• 천문학회지
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• 제36권spc1호
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• pp.83-91
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• 2003

There are terrestrial signatures of the solar activity cycle in ice core data (Ram & Stoltz 1999), but the variations in the sun's irradiance over the cycle seem too small to account for the signature (Lean 1997; Goode & Dziembowski 2003). Thus, one would expect that the signature must arise from an indirect effect(s) of solar activity. Such an indirect effect would be expected to manifest itself in the earth's reflectance. Further, the earth's climate depends directly on the albedo. Continuous observations of the earthshine have been carried out from Big Bear Solar Observatory since December 1998, with some more sporadic measurements made during the years 1994 and 1995. We have determined the annual albedos both from our observations and from simulations utilizing the Earth Radiation Budget Experiment (ERBE) scene model and various datasets for the cloud cover, as well as snow and ice cover. With these, we look for inter-annual and longer-term changes in the earth's total reflectance, or Bond albedo. We find that both our observations and simulations indicate that the albedo was significantly higher during 1994-1995 (activity minimum) than for the more recent period covering 1999-2001 (activity maximum). However, the sizes of the changes seem somewhat discrepant. Possible indirect solar influences on the earth's Bond albedo are discussed to emphasize that our earthshine data are already sufficiently precise to detect, if they occur, any meaningful changes in the earth's reflectance. Still greater precision will occur as we expand our single site observations to a global network.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.106.1-106.1
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• 2011

The Cu(In,Ga)Se2 (CIGS) thin film solar cells have been achieved until almost 20% efficiency by NREL. These solar cells include chemically deposited CdS as buffer layer between CIGS absorber layer and ZnO window layer. Although CIGS solar cells with CdS buffer layer show excellent performance, the short wavelength response of CIGS solar cell is limited by narrow CdS band gap of about 2.42 eV. Taking into consideration the environmental aspect, the toxic Cd element should be replaced by a different material. Among Cd-free candidate materials, the CIGS thin film solar cells with ZnS buffer layer seem to be promising with 17.2%(module by showa shell K.K.), 18.6%(small area by NREL). However, ZnS/CIGS solar cells still show lower performance than CdS/CIGS solar cells. There are several reported reasons to reduce the efficiency of ZnS/CIGS solar cells. Nakada reported ZnS thin film had many defects such as stacking faults, pin-holes, so that crytallinity of ZnS thin film is poor, compared to CdS thin film. Additionally, it was known that the hetero-interface between ZnS and CIGS layer made unfavorable band alignment. The unfavorable band alignment hinders electron transport at the heteo-interface. In this study, we focused on growing defect-free ZnS thin film and for favorable band alignment of ZnS/CIGS, bandgap of ZnS and CIGS, valece band structure of ZnS/CIGS were modified. Finally, we verified the photovoltaic properties of ZnS/CIGS solar cells.

• 에너지공학
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• 제23권2호
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• pp.175-182
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• 2014

신재생에너지 분야 중 특히 태양에너지를 이용하는 분야는 자원의 무한 및 청정성 때문에 그 사용량이 증가 추세에 있다. 우리나라에서 태양열에너지의 이용률이 전체 에너지 사용량 중 아직 미미한 실정이지만, 근래 정부의 정책적 지원에 힘입어 이 분야에 대한 연구가 활발히 이루어지고 있다. 본 연구는 외부 날씨의 영향을 받지 않고 실내에서 안정적으로 태양열집열기에 관한 실험을 수행할 수 있는 태양열집열기 성능검사 시스템을 구축하고 또한 새로운 형태의 열사이폰관형 태양열집열기를 연구 개발하여 기존의 이중진공관형 태양열집열기와 집열효율을 비교하고자 하였다. 그 결과 할로겐 램프를 이용한 실내 측정의 경우, 열사이폰관형 태양열집열기의 집열효율이 이중진공관형 태양열집열기보다 120분 직후 약 15~22% 증가하였다. 또한 실제 태양을 이용한 실외 측정의 경우도 열사이폰관 형 집열기가 이중진공관형 집열기보다 최대 약 46% 높았다.

• 신재생에너지
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• 제8권1호
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• pp.24-34
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• 2012

The main issue of boron doped p-type czochralski-grown silicon solar cells is the degradation when they are exposed to light or minority carriers injection. This is due to the meta-stable defect such as boron-oxygen in the Cz-Si material. Although a clear explanation is still researching, recent investigations have revealed that the Cz-Si defect is related with the boron and the oxygen concentration. They also revealed how these defects act a recombination centers in solar cells using density function theory (DFT) calculation. This paper reviews the physical understanding and gives an overview of the degradation models. Therefore, various methods for avoiding the light-induced degradation in Cz-Si solar cells are compared in this paper.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권4호
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• pp.269-275
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• 2004

Photovoltaic(PV) system has been studied and watched with keen interest due to a clean and renewable power source. But, the output power of PV system is not only unstable but uncontrollable, because the maximum power point tracking (MPPT) of PV system is still hard with the tracking failure under the sudden fluctuation of irradiance. Authors suggest that the optimal voltage for MPPT be obtained by only solar cell temperature. Having an eye on that the optimal voltage point of solar cell is in proportion to its panel temperature, with operating the power converter whose operating point keeps its input voltage to the optimal voltage imagined by the surface's temperature of PV panel, the maximum power point becomes tenderly possible to be tracked. In order to confirm the availability of the proposed control scheme. And both control methods are simulated not only on the various angle of sampling time of switching control, but also with the real field weather condition. As the results of that, the conversion efficiency between PV panel and converter of the proposed control scheme was much better than that of the power comparison MPPT control, and what is better, the output voltage of PV panel was extremely in stable when the optimal voltage for MPPT is obtained by only solar cell temperature.

