온실내 잉여 태양에너지 산정 (I) - 1-2W형을 중심으로 -

This study was carried out in order to reduce the amount of underground water which is used in the double layered single span plastic greenhouse for retaining heat. For this research, two plastic green houses of the double layered single span plastic greenhouse were installed. There was equipped of internal small tunnel for keeping warm air in the interior of the house. Then the internal small tunnel for keeping warm air was fitted with PVC duct of 50 cm in diameter filled with subsurface water. The surplus solar energy in the greenhouse was stored in the water in the PVC duct. Four FCUs (Fan Coil Unit), which has the capacity of 8,000 kcal per hour, were installed in the middle of the house, and a circulation motor in heat storage water tank was operated from 10:30 a.m. to 16:00 p.m. in order to circulate water between the water tank and the FCUs. Consequently about 5 degrees celsius could be maintained in the interior of the internal small tunnel for keeping warm air with the external temperature of lower than minus 5 degrees celsius. It appeared that the alteration of an internal temperature of the house was flexible depending on the sunlight during daytime. To prevent the water freezing, mixing antifreezing liquid in the water or operating FCU continuously was needed. Also, in order to use the surplus solar thermal energy on plastic green house of water curtain system efficiently, storing the surplus heat during daytime simultaneously finding a method of using water curtain systematic underground water happened to be important. As a result of this research, when the house's interior temperature is below zero the operation of FCU appeared to be impossible. Considering the amount of water used in the house with water-curtain-heating system is 150~200 ton per day, using the system mentioned in this research showed that reducing the underground water more than 80% in order to maintain the internal temperature as the level of 5 degree celsius at the extreme temperature of minus 5 degrees celsius.

Hydrogen production by water electrolysis driven by a photovoltaic source: A review

Feasibility study for combining cooling and high grade energy production in a solar greenhouse

Over a year, net zero energy (NZE) houses produce and feed zero net metered electrical energy to the grid. Technical challenges, notably the ‘duck curve’ arise due to the fact that peak solar generation and load demand are seldom coincident. Common approaches to mitigate this limitation include the curtailment of solar power, and the use of storage. Surplus solar energy may be stored in a battery, which can subsequently be discharged to supply the home electricity needs when demand is in excess. In addition to batteries, less expensive electric water heaters, which are ubiquitous, can be modified as energy storage systems, functioning as ‘uni-directional batteries’ by virtue of their high thermal mass. This paper proposes the use of a hybrid energy storage system including both batteries and variable power electric water heaters in NZE residences. It is demonstrated that the hybrid energy storage system along with solar PV generation coordinated and virtual power plant (VPP) controls would reduce the required battery size and ratings while still harvesting the maximum solar energy potential. The proposed control strategy enables the NZE homes to produce dispatchable power or behave like controllable loads, and benefits at the utility level are demonstrated by interconnection of NZE homes with an IEEE 13 node test feeder system. The technology has the potential to mitigate all issues related to solar power variability.

Demonstration of reusing electric vehicle battery for solar energy storage and demand side management

Solar energy is an abundant and secure source of vitality and thus is described as one of the most promising alternative energy options. Nevertheless, solar energy is intermittent in nature as there is no sun at night. Its total availability value is seasonal and is hooked on the meteorological conditions of locations. Hence, solar energy presents an unsteady energy resource. So, thermal energy storage will be necessary to save the available solar energy at a period of no load or when excessive solar energy is available, and to make up for the shortage of energy when the load is in need of energy. This article reviews the different energy storage materials tried by various researchers to improve the distillate output of solar stills.

Photosynthesis is the process that enables higher plants, algae and a broad class of bacteria to transform light energy and store it in the form of energy‐rich organic molecules. In plants and algae, as well as some species of bacteria, photosynthesis removes carbon dioxide from the atmosphere, produces the molecular oxygen we breath and stores energy in biomass. In addition some bacteria use light energy to create energy‐rich molecules, but do not split water to produce oxygen. Photosynthesis is finely regulated to avoid damage caused by excess solar energy. At the same time, though, this regulation also decreases the efficiency of photosynthesis. Current research is aimed at understanding these responses to improve photosynthetic efficiency, thus increasing the production of food and fuel. Key Concepts: Photosynthesis is the transformation of light energy to chemical energy by higher plants, algae and certain bacteria. In higher plants, the initial capture of light energy and conversion to the stable, high‐energy products of NADPH and ATP occurs within and around the thylakoid membranes of the chloroplast. The NADPH and ATP produced are used by enzymes in the stroma to ‘fix’ carbon dioxide and produce carbohydrates. Although photosynthesis is driven by light, the photosynthetic apparatus must protect itself from excess solar energy which causes a decrease in photosynthetic efficiency.

