Keiichi Okajima

PV System With Reconnection to Improve Output Under Nonuniform Illumination

Photovoltaic (PV) systems are often nonuniformly illuminated owing to shadows of neighboring buildings, trees, clouds, etc. In order to reduce the effect of shadows on solar panels, we propose the concept of a PV system with reconnection; this system consists of PV arrays that can be reconnected to minimize the mismatch loss, depending on the output of each of its module, measured at regular time intervals. In this study, the relationship between the output improvement with reconnection and the switching interval is shown. For a 3-kW PV system, under conditions of cloudlessness and cloudiness, a sharp difference in the output improvement relative to the switching interval is not observed. However, under the condition of shading, the output improvement sharply decreases relative to the switching interval; the output improvement at a 1-min switching interval is 0.15 kWh·h (+22.4%). For the 90-kW building-integrated photovoltaic system, during the summer solstice, a sharp difference in the output improvement relative to the switching interval is not observed. However, during the vernal equinox and winter solstice, when a large area of the PV system is shaded for a long period of time, the output improvement sharply decreases relative to the switching interval. The output improvement at a 1-min switching interval is 6.5 kWh·d (+2.9%) during the vernal equinox and 2.3 kWh·d (+3.7%) during winter solstice.

Study of Current Distribution in PEMFC Stack Using Magnetic Sensor Probe

AbstractThe current distribution in a 1.2-kW PEMFC stack has been investigated using a triaxial magnetic sensor probe with the objective of determining the operating state of the PEMFC. The results show that the current distribution tended to concentrate on the underside of the cell. Current distribution was different in each cell because each cell had a different performance. In order to evaluate the performance of each cell, the I—V curve based on a model formula was calculated using the voltages obtained for each cell. Three cells having different cell performances were chosen and the relationship between the cell performance and the current distribution in the cell was evaluated. The results indicated that the standard deviations of current densities in the first and second cells were greater than that in the last one.

Semi-Empirical Equation of PEMFC Considering Operation Temperature

Abstract The characteristic of a proton exchange membrane fuel cell is shown by the relationship between its output voltage and current. The output cell voltage determines the activation loss, ohmic loss, and concentration loss. Studying these losses is important to understand their effect of the reduction factor of the output of the fuel cell. One method of calculating these losses is by the curve-fitting using a semi-empirical equation. This method is useful for quickly predicting the performance. In previous studies, the fuel cell temperature has been assumed to be steady. However, the operation temperature of the fuel cell is not constant in the real fuel cell systems, such as residential and vehicular fuel-cell stacks. Therefore, it is difficult to separate the different types of losses on a polarization curve. In this study, we propose a new semi-empirical equation considering the fuel cell’s operation temperature. Through thermodynamic, mechanistic, and electrochemical modeling, we express the initial voltage, activation loss, ohmic loss, and the concentration loss. We compare the fitting parameters of the proposed equation with those of equations proposed in previous studies. We also study the effects of operating temperature and cathode gas on the parameters that influence the performance.

Minimizing mismatch loss in BIPV system by reconnection

Recently, building-integrated photovoltaic (BIPV) systems have become increasingly popular because they provide increased available space and have great environmental appeal. However, these systems may be adversely affected by shadows of surrounding buildings. In order to reduce the effect of shadows on solar panels, we propose the concept of a PV system with reconnection (smart PV), where PV arrays can be reconnected to minimize the mismatch loss depending on the output of each module measured at regular time intervals. In this study, the effects of minimizing the mismatch loss of a BIPV system by reconnection are evaluated by studying shadow patterns. The PV system with reconnection showed good performance for typical shadow patterns. In the evaluation, the optimized connection is determined by calculating the outputs of several array connection patterns. To analyze the daily impact of the PV system with reconnection, the daily output energy by the BIPV system that is partially shaded by a neighboring building is considered as a case study. The maximum improvement in the daily mismatch loss with the reconnection was 8.1 kWh per day compared with that of conventional array connections. In conclusion, it is shown that the PV system with reconnection shows better performance compared with conventional fixed array connections.

Evaluation for the Adoption of Renewable Energy in China using Geographic Information System

AbstractRenewable energy is one of effective measures to decrease GHG emission. Its installed potential should be evaluated in a specific area, because renewable energy is a local energy. Especially, biomass energy should be evaluated in a region, because it has a wide geographical distribution. High costs for transportation, feedstock, and energy conversion are obstacles to promote the utilization of biomass energy sources. In this study, usable biomass potential and locations of biomass power plants are estimated by using Geographic Information System (GIS) and an optimal method in Guangdong Province. From the model analysis, we can obtain an optimal transportation process and the number of profitable conversion plants for woody biomass resource. In the optimal case, the installed biomass power plants are five units with the range of power capacity from 23.5 to 43.5 [MW], and its total annual power generation is 1135.5—1228.8 [106kWh/yr] in Guangdong.

