Yong-Heack Kang

A study on thermal characteristics of the solar collector made with a closed loop thermosyphon

The natural circulation type and the closed loop type thermosyphon systems are widely used for solar domestic hot water systems(SDHWS). Of these, the closed loop type thermosyphon system, which hires the concept of a wickless heat pipe, is extensively studied in the present analysis. The system under consideration consists of a rectangular shape solar collector and a circular cylindrical shape storage tank, the most common design of a natural circulation type SDHWS. A closed circulation loop runs through these units carrying heat from the collector to the storage tank. The working fluid(heat transfer medium) makes infinite number of roundtrips via this loop as long as the suns energy hit the collector area and delivers the fuel needed for the trip. This paper reports the experimental results obtained in a series of tests where the operational characteristics of various working fluids are examined along with the whole performance of the system. The working fluids experimented in the present study are ethanol, water, and a binary mixture of ethanol and water(ethanol/water). Various amounts of working fluid were tested where the working fluid occupies 30%, 40%, 50%, 60% or 70% of the loop volume. Among these, in the cases of 30% and 40%, dry-out phenomena were observed. Also investigated in this study were the flow patterns and the mechanism of heat transfer within the loop. Flow patterns of the binary mixture of working fluid near the entry of the storage tank were analyzed where they were recorded with the aid of a high speed camera.

Operation Results of Dish-Stirling Solar Power System

As the final step for developing a small-scale solar thermal power generation technology in Korea, a demonstration project for a dish-Stirling power system has been carried out by KIER. During the two years project period, 10 kW dish-Stirling power system was built in Jinhae city and successful solar operations were demonstrated. The system consists of mechanical part for solar tracking, parabolic dish-type concentrator, a number of mirror facets, Stirling engine generator, and control/monitoring devices. Close analysis of operation results revealed that the minimum DNI value for power generation by the system was around 200 W/m2 and the efficiency of solar-to-power conversion reached over 19 % at above 400 W/m2 DNI condition. In this paper an example of typical clear day operation and analysis results were introduced.

Theoretical Simulation Investigation of the Pioneer 1 Mw Solar Power Tower System In China

Preliminary results in predicting performance of the first 1 MW solar power tower system in China named “DAHAN” locating in north-west of Beijing nearby The Great Wall are presented in this paper. DAHAN consists of collector system (CS), receiver system (RS), thermal storage system (TSS), steam generation system (SGS), electrical power generation system (EPGS) and the balance of plant (BOP).

Evaluation of wind resource potential in mountainous region considering morphometric terrain characteristics

In South Korea, where 64% of the national territory is mountainous, good wind resources in inland areas are mostly situated in high mountain regions. To develop a wind farm in a mountain region, the sloping of mountains and their shielding from wind by the surrounding topology should be considered. It is generally most advantageous to install wind turbines along a ridge that is open in all directions. This article presents a methodology for evaluating suitable sites for wind farm development by identifying suitable ridges using morphometric analysis, while excluding the geographical and social environmental exclusion factors and superposing them on the wind resource map to find the area having a specific level or higher wind power density. The result of the proposed suitable site analysis and existing wind farms was assessed to verify the feasibility of the method of analyzing suitable sites on ridges. The wind resource potential in Gangwon Province when calculated using a method based on conventionally suitable site and the method based on ridge analysis was 9 and 5 GW, respectively. The result confirmed that the conventional area-based potential calculation without consideration of the morphometric terrain characteristics overestimated wind resource potential by around 80% compared to the ridge analysis method of calculation presented in this article.

An Experimental Study on the Heat Transfer Characteristics of the Hybrid Solar Receiver for a Dish Concentrating System

The dish/stirling system is used to convert solar energy directly to electricity. Therefore, in order to improve economical efficiency of a solar power system, the stirling unit must be operated continuously. For continuous operation of the stirling unit, the receiver must be continuously provided with thermal energy from solar as well as additional combustion heat. It is possible for a hybrid solar receiver system equipped with an additional combustion system to be operated 24 hrs/day.

