is considered to be a promising feedstock for biodiesel production. In addition, this plant, which can thrive on marginal lands, is classified as a non-edible oil since it [...] Read more.

Reutealis trisperma, due to its high kernel-oil yield (±50%) and long productivity (±70 years), is considered to be a promising feedstock for biodiesel production. In addition, this plant, which can thrive on marginal lands, is classified as a non-edible oil since it contains a toxin known as eleostearic acid. The present study aimed to optimize the esterification step in biodiesel production from R.trisperma oil catalyzed using sulfonic ion exchange resin Lewatit K2640. The optimization step was performed using a response surface methodology through the incorporation of a central composite design. A kinetic study was performed as well, based on the assumption of a pseudo-homogeneous second-order model. Catalyst loading was found to have the most significant impact on acid value, followed by temperature and methanol-to-oil molar ratio. The optimal conditions for the esterification step were 92 °C temperature, 5.34% catalyst loading, and 5.82:1 methanol-to-oil molar ratio. The acid value and FFA conversion of R.trisperma oil under these conditions were 2.49 mg KOH/g and 91.75%, respectively. The kinetics study revealed that the constructed model could fit the experimental data well with relatively high reliability. The activation energy required for the esterification of R.trisperma oil was 33.2 kJ/mol. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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16 pages, 1984 KiB

Open AccessArticle

Thermogravimetric Kinetic Study of Automobile Shredder Residue (ASR) Pyrolysis

by Soyoung Han, Yong-Chul Jang, Yeon-Seok Choi and Sang-Kyu Choi

Energies 2020, 13(6), 1451; https://doi.org/10.3390/en13061451 - 20 Mar 2020

Cited by 7 | Viewed by 2366

Abstract

The separated and sorted combustibles from automobile shredder residue (ASR) can be pyrolyzed and used as a heat source or liquefied to produce materials with added value. In this study, the thermal decomposition properties of ASR were determined and thermal kinetic studies were [...] Read more.

The separated and sorted combustibles from automobile shredder residue (ASR) can be pyrolyzed and used as a heat source or liquefied to produce materials with added value. In this study, the thermal decomposition properties of ASR were determined and thermal kinetic studies were performed. Four types of raw materials were separated from ASR and mixed at a constant ratio: 38.5 wt.% of plastic; 31.6 wt.% of fiber; 17.3 wt.% of sponge; and 12.3 wt.% of rubber. Pyrolysis kinetics analysis was carried out using the Thermogravimetric analysis-derivative thermogravimetry (TGA-DTG) technique and activation energy were calculated by differential and integral isoconversional model methods, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Friedman. Thermogravimetric analysis was performed under nitrogen with four temperature rate conditions from room temperature to 800 °C. In the thermal degradation profile, peaks representing mass loss rates were observed for each sample at different temperature ranges. It was observed that the final mass reduction temperature in the mixed samples was lower than in the individual samples. The activation energies of plastics and rubbers were 105.39 kJ/mol and 115.20 kJ/mol respectively. The sponge foams and fibers were 172.59 kJ/mol and 160.30 kJ/mol respectively. The mixed sample had an activation energy value of 159.56 kJ/mol. The basic physicochemical and pyrolysis characteristics of ASR were examined to be used as basic data for the recycling of ASR for future pyrolysis. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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10 pages, 3155 KiB

Open AccessArticle

Fabrication and Characterization of Cu₂ZnSnSe₄ Thin-Film Solar Cells using a Single-Stage Co-Evaporation Method: Effects of Film Growth Temperatures on Device Performances

by Muhammad Rehan, Hyeonmin Jeon, Yunae Cho, Ara Cho, Kihwan Kim, Jun-Sik Cho, Jae Ho Yun, Seungkyu Ahn, Jihye Gwak and Donghyeop Shin

Energies 2020, 13(6), 1316; https://doi.org/10.3390/en13061316 - 12 Mar 2020

Cited by 14 | Viewed by 2668

Abstract

Kesterite-structured Cu₂ZnSnSe₄ (CZTSe) is considered as one of the Earth-abundant and non-toxic photovoltaic materials. CZTSe films have been prepared using a single-step co-evaporation method at a relatively low temperature (i.e., below 500 °C). Due to the volatile nature of tin-selenide, [...] Read more.