• Advances in Energy Research
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• 제6권2호
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• pp.145-160
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• 2019

The world population reaches to about 7.7 billion in 2018 from 6.2 billion in 2000. This much growth in population results in increased energy demand and increased food supply. As the conventional energy sources are limited. These may deplete soon if consumed at this rate. So, the world is switching towards the utilization of non-conventional sources of energy. Energy from sun is the best method as it can not only solve the energy issue but also helps in meeting food demand by conserving it. Greenhouses are made for the purpose of food conservation. Various types of solar dryers are developed by researchers till now and still the effort is being putted to make them more efficient. Hybrid greenhouse is also effort toward utilization of solar energy in more efficient way. The paper presents the heat and mass transfer analysis of hybrid greenhouse solar dryer developed by different researchers till now. The review helps the researcher in understanding the heat and mass transfer taking place inside the hybrid greenhouse and how it can be further improved.

• 천문학회보
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• 제37권2호
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• pp.106.1-106.1
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• 2012

The Gegenschein is a faint glow around the anti-solar point caused by the interplanetary dust particle(IDP)'s back-scattering enhancement. From the previous low resolution observations, the overall morphology of the Gegenschein has been intensively studied. However, sub-degree scale fine structure of the Gegenschein is still not well known, even though the detailed morphology of the Gegenschein within a few degree from the anti-solar point may supply pivotal information about the property of the IDPs. We made optical CCD observations of the Gegenschein between 2003 March and 2006 November. From the observations, we succeeded in making high resolution images of the Gegenschein, with unprecedented 1.'4 resolution. Our results concur with IDP cloud model based on the infrared observations combined with scattering phase function derived from low resolution data. The only exception is the anti-solar point. We found a steep additional brightness enhancement existing at the exact anti-solar point. Plausible explanation of the finding is that the IDPs are significantly larger than observing wavelength, and have irregular morphology or inhomogeneous internal structure. Furthermore, we measured average geometric albedo of the IDPs from the optical brightness of the anti-solar point. The geometric albedo was $0.06{\pm}0.01$, similar to those of comets or C-type asteroids.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.221-239
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• 2014

The global demand for energy has been increasing since past decades. Various technologies have been working to find a suitable alternative for the generation of sustainable energy. Photovoltaic technologies for solar energy conversion represent one of the significant routes for the green and renewable energy production. Despite of remarkable improvement in solar cell technologies, the generation of power is still suffering with lower energy conversion efficiency, high production cost, etc. The major problem in improving the PV efficiency is spectral mismatch between the incident solar spectrum and bandgap of a semiconductor material used in solar cell. Luminescent materials such as rare-earth doped phosphor materials having the quantum efficiency higher than unity can be helpful for photovoltaic applications. Quantum cutting phosphors are the most suitable candidates for the generation of two or more low-energy photons for the absorption of every incident high-energy photons. The phosphors which are capable of converting UV photon to visible and near-IR (NIR) photon are studied primarily for photovoltaic applications. In this review, we will survey various near IR quantum cutting phosphors with respective to their synthesis method, energy transfer mechanism, nature of activator, sensitizer and dopant materials incorporation and energy conversion efficiency considering their applications in photovoltaics.

• 한국태양에너지학회 논문집
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• 제34권3호
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• pp.75-81
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• 2014

Recently, the use of renewable energy has been attracted due to the interest in energy-saving and the reduction of CO2 emission. In order to reduce the energy consumption of the cooling and the heating in the field of the architectural engineering, heat pump systems using renewable energy have been developed and used in various applications. In many researches, integrated heat pump systems are suggested which use solar and geothermal heat as the heat source for cooling and heating. However, it is still difficult to predict the performance of the systems, because the characteristic of heat exchange in each system is complicated and various. In this system, the performance prediction simulation of the heat pump was developed using a dynamic simulation model. This paper describes the summary of the suggested systems and the result of the simulation. The average temperature of the heat source, heating loads and COP were calculated with the cases of different local conditions, different system composition and different operation time by TRNSYS 17.

• 에너지공학
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• 제23권4호
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• pp.189-195
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• 2014

신재생에너지 분야 중 특히 태양에너지를 이용하는 분야는 자원의 무한 및 청정성 때문에 그 사용량이 증가 추세에 있다. 우리나라에서 태양열에너지의 이용률이 전체 에너지 사용량 중 아직 미미한 실정이지만, 근래 정부의 정책적 지원에 힘입어 이 분야에 대한 연구가 활발히 이루어지고 있다. 본 연구는 태양열집열기의 형상 변화에 따른 집열효율을 조사하기 위하여 단일진공관 태양열집열기를 이용한 실험 및 이중진공관 태양열집열기와의 비교 실험을 수행하였다. 그 결과, 본 실험장치에서 히트 파이프의 최고온도의 차이로부터 태양열집열기 형상 변화에 따른 집열효율의 변화를 확인할 수 있었다. 또한 본 연구대상 태양열집열기의 히트파이프의 온도가 비교대상 태양열집열기보다 높음에도 불구하고 방열핀의 온도가 낮게 관측되었다. 이것은 본 연구대상의 태양열집열기는 히트파이프 방열부인 헤드부와 방열핀 사이의 접촉저항이 비교대상의 접촉저항보다 크다는 것을 나타내며, 집열효율을 높이기 위해서는 태양열집열기의 여러 부분의 성능개선뿐만 아니라 접촉저항에 의한 집열손실도 감소시켜야 함을 확인할 수 있었다.