• Journal of Hydrogen and New Energy
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• v.26 no.3
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• pp.234-240
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• 2015

In the face of the world's growing energy storage needs, liquid hydrogen offers a high energy density solution for the storage and transport of energy throughout society. A 5 L liquid hydrogen storage tank has been designed, fabricated and tested to investigate boil-off rate of liquid hydrogen. As the insulation plays a key role on the cryogenic vessels, various insulation methods have been employed. To reduce heat conduction loss, the epoxy resin-based insulation supports G-10 were used. To minimize radiation heat loss, vapor cooled radiation shield, multi-layer insulation, and high vacuum were adopted. Mass flow meter was used to measure boil-off rate of the 5 L cryogenic vessel. A series of performance tests were done for liquid nitrogen and liquid hydrogen to compare with design parameters, resulting in the boil-off rate of 1.7%/day for liquid nitrogen and 16.8%/day for liquid hydrogen at maximum.

• Journal of Hydrogen and New Energy
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• v.25 no.3
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• pp.289-296
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• 2014

Here, we have studied the effect of water added electrolyte on the photovoltaic performance of dye-sensitized solar cells (DSSCs). It was found that open-circuit voltage ($V_{oc}$) increased and short-circuit current density ($j_{sc}$) decreased with the increase of the amount of added water in the electrolyte of the DSSCs. Electrochemical impedance spectroscopy (EIS) study showed that the electrolyte with added water shifted the dye loaded $TiO_2$ conduction band upward that eventually increased $V_{oc}$ of the cells. On the other hand, the upward shift of $TiO_2$ conduction band decreased the driving force for the electron injection from the lowest unoccupied molecular orbital (LUMO) of the dye molecules to the conduction band of $TiO_2$ that resulted in decreased $j_{sc}$.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.45-48
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• 2007

Thermochemical 2-step methane reforming, involving the reduction of metal oxide with methane to produce syn-gas and the oxidation of the reduced metal oxide with water to produce pure hydrogen, was investigated on ferrite-based metal oxide mediums and $WO_{3}/ZrO_{2}$. Thermochemical 2-step methane reforming were accomplished at 900 $^{\circ}C$(syn-gas production step) and 800 $^{\circ}C$(water-splitting step). In syn-gas production step, it appeared carbon deposition on metal oxides with increasing react ion time. Various mediums showed the different starting point of carbon deposition each other. To minimize the carbon deposition, the reaction time was controlled before the starting point of carbon deposition. As a result, $CO_{x}$ were not evolved in water-splitting step, Among the various metal oxides, $Mn-ferrite/ZrO_{2}$ showed high reactivity, proper $H_{2}/CO$ ratio, high selectivity of undesired $CO_{2}$ and high evolution of $H_{2}$.

• Journal of Hydrogen and New Energy
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• v.24 no.5
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• pp.421-427
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• 2013

We report on the time dependent degradation of cell in dye-sensitized solar cells (DSSC). The photovoltaic performance of DSSC over a period of time was investigated in liquid electrolyte based on triiodide/iodide during six days. It was found that the short circuit current density ($j_{sc}$) of the cell dropped from 9.9 to $7mA/cm^2$ while efficiency (${\eta}$) of the cell decreased from 4.4 to 3.3%. The parameters corresponding to fundamental electronic and ionic processes in a working DSSC are determined from the electrochemical impedance spectrascopy (EIS) at open-circuit potential ($V_{oc}$). EIS study of the DSSC in the this work showed that the electron life time ${\tau}_r$ and chemical capacitance $C_{\mu}$ decreased significantly after six days. It was correlated the $j_{sc}$ and efficiency decreased after six days.

• Journal of Hydrogen and New Energy
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• v.27 no.5
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• pp.540-546
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• 2016

Besides high-efficient photovoltaics based on silicon, polymers, dye-sensitization and hybrid perovskite materials, biomimetic solar cells inspired by a leaf in nature has also been actively studied. As one example, a hydrogel based photovoltaics (HGPV) is a low-cost, environmentally friendly device and requires easy fabrication process. In this paper, the effect of hydroquinone additive on the performance of the HGPV is discussed. The photocurrent increases ~14 times upon the addition of hydroquinone into the agarose hydrogel medium. The photocurrent increase is maximum at the optimum dye concentration, while the photovoltage is barely affected by the dye concentration. The effect of the agarose content in the hydrogel and the types of dyes on the photocurrent is also investigated. Finally, it is shown that the photovoltaic performance of HGPV with hydroquinone can be drastically improved when $TiO_2$ film is deposited on the anode electrode.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.4
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• pp.94-101
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• 2015

Each of power systems of solar cell and fuel cell were configured and validated for long endurance UAV, as the preliminary research for the integration of power systems. Solar power system consisted of solar modules fabricated by solar cells of Sunpower's C60, commercial solar MPPT controller and Li-po battery, and then was validated. The re-start characteristics of hydrogen production from $NaBH_4$ hydrolysis was validated for operating the commercial fuel cell. The average voltage drop of Li-po battery in solar power system was -2.9 V/hour. The performance of re-start characteristics of $NaBH_4$ hydrolysis was stable in sequence mode of mission profile. Each of single systems were satisfied for the proposed mission profile.