Kesterite-structured Cu₂ZnSnSe₄ (CZTSe) is considered as one of the Earth-abundant and non-toxic photovoltaic materials. CZTSe films have been prepared using a single-step co-evaporation method at a relatively low temperature (i.e., below 500 °C). Due to the volatile nature of tin-selenide, the control over substrate temperature (i.e., growth temperature) is very important in terms of the deposition of high-quality CZTSe films. In this regard, the effects of growth temperatures on the CZTSe film morphology were investigated. The suitable temperature range to deposit CZTSe films with Cu-poor and Zn-rich compositions was 380–480 °C. As the temperature increased, the surface roughness of the CZTSe film decreased, which could improve p/n junction properties and associated device performances. Particularly, according to capacitance-voltage (C-V) and derived-level capacitance profiling (DLCP) measurements, the density of interfacial defects of CZTSe film grown at 480 °C showed the lowest value, of the order of ~3 × 10¹⁵ cm⁻³. Regardless of applied growth temperatures, the formation of a MoSe₂ layer was rarely observed, since the growth temperature was not high enough to have a reaction between Mo back contact layers and CZTSe absorber layers. As a result, the photovoltaic (PV) device with CZTSe film grown at 480 °C yielded the best power conversion efficiency of 6.47%. It is evident that the control over film growth temperature is a critical factor for obtaining high-quality CZTSe film prepared by one-step process. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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12 pages, 5181 KiB

Open AccessArticle

Study on Polymer Electrolyte Fuel Cells with Nonhumidification Using Metal Foam in Dead-Ended Operation

by Myo-Eun Kim and Young-Jun Sohn

Energies 2020, 13(5), 1238; https://doi.org/10.3390/en13051238 - 07 Mar 2020

Cited by 7 | Viewed by 2276

Abstract

Portable power sources have attracted increasing interest and attention, with a focus on the reduction of the system volume. Thus, portable power sources often use polymer electrolyte fuel cell (PEFC) systems with dead-ended operation—which are simpler and more fuel-efficient than conventional PEFC systems. [...] Read more.

Portable power sources have attracted increasing interest and attention, with a focus on the reduction of the system volume. Thus, portable power sources often use polymer electrolyte fuel cell (PEFC) systems with dead-ended operation—which are simpler and more fuel-efficient than conventional PEFC systems. In these systems, the fuel may be supplied under nonhumidified conditions to minimize the balance of plant (BOP). In recent studies, metal foams have been used as flow fields to improve fuel diffusion and water management in the PEFC; the performance can be compared to that of a conventional channel. This study compared the performance and water management ability of channel and metal foam flow fields under nonhumidified conditions with dead-ended operation. The results demonstrate that the average output was similar for both flow fields. In terms of fuel efficiency, the PEFC with the metal foam could be operated for a significantly longer time without purging than that with the channel. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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12 pages, 6651 KiB

Open AccessArticle

Linear-Gompertz Model-Based Regression of Photovoltaic Power Generation by Satellite Imagery-Based Solar Irradiance

by Alba Vilanova, Bo-Young Kim, Chang Ki Kim and Hyun-Goo Kim

Energies 2020, 13(4), 781; https://doi.org/10.3390/en13040781 - 11 Feb 2020

Cited by 6 | Viewed by 3479

Abstract

A simple yet accurate photovoltaic (PV) performance curve as a function of satellite-based solar irradiation is necessary to develop a PV power forecasting model that can cover all of South Korea, where more than 35,000 PV power plants are currently in operation. In [...] Read more.

