• Current Photovoltaic Research
• /
• v.8 no.1
• /
• pp.6-11
• /
• 2020

The power conversion efficiency (PCE) of a two-terminal tandem solar cell depends upon the tunnel-recombination junction (TRJ) between the top and bottom sub-cells. An optimized TRJ in a tandem cell helps improve its open-circuit voltage (V_oc), short-circuit current density (J_sc), fill factor (FF), and efficiency (PCE). One of the parameters that affect the TRJ is the buffer layer thickness. Therefore, we investigated various TRJs by varying the thickness of the buffer or intermediate layer (TRJ-buffer) in between the highly doped p-type and n-type layers of the TRJ. The TRJ-buffer layer was p-type nc-Si:H, with a doping of 0.06%, an activation energy (E_a) of 43 meV, an optical gap (E_g) of 2.04 eV, and its thickness was varied from 0 nm to 125 nm. The tandem solar cells we investigated were a combination of a heterojunction with intrinsic thin layer (HIT) bottom sub-cell and an a-Si:H (amorphous silicon) top sub-cell. The initial cell efficiency without the TRJ buffer was 7.65% while with an optimized buffer layer, its efficiency improved to 11.74%, i.e., an improvement in efficiency by a factor of 1.53.

• Journal of Internet of Things and Convergence
• /
• v.7 no.3
• /
• pp.9-14
• /
• 2021

This paper discovers the energy loss factors through the insulation diagnosis of houses or buildings, and proposes directions for energy efficiency improvement. The energy efficiency factor of a building consists of insulation diagnosis, thermal bridge diagnosis, window diagnosis, airtight diagnosis, and equipment diagnosis. Among the residents and facilities in the energy welfare blind spot, an energy efficiency diagnosis was conducted for one senior citizen building located in Naju-si, Jeollanam-do, and energy efficiency diagnosis was conducted after insulation was installed. Energy measurement, diagnosis and analysis were performed using the IoT-based integrated wired/wireless energy diagnosis platform, Energy Finder. As a result of comparison, an overall energy saving rate of 16.38% was achieved. Annual heating energy consumption per unit area decreased from 333.51kWh before construction to 277.35kWh after construction, and annual cooling energy consumption per unit area decreased from 5.51kWh before construction to 5.22kWh after construction. The annual primary energy consumption per unit area decreased from 464.52kWh before construction to 403.69kWh after construction, and the annual energy cost was reduced from 3,063,307.14 won before construction to 2,641,072.49 won after construction. The additional improvement work is needed on the standards affecting energy efficiency other than insulation.

• Journal of Advanced Marine Engineering and Technology
• /
• v.21 no.2
• /
• pp.178-185
• /
• 1997

According to the wide - spread use of rectifier in electronic equipments, such problems as electronic components failures or equipment disorders have been occurred due to current harmonics. To overcome these problems, power factor correction circuits employing boost converter have been used. The high switching stress of boost converter can be reduced by snubber circuit. Recently, research activities in snubber circuits have been directed to energy recovery snubber for improving the efficiency of power converter. In this study, a new passive snubber circuit which can recover trapped snubber energy without added control is proposed for boost converter. The control of boost converter with proposed snubber is the same as the conventional one. In addition, the energy recovery circuit can be implemented with a few passive components. The circuit operation is confirmed through simulation.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2017.05a
• /
• pp.275-278
• /
• 2017

The automotive society is facing many challenges in minimizing the energy loss to improve performance and fuel economy of the vehicle. This work "Implement of Power Density for AC Generator Using a Fill Factor of Slot" is a research in Electrical Generator design, to improve power density of Alternator used in conventional IC engine powered vehicles. The power density of the alternator directly influences the fuel economy and performance in the motor vehicle. The size and weight of the alternator can be reduced by suitably designing power density of alternator. The simulation model of alternator is made and tested for different stator space factor using solid and round conductor to demonstrate the improvement in the output performance and efficiency. The result shows that there is an average 10% improvement in efficiency of alternator by using the solid conductor. The energy balance of the system also increased SOC in the base model.

