• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.4
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• pp.376-386
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• 2013

This paper proposes an improved Maximum Power Point Tracking method and design methods of unmanned solar vehicle system by parts of hardware, unmanned driving control and power conversion. The hardware design is offered on the weight reduction and structural reliability by using structural analysis software. The technique of curve fitting is applied to unmanned control system due to minimizing the vehicle's behavior. Furthermore, lateral controller applying actuator dynamics is robust enough to prevent performance degradation by measurement noise regarding position and heading angle. The power conversion system contains battery charger system and tapped-inductor boost converter. In the battery charger system, variable step-size MPPT is conducted for quick response of maximum power point tracking. The validity of the proposed algorithm are verified by simulations and experiments.

• Applied Chemistry for Engineering
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• v.18 no.4
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• pp.356-360
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• 2007

Recently, dye sensitized solar cells (DSSCs) composed of nanoporous $TiO_2$, light-sensitive dyes, electrolytes, and counter electrode have been received much attention. Nanostructured particles with higher surface area for the higher adsorption of Ru (II) dye are required to increase the quantity of light absorption. Also, it has been reported that the key factor to achieve high energy conversion efficiency in the photoelectrode of DSSC is the heat treatment of $TiO_2$ paste with acid addition. In this work, we investigated the influence of acid treatment of $TiO_2$ solar cell on the photovoltaic performance of DSSC. The working electrodes fabricated in this work were characterized by X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), field emission scanning electron microscope (FE-SEM), and atomic force microscope (AFM). In addition, the influence of nanostructured photoelectrode fabricated with the acid-treated paste on the energy conversion efficiency was investigated on the basis of photocurrent-potential curves. It was found that the influence of acid-treated paste on the photovoltaic efficiency was significant.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.672-680
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• 2017

A solar photovoltaic system is composed of a module mounting structure, supporting trunk, and a control unit that supplies generated electrical power to an external power grid or a load. The efficiency of the system depends on the incident solar light, so the mounting structure is installed to face the sun. However, because the sun always moves, systems that track the sun have better efficiency than fixed systems. The structure experiences wind pressure, snow load, seismic load, and structure weight. The wind pressure has the most serious effect on the structure. The pressure was obtained using finite element method for various gaps between modules and angles between the panel and the ground. The wind pressure is lowest when the gap is zero, and it increases with the inclination angle. Based on the results, a mounting structure module was designed.

• Bulletin of the Korean Chemical Society
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• v.32 no.11
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• pp.4035-4040
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• 2011

Long $TiO_2$ nanotube (NT) arrays, prepared by electrochemical anodization of Ti foils, have been utilized as dye-adsorbing electrodes in dye-sensitized solar cells (DSCs). By anodizing for 1-24 hr and subsequent annealing, highly crystallized and tightly-adhered NT arrays were tailored to 11-150 ${\mu}m$ lengths, ~90 nm innerpore diameter and ~30 nm wall thickness. I-V curves revealed that the photovoltaic conversion efficiency (${\eta}$) was proportional to the NT length up to 36 ${\mu}m$. Beyond this length, the ) was proportional to the NT length up to ${\eta}$ was still steadily increased, though at a much lower rate. For example, an ${\eta}$ of 5.05% at 36 ${\mu}m$ was increased to 6.18% at 150 ${\mu}m$. Transient photoelectron spectroscopic analyses indicated that NT array-based DSCs revealed considerably higher electron diffusion coefficient ($D_e$) and life time (${\tau}_e$) than those with $TiO_2$ nanoparticles (NP). Moreover, the electron diffusion lengths ($L_e$) of the photo-injected electrons were considerably larger than the corresponding NT lengths in all the cases, suggesting that electron transport in NT arrays is highly efficient, regardless of tube length.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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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.