A simple yet accurate photovoltaic (PV) performance curve as a function of satellite-based solar irradiation is necessary to develop a PV power forecasting model that can cover all of South Korea, where more than 35,000 PV power plants are currently in operation. In order to express the nonlinear power output of the PV module with respect to the hourly global horizontal irradiance derived from satellite images, this study employed the Gompertz model, which is composed of three parameters and the sigmoid equation. The nonphysical behavior of the Gompertz model within the low solar irradiation range was corrected by combining a linear equation with the same gradient at the conjoint point. The overall fitness of Linear-Gompertz regression to the 242 PV power plants representing the country was R² = 0.85 and nRMSE = 0.09. The Gompertz model coefficients showed normal distributions and equivariance of standard deviations of less than 15% by year and by season. Therefore, it can be conjectured that the Linear-Gompertz model represents the whole country’s PV system performance curve. In addition, the Gompertz coefficient C, which controls the growth rate of the curve, showed a strong correlation with the capacity factor, such that the regression equation for the capacity factor could be derived as a function of the three Gompertz model coefficients with a fitness of R² = 0.88. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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12 pages, 5542 KiB

Open AccessArticle

Effect of RF Power on the Properties of Sputtered-CuS Thin Films for Photovoltaic Applications

by Donghyeok Shin, SangWoon Lee, Dong Ryeol Kim, Joo Hyung Park, Yangdo Kim, Woo-Jin Choi, Chang Sik Son, Young Guk Son and Donghyun Hwang

Energies 2020, 13(3), 688; https://doi.org/10.3390/en13030688 - 05 Feb 2020

Cited by 14 | Viewed by 3359

Abstract

Copper sulfide (CuS) thin films were deposited on a glass substrate at room temperature using the radio-frequency (RF) magnetron-sputtering method at RF powers in the range of 40–100 W, and the structural and optical properties of the CuS thin film were investigated. The [...] Read more.

Copper sulfide (CuS) thin films were deposited on a glass substrate at room temperature using the radio-frequency (RF) magnetron-sputtering method at RF powers in the range of 40–100 W, and the structural and optical properties of the CuS thin film were investigated. The CuS thin films fabricated at varying deposition powers all exhibited hexagonal crystalline structures and preferred growth orientation of the (110) plane. Raman spectra revealed a primary sharp and intense peak at the 474 cm⁻¹ frequency, and a relatively wide peak was found at 265 cm⁻¹ frequency. In the CuS thin film deposited at an RF power of 40 W, relatively small dense particles with small void spacing formed a smooth thin-film surface. As the power increased, it was observed that grain size and grain-boundary spacing increased in order. The binding energy peaks of Cu 2p_3/2 and Cu 2p_1/2 were observed at 932.1 and 952.0 eV, respectively. Regardless of deposition power, the difference in the Cu²⁺ state binding energies for all the CuS thin films was equivalent at 19.9 eV. We observed the binding energy peaks of S 2p_3/2 and S 2p_1/2 corresponding to the S²⁻ state at 162.2 and 163.2 eV, respectively. The transmittance and band-gap energy in the visible spectral range showed decreasing trends as deposition power increased. For the CuS/tin sulfide (SnS) absorber-layer-based solar cell (glass/Mo/absorber(CuS/SnS)/cadmium sulfide (CdS)/intrinsic zinc oxide (i-ZnO)/indium tin oxide (ITO)/aluminum (Al)) with a stacked structure of SnS thin films on top of the CuS layer deposited at 100 W RF power, an open-circuit voltage (V_oc) of 115 mA, short circuit current density (J_sc) of 9.81 mA/cm², fill factor (FF) of 35%, and highest power conversion efficiency (PCE) of 0.39% were recorded. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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9 pages, 355 KiB

Open AccessArticle

The Electrification of Cooking Methods in Korea—Impact on Energy Use and Greenhouse Gas Emissions

by Hyunji Im and Yunsoung Kim

Energies 2020, 13(3), 680; https://doi.org/10.3390/en13030680 - 05 Feb 2020

Cited by 5 | Viewed by 3302

Abstract

The electrification of cooking methods in Korea was investigated to understand the impact of different cooking methods on energy use and greenhouse gas (GHG) emissions in the building sector. Annual household cooking energy consumption was compared for the Nowon Energy Zero House Project, [...] Read more.

