Applied Mechanics and Materials Vols. 291-294

Abstract: A cluster control method for grid-connected PV system has been presented in the paper. In the method, the operation of DC switches is controlled by optimization model for conversion efficiency of cluster of inverters and a 3MW PV system has been built on PSCAD/EMTDC. The simulation model run normally and stable by using the cluster control method which indicated the method is feasible.

Abstract: This research focus on two PTC designs, one in Runzhen-school, China (latitude 36.5°N, longitude110°E and 386m altitude) and the second PTC with tracking system. The study showed that, using one tube concentrate in the focal point with fixed PTC gives lower efficiency compared with using two vacuum tubes, as the variation of solar altitude angle is large. So using two focal points results a better heating. The new system uses PTC with sun tracking system to maximize solar radiation absorptions, that leading to increase the hot water temperature and has higher system efficiency. In addition, this system supplies two batteries by electricity coming from two solar-cells and it’s produced for the tracking system working during hours of sunlight. The photovoltaic electricity provided is stored in batteries and then used for tracking motion. The tracing motion receives orders from a control unit, which works at different voltage in two solar cells.

Abstract: This paper presents an in-depth economic analysis on Photovoltaic power generation (PV) project. The research is based on nine business and technical proposals which with different investment operational pattern and different distributed generation (DG) integration technology of PV project. An all-life-cycle benefit/cost (B/C) assessment methods was used to assess the feasibility of the project. Through the accurately simulate of an annual PV output and load curves from typical time, received electric power and energy balance calculations and revenue forecast results. And then different operators’ electricity price benefits based on china’s complex tariff mechanism was estimated in this paper, while the initial PV panel investment, operation and maintenance, distribution network investment and losses of PV projects were calculated. Finally, through the PI value come to the best business model. Calculation results show that if power grid enterprise as the PV power producer, and use of virtual power plant technology for DG integration means more investment value than other business mode.

Abstract: The Photovoltaic (PV) cell which can convert directly sunlight into electricity has a nonlinear power vs. voltage curve, and a digital controlled power converter is required to implement the Maximum Power Point Tracker (MPPT) function. This paper aims to investigate the influence of current ripple amplitude which results from the operation of power converter on the efficiency of capturing the available solar energy. By simulation, a tradeoff between the filter size, the current ripple amplitude and the solar energy capture efficiency is found.

Abstract: The integration between photovoltaic systems and tradition grid have a lot of challenges. To accurately predict is a key to solve these challenges. Due to complex, non-linear and non-stationary characteristics, it is difficult to accurately predict the power of photovoltaic systems. In this paper, a short-term prediction model based on empirical mode decomposition (EMD)and back propagation neural network(BPNN) was constructed, and use genetic algorithm as the learn algorithm of BPNN. The power data after pre-processing is decomposed into several components, then using prediction model based on BPNN and genetic algorithm to predict each component, and all the component prediction values were aggregated to obtain the ultimate predicted result. The simulation shows the purposed prediction model has higher prediction precision compare with traditional neural network prediction method and it is an effective prediction method of photovoltaic systems.

Abstract: The PV generation system is an uncontrollable source and has an affect on the grid by randomness of output power. So we need to strengthen the study of PV output power forecast. In this paper, according to the related information of recent day with the same weather type, an improved wavelet neural network forecasting model without solar radiation was proposed. Furthermore, with the measured data came from a PV power plant, comparison experiments were made as opposed to improved wavelet neural network forecasting model and the wavelet neural network forecasting model with traditional learning algorithm. The experimental results indicate that the improved wavelet neural network forecasting model can significantly improve the precision of PV output power prediction. The comparison experiments considering solar radiation were also given, which also show the high precision and high efficiency of proposed model and algorithm.

Abstract: The biogas amounts with stable flowing rate require heating in cold weather. This study focuses on using solar energy for heating biogas digester. In this research we used energy plus building energy simulation software and real weather data for simulation the heating of biogas digester with 8760 hours simulation .The research was carried out in two parts: The first one is one biogas digester above ground without heating. The Second part of this study is a simulation of one biogas digester with solar heating by using a new design based on double plastic cover. It has shown that the use of solar energy can achieve the optimum temperature for biogas production process almost the year time. Using double plastic cover is the most suitable method with economic form for heating biogas digester above ground.

Abstract: In this work, sky thermal radiation fallen on the horizon and inclined collector surface at clear nights were directly measured by pyr-radiometers, and an empirical correlation to estimate the emissivity of clear night sky was obtained by linearly fitting the measured data. Results showed that the sky emissivity at clear nights in Yunnan Highlands of China was slightly lower than that expected from correlations of Berdahl et al. and Tang et al. under climatic conditions during the period of measurements, implying that the actual sky over Yunnan highlands was “cooler” than that predicted by other correlations. Results also showed that atmosphere radiation fallen on the surface inclined at 30o from the horizon was slightly lower than that expected from other empirical correlations, the equivalent sky temperature over all the sky dome in Yunnan highlands was almost uniform, and the atmosphere radiation from the sky dome could be regarded as to be isotropic.

Abstract: As one of the core components of the disc type solar thermal power generation system, endothermic performance of cavity absorber has an important impact on photoelectric efficiency of the system. So developed a new type hemispherical heat pipe cavity heat receiver, and experimental studied endothermic performance of the new cavity receiver in disc dual-axis tracking system. The results showed that when the direct solar radiation was 505.5W/m2, the endothermic power was 1686W, and solar thermal efficiency was 75.1%.

Abstract: This paper investigates the radiation transmission model and heat conduction model of a solar pond which are covered with ice in the surface in winter. Combined radiation transmission functions of the natural ice which is based on experiments and the Wang and Seyed-Yagoobi model of the solar pond, temperature changing of LCZ is obtained by numerical simulation. It is revealed that surface ice of pond influences temperature changing of LCZ in two different sides. Solar energy-transmitted to the pond, on the one hand, is reduced which is disadvantageous to temperature ascending. On the other hand, the long wave from the bottom of pond is reflected downwards by lower surface of ice. Formation of greenhouse effect below the ice prevents bottom energy losing. This provides a positive influence on keeping heat stability of a salinity gradient solar pond.