Advanced Materials Research Vols. 805-806

Abstract: To improve the utilization efficiency of the solar energy with certain conversion efficiency, the principle of MPPT control with Boost converter is explained according to photovoltaic array output characteristics. The disadvantage of the conventional perturbation and observation (P&O) is analyzed. A novel MPPT system based on a digital signal processor (DSP) with Boost converter and an improved P&O algorithm is proposed in this paper. The proposed MPPT system model is developed under Matlab/Simulink. At last, theory analysis indicates its feasibility while the simulation results verify its validity.

Abstract: From the viewpoint of improving heating quality and saving energy, the paper proposes the use of Joint Heating Systems about Solar Collectors and Ground Source Heat Pump (JHSSCGSHP). The typical architecture in Shenyang is analyzed about dynamic simulation by the use of JHSSCGSHP. MATLAB is used to operate comparative analysis of simulation. It focuses on the impact of water temperature of inlet and outlet of heat pump systems in different series of separate heating of ground source heat pump and JHSSCGSHP. Thus the influence of the system operation efficiency based on different operation modes is compared.

Abstract: A power characteristic model of photovoltaic (PV) modules on the wing of solar-powered airplanes operated from sea level to the stratosphere is established. Because the efficiency of PV modules is a function of surface temperature, the proposed model includes thermodynamic effects. Firstly, the real-time power characteristics are analyzed at the altitudes of 10 km and 30 km and during the summer and winter solstice. Then, further investigations are conducted to research the daily averaged power per unit area from 0 km to 35 km throughout a whole year. The results show that the low atmosphere temperature is favorable condition for PV modules to obtain high absorption efficiency, and total solar radiation increases with the altitude increasing. However, the thinness of atmosphere density at high altitudes leads the deduction of Reynolds number, resulting in less heat carried away and the efficiency deterioration of PV modules. The maximum power collected occurs around 11 km. The research work shows that it is necessary to take into consideration the thermal effects on the efficiency of PV modules at high altitudes.

Abstract: Solar thermal power generation technology is the most feasible technology to compete with fossil fuels in the economy, and is considered to be one of the most promising candidates for providing a major share of the clean and renewable energy needed in the future. The appropriate heat transfer fluid and storage medium is a key technological issue for the future success of solar thermal technologies. Molten salt is one of the best heat transfer and thermal storage fluid for both parabolic trough and tower solar thermal power system. It is very important that molten salt heat transfer mechanisms are understood and can be predicted with accuracy. But studies on molten salts heat transfer are rare. This study will lay a foundation for the application of carbon nanotubes in molten salt which can remarkably improve the stability and capacity of thermal storage. Thermal analysis methods and scanning electron microscope (SEM) are utilized to provide a review of thermophysical properties and thermochemical characteristics of the MWCNTs-salt composite materials.

Abstract: A novel voltage sag generator (VSG) is proposed for grid-connected photovoltaic (PV) systems low voltage ride-through (LVRT) test. The topology and parameters of the current-limiting reactor group, grounding reactor group and bi-directional thyristor valve of the VSG is designed to generator voltage sags with several sag depths and phase angles. Furthermore, for a 250kW grid-connected PV inverter modeled by real-time digital simulator (RTDS), LVRT simulations in different sag depths at different phase angles are done with the VSG. Simulation results show that the proposed VSG has reasonable design and can reveal adequately how the voltage sag depths and phase angles influent the LVRT results.

Abstract: An experimental study on the evolution of the salinity profiles in the salinity gradient solar ponds was executed using a small model pond. The body of the simulated pond is a cylindrical plastic tank, with 50 cm height and 45 cm diameter. The salinity gradient was established in the laboratory tank by using the salinity redistribution technique. The measurements were taken during a period of 20 days of experimentation. This period of time allowed the existence of salt diffusion from the storage zone to the surface. Results obtained from this study show that when the ratio of brine/water is 1/1, the salinity gradient layer can sustain a longer time and the lower convective zone is thicker, which is benefit to store solar energy.

Abstract: A novel technique using solar power to irrigation was proposed. In order to obtain better sensitivity, small dense probe, single strand copper probe, bifilar winding type probe and rectangular cross section type probe were designed. Through the experiments, the electrical resistance of four kinds of probe structure was determined. Test results show that conductivity of small dense probe is the worst, conductivity of single strand copper probe is better. Graphite content has great influence to probe resistance value, resistance and graphite content in the relationship is not linear.

Abstract: The standards of grid-connected photovoltaic (PV) system and the cause of islanding in formation are introduced at first, and then common passive and active detecting islanding methods are discussed in this paper. Considering the shortcomings of traditional methods, such as failing to detect islanding, larger non-detection zone and poor quality of output power of the inverter, etc., a novel detecting method which is called as positive power feedback disturbance is proposed, so as to overcome these problems. The proposed method has the characteristics of no non-detection zone, little influence on power quality and rapid respond. Finally, according to professional standards of IEEE Std. 2000-929 and UL1471, the simulation as well as the experiment of the proposed method was carried out. The results of simulation and experiment showed the good expressions from the novel method.

Abstract: Taking Changchun area with cold construction characteristics as an example, this paper studies the design of building integrated photovoltaic on rooftop. It proposes some problems for attention in design content and design of building integrated photovoltaic, and puts forward a set of design scheme of villa roof grid-connected system, providing some ideas for similar design in this area for future.

Abstract: The photovoltaic (PV) systems are the most promising options to meet the rapidly increasing energy demand for renewable energy resources development. A simple and well fault diagnosis system can guarantee the normal operation of photovoltaic systems. This paper proposes a simple diagnostic method to tell the operating status of the PV systems by contrasting the simulation parameters and the measured parameters. The diagnostic algorithm uses the irradiance level, the PV modules temperature, the number of PV modules and its output power as the inputs. So, just temperature and irradiance sensors, as well as several power meters are needed in the monitoring system forming part of the fault diagnostic system. The proposed fault detection method has been successfully validated in simulation and experiment.