Novel approaches and recent developments on potential applications of phase change materials in solar energy

The efficient utilization of solar energy technology is significantly enhanced by the application of energy storage, which plays an essential role. Nowadays, a wide variety of applications deal with energy storage. Due to the intermittent nature of solar radiation, phase change materials are excellent options for use in several types of solar energy systems. This overview of the relevant literature thoroughly discusses the applications of phase change materials, including solar collectors, solar stills, solar ponds, solar air heaters, and solar chimneys. Despite the complexity of their availability and high costs, phase change materials are utilized in the majority of solar energy techniques because of the considerable technical improvements they provide. While numerous studies have investigated the progress of phase change materials used in solar energy applications such as photovoltaic systems, it is vital to understand the conceptual knowledge of employing phase change materials in various types of solar thermal energy systems. Investigations into the use of phase change materials in solar applications for the purpose of storing thermal energy are still being carried out to upgrade the overall performance. This paper briefly reviews recently published studies between 2016 and 2023 that utilized phase change materials as thermal energy storage in different solar energy systems by collecting more than 74 examples from the open literature. This study focuses on demonstrating the maturity of phase change materials and their integration into solar energy applications. Based on the findings, proposals for new research projects are made.

Stanghellini model is one of the few models primarily developed to predict the evapotranspiration of crops (ETc) in naturally ventilated greenhouses. However, there are insufficient data on the model regarding its use, particularly in China where solar greenhouses without heating systems are fast spreading for vegetable growth and production. The application of Stanghellini model and the evaluation of its performance using meteorological and tomato plant data generated inside an unheated and naturally ventilated multi-span Venlo-type greenhouse is exploited in this study. Model capability was evaluated by utilizing data from sap flow measurements, meteorological and crop data. Measured meteorological data included solar radiation (Rs), air temperature (Ta), relative humidity (RH) and net radiation (Rn). Average leaf area index (LAI) values measured during the experimental period were 1.00, 3.30, 4.05 and 2.93; while determined crop coefficients (Kc) changed from 0.40, 0.62, 1.12 to 0.83 for the initial stage, development stage, mid-season stage and late-season stage, respectively. Results from the study indicated that the average hourly ETc values of tomato plants using sap flow measurements were 0.165 mm/h, 0.148 mm/h, 0.192 mm/h and 0.154 mm/h for the initial stage, development stage, mid-season stage and late-season stage, respectively. Meanwhile, the ETc values obtained from calculation using Stanghellini model were 0.158 mm/h, 0.152 mm/h, 0.202 mm/h and 0.162 mm/h for the initial stage, development stage, mid-season stage and late-season stage, respectively. These ETc values calculated by the Stanghellini model were close to the measured values within the same period. The coefficients of correlation (R2) based on hourly ETc for the calibration data was 0.94 and that of the validation dataset was 0.90. Scatter plots of the estimated and measured hourly ETc revealed that the R2 and the slope of the regression line for May, June and July were 0.94, 0.90, 0.96 and 1.15, 0.97, 1.10 respectively. These data were well represented around the 1:1 regression line. A model sensitivity analysis carried out illustrates how the changes in Rs and Ta affect greenhouse ETc. Stanghellini model was therefore proven to be suitable for ETc estimation with acceptable accuracy in unheated and naturally ventilated greenhouses in the Northeast region of China. Keywords: calibration, verification, crop evapotranspiration, naturally ventilated greenhouse, sap flow DOI: 10.25165/j.ijabe.20181106.3972 Citation: Acquah S J, Yan H F, Zhang C, Wang G Q, Zhao B S, Wu H M, et al. Application and evaluation of Stanghellini model in the determination of crop evapotranspiration in a naturally ventilated greenhouse. Int J Agric & Biol Eng, 2018; 11(6): 95–103.

