• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2009년도 추계학술발표대회 논문집
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• pp.320-323
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• 2009

Weather data is an important variable for the estimation value of the program for evaluating energy performance. The difference in data value of major weather elements used in weather data (temperature, insolation amount) were compared and analyzed. It was found that temperature showed similar values but insolation amount took different values. Especially in Ulsan, since the Meteorological Association does not measure insolation amount. To optimize the incident solar radiation, the solar azimuth angles are needed for solar photovoltaic systems. Test results shows that the $60^{\circ}$installation angel higher efficient than the $30^{\circ}$ installation angel in winter.

• 자원ㆍ환경경제연구
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• 제21권2호
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• pp.271-299
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• 2012

환경과 경제성장과의 관계는 환경경제학 분야에서 오랜 동안 논란이 되어왔으며, 논란의 핵심은 두 변수간의 내생성(endogeneity)과 생략변수(omitted variables)들에 관한 문제들이다. 본 연구는 논란의 핵심들을 고려하여 우리나라의 1981년~2008년까지의 시계열자료를 바탕으로 $CO_2$ 배출량과 경제성장 간의 인과관계 및 에너지믹스의 영향을 실증적으로 분석하였다. 에너지믹스와 계량경제학 문제들을 고려한 대부분의 모형에서 $CO_2$ 배출량과 경제성장의 관계가 역 U자형이라는 EKC 가설을 확인할 수 있었으며, 에너지믹스가 국내 온실가스 감축에 크게 기여하는 것으로 나타났다. 에너지믹스가 $CO_2$ 배출에 미치는 영향은 원자력에너지가 다른 에너지원에 비해 $CO_2$ 배출량 감축에 가장 큰 기여를 하였으나, 신재생에너지는 $CO_2$ 감축에 거의 기여하지 못한 것으로 분석되었다. 이는 지금까지 국내에서 신재생에너지 비중이 다른 에너지원에 비해 적었기 때문이다. 또한 최종 에너지 소비부문은 $CO_2$ 증가와 수송부문의 연관성이 통계적으로 유의한 것으로 나타났다.

• 신재생에너지
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• 제5권3호
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• pp.4-12
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• 2009

The effect of change in DFIG (doubly-fed wind power generator) rotating speed and active power on the grid was analyzed to understand the characteristics of wind power using the wind power simulator connected to the grid at Gochang Power Quality Test Center. Electric power quality improvement devices (DVR, STATCOM, SSTS) and electric power quality disturbance application devices for 22.9 kV grid are equipped at Gochang Power Quality Test Center. Induction motor and VVVF inverter were used to emulate the blade of a wind power generator, and a simulator for Cage wound induction generator and DFIG was developed. The trial line were assumed to be 20 km and 40 km in length, and variable wind speed pattern was set using wind speed data from Ducjeokdo to verify the power characteristics of the wind power generator according to rotating speed.

• 신재생에너지
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• 제7권4호
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• pp.30-36
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• 2011

The objective of this study is to investigate the effects of the refrigerant charge amount on the performance of a water-to-water ground source heat pump with a variation of compressor speed and the secondary fluid flow rate. The water-to-water ground source heat pump was tested by varying refrigerant charge amount from -40% to 20% of full charge. Compressor speed was changed from 30 Hz to 75 Hz and the secondary fluid flow rate was adjusted from 6 LPM to 14 LPM. For all test conditions, EWTs of an indoor heat exchanger and an outdoor heat exchanger were maintained at standard conditions of ISO 13256-2. The slope of the COP with the variation of charge amount is much steeper at undercharged conditions than that at overcharged conditions. For all compressor speed, the variation of the system performance according to charge amounts showed the similar trends. However, the optimum charge amount of the system increased a little with an increment of compressor speed. When the secondary fluid flow rate decreased, the system was optimized at higher refrigerant charge amount conditions.

• 신재생에너지
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• 제7권2호
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• pp.36-42
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• 2011

The wind speed at the altitude around 300 m is much higher and less variable than at the altitude around 80 m which is the same height of the MW class tower turbine's hub height. The wind power density is increased 0.37 W/$m^2$ per meter at the altitude around 6 to 7 km and 0.25 W/$m^2$ per meter at the altitude around 80 to 500 m. There are two types of power generation systems using lifting bodies. The one is that The generator is installed in the ground station and stretched into the lifting body through the tether. The other is that the generator is installed in the lifting body and stretched into the ground station through the tether. Many kinds of lifting bodies are also researched in the world, called kites, wings, single or twin aerostat, and so on. This article introduced the technical development status and the market prospects of the high altitude wind power generation system all over the world in detail.

