Hideaki Kawamura

Simulation of I–V characteristics of a PV module with shaded PV cells

The authors are studying a diagnostic method of a PV power generating system. We consider that the change of I–V characteristics can be utilized for the diagnosis. However, the report on the change of I–V characteristics is very little. In this paper, we investigate the relation between the output lowering due to shaded PV cells and the change of I–V characteristics, utilizing the computer simulation. It was proven from the simulation that I–V characteristics are changed by the condition of the shadow, which covered the module. The change of I–V characteristics of a PV module with shaded PV cells is discussed by the shift of the avalanche breakdown voltage of shaded PV cells.

Diagnosis of a Power Output Lowering of PV Array with a (-dI/dV)-V Characteristic

It is reported that the volume of an estimated PV system installations in Japan must be set at about 4.82 [GW] up to 2010. As a result, it seems that PV systems must spread in the future in a general household, and therefore the maintenance and management of PV systems must become important keeping to the normal output performance of a PV system. However, it will be very difficult to locate the lowering factors to affect to output performance of the PV system installed in a residential rooftop. Besides, even if a cause of the output lowering of the PV system was found more, it will be very difficult to remove these. The authors paid attention to that shape of an I-V characteristic of a PV system changed by the output lowering caused by loss factors such as deterioration of a PV module, a shadow, and so on, and study the method to simply and automatically evaluate the output lowering of a PV system. In this paper, the (dI/dV)-V characteristic to be obtained from the I-V characteristic of a PV array is adopted as the standard characteristic for the automatic analysis. The (dI/dV)-V characteristic was simulated with an abnormal I-V characteristic of PV array covered in a shadow partially. A performance fall of PV array to be caused by a partial shadow is evaluated by an appearance of a peak of the (dI/dV)-V characteristic, and an appearance position of this peak changes by a condition of a shadow. From these results, it became clear that an appearance of a peak of a (dI/dV)-V characteristic must be means to be effective to diagnose the output lowering of a PV system

Effect of additives on DC treeing breakdown in polyethylene under divergent fields

The effect of additives on DC treeing breakdown phenomena and space-charge formation in polymeric materials is studied under divergent fields. Experimental results are presented to show that: (1) The DC treeing breakdown phenomena are considerably affected by the space charge. (2) The presence of acetophenon in low-density polyethylene (LDPE) enhances the amount of accumulated space charge, while blending with ionomer or polyamide suppresses it. (3) Blending ionomer or polyamide into LDPE improves the DC tree resistance. >

Diagnostic method of performance of a PV module with estimated power output in considering four loss factors

Recently, PV systems are rapidly spreading. It is necessary to establish a diagnostic method for maintenance of the PV systems. The authors are studying diagnostic methods of PV systems. Even if a PV module is normally operated, the generated power is less than the rated power. It means that the normal PV module has some kinds of loss in the generated power. These losses are caused by irradiance, reduction of sunlight transmittance on glass of module, temperature and series resistance. The generated power can be estimated by considering these four kinds of loss. The estimated power is calculated by subtracting these power losses from the rated line. As the results, the diagnostic method is devised by using the estimated power. And it is clear that the method can diagnose bit degradation of generated power on the module.

Loss factors affecting power generation efficiency of a PV module

The authors are studying the diagnostic method of a PV system. In order to diagnose a PV system in detail, it is necessary to separate the loss factors affecting power generation efficiency. In this paper, we are investigating the influence of the solar irradiance and the incident angle on power generation efficiency of the PV module installed at tilt angle of 90 degree and azimuth angle of east and west, respectively. Especially, the influence of the incident angle on power generation efficiency is estimated in detail by separating direct and diffuse component of solar irradiance. We investigate the comparison between the measurement and the calculation results related to the change of power generation efficiency with time. The calculation value considering solar irradiance and incident angle of direct and diffuse solar irradiance almost corresponded to measurement value. As a result, it is clear that the change of power generation efficiency with time can be estimated by separating the influence of solar irradiance and incident angle of direct and diffuse solar irradiance and considering these loss factors.

Crystal orientation control of YBa2Cu3Oy thin films on MgO prepared by excimer laser ablation with CO2 laser irradiation

Superconducting YBa2Cu3Oy (YBCO) thin films were prepared on a MgO (100) substrate by XeCl excimer laser ablation with CO2 laser irradiation. Control experiments of crystal orientation of YBCO thin films were carried out by varying the substrate temperature during deposition; c‐axis oriented YBCO film, a‐axis oriented YBCO film, and a‐axis oriented YBCO film on the c‐axis were obtained on the MgO (100) substrates. a‐axis oriented YBCO films normal to the MgO (100) substrate were fabricated using the modified self‐template method.

A study of the automatic analysis for the I-V curves of a photovoltaic subarray

The authors are studying a diagnostic method of a PV array by utilizing the I-V curve. In this paper, the standard dI/dV-V curve obtained by the I-V curve of normal PV subarray is decided as the standard characteristic for the automatic analysis. This dI/dV-V curve is used to compare with dI/dV-V curves of abnormal shaped I-V curves such as the PV subarray with partial shadow. The dI/dV-V curve of abnormal PV subarray is remarkably different from the standard dI/dV-V curve. And the variance value to evaluate the difference between the standard dI/dV-V curve and the abnormal dI/dV-V curve is calculated. It is clear that the degradation of generating power characteristics of PV subarray can be analyzed by the variance value quantitatively.

Space charge accumulation in water tree degraded LDPE and its evaluation by TSC method

The space charge in water tree degraded LDPE has been measured by the thermally stimulated current (TSC) method. The shape of the TSC spectra does not change with the degradation of polymeric insulation containing water trees, but the TSC peak increases linearly with the increase of the length of the water tree. It is shown that the TSC measuring method can adapt to evaluate the degradation caused by water treeing.<<ETX>>

Effect of copolymerization on electrical and water trees of polyethylene

Electrical- and water-treeing breakdown phenomena were investigated on polyethylene copolymerized with various monomers. The resistance to electrical treeing in copolymerized specimens was evaluated according to the tree-inception voltages. The AC-tree-inception voltage decreased with increase in halogen atom content in the monomers. The resistance to water treeing in copolymerized specimens was evaluated according to the growth of water trees that arose from the tip of a needle-like water electrode. The growth of water treeing decreased with increase in halogen atom content in the monomers. Halogen atoms which were copolymerized in polyethylene improved the AC-electric-tree resistance and the water-tree resistance.<<ETX>>

Effect of additives on DC treeing breakdown in polyethylene under divergent field

The effect of additives on DC treeing breakdown phenomena and the space charge formation near the tip of a needle electrode inserted into polymeric material were studied under various conditions. Ionomer-blended low density polyethylene (LDPE), polyamide-blended LPDE, and cross-linked samples which include acetophenone were investigated. The DC tree inception voltage for the positive point is almost independent of ionomer content. But the DC tree inception voltage for the negative point which is greater than that for the positive one decreases with an increase of ionomer or polyamide content. The extension length of the polarity-reversal tree which occurs on the application of impulse voltage of inverse polarity after the DC prestress decreases with an increase of ionomer or polyamide content. On the other hand, the DC tree inception voltage of the crosslinked samples with acetophenone is greatly higher than that of blended LDPE. Furthermore, the extension length of the polarity-reversal tree of crosslinked samples with acetophenone is longer than that of blended LDPE. From these results, it is suggested that ionomer or polyamide which is blended into LDPE improves the DC tree resistance, and that acetophenone in crosslinked samples enhances the amount of accumulated space charge.<<ETX>>