Advanced analysis of grid‐connected PV system's performance and effect of batteries

An advanced method of analysis for grid‐connected PV systems is developed in this research. To investigate the issues which may arise in the clustered PV systems, a “Demonstration Project on Clustered PV Systems” was initiated in December 2002 in Oota, Japan, involving the installation of more than 500 residential PV systems in the demonstrative research area, and the development of battery‐integrated PV systems to avoid restrictions on output power due to the raising of the grid voltage. The annual performance of commercial PV systems without battery was analyzed and a performance ratio of 80% on average was found to have been achieved. Overvoltage of power distribution lines and snow are two major factors capable of causing very low performance ratio on a daily basis. The effects of batteries have also been analyzed, and the results indicate that there will be some reduction of energy losses due to the grid voltage, but the PCS efficiency will be at least 8% worse than that of commercial PV systems. It was also found that nonoptimized battery operation sometimes results in a fully charged situation at noontime and maximum reverse power flow may not be minimized in this situation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 21–33, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20660     

Passive Control of Steady Condensation Shock Wave

IntroductionA rapid expansion of moist air or steam in asupersonic nozzle gives rise to nonequilibriumcondensation phenomena. Thereby, the nozzle flow isaffected by the latent heat released by condensation ofwater vapouf, and if the heat released exceeds a certainquantity, a condensation shock wave will occur[1-4].Many works for the passive contfol of shockboundary layer interaction using the porous wall with aplenum underneath have been repofted on the applicationof the technique tO tfansonic…     

Key near-term R&D issues for continuous improvement in CIS-based thin-film PV modules

In a large-area approach up to 60 cm×120 cm size, monolithically integrated CIS-based thin-film PV modules have come to the efficiency level of 13%. The key near-term R&D issues to realize continuous improvement in CIS-based thin-film PV modules are related to their competitiveness against the crystalline-Si PV modules. In this contribution, the following three issues are discussed. The first and main issue is how important it is to understand the interfaces in the CIS-based thin-film circuit to improve the efficiency, because CIS-based thin-film circuits are fabricated in a stacked structure of four or five thin films. The second and third issues are how beneficial it is to develop the packaging and material recycle technologies in order to reduce the production cost.     

Performance analysis of various system configurations on grid-connected residential PV systems

Performance and loss analysis of residential photovoltaic (PV) systems are conducted using the sophisticated verification (SV) method. Performance of the various system configurations is quantitatively analyzed and compared in this paper. The south-oriented systems have approximately 22% more reference yield than the systems that are not oriented south. Difference of the module manufacturers shows more than 10% differences of the performance ratio whereas array configuration shows less difference. Imbalance of the string voltages causes system peak power loss and MPP mismatch. This loss cannot be minimized by the DC/DC converter in most of the systems.     

Self‐sensing active magnetic bearings with zero‐bias‐current control

A zero‐bias‐current self‐sensing active magnetic bearing is proposed. One degree‐of‐freedom (DOF) of the rotor is controlled by a pair of electromagnets which are alternatively energized by the proposed circuit. The rotor position of the one DOF is measured by using both electromagnets: the nonenergized electromagnet also contributes to the position sensing. The proposed method gives good linearity in the position estimation. The controller of the magnetic levitation consists of a digital signal processor, DSP, which compensates the nonlinearity of the magnetic force and achieves good damping. In the experiment, the rotor can run at 45,000 min^‐1. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 69–76, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20616     

Si-film growth using liquid phase epitaxy method and its application to thin-film crystalline Si solar cell

We have developed a new apparatus for the growth of liquid-phase epitaxy (LPE)-Si films on 5 in Si wafers. We have obtained high growth rates of 0.1–1.0 μm/min and minority-carrier lifetime of average value of 10 μs over the whole of wafer, whereas the thickness uniformity was degraded when rotating the wafers in the solvent. We also demonstrated to growth of LPE-Si films on porous Si layers and to separate the Si films from the porous layers. A 9.5% cell was obtained using a LPE-Si film after separation.     

Formation mechanism of porous structure in polytetrafluoroethylene (PTFE) porous membrane through mechanical operations

Polymeric porous membranes were prepared from polytetrafluoroethylene (PTFE) fine powder by a series of mechanical operations, such as extrusion, rolling, and stretching. The structure of the prepared porous membrane was well characterized by a spatial periodicity of nodes (domain of agglomerated PTFE particles) and fibril domains. The fibrils were highly oriented in the direction of the stretching operation, providing pores in the polymeric membrane as slit-like voids between adjoining fibrils. The unit size of the periodic structure varied depending on the number averaged molecular weight of PTFE and the stretching conditions, the temperature of stretching, and the stretching rate and stretching ratio. A fibril consisted of several thread-like structures that were easily formed between PTFE particles due to the rolling operation in parallel with their direction. The dependence of the steady tensile stress in the stretching operation on the PTFE molecular weight was much weaker than that presumed for noncrystalline polymeric systems. The activation energy of 11.3 kJ/mol for the growth of fibrils was only several times as large as the thermal energy at the ambient temperature. These results imply that the thread-like structures can easily be pulled out of PTFE particles. This view is in accordance with the previously proposed microstructure in PTFE particles.     

Effect of Substitutional Monovalent and Divalent Metal Ions on Mechanical Properties of β-Tricalcium Phosphate

β-tricalcium phosphate (β-TCP) powder doped with monovalent or divalent metal ions was hot pressed at 1100°C, and the effect of substitutional monovalent and divalent metal ions on mechanical properties of β-TCP was investigated. The sinterability of β-TCP would be enhanced by the substitution of monovalent and divalent metal ions for β-TCP. Sintered β-TCP doped with 7.6 mol% of Mg²⁺ ion showed a bending strength of 160 MPa. It was found that the substituition of Mg²⁺ ion up to 9.6 mol% and a small amount of monovalent metal ions for β-TCP is effective to improve the mechanical strength of β-TCP.     

Physicochemical Properties of Starches from Lotus Rhizomes Harvested in Different Months

We investigated the physicochemical properties of starches extracted from 8 lotus (Nelumbo nucifera Gaertn.) rhizomes harvested in different months (September 2012 to May 2013). The physicochemical properties of the lotus starches depended on the harvest date. The peak viscosity (PV) in the Rapid Visco-Analyser analysis, and the viscosity at 65 °C (V₆₅) in the rotational viscometer analysis were significantly lower in SEP starch (extracted from the September-harvested sample) than in the other lotus starches. The Spearman’s rank correlation coefficients of potassium ion (K) content vs. V₆₅ and of K content vs. PV were 0.905 and 0.714, respectively, indicating that potassium ions are important for expressing the pasting properties of lotus starch. Principal component analysis suggested that the potassium, magnesium, calcium, and phosphorus contents are important for displaying both the pasting and gelatinization properties of the lotus starches. Meanwhile, the cluster analysis revealed that physicochemical properties of the SEP starch were different from those of the starches harvested in other months.