• 한국태양에너지학회:학술대회논문집
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• 2008.04a
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• pp.227-232
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• 2008

Stirling engine for solar thermal power is an essential part of Dish-Stirling system which generates electricity by using direct normal irradiation and will go into commercialization in near future. For the Stirling engine used in this study is Solo 161 model the capacity of which is 10 kWe and was already used for the Dish-Stirling system of KIER in Jinhae. The receiver of Stirling engine absorbes concentrated solar radiation and transfer it to working fluid of Hydrogen. The working condition of striling engine is high temperature and high pressure to make high efficiency. Therefore the receiver should stand against high temperature of above 800 $^{\circ}C$ and high pressure of max. 150 bar with good performance of heat transfer. The receiver is composed of 78 Inconel tubes of 1/8" with thickness of 0.71 mm and two reserviors which is connected with two cylinders. In order to know the charaterristics of heat transfer of Stirling engine receiver, simulation on the heat transfer of the receiver of Solo 161 is conducted by using CFD code of Fluent. The heat flux on the receiver surface has a shape of Gaussian distribution so, it is necessary to simulate a whole receiver. However, It is difficult and time consuming to simulate the whole receiver that one tube with different heat flux conditions are considered in this study. From the simulation results, heat transfer charateristics of receiver are observed and tube wall and fluid temperature and heat transfer coefficient are obtained and compared with the calculated results from Dittus-Boelter's correlation.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.70-70
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• 2011

The prospects of current and coming solar-photovoltaic (PV) technologies are envisioned, arguing this solar-electricity source is beyond a tipping point in the complex worldwide energy outlook. Truly, a revolution in both the technological advancements of solar PV and the deployment of this energy technology is underway; PV is no longer an outlier. The birth of modern photovoltaics (PV) traces only to the mid-1950s, with the Bell Telephone Laboratories' development of an efficient, single-crystal Si solar cell. Since then, Si has dominated the technology and the markets, from space through terrestrial applications. Recently, some significant shift toward technology diversity have taken place. Some focus of this presentation will be directed toward PV R&D and technology advances, with indications of the limitations and relative strengths of crystalline (Si and GaAs) and thin-film (a-Si:H, Si, Cu(In,Ga)(Se,S)2, CdTe). Recent advances, contributions, industry growth, and technological pathways for transformational now and near-term technologies (Si and primarily thin films) and status and forecasts for next-generation PV (nanotechnologies and non-conventional and "new-physics" approaches) are evaluated. The need for R&D accelerating the now and imminent (evolutionary) technologies balanced with work in mid-term (disruptive) approaches is highlighted. Moreover, technology progress and ownership for next generation solar PV mandates a balanced investment in research on longer-term (the revolution needs revolutionary approaches to sustain itself) technologies (quantum dots, multi-multijunctions, intermediate-band concepts, nanotubes, bio-inspired, thermophotonics, ${\ldots}$ and solar hydrogen) having high-risk, but extremely high performance and cost returns for our next generations of energy consumers. This presentation provides insights to the reasons for PV technology emergence, how these technologies have to be developed (an appreciation of the history of solar PV)-and where we can expect to be by this mid-21st century.

• Journal of Hydrogen and New Energy
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• v.19 no.4
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• pp.305-312
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• 2008

ZnO/Zn redox cycle is the one of the promising thermochemical cycles for hydrogen production via water splitting with high temperature heat source like a concentrated solar energy. This paper reports the particle size effect of Zinc on water splitting behavior. Water splitting reaction experiments were carried out at isothermal conditions of 350 and 400$^{\circ}C$ in TGA (Thermo Gravimetric Analyzer) using four commercial Zinc powders (nano, <10 ${\mu}m$, <150 ${\mu}m$ and $150{\sim}600\;{\mu}m$ particle sizes). Before the experiments, average particle size of Zinc powders was analyzed by PSA (Particle Size Analysis). After the experiments, XRD (X-Ray Diffraction) and SEM (Scanning Electron Microscope) analyses were conducted on the samples. The experimental results showed that particle size had a effect on the conversion of Zinc to ZnO. Zinc conversion was increased, as the particle size decreased. Especially, the nano size particles were aggregated and the particle's morphology changed on the surface during hydrolysis reaction.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.1009-1014
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• 2012

Hydrogenated amorphous silicon (${\alpha}$-Si:H) layers deposited by plasma enhanced chemical vapor deposition (PECVD) are investigated for use in silicon hetero-junction solar cells employing n-type crystalline silicon (c-Si) substrates. The optical and structural properties of silicon hetero-junction devices have been characterized using spectroscopy ellipsometry and high resolution cross-sectional transmission electron micrograph (HRTEM). In addition, the effective carrier lifetime is measured by the quasi-steady-state photocoductance (QSSPC) method. We have studied on the correlation between the order of ${\alpha}$-Si:H and the passivation quality at the interface of ${\alpha}$-Si:H/c-Si. Base on the result, we have fabricated a silicon hetero-junction solar cell incorporating the ${\alpha}$-Si:H passivation layer with on open circuit voltage ($V_{oc}$) of 637 mV.