Koichi Sakuta

Energy pay-back time and life-cycle CO2 emission of residential PV power system with silicon PV module

The concerns about environmental impacts of photovoltaic (PV) power systems are growing with the increasing expectation of PV technologies. In this paper, three kinds of silicon-based PV modules, namely single-crystalline silicon (c-Si), polycrystalline silicon (poly-Si) and amorphous silicon (a-Si) PV modules, are evaluated from the viewpoint of their life-cycle. For the c-Si PV module it was assumed that off-grade silicon from semiconductor industries is used with existing production technologies. On the other hand, new technologies and the growth of production scale were presumed with respect to the poly-Si and a-Si PV modules. Our results show that c-Si PV modules have a shorter energy pay-back time than their expected lifetime and lower CO2 emission than the average CO2 emission calculated from the recent energy mix in Japan, even with present technologies. Furthermore the poly-Si and the a-Si PV modules with the near-future technologies give much reduction in energy pay-back times and CO2 emissions compared with the present c-Si PV modules. The reduction of glass use and the frameless design of the PV module may be effective means to decrease them more, although the lifetime of the PV module must be taken into account.

An evaluation on the life cycle of photovoltaic energy system considering production energy of off-grade silicon

In this study, single-crystalline silicon (c-Si) photovoltaic (PV) cells and residential PV systems using off-grade silicon supplied from semiconductor industries were evaluated from a life cycle point of view. Energy payback time (EPT) of the residential PV system with the c-Si PV cells made of the off-grade silicon was estimated at 15.5 years and indirect CO2 emission per unit electrical output was calculated at 91 g-C/kWh even in the worst case. These figures were more than those of the polycrystalline-Si and the amorphous-Si PV cells to be used in the near future, but the EPT was shorter than its lifetime and the indirect CO2 emissions were less than the recent average CO2 emissions per kWh from the utilities in Japan. The recycling of the c-Si PV cells should be discussed for the reason of the effective use of energy and silicon material.

Measurements, analyses and evaluation of residential PV systems by Japanese monitoring program

Abstract This paper is about measurements, analyses and evaluation of residential PV systems in the Japanese Monitoring Program, on which JQA was subsidized by NEDO (New Energy Development and Industrial Technology Organization) that is currently proceeding [NSS R&D] from FY1997 to FY 2000. The aim of this investigation refers, through the data evaluation and analyses, to obtain knowledge required for optimizing design of PV systems, such as system performance, characteristics and regional dependency under practical operation and to develop the system evaluation technology on the design parameter method.

Improvement of performance in redox flow batteries for PV systems

Abstract A redox flow battery (RFB) is a new type battery. A new piping sytem to improve the performance of RFBs for PV systems is introduced. In this new system, the piping for the electrolytes also connects each stack in series just like the electric circuit. In this system, the leak current through the electrolytes in the piping between each stack is suppressed. This system is called multitank system because it has many minitanks between each stack. It is clarified from the experimental and simulation results of the multitank system that this system improves the performance of RFBs.

Data analysis on solar irradiance and performance characteristics of solar modules with a test facility of various tilted angles and directions

We examined and evaluated the output characteristics and the deterioration lowering factors of modules installed under various conditions (module directions and tilted angles) based on the data collected at the multi-position test facility, which was produced and installed in order to conduct evaluation using design parameters (correction coefficient). This report introduces example data and the results of our evaluation.

Reflection loss analysis by optical modeling of PV module

As an evaluation method of the photovoltaic (PV) system, it is necessary to clarify loss factor which decreases system efficiency. One of the factors mentioned is the reflection loss that depends on an incident angle. It is believed that the factor is simulated by reflections and transmissions in a module. Using the optical performance of a four-layer encapsulation, a simulation was made on the reflection loss according to Fresnels law. Further, the incident angle modification factor as the coefficient for evaluating energetic reflection loss was described by a computer program simulation. The result was that the modification factor is between 0.96 and 0.98. Consequently, to obtain the optical property of module materials, the module tilt angle and its latitude location, the simulation could give the evaluation of annual reflection losses by such a factor at various regions.

On-site BIPV array shading evaluation tool using stereo-fisheye photographs

It is difficult to estimate precisely total irradiance on photovoltaic (PV) arrays without consideration of the effect of shadow by surroundings, especially for building integrated photovoltaic (BIPV) systems in an urban area. The accurate evaluation of actual irradiation on the arrays may contribute to the verification of the performance of PV systems. In this research, the authors propose the method of calculating the shading factor by applying the photo survey method using fisheye photographs to capture whole surroundings. The shading factor is defined as the ratio of actual irradiation on PV arrays to ideal irradiation with no shading modules. Actual irradiation on a certain array can be calculated easily by using the shading factor.

Extended performance analysis of 70 PV systems in Japanese field test program

Under the Government Basic Guidelines for the new energy introduction, New Energy Development and Industrial Technology Organization (NEDO) installed and is installing 177 PV sites having a total capacity of 4860 kW from FY1992 to FY1997. Those systems have been being monitored and all the data have been collected by Japan Quality Assurance Organization (JQA). Simple operational reports have been compiled from the beginning of the project. More detailed, systematic performance analysis routine has been introduced to the existing database. Analyzed performance parameters are given by a set of 2 graphs. Detailed parameter definitions and analyzed results for selected sites are given. Statistical evaluation for the 70 available systems are also presented.

Practical values of various parameters for PV system design

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. In order to reasonably design a PV system, it is important to use appropriate parameter values. Few papers, however, describe design parameters that are defined systematically. The authors have been entrusted by the New Energy and Industrial Technology Development Organization (NEDO) with research and development of PV system evaluation since 1990 in order to establish optimum design and operation methods of various kinds of PV systems which are expected to be put into commercial use in the future. In this research, which is based on the data obtained from test facilities which were constructed at Hamamatsu site, various design parameters were calculated and reported as primary values provisionally estimated. This paper presents practical values of various parameters for PV system design as a table, revised with design parameter values studied later on. In particular, cell temperature factor was studied in view of regional differences and module mounting. The authors will confirm reasonable design of PV system by using such various design parameter values.

Energy payback and GHG emissions of renewable power generation systems in Japan: A review

This report summarizes the latest studies on energy payback and Greenhouse Gas (GHG) emissions of power generation systems in Japan. Listed power generation systems are: hydropower (large scale only), geothermal, wind power, photovoltaic, forest biomass, nuclear and fossil-fuel-fired. All data were calculated under Japans local conditions, coordinating with independent studies done in other countries.