To coordinate the conflict between the high-altitude task and long-term energy efficiency of high-altitude long endurance solar UAV, it is one of the core issues of UAV control. A strategy combining the energy management with the route tracking is presented. Firstly, based on the three-dimensional particle motion model, energy storage battery model and solar energy acquisition model for the solar UAV, according to the aerodynamic parameters of the solar UAV and the typical horizontal flight, climb, descent and other motion processes of the solar UAV, the energy management strategy of the solar UAV is designed, and the allocation mechanism and optimal flight parameters of the energy acquisition, storage and consumption of the solar UAV in different flight stages are determined. The surplus solar energy is stored by using the gravitational potential energy, and then the energy management based on height adjustment is carried out to realize the longitudinal tracking control of the solar UAV under different lighting and energy conditions. Then based on the task requirements of the lateral movement of the solar UAV, a track tracking control method based on the feedback linearization method is established by decoupling the particle dynamics equation of the solar UAV, and the track tracking control of the solar UAV in the lateral direction is realized. Finally, a simulation throughout 24 hours is implemented and illustrated the effectiveness of the energy management strategy and route tracking control law.

Use of thermal energy storage materials for enhancement in distillate output of solar still: A review

The implementation of practical solar-fuel technologies can trigger a significant increase in the use of renewables in our energy ecosystem. These technologies can directly capture and store solar energy in the form of energy rich molecules, which could be used at a later stage as fuels for transportation or electricity generation. Storing solar-energy into fuels can also serve as a mean of seasonal energy storage, so that excess solar energy in the summer can be used during the periods of low solar irradiation in the winter. Also, solar-fuel generators can be operated in centralized facilities without disrupting the operation of the electricity grid. The spatio-temporal decoupling of the energy capture and utilization that solar-fuel technologies provide makes them an attractive renewable energy storage solution. For solar-hydrogen generators to be implemented, they need to be able to operate robustly, stably and continuously for prolonged periods of time – in the order of several years to decades. They also need to produce fuels in a cost-effective way and the energy produced over their lifetime needs to exceed the energy inputted into their manufacturing and operation. In this presentation, we describe a system agnostic approach to assess promising designs and components of solar-hydrogen generators from a technoeconomic perspective. Using this framework, we evaluate the effects of device design and material selection on the cost of the generated hydrogen. The results presented here provide insights and device engineering directions that would lead to cost-optimized solar-hydrogen generators. Our findings demonstrate that in order to minimize hydrogen production costs, optimized devices will need to be manufactured with water splitting components that are significantly smaller in area than photovoltaic units (by a factor of 10-100’s). Additionally, the analysis points out that devices based on silicon (Si) photovoltaics (either thin-film or crystalline Si cells) could reach hydrogen production costs that approach those of hydrogen from fossil fuels resources. As the cost of hydrogen is primarily driven by the light-absorbing units, further economic gains can be obtained by improving the overall solar-to-hydrogen efficiencies of devices. These efficiency improvements can be achieved by the implementation of Silicon heterojunction (SHJ) solar cells into solar-hydrogen devices. SHJ cells present higher open-circuit voltages (VOC) than crystalline Si cells and can reach levels above 700 mV. Their high VOC values are mainly due to an interfacial passivation with a thin (~5 nm) film of hydrogenated intrinsic amorphous silicon between the c-Si wafer and the oppositely doped emitter, forming the p-n junction. Thanks to the high VOC of SHJ cells, we demonstrate that modules of three cells in series can provide enough potential to drive the water splitting reaction at high current densities in electrolysis units. Devices based on SHJ modules and Nafion-based membrane-electrode assemblies with platinum and iridium oxide electrocatalysts show stable performance over 100 hrs of operation at an unprecedented SHE of 14.2%. The same efficiency level is demonstrated for devices operated under alkaline conditions using microstructured nickel electrodes; representing the highest SHE achieved with earth-abundant components to date. As both the SHJ cells and electrolysis units implemented in this study are commercially viable, easily scalable and have long lifetimes, the devices presented here have the potential to disruptively accelerate the deployment of cost effective solar-hydrogen generators.

Geographical variations in gross primary production and evapotranspiration of paddy rice in the Korean Peninsula

Energy performance of decentralized solar thermal feed-in to district heating networks