• Journal of the Korean Solar Energy Society
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• v.36 no.2
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• pp.31-39
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• 2016

This study did quantitative comparative evaluation of changes in generation consequent on reflectivity of the protruding wall near the widow in case of application of PV window system to an apartment house. To be concrete, this study did comparative analysis of the generation of (B) through the process of composing Mock-up (A)comprising the protruding window near the window and Mock-up(B) free of nearby wall interference, and giving change to the reflectivity of the wall (Case_1~3). The analysis result showed that the difference in generation was slight in case solar radiation was less than 10,000Wh in all three conditions. On the contrary, in case solar radiation was more than 10,000 Wh, the generation as against Module(B), was analyzed to be 87~91% in Case_1(5% reflectivity), 18~60% in Case_2(85% reflectivity), and 16~71% in case_3(93% reflectivity), respectively.

• Current Photovoltaic Research
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• v.10 no.2
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• pp.33-38
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• 2022

Planner configuration thin film solar cells (TFSCs) with SnS/CdS heterojunction performed a lower short-circuit current (J_SC). In this study, we have demonstrated a path to overcome deficiency in J_SC by the incorporation of Se in the SnS absorber. We carried out the incorporation of Se in VTD grown SnS absorber by rapid thermal annealing (RTA). The diffusion of Se is mostly governed by RTA temperature (T_RTA), also it is observed that film structure changes from cube-like to plate-like structure with T_RTA. The maximum J_SC of 23.1 mA cm^-2 was observed for 400℃ with an open-circuit voltage (V_OC) of 0.140 V for the same temperature. The highest performance of 2.21% with J_SC of 18.6 mA cm^-2, V_OC of 0.290 V, and fill factor (FF) of 40.9% is observed for a T_RTA of 300℃. In the end, we compare the device performance of Se- incorporated SnS absorber with pristine SnS absorber material, increment in J_SC is approximately 80% while a loss in V_OC of about 20% has been observed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.3
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• pp.549-557
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• 2012

In this paper an on-chip photo energy harvesting system with MPPT(Maximum Power Point Tracking) control is proposed. The ISC(Integrated Solar Cell) is implemented using p-diff/n-well diodes available in CMOS processes. MPPT control is implemented using the linear relationship between the open-circuit voltage of a PV(Photovoltaic) cell and its MPP(Maximum Power Point) voltage such that a small pilot PV cell can track the MPP of a main PV cell in real time. Simulation results show that the designed circuit with the MPPT control delivers the MPP voltage to load even though the load is heavy such that the load circuit can operate properly. The proposed circuit is designed in 0.18um CMOS process. The designed main PV cell and pilot PV cell occupy $8mm^2$ and $0.4mm^2$ respectively.

• Transactions on Electrical and Electronic Materials
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• v.18 no.4
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• pp.190-194
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• 2017

Present-day solar panels incorporate inverters as their core components. Switching devices driven by specialized power controllers are operated in a transformerless inverter topology. However, some challenges associated with this configuration include the absence of isolation, causing leakage currents to flow through various components toward ground. This inevitably causes power losses, often being also the primary reason for the power inverters' analog equipment failure. In this paper, various aspects of the leakage currents are studied using different circuit analysis methods. The primary objective is to convert the leakage current energy into a usable DC voltage source. The research is focused on harvesting the leakage currents for producing circa 1.1 V, derived from recently developed rectifier circuits, and driving a $200{\Omega}$ load with a power in the milliwatt range. Even though the output voltage level is low, the harvested power could be used for charging small batteries or capacitors, even driving light loads.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.6
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• pp.105-113
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• 2013

In this paper a micro solar energy harvesting system with MPPT(Maximum Power Point Tracking) control using a miniature PV(photovoltaic) cell of which the output is less than 0.5V is proposed. The MPPT control is implemented using linear relationship between the open-circuit voltage of a PV cell and its MPP(Maximum Power Point) voltage such that a pilot PV cell can track the MPP of the main PV cell in real time. The proposed circuit is designed in 0.18um CMOS process. The designed chip area is $900um{\times}1370um$ including a load charge pump and pads. Measured results show that the designed system can track the MPP voltage changes with variations of light intensity. The designed circuit with MPPT control delivers MPP voltages to load even though the load is heavy such that it can supply more power when the MPPT control is applied. The proposed circuit does not require any precharged battery resulting in more suitability for miniaturized self-powered systems compared to the existing works.