Advanced Materials Research Vol. 773

Abstract: Existing model of solar cells is not suitable for partial shading condition, which makes output current-voltage (I-V) curve of photovoltaic (PV) array staid-stepping. Furthermore, Power-Voltage (P-V) characteristics may exist more than two local peak value in partially shading which bring interferences to maximum power point tracking (MPPT). Based on modified engineering model of solar cells, an accurate model of array was proposed considering variation of shadows. And the I-V characteristic, P-V characteristic and yield of PV modules were analyzed. At last, the optimum output power with different shadows arrangement was discussed.

Abstract: Corn straw biogas slurry always contains humic substances, which poses particular challenges in obtaining PCR-amplifiable DNA for analysis of microbial community. To establish an efficient and reliable DNA extraction method for straw biogas slurry, four approaches: i.e., direct SDS-based method, direct bead-based method, indirect SDS-based method, and indirect bead-based method were evaluated by comparing DNA yield, humic acid contamination, PCR amplifiability, and restriction fragment length polymorphisms (RFLP) of amplified 16S rRNA genes. Direct DNA extraction methods yielded 3-fold higher amounts of DNA than indirect procedures, but its DNA purity was lower. The A₂₆₀/A₂₃₀ ratio of DNA from indirect methods (0.8-0.85) were higher than that of DNA from direct methods (0.5-0.6), indicating DNA from direct methods contained high levels of humate contamination. PCR amplification was successful with crude DNA from indirect methods, but not with crude DNA from direct methods. PCR products could also be obtained with purified DNA from direct bead-based method, whereas not direct SDS-based method. Among the four methods, direct bead-based method, indirect SDS-based method and indirect bead-based method could obtain high-quality DNA extracts from corn straw biogas slurry. RFLP analysis further demonstrated the restriction patterns of amplified 16S rRNA genes from three methods were relatively identical microbial diversity.

Abstract: We explain the experimental improvement in long wavelength response by hydrogen plasma treatment (HPT) in n/i interface. The absorption coefficient of the intrinsic microcrystalline silicon (μc-Si) is decreased in the low energy region (0.8~1.0 eV) by HPT, which indicates a lower defect density in μc-Si layer deposited with HPT than its counterpart without HPT. Simulation by one-dimensional device simulation program for the Analysis of Microelectronic and Photonic Structures (AMPS-1D) shows a higher long wavelength response in μc-Si solar cell if the defect density in intrinsic μc-Si layer is smaller. Our simulation results also disclose that the less defect density in intrinsic layer, the lower recombination rate and the higher electric field is. Higher electric field results in longer drift length which will promote collection of carriers generated by photons with long wavelength. Thus we deduce that HPT decreased defect density in absorber layer and improved the performance of μc-Si solar cells in long wavelength response.

Abstract: In this paper, we have focused on the influence of interface state density and band offsets on the performance of HIT solar cells by simulation. The interface state density D_it have negative influence on the open-circuit voltage V_OC, fill factor FF and the short circuit current J_SC, beyond different D_it respectively. V_OC decreases monotonically with increasing D_it only when D_it is greater than 10¹⁰ cm^-2, and for FF and J_SC D_it is 10¹² cm^-2, 10¹³ cm^-2, respectively. Observed reduction in V_OC (D_it is from 1×10¹⁰ cm^-2 to 5×10¹³ cm^-2) may be due to the enhanced recombination possibility, which diminishes the difference in quasi Fermi energies from 0.8 eV to 0.46 eV. Reduction of J_SC (D_it is from 1×10¹³ cm^-2 to 5×10¹³ cm^-2) is connected with the carrier recombination rate that is heightened from 2.43×10²⁴cm^-3/s to 3.1×10²⁶cm^-3/s, which is markedly by two orders of magnitude. In addition, our research results demonstrate that by increasing the conduction band offset E_C (from 0.09eV to 0.15 eV), the V_OC could be increased by 15.9 mV, while the performance of HIT solar cells is not affected by the valence band offset E_V. The increase of E_C results in the rising of V_bi and thus improves V_OC. It is worth mention that, the recombination potential V_Re could be decreased from 232 meV to 208 meV by the increase of E_C (from 0.09eV to 0.15eV) and thus is favorable to V_OC. Consequently, when the interface state density is less than 10¹⁰ cm^-2 and the conduction band offset reaches 0.15eV, we can optimize the performance of HIT solar cells to achieve 24.95% efficiency.