• 신재생에너지
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• 제1권4호
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• pp.30-37
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• 2005

Cycle simulation of Ground Source Heat Pump[GSHP] system was carried out to determine the design specification of basic components such as turbo compressor and heat exchangers. Part load operation characteristics of the designed GSHP system was estimated using the compressor and heat exchanger performance data. A 50RT class turbo compressor for GSHP system is now under development, in which R134a refrigerant is adopted as working fluid. The compressor with variable cascade diffusers is designed to work both in cooling and heating modes so that it can actively keep up with the climate change with high efficiency. The normal running speeds of the compressor are 59000rpm for heating mode and 70000rpm for tooling mode respectively. It has two identical impellers at both ends of the rotor so as to minimize aero-induced thrust force effectively. GSHP system was coupled with a vortical type heat exchanger, and heat gain and heat loss from ground were evaluated per a bore hole. For the optimal integration of the heat pump system, its header for circulating fluid was combined with the ground heat exchangers in parallel and series configuration.

• Journal of Information Processing Systems
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• 제16권6호
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• pp.1343-1358
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• 2020

In the stagewise arithmetic orthogonal matching pursuit algorithm, the weak threshold used in sparsity estimation is determined via maximum iterations. Different maximum iterations correspond to different thresholds and affect the performance of the algorithm. To solve this problem, we propose an improved variable weak threshold based on the stagewise arithmetic orthogonal matching pursuit algorithm. Our proposed algorithm uses the residual error value to control the weak threshold. When the residual value decreases, the threshold value continuously increases, so that the atoms contained in the atomic set are closer to the real sparsity value, making it possible to improve the reconstruction accuracy. In addition, we improved the generalized Jaccard coefficient in order to replace the inner product method that is used in the stagewise arithmetic orthogonal matching pursuit algorithm. Our proposed algorithm uses the covariance to replace the joint expectation for two variables based on the generalized Jaccard coefficient. The improved generalized Jaccard coefficient can be used to generate a more accurate calculation of the correlation between the measurement matrixes. In addition, the residual is more accurate, which can reduce the possibility of selecting the wrong atoms. We demonstrate using simulations that the proposed algorithm produces a better reconstruction result in the reconstruction of a one-dimensional signal and two-dimensional image signal.

• 에너지공학
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• 제23권1호
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• pp.7-20
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• 2014

본 연구에서는 전국적으로 48만ha에 걸쳐 연료림으로 조성되어 있는 리기다소나무를 에너지연료로 활용하기 위해 최적의 생산시스템을 개발하고 이에 따른 공급가격과 전기 열 판매가격 및 이용률 등을 고려한 우드칩 연료한계가격을 산출하였으며 다양한 시나리오에 따른 경제성 민감도 분석을 수행하였다. 열 및 발전 전용시설에서의 경제성을 결정짓는 가장 중요한 변수는 연료공급가격이다. 열 전용시설에서는 본 연구에서 제안된 모든 생산시스템에서 생산되는 우드칩 연료의 활용이 가능하며 발전 전용시설에서는 생산비가 가장 높은 연료사용에는 일부 한계가 있으나 전기 판매가격이 현재의 SMP(pitch pine : 계통한계가격)보다 높아지거나 이용률이 80%이상으로 되는 경우 모두 활용 가능한 것으로 분석되었으며, 더욱이 RPS제도 시행에 따른 신재생에너지 인증서(REC:Renewable Energy Certificate)편익과 온실가스 절감효과로 CDM(Clean Development Mechanism)편익 등을 고려할 경우 충분히 활용 가능한 것으로 분석되었다. 따라서, 국내 발전부문에서의 RPS 공급의무율 이행을 위해서 산림 바이오매스의 활용이 적극 권장된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.1342-1344
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• 2002

Wind is a significant and valuable renewable energy resource. It is safe and abundant and can make an important contribution to future clean, sustainable and diversified electricity supplies. Unlike other sources of energy, wind does not pollute the atmosphere nor create any hazardous waste. In some countries wind energy is already competitive with fossil and nuclear power even without accounting for the environmental benefits of wind power. The cost of electricity from conventional power stations does not usually take full account of its environmental impact (acid rain, oil slick clean up, the effects of climate change, etc). In this paper, a transient phenomenon simulation method for Wind Power Generation System(WPGS) under real weather conditions has been proposed. The simulation method is expected to be able to analyze easily under various conditions with considering the sort of wind turbine, the capacity of system and the converter system. Wind turbine connected to the synchronous generator and power converter was simulated.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.87.1-87.1
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• 2017

High functional catalyst to efficiently produce clean and earth-abundant renewable fuels plays a key role in securing energy sustainability and environmental protection of our society. Hydrogen has been considered as one of the most promising energy carrier as represented by focused research works on developing catalysts for the hydrogen evolution reaction (HER) from the water hydrolysis over the last several decades. So far, however, the major catalysts are expensive transition metals. Here using first principles density functional theory (DFT) calculations we screen various pyrites for HER by identifying fundamental descriptor governing the catalytic activity. We enable to capture a strong linearity between experimentally measured exchange current density in HER and calculated adsorption energy of hydrogen atom in the pyrites. The correlation implies that there is an underlying design principle tuning the catalytic activity of HER.