• Journal of the Korea Convergence Society
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• v.2 no.2
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• pp.47-56
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• 2011

Korea Ministry of Knowledge Economy has estimated that wind power (WP) will be occupied 37% in 2020 and 42% in 2030 of the new energy sources, and also green energies such as photovoltaic (PV) and WP are expected to be interconnected with the distribution system because of Renewable Portfolio Standard (RPS) starting from 2012. However, when a large scale wind power plant (over 3[MW]) is connected to the traditional distribution system, protective devices (mainly OCR and OCGR of re-closer) will be occurred mal-function problems due to changed fault currents it be caused by Wye-grounded/Delta winding of interconnection transformer and %impedance of WP's turbine. Therefore, when Double-Fed Induction Generator (DFIG) of typical WP's Generator is connected into distribution system, this paper deals with analysis three-phase short, line to line short and a single line ground faults current by using the symmetrical components of fault analysis and PSCAD/EMTDC modeling.

• Journal of the Korea Organic Resources Recycling Association
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• v.29 no.4
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• pp.67-76
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• 2021

Biogasification is a technology that produces environmentally friendly fuel using methane gas generated in the process of stably decomposing and processing organic waste. Biogasification is the most used method for energy conversion of organic waste with high moisture content, and is a useful method for organic waste treatment following the prohibition of direct landfill (2005) and marine dumping (2013). Due to African Swine Fever (ASF), which recently occurred in Korea, recycling of wet feed is prohibited, and consumers such as dry feed and compost are negatively recognized, making it difficult to treat food waste. Accordingly, biogasification is attracting more attention for the treatment and recycling of food waste. Korea's energy consumption amounted to 268.41 106toe, ranking 9th in the world. However, it is an energy-poor country that depends on foreign imports for about 95.8% of its energy supply. Therefore, in Korea, the Renewable Energy Portfolio Standard (RPS) is being introduced. The domestic RPS system sets the weight of the new and renewable energy certificate (REC, Renewable energy certificate) of waste energy lower than that of other renewable energy. Therefore, an additional incentive system is required for the activation of waste-to-energy. In this study, the operation of an anaerobic digester that treats food waste, food waste Leachate and various organic wastes was confirmed. It was intended to be used as basic data for preparing the waste-to-energy incentive system through precise monitoring for a certain period of time. Four sites that produce biogas from organic waste and use them for power generation and heavy gas were selected as target facilities, and field surveys and sampling were conducted. Basic properties analysis was performed on the influent sample of organic waste and the effluent sample according to the treatment process. As a result of the analysis of the properties, the total solids of the digester influent was an average of 12.11%, and the volatile solids of the total solids were confirmed to be 85.86%. BOD and CODcr removal rates were 60.8% and 64.8%. The volatile fatty acids in the influent averaged 55,716 mg/L. It can be confirmed that most of the volatile fatty acids were decomposed and removed with an average reduction rate of 92.3% after anaerobic digestion.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.2
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• pp.145-152
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• 2012

As the problems of global warming are brought up recently, many skillful solutions for developing new renewable energy are suggested. One of the most remarkable things is ocean energy. Korea has abundant ocean energy resources owing to geographical characteristics surrounded by sea on three sides, thus the technology of commercialization about tidal current power, wave power is demanded. Especially, Tidal energy conversion system is a means of maintaining environment naturally. Tidal current generation is a form to produce electricity by installing rotors, generators to convert a horizontal flow generated by tidal current into rotating movement. According to rotor direction, a tidal current turbine is largely distinguished between horizontal and vertical axis shape. Power capacity depends on the section size crossing a rotor and tidal current speed. We therefore investigated three dimensional flow analysis and performance evaluation using commercial ANSYS-CFX code for an 100 kW class horizontal axis turbine for low water level. Then We also studied three dimensional flow characteristics of a rotating rotor and blade surface streamlines around a rotor. As a result, We found that torque increased with TSR, the maximum torque occurred at TSR 3.77 and torque decreased even though TSR increased. Moreover we could get power coefficient 0.38 at designed flow velocity.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.619-619
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• 2009

