Takashi Oozeki

A Good Fit: Japan¿s Solar Power Program and Prospects for the New Power System

The Japanese earthquake and tsunami of 11 March 2011 spurred numerous discussions and debates regarding the national energy policy of Japan. One of the outcomes of this process was a new feed-in tariff (FIT) program to promote renewable energy, including photovoltaic (PV) systems, that went into effect on 1 July 2012. This new incentive program is expected to completely change the PV market in Japan, which has historically been dominated by residential PV applications. The FIT will drive not only the residential sector but also the nonresidential sector, including the new entrants to the Japanese power generation business: megawatt-scale PV power plants. Accelerating the introduction of renewable energy is important not only for diversifying Japans sources of energy (for energy security) and combating global warming (for the environment) but also for the development of green industries (for the economy). It is essential that Japan create an environment conducive to the expansion of renewable energy in Japan by identifying the appropriate mix of regulatory measures (e.g., FITs), public support, and private-sector voluntary efforts best suited to each energy source. This article describes the current status of the PV market in Japan; the new FIT program and its impacts on the PV market; and further institutional, technical, and R&D challenges for PV dissemination.

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.

An Evaluation Method for PV System to identify system losses by means of utilizing monitoring data

The rapid growth and expansion of grid-connected photovoltaic (PV) systems utilization is significantly beneficial to the mitigation of environmental issues. Even though they are known as the maintenance free generation, PV systems have to be monitored and evaluated their output energy since certain troubles have been reported. Therefore, an evaluation method for PV systems seems to be necessary. In our laboratory with TUAT, the sophisticated verification (SV) method, which is the evaluation method for PV systems, has been developed. The method can estimate system losses by using a few utilized monitoring data items despite of numerous kinds of losses. The paper describes to summarize the SV method, and examples of evaluation results

Photovoltaic power production forecasts with support vector regression: A study on the forecast horizon

The objective of this study is to verify how different forecast horizons affect the accuracy of a method to forecast photovoltaic power production using support vector regression and numerically predicted weather variables. One year of power production forecasts were done for a 1 MW photovoltaic power plant in Kitakyushu, Japan. Two forecast horizons were evaluated, up to 2 hours ahead and up to 25 hours ahead. The results showed a variation of the accuracy of the forecasts according to the forecast horizon. The root mean square error for 1 year of up-to-2-hours-ahead forecasts was 0.104 MWh; whereas for the up-to-25-hours-ahead it was 0.118 MWh. The mean absolute error was 0.065 MWh for the up-to-2-hours-ahead forecasts and 0.076 MWh for the up-to-25-hours-ahead forecasts. In percentage terms, the root mean square error and the mean absolute error increased 13% and 17%, respectively, with the increase of the forecast horizon.

On the Use of Maximum Likelihood and Input Data Similarity to Obtain Prediction Intervals for Forecasts of Photovoltaic Power Generation

The objective of this study is to propose a method to calculate prediction intervals for oneday-ahead hourly forecasts of photovoltaic power generation and to evaluate its performance. One year of data of two systems, representing contrasting examples of forecast’ accuracy, were used. The method is based on the maximum likelihood estimation, the similarity between the input data of future and past forecasts of photovoltaic power, and on an assumption about the distribution of the error of the forecasts. Two assumptions for the forecast error distribution were evaluated, a Laplacian and a Gaussian distribution assumption. The results show that the proposed method models well the photovoltaic power forecast error when the Laplacian distribution is used. For both systems and intervals calculated with 4 confidence levels, the intervals contained the true photovoltaic power generation in the amount near to the expected one.

Impact of forecast error of photovoltaic power output on demand and supply operation in power systems

Increasing the proportion of power generation from renewable energy sources has become increasingly important in Japan since the nuclear accident caused by the 2011 Tohoku earthquake. Photovoltaic (PV) generation in particular has gained much attention in Japan. In general, the supply and demand of electricity are maintained by economic-load dispatching control (EDC), which refers to regulation of the output of conventional (thermal or hydro) power plants to minimize their operational costs. Using the PV generation forecast in EDC, which includes the unit commitment (UC) of conventional power plants, is essential to maintain the economy and reliability of the power system with large-scale integration of PV generation. In this study, we consider an EDC that determines the UC on the basis of the day-ahead PV generation forecast. The frequency and trend of outages and power surpluses due to the forecast errors of the PV power output are evaluated.

An evaluation method for smoothing effect on photovoltaic systems dispersed in a large area

PV is expected as a major carbon-free primary energy source which is inevitable to proceed to a carbon-free economy. However, as a variable power source, the large PVs penetration into the power system may cause various kinds of power system operation issues and/or expansion needs. In order to technically-and economically-feasible solution for these issues and needs, it is quite important to quantitatively analyze and evaluate the variation of PV generation. This paper will present the smoothing effect of the total PV generation output in a broad area by means of the maximum output fluctuation as fluctuation index.

An Analysis of Reliability for Photovoltaic Systems on the Field Test Project for Photovoltaic in Japan

To develop a Photovoltaic (PV) module and cell efficiency are not only important, but also improving PV system performances is the significant technology. The long term reliability is one of the most important in PV systems’ performances. In Japan, NEDO (New Energy and Industrial Technology Development Organization) has organized “Field test (FT) project in Japan” from FY 1992 up to now. The user of PV systems in the project cooperates for collecting monitoring data and reports the information of maintenance and some failures of PV systems for four years. In this paper, the failures and maintenance information are reported by using MTBF, MTTR, and so on. Moreover, thje power conditioner is suspended by some protection or other reason — it is not failure, and the power conditioner can be restarted-which are obtained by PV system user’s reports.

Reduction of PV Reverse Power Flow through the Usage of EV's Battery with Consideration of the Demand and Solar Radiation Forecast

This paper presents an evaluation of the usage of electric vehicle battery as an energy storage device for surplus power generated by Photovoltaic power generation system (PV) installed at home. The main goals are the reduction of the reverse power flow caused by PV power generation, and the mitigation of the dependency on the power system grid to charge the EVs battery. We conducted a study based on the forecast of electricity load and solar radiation. The study shows that by using PV-EV system, yhe amount of power bought from power utility can be reduced while keeping. The study shows that by using PV-EV system, the amount of power bought from power utility can be reduced while keeping the reverse power flow level controlled.

Comparative performance evaluation of different technologies of photovoltaic modules in Algeria

The aim of this paper is to present a comparative study of performance evaluation of photovoltaic (PV) modules as part of the Sahara Solar Breeder project (SSB). In the end of 2013, five different PV module technologies which are: m-Si, CIS, HIT, Back Contact and a-Si_μc-Si, and a weather station were installed at the city of Saida located at the gate of the great Algerias Sahara desert. The objective of the present work is the study of the behavior of solar PV modules in outdoor conditions and to compare their performance parameters in order to find which technologies are suitable for the Saharan climate conditions. The modules were characterised by measuring their I-V curve in outdoor at the location without shadow. Moreover measurements of various parameters such as irradiance, temperature and humidity, using the weather station were performed. Finally performance parameters as performance ratio, energy yield and temperature losses are given and analysed.