• Nuclear Engineering and Technology
• /
• v.53 no.1
• /
• pp.337-343
• /
• 2021

In this work, self-absorption correction factor related to the variation of the composition and the density of soil samples were evaluated using the p-type HPGe detector. The validated MCNP5 simulation model of this detector was used to evaluate its Full Energy Peak Efficiency (FEPE) under the variation of the composition and the density of the analysed samples. The results indicates that FEPE calculation of low gamma ray is affected by the composition and the density of soil samples. The self-absorption correction factors for different gamma-ray energies which was fitted as a function of FEPEs via density and energy and fitting parameters as polynomial function for the logarithm neper of gamma ray energy help to calculate quickly the detection efficiency of detector. Factor Analysis for the influence of the element composition in analysed samples on the FEPE indicates the FEPE distribution changes from non-metal to metal groups when the gamma ray energy increases from 92 keV to 238 keV. At energies above 238 keV, the FEPE primarily depends only on the metal elements and is significantly affected by aluminium and silicon composition in soil samples.

• Environmental and Resource Economics Review
• /
• v.12 no.1
• /
• pp.29-48
• /
• 2003

The Steel Industry has made a significant contribution to the increase of energy use in Korea. This paper presents a method for development energy efficiency indicator in the steel industry based on the decomposing approach. This paper develops a logically consistent method for decomposing a change in energy consumption into the effects of three factors structural change, energy intensity and output level. Numerical illustration of the method is given using 1992~2001 data for energy consumption in a virtual works. The most dominant factor is revealed to be the output effect. The energy intensity for the steel industry has increased and the effect of such a growth was relatively strongly reflected in the decomposition analysis. The structural effect turned out to be also important during the periods.

• New & Renewable Energy
• /
• v.1 no.1 s.1
• /
• pp.37-43
• /
• 2005

High-efficiency silicon solar cells have potential applications on mobile electronics and electrical vehicles. The fabrication processes of the high efficiency cells necessitate com placated fabrication precesses and expensive materials. Ti/Pd/Ag metal contact has been used only for limited area In spite of good stability and low contact resistance because of Its expensive material cost and precesses. Screen printed contact formed by Ag paste causes a low fill factor and a high shading loss of commercial solar cells because of high contact resistance and a low aspect ratio. Low cost Ni/Cu metal contact has been formed by using a low cost electroless and electroplating. Nickel silicide formation at the interface enhances stability and reduces the contact resistance resulting In an energy conversion efficiency of $20.2\%\;on\;0.50{\Omega}cm$ FZ wafer. Tapered contact structure has been applied to large area solar cells with $6.7\times6.7cm^2$ in order to reduce power losses by the front contact The tapered front metal contact Is easily formed by the electroplating technique producing $45cm^2$ solar cells with an efficiency of $21.4\%$ on $21.4\%\;on\;2{\Omega}cm$ FZ wafer.

• Journal of Hydrogen and New Energy
• /
• v.20 no.2
• /
• pp.104-115
• /
• 2009

In case of residential fuel cell system, it is significant to stably supply heat and power to a house with high efficiency and low cost for the successful commercialization. In this paper, the control strategy analysis has been performed to minimize the total cost including capital and operating cost of the residential fuel cell system. The proposed analysis methodology is based on the simulator including the efficiency models as well as the cost data for fuel cell components. The load control strategy is the key factor to decide the system efficiency and thus the cost analysis is performed when the fuel cell system is operated for several different load control logics. Additionally, annual efficiency of the system based on the seasonal load data is calculated since system efficiency is changeable according to the electric and heat demand change. As a result, the hybrid load control combined electricity oriented control and heat oriented control has the most economical operation.

• Journal of the Korean Solar Energy Society
• /
• v.32 no.3
• /
• pp.114-122
• /
• 2012

Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed -loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As results, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.

• Environmental Engineering Research
• /
• v.25 no.1
• /
• pp.71-79
• /
• 2020

This paper uses super-efficiency DEA model and Malmquist index to evaluate the carbon emission efficiency (CEE) values of the nine western provinces along the "Silk Road Economic Belt" for the period from 2000 to 2015, and analyses the influencing factors of the CEE. The major findings of this study are the following: (1) the overall CEE of the nine western provinces is not high, and there are significant inter-provincial differences in the CEE. Meanwhile, the provinces with higher levels of economic development generally have higher CEE. (2) The annual total factor productivity (TFP) of the nine western provinces, which is mainly determined by technological change, is greater than 1. Moreover, the total average growth rate of the TFP is 15.5%. (3) The CEE of the nine western provinces is not spatially dependent. In addition, the urbanization, openness, use of energy-saving technologies and research and development (R&D) investment have a significant positive impact on the CEE values, while the industrial structure, foreign direct investment, fixed asset investment, government expenditure levels and energy structure have a significant negative impact on the CEE. Among them, R&D investment is the primary factor in promoting the development of CEE, and the government expenditure has the greatest negative impact on the CEE.