Recently, silica nanostructures are widely used in various applicationary areas such as chemical sensors, biosensors, nano-fillers, markers, catalysts, and as a substrate for quantum dots etc, because of their excellent physical, chemical and optical properties. Additionally, these days, semiconductor silica and silicon with high purity is a key challenge because of their metallurgical grade silicon (MG-Si) exhibit purity of about 99% produced by an arc discharge method with high cast. Tremendous efforts are being paid towards this direction to reduce the cast of high purity silicon for generation of photovoltaic power as a solar cell. In this direction, which contains a small amount of impurities, which can be further purified by acid leaching process. In this regard, initially the low cast rice-husk was cultivated from local rice field and washed well with high purity distilled water and were treated with acid leaching process (1:10 HCl and $H_2O$) to remove the atmospheric dirt and impurity. The acid treated rice-husk was again washed with distilled water and dried in an oven at $60^{\circ}C$. The dried rice-husk was further annealed at different temperatures (620 and $900^{\circ}C$) for the formation of silica nanospheres. The confirmation of silica was observed by the X-ray diffraction pattern and X-ray photoelectron spectroscopy. The morphology of obtained nanostructures were analyzed via Field-emission scanning electron microscope(FE-SEM) and Transmission electron microscopy(TEM) and it reveals that the size of each nanosphares is about 50-60nm. Using the Inductively coupled plasma mass spectrometry(ICP-MS), Silica was analyzed for the amount of impurities.

• Journal of the Korean Association of Geographic Information Studies
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• v.13 no.2
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• pp.146-156
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• 2010

The objective of this study was to improve the accuracy of calculation and estimation of solar radiation and duration of sunshine, which are the most important variables of photovoltaic power generation in deciding the location of photovoltaic facilities efficiently. With increasing interest in new and renewable energies, research on solar energy is also being conducted actively, but there have not been many studies on the location of photovoltaic facilities. Thus, this study calculated solar duration and solar radiation based on geographical factors, which have the most significant effect on solar energy in GIS environment, and corrected the results of analysis using diffuse radiation. Moreover, we performed ordinary kriging, a spatial statistical analysis method, for estimating values for parts deviating from the spatial resolution of input data, and used variogram, which can determine the spatial interrelation and continuity of data, in order to estimate accurate values. In the course, we compared the values of variogram factors and estimates from applicable variogram models, and selected the model with the lowest error rate. This method is considered helpful to accurate decision making on the location of photovoltaic facilities.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.8
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• pp.1058-1063
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• 2020

This paper presents a new insulation resistance calculation technique to prevent electric shock and fire accidents due to the dielectric breakdown in the primary insulation section of the IT ground system. The solar power generation market is growing rapidly due to the recent expansion of renewable energy and energy storage systems, but as the insulation is destroyed and fire accidents frequently occur, a device for monitoring the insulation resistance state is indispensable to the IT grounding method. Compared to the conventional algorithm that use a method of multiplying a time constant to a fixed coefficient, the proposed insulation resistance calculation method has a fast response time and high accuracy over a wide insulation resistance range by applying a different coefficient according to the values of the insulation impedance. The proposed dynamic time constant based insulation resistance calculation technique reduces the response time by up to 39.29 seconds and improves the error rate by 20.11%, compared to the conventional method.

• Journal of Energy Engineering
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• v.28 no.3
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• pp.65-79
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• 2019