Evaluation of WRF model-derived direct irradiance for solar thermal resource assessment over South Korea

The South Korean government has been started monitoring and reassessment for new and renewable resource under greenhouse reduction related with the climate agreement in Paris. This study investigated characteristics of the model-derived direct normal irradiance(DNI) using ten-minute data of the Weather Research and Forecasting(WRF) model with 1 km grid spacing. First, ground horizontal irradiance(GHI) and direct normal irradiance(DNI) from the model was compared with those of ground stations throughout South Korea to evaluate the uncertainty of the GHI-derived DNI. Then solar thermal resource potential was assessed using a DNI map. Uncertainty of irradiances appeared highly dependent on sky conditions. Root mean square errors in DNI(GHI) was 45.39%(18.06%) for all sky with the range of 9.92∼51.93%(14.49∼51.47%) for clear to overcast sky. These indicate DNI is further sensitive to cloud condition in Korea which is around 72% of cloud days during a whole year. Finally DNI maps showed high value over most areas except southeastern areas and Jeju island which is humid regions in South Korea.The South Korean government has been started monitoring and reassessment for new and renewable resource under greenhouse reduction related with the climate agreement in Paris. This study investigated characteristics of the model-derived direct normal irradiance(DNI) using ten-minute data of the Weather Research and Forecasting(WRF) model with 1 km grid spacing. First, ground horizontal irradiance(GHI) and direct normal irradiance(DNI) from the model was compared with those of ground stations throughout South Korea to evaluate the uncertainty of the GHI-derived DNI. Then solar thermal resource potential was assessed using a DNI map. Uncertainty of irradiances appeared highly dependent on sky conditions. Root mean square errors in DNI(GHI) was 45.39%(18.06%) for all sky with the range of 9.92∼51.93%(14.49∼51.47%) for clear to overcast sky. These indicate DNI is further sensitive to cloud condition in Korea which is around 72% of cloud days during a whole year. Finally DNI maps showed high value over most ar...

Toward Improved Solar Irradiance Forecasts: Comparison of the Global Horizontal Irradiances Derived from the COMS Satellite Imagery Over the Korean Peninsula

This study introduces the University of Arizona Solar Irradiance Based on Satellite/Korea Institute of Energy Research, which is usually called UASIBS/KIER model. Then the evaluation of modeling performance is done against the ground observations for the instantaneous, hourly, and daily time scales over the Korean Peninsula in this study. The relative root mean square error for the instantaneous time scale is 7.4 and 16.7% for the clear and cloudy skies, respectively. The hourly mean estimates are compared with the in situ measurements from 35 ground observation stations, resulting in a relative root mean square error ranging from 9.1 to 15.5%. The daily aggregates are proven as the most reliable estimates. The UASIBS/KIER estimates are also compared with the routine solar insolation product from the Korea Meteorological Administration. Finally, the solar energy resource map has been built by the daily solar irradiance derived from the UASIBS/KIER model, followed by its comparison with the other gridded datasets.

Analysis of the turbulent heat transfer in solar power tower molten salt receiver tube

Central Receiver System (CRS) with molten salt (MS) technology represents the most cost effective and leading candidate technology for electricity generation for stand-alone Solar Power Plants. But MS has a high freezing point, and the tube alloy also can not stand long time with high temperature in MS circumstances. Tube freezing, leaking and salt decomposing are very likely to happen during the operation, especially under the unstable and non-uniform solar incidence flux. The conventional heat transfer correlations are not well available to deal with the MS receiver, for the heat flux are inconstant and non-uniform and only heat one side of the receiver tube, and the thermal properties of MS are also changed with temperature. By using a commercial CFD software FLUENT, this paper presents the results and analysis of the heat transfer in MS receiver tube with steady non-uniform heat flux around the circumference. This results will do some help to the 100kW MS receiver design and fabrication in the next step in DAHAN SPT project.