The electrification of cooking methods in Korea was investigated to understand the impact of different cooking methods on energy use and greenhouse gas (GHG) emissions in the building sector. Annual household cooking energy consumption was compared for the Nowon Energy Zero House Project, a zero-energy housing complex using induction cooktops, and a sample of households that used natural gas for cooking. The results showed that the former consumed less calories (a difference of 2.2 times) and emitted less GHGs (a difference of 2.6 times) compared to gas cooking households. A countrywide scenario analysis was conducted by combining the share of electric cooking households with the projected power generation mix in 2030. Under the 2030 Policy scenario for power generation, and with an electricity cooking share of 20%, cooking-related GHG emissions were projected to be 3.79 million t CO₂/year; 3.8% (150,000 t CO₂/year) lower than those in the present day, despite a total population increase. The electrification of cooking methods in Korea has the potential to reduce both the energy demand of the building sector and GHG emissions, in synergy with the decarbonization of the power generation sector. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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12 pages, 1850 KiB

Open AccessArticle

Prefeasibility Study of Photovoltaic Power Potential Based on a Skew-Normal Distribution

by Shin Young Kim, Benedikt Sapotta, Gilsoo Jang, Yong-Heack Kang and Hyun-Goo Kim

Energies 2020, 13(3), 676; https://doi.org/10.3390/en13030676 - 04 Feb 2020

Cited by 5 | Viewed by 3274

Abstract

Solar energy does not always follow the normal distribution due to the characteristics of natural energy. The system advisor model (SAM), a well-known energy performance analysis program, analyzes exceedance probabilities by dividing solar irradiance into two cases, i.e., when normal distribution is followed, [...] Read more.

Solar energy does not always follow the normal distribution due to the characteristics of natural energy. The system advisor model (SAM), a well-known energy performance analysis program, analyzes exceedance probabilities by dividing solar irradiance into two cases, i.e., when normal distribution is followed, and when normal distribution is not followed. However, it does not provide a mathematical model for data distribution when not following the normal distribution. The present study applied the skew-normal distribution when solar irradiance does not follow the normal distribution, and calculated photovoltaic power potential to compare the result with those using the two existing methods. It determined which distribution was more appropriate between normal and skew-normal distributions using the Jarque–Bera test, and then the corrected Akaike information criterion (AICc). As a result, three places in Korea showed that the skew-normal distribution was more appropriate than the normal distribution during the summer and winter seasons. The AICc relative likelihood between two models was more than 0.3, which showed that the difference between the two models was not extremely high. However, considering that the proportion of uncertainty of solar irradiance in photovoltaic projects was 5% to 17%, more accurate models need to be chosen. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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7 pages, 1408 KiB

Open AccessArticle

The Effect of ALD-Zn(O,S) Buffer Layer on the Performance of CIGSSe Thin Film Solar Cells

by Woo-Jin Choi, Wan Woo Park, Yangdo Kim, Chang Sik Son and Donghyun Hwang

Energies 2020, 13(2), 412; https://doi.org/10.3390/en13020412 - 15 Jan 2020

Cited by 5 | Viewed by 2413

Abstract

In this paper, we report the development of Cd-free buffers using atomic layer deposition (ALD) for Cu(In,Ga)(S,Se)₂-based solar cells. The ALD process gives good control of thickness and the S/S +O ratio content of the films. The influence of the growth per [...] Read more.

In this paper, we report the development of Cd-free buffers using atomic layer deposition (ALD) for Cu(In,Ga)(S,Se)₂-based solar cells. The ALD process gives good control of thickness and the S/S +O ratio content of the films. The influence of the growth per cycle (GPC) and the S/(S+O) ratio, and the glass temperature of the atomic layer deposited Zn(O,S) buffer layers on the efficiency of the Cu(In,Ga)(S,Se)₂ solar cells were investigated. We present the first results from our work on cadmium-free CIGS solar cells on substrates with an aperture area of 0.4 cm². These Zn(O,S) layers were deposited by atomic layer deposition at 120 °C with S/Zn ratios of 0.7, and layers of around 30 nm. The Zn(O,S) 20% (Pulse Ratio: H₂S/H₂O+H₂S) process results in a S/Zn ratio of 0.7. We achieved independently certified aperture area efficiencies of 17.1% for 0.4 cm² cells. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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12 pages, 1234 KiB

Open AccessArticle

Analysis of Climate Mitigation Technology and Finance in Relation to Multilateral Development Banks

by Joo Young Lee and Su Hyeon Han

Energies 2020, 13(2), 311; https://doi.org/10.3390/en13020311 - 08 Jan 2020

Cited by 4 | Viewed by 2282

Abstract

This paper looks at the current state of multilateral development banks (MDBs) for climate change measures and the funding status of those invested in mitigation technology in order to briefly review the current outcome of the technology transfer and financial support. In other [...] Read more.