The study attempted to estimate the optimal facility capacity by combining renewable energy sources that can be connected with gas CHP in industrial complexes. In particular, we reviewed industrial complexes subject to energy use plan from 2013 to 2016. Although the regional designation was excluded, Sejong industrial complex, which has a fuel usage of 38 thousand TOE annually and a high heat density of $92.6Gcal/km^2{\cdot}h$, was selected for research. And we analyzed the optimal operation model of CHP Hybrid System linking fuel cell and photovoltaic power generation using HOMER Pro, a renewable energy hybrid system economic analysis program. In addition, in order to improve the reliability of the research by analyzing not only the heat demand but also the heat demand patterns for the dominant sectors in the thermal energy, the main supply energy source of CHP, the economic benefits were added to compare the relative benefits. As a result, the total indirect heat demand of Sejong industrial complex under construction was 378,282 Gcal per year, of which paper industry accounted for 77.7%, which is 293,754 Gcal per year. For the entire industrial complex indirect heat demand, a single CHP has an optimal capacity of 30,000 kW. In this case, CHP shares 275,707 Gcal and 72.8% of heat production, while peak load boiler PLB shares 103,240 Gcal and 27.2%. In the CHP, fuel cell, and photovoltaic combinations, the optimum capacity is 30,000 kW, 5,000 kW, and 1,980 kW, respectively. At this time, CHP shared 275,940 Gcal, 72.8%, fuel cell 12,390 Gcal, 3.3%, and PLB 90,620 Gcal, 23.9%. The CHP capacity was not reduced because an uneconomical alternative was found that required excessive operation of the PLB for insufficient heat production resulting from the CHP capacity reduction. On the other hand, in terms of indirect heat demand for the paper industry, which is the dominant industry, the optimal capacity of CHP, fuel cell, and photovoltaic combination is 25,000 kW, 5,000 kW, and 2,000 kW. The heat production was analyzed to be CHP 225,053 Gcal, 76.5%, fuel cell 11,215 Gcal, 3.8%, PLB 58,012 Gcal, 19.7%. However, the economic analysis results of the current electricity market and gas market confirm that the return on investment is impossible. However, we confirmed that the CHP Hybrid System, which combines CHP, fuel cell, and solar power, can improve management conditions of about KRW 9.3 billion annually for a single CHP system.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.196.2-196.2
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• 2011

지구온난화와 화석연료 고갈에 대한 우려로 전세계적으로 신재생에너지의 개발 및 활용이 본격화되고 있다. 특히, 다양한 신재생에너지원 중에서 날씨 및 계절에 의한 영향, 기저부하 담당, 지상 점유 면적, 소음 등 생활환경 영향, 경제성 등을 고려할 때 지열에너지는 미래 청정에너지원로서 기대와 관심이 집중되고 있다. 화산이 존재하지 않는 우리나라에서의 지열발전은 거의 불가능한 것으로 인식되어 지금까지의 심부 지열에너지 개발 프로젝트는 대부분 지역난방, 시설영농 등 직접이용을 목표로 추진되어 왔다. 그러나, 2003년부터 한국지질자원연구원에서 수행한 포항 심부지열에너지 개발사업의 결과로 얻어진 다양한 지질학적/지열학적 증거들을 토대로 분석한 결과, 국내 일부 지역에서는 지하 5 km 심도에서 최대 약 $180^{\circ}C$의 지온이 예상되어 국내에서도 심부 지열에너지를 이용한 지열발전에 대한 가능성이 제기되어 왔다. 여기에, 유럽과 미국 그리고 호주 등 선진국을 중심으로 비화산 지역에서 지하 심부에 인공적으로 지열저류층(파쇄대)을 생성하고 이를 통해 열매체(물)를 순환시킴으로써 생산된 증기를 발전에 활용하는 EGS (Enhanced Geothermal System) 기술이 개발되고 몇몇 성공사례가 발표되었다. 또한, 이러한 기술개발에 힘입어 EGS 지열발전에 대한 선진국의 과감한 연구비 투자가 이어졌다. 이러한 기술적 배경에 발맞추어 우리나라에서도 2010년 12월에 EGS 지열발전 과제가 착수되었다. 이 프로젝트는 아시아에서는 최초로 수행되는 EGS 기술 개발과제로서 2015년까지 약 480억원의 R&D 예산을 투입하여 MW급의 지열발전 pilot plant의 구축을 목표로 하고 있다. 프로젝트가 성공적으로 추진될 경우 국내외적인 파급효과는 매우 클것이다. 특히 2015년까지 1.5 MW의 pilot plant의 구축이 성공적으로 추진될 경우 국내에서는 2017년까지 3 MW 이상, 2020년까지 20 MW이상, 2030년까지 200 MW 이상의 지열발전이 가능할 것으로 기대된다. 또한 축적된 기술개발 경험을 바탕으로 인도네시아, 필리핀 등의 해외의 지열발전 사업에도 진출할 수 있는 계기가 될 것이다. 프로젝트는 넥스지오를 주관기관으로 하고 한국지질자원연구원, 한국건설기술연구원 및 서울대학교 등의 지질자원 관련 연구 및 교육기관과 포스코, 이노지오테크놀로지 등의 산업체가 참여하여 컨소시엄 형태로 추진하고 있으며, 향후 관심있는 여러 기관 및 산업체의 지원과 참여를 기대한다.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.163.1-163.1
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• 2010