Evaluation of Potential Geographic Distribution for Large-Scale Photovoltaic System in Suburbs of China

Since China is the largest CO2 emitting country in the world, photovoltaic (PV) systems are expected to be widely installed to reduce CO2 emission. In general, available area for PV installation depends on urban area due to differences in land use and slope. Amount of electricity generated by a PV system also depends on urban area because of differences in solar irradiation and ambient temperature. The aim of this study is to evaluate the installation of large-scale PV systems in suburbs of China, taking these differences into consideration. We have used a geographic information system (GIS) to evaluate amounts of installation capacity of large-scale PV systems, electricity generated, and CO2 emission reduction by the installation capacity of large-scale PV systems in suburbs of Liaoning, Shanghai, Anhui, and Guangdong. In Liaoning, the amount of CO2 emission reduction by the installation capacity of large-scale PV systems was estimated to be the largest, 3,058 kt-CO2/yr, due to its larger amount of the installation capacity, 2439.4 MW, than the amount of the installation capacity in other regions.

CO2 Emission from Electricity Generation in Malaysia: A Decomposition Analysis

In tenth Malaysian Plan, Malaysian government had voluntarily targeted to reduce its emission intensity to 40% compared to the 2005 level by the year 2020 and recently re-pledge to reduce more and declared for 45% emission reduction by 2030. Looking at the country’s high dependency to the fossil fuel generation it is a high concern on the increasing CO2 emission in Malaysia. This paper intends to analyze the current status of CO2 emissions from electricity generation in Malaysia during the period 1992-2014 by applying the LMDI (logarithmic mean Divisia index) technique to find the nature of the factors influencing the changes in CO2 emissions. The decomposition analysis observed three biggest factors contributed to the reduction of CO2 emission throughout the period which is thermal generation effect, electricity generation efficiency effect and electricity structure effect.

Evaluation of Heat and Current Characteristics of Bypass Diodes for Fault Detection in Photovoltaic Module

In recent years, PV (photovoltaic) systems have been installed rapidly around the world. However, there is often a delay in the practical application of fault detection in PV systems. In this study, the temperature of BD (bypass diodes) mounted on PV modules was measured for simple and practical fault detection. The temperature of the BD of Module 31 was higher than other modules and a large current passed through one of the BDs. Measuring BD temperatures is easier than other conventional methods of fault detection. From the results of the rise in BD temperature under dark conditions, the increase in temperature increased linearly with increasing current flow. There is a proportional relationship between heat generated and the increasing temperature of the terminal box. The experimental results about surface temperature of the junction box in actual system operation suggested that the electric current through a BD in a terminal box can be known by measuring the surface temperature of the terminal box for PV module fault detection without a system shutdown. Moreover, we tried to evaluate temperature distribution of a terminal box using heat conduction equations. The evaluated results agreed well with the measured results.

Power drop detection in PV string by analyzing I–V characteristics

AbstractPhotovoltaic (PV) systems have been regarded as maintenance-free; however, numerous failures have been reported recently during their operation. These failures not only cause power drops in the PV system but can also lead to serious accidents. This paper proposes a diagnosis method that utilizes the current–voltage (I–V) measurements of the PV string to detect the existence of a power drop module in the PV system. This diagnostic methodology is based on the calculation of the decrease in the area of the string I–V curve and dP/dV–V characteristic from the obtained data. A power drop module in the PV string is assumed and calculated. First, the normal and failed versions of the PV string are distinguished by plotting the decrease in the area of the I–V curve on one axis and the ratio of the power drop on the other axis. The differences among each failure mode are then obtained by evaluating the dP/dV–V characteristic of the PV string. Finally, experimental tests are performed on the PV string to va...

In situ approach for characterizing PEMFC using a combination of magnetic sensor probes and 3DFEM simulation

Abstract Non-uniform current distributions of proton-exchange membrane fuel cells (PEMFCs) result in unequal utilization of reactants and catalysts in solution. To prevent the degradation of PEMFC, an in situ approach for characterizing PEMFC stacks is needed. In this study, the current distribution of two-cell PEMFC stacks is replicated from measured magnetic flux densities and operating conditions produced by three-dimensional finite element modeling that included electromagnetic field modeling and electrochemical reactions. I–V curves under normal conditions were replicated from electrochemistry and compared to the measured curves, and magnetic flux density distributions were investigated to determine the operating state. From these results, we discuss the potential use of the proposed approach in in situ applications.