This paper looks at the current state of multilateral development banks (MDBs) for climate change measures and the funding status of those invested in mitigation technology in order to briefly review the current outcome of the technology transfer and financial support. In other words, the aim of this study is to collect and analyze information about the current status of total investment in the field of technology for mitigating GHGs (Greenhouse Gases) from MDBs and identify implications of the status. In this study, a screening technique has been used three times to make a database for project information in the field of mitigation of climate change. So far, based on the finalized DB (Database), mitigation technology projects supported by MDBs have been investigated; based on the result, a connected analysis has been conducted between MDBs, mitigation technology, and countries. According to the derived current status, project support in renewable energy and energy demand areas turned out to be the highest at 75% of the entire mitigation technology. Rather than the renewable energy and energy demand areas where climate technology projects have frequently been performed throughout the world, it was confirmed that long-term climate technology projects for GHG fixation were being performed. According to the results of comparison and analysis of countries with high GHG emissions and their centrality, centrality turned out to be high in the field of GHG fixation in China, the country with the highest GHG emissions. This seems to indicate that countries emitting a substantial amount of GHGs will invest more on projects in the field of GHG fixation as well as on projects on renewable energy. Thus, this study is expected to contribute to understanding the trends of climate technology projects for coping with climate change and using them in establishing future policies on climate technology. In addition, it is expected to be used as a reference for countries with insufficient investment in climate technology despite the high Climate Risk Index (CRI). Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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14 pages, 5307 KiB

Open AccessArticle

Effect of Oxidants on Syngas Synthesis from Biogas over 3 wt % Ni-Ce-MgO-ZrO₂/Al₂O₃ Catalyst

by Danbee Han, Yunji Kim, Wonjun Cho and Youngsoon Baek

Energies 2020, 13(2), 297; https://doi.org/10.3390/en13020297 - 07 Jan 2020

Cited by 11 | Viewed by 2442

Abstract

The utilization of fossil fuels has led to a gradual increase in greenhouse gas emissions, which have accelerated global climate change. Therefore, there is a growing interest in renewable energy sources and technologies. Biogas has gained considerable attention as an abundant renewable energy [...] Read more.

The utilization of fossil fuels has led to a gradual increase in greenhouse gas emissions, which have accelerated global climate change. Therefore, there is a growing interest in renewable energy sources and technologies. Biogas has gained considerable attention as an abundant renewable energy resource. Common biogases include anaerobic digestion gas and landfill gas, which can be used to synthesize high-value-added syngas through catalytic reforming. Because syngas (CO and H₂) is synthesized at high reaction temperature, carbon is generated by the Boudouard reaction from CO and CH₄ cracking; thus, C blocks the pores and surface of the catalyst, thereby causing catalyst deactivation. In this study, a simulation was performed to measure the CH₄ and CO₂ conversion rates and the syngas yield for different ratios of CO₂/CH₄ (0.5, 1, and 2). The simulation results showed that the optimum CO₂/CH₄ ratio is 0.5; therefore, biogas reforming over the 3 wt% Ni/Ce-MgO-ZrO₂/Al₂O₃ catalyst was performed under these conditions. CH₄ and CO₂ conversion rates and the syngas yield were evaluated by varying the R values (R = (CO₂ + O₂)/CH₄) on the effect of CO₂ and O₂ oxidants of CH₄. In addition, steam was added during biogas reforming to elucidate the effect of steam addition on CO₂ and CH₄ conversion rates. The durability and activity of the catalyst after 200-h biogas reforming were evaluated under the optimal conditions of R = 0.7, 850 °C, and 1 atm. Full article

(This article belongs to the Special Issue Selected Papers from the 9th Asia-Pacific Forum on Renewable Energy (AFORE 2019))

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