2030년까지 신재생에너지발전 비중을 11%로 높이겠다는 정책목표 달성을 위한 정부의 지원방안이 현행 발전차액지원제도(FIT)에서 2012년부터는 신재생에너지의무할당제(RPS)로 전환된다. 전원별로 정해진 발전량에 대해 정부가 일정한 가격으로 구매해주는 현행 제도 하에서 신재생에너지발전사업자는 중장기 가격을 보장받음으로써 수익성을 초기에 확정할 수 있는 장점이 있는 반면 정부 입장에서는 보급이 확대될수록 막대한 재정부담이 발생하고 경쟁을 통해 생산 비용을 낮추기 위한 유인이 부족한 단점이 있다. 이러한 단점을 보완하기 위해 도입되는 의무할당제는 일정 설비규모 이상의 발전사업자에게 신재생에너지발전 의무량을 부과하고 의무대상자가 의무이행의 수단으로 공급인증서(REC)를 발급받거나 구매하여 의무를 이행토록 하는 제도로서 공급인증서 가격 결정을 시장기능에 맡김으로써 신재생에너지 사업자간 경쟁을 촉진시켜 생산비용을 절감하고 정부의 재정부담을 완화하는 장점이 있는 반면 신재생에너지발전사업자 입장에서는 수익성 분석이 복잡해지고 리스크가 증가하는 문제점이 있다. 특히 발전용 연료전지를 활용한 발전사업의 경우 다른 신재생에너지원과 달리 설비투자비용(CAPEX) 외에 가스요금 및 핵심부품의 주기적인 교체 등을 위한 운영비용(OPEX)의 비중이 작지 않기 때문에 더욱 정밀한 분석이 필요하다. 본 연구에서는 신재생에너지발전사업자 입장에서 비용과 편익에 영향을 미치는 각 요소와 그 영향을 파악함으로써 발전용 연료전지의 경제성 분석을 시도해 보았다.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.1
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• pp.21-28
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• 2019

Reversible solid oxide fuel cell (ReSOC) system was integrated with waste steam for electrical energy storage in distributed energy storage application. Waste steam was utilized as external heat in SOEC mode for higher hydrogen production efficiency. Three system configurations were analyzed to evaluate techno-economic performance. The first system is a simple configuration to minimize the cost of balance of plant. The second system is the more complicated configuration with heat recovery steam generator (HRSG). The third system is featured with HRSG and fuel recirculation by blower. Lumped models were used for system performance analyses. The ReSOC stack was characterized by applying area specific resistance value at fixed operating pressure and temperature. In economical assessment, the levelized costs of energy storage (LCOS) were calculated for three system configurations based on capital investment. The system lifetime was assumed 20 years with ReSOC stack replaced every 5 years, inflation rate of 2%, and capacity factor of 80%. The results showed that the exergy round-trip efficiency of system 1, 2, 3 were 47.9%, 48.8%, and 52.8% respectively. The high round-trip efficiency of third system compared to others is attributed to the remarkable reduction in steam requirement and hydrogen compression power owning to fuel recirculation. The result from economic calculation showed that the LCOS values of system 1, 2, 3 were 3.46 ¢/kWh, 3.43 ¢/kWh, and 3.14 ¢/kWh, respectively. Even though the systems 2 and 3 have expensive HRSG, they showed higher round-trip efficiencies and significant reduction in boiler and hydrogen compressor cost.