Abstract: This paper presents the coordination of wind and thermal generation dispatch using Ant Colony Approach. Wind power is unpredictable and intermittent. As wind power penetrations increase in current power systems, its impact to conventional thermal unit should be investigated. The objective of this paper is the development of better wind thermal coordination economic dispatch which is necessary to determine the optimal dispatch scheme that can integrate wind power reliably and efficiently. In this paper Ant Colony Algorithm (ACA) is utilized to coordinate the wind and thermal generation dispatch and to minimize the total production cost in the economic dispatch considering wind power generation and valve effect of thermal units. A ten generator system with one wind power plant is tested to validate the effectiveness of the proposed model and method. Different simulations with and without wind power production are simulated. Simulation result shows the effect of wind power generation in reducing total fuel cost.

Abstract: Grid-connected inverter topologies and control methods are analyzed and compared on the basis of two non-isolated PV grid-connected inverter circuit topology as 3kVA grid connected PV systems. In this paper, the current control method, the DC bus voltage outer grid current inner loop of the dual closed-loop PI control method. Sampled signal through the system circuit for processing, resulting in a SPWM drive signal to control the conduction of the power devices off the grid current control.

Abstract: A thermal energy storage unit laboratory with solar heat sources being designed and constructed. The spherical capsules which filled in phase change material (PCM) were put into the unit. Many groups' experiment schemes was designed and the discharging experiment is done, different import temperature and flow rate of HTF were experimented repeatedly, the effects of inlet fluid temperature and flow rate of HTF on the performance of the storage unit was analyzed. The experimental result shows that, with the import temperature and flow rate of HTF increased, the time finishes discharging reducing constantly, the efficiency of thermal energy storage is improved. The results offer the reference basis for design, optimization, and appreciation of the TES unit.The test data was compared with simulation data,the simulated results and experimental results agree well with the experimental results.

Abstract: Aiming at the management problem of real-time data created while intelligent solar street lamps working, sectional data acquisition and control system based on internet of things is introduced in the paper. Communication protocol with unified form and flexible function is designed in the system, and communication address is composed of sectional address and subsection address. Three-level data structure is built in the polling algorithm to trace real-time state of lamps and to detect malfunction in time, which is suitable for sectional lamps management characteristics. The system reflects necessary statistic data and exception information to remote control centre through GPRS to short interval expend on transmission and procession and save network flow and system energy. The result shows the system brings improved management affection and accords with the idea of energy-saving and environmental protection.

Abstract: In order to improve the photovoltaic maximum power point tracking (MPPT) system efficiency and electrical performance, the multiple DC/DC converter technology is introduced into the photovoltaic MPPT system. And a novel control strategy is proposed, which make the multiple DC/DC converter can change operating mode according to the ambient light intensity, to achieve a more flexible and effective photovoltaic MPPT control. The working process and implementation of the new photovoltaic MPPT system with multiple DC/DC converters was analyzed, and the experimental results are provided to verify the feasibility of superiority and the proposed system solutions.

Abstract: The exploitation and utilization of renewable energy, construction of sustainable energy system has gradually become the consensus of the international community, the research of microgrid technology with solar, wind and other renewable energy generation is becoming more and more deeply. According to the needs of the development of microgrid technology, in this paper a better functional architecture system of centralized control system for optimizing microgrids with new energy power generation system is proposed. First, according to the layered and distributed idea, a system of physical architecture which can run in the situations of both coordination control and self-control is designed, the system is mainly divided into physical components layer and the central station layer; and then the paper proposes the functional architecture system, it describes all the function modules and their interactions. Finally emphatically introduces the real-time security and stability control, energy optimization scheduling and other function modules which can improve the utilization ratio of renewable energy. The research of this system will play an important role in improving the absorption capacity of renewable energy; reducing fossil energy consumption and environment pollution.