The new national R&D project on PV system has been started since last year. The target of this project is to solve technical problems such as restriction of PV system output, higher harmonics and islanding operation where PV systems are clustered in a residential district. In this project, about 400 to 600 grid-connected PV systems with battery installed at residential houses and are monitored at all times. The results obtained in this project are expected to provide information and technologies to increase the further introduction of PV systems.


1 Development of technology to avoid restriction of PV system output In some cases of inverse flows, which mean a PV system supplies its output power to the power line, the voltage in the distribution line are beyond threshold voltage of 107 or 222 V. Those cases result in depression of the output power of the PV systems, which reduces merits of the systems.In this R&D, the various phenomena of the suppression of the output of the PV systems are observed and analyzed to develop the technology to reduce the suppression.

2 Analyses and evaluation of higher harmonics Higher harmonics emitted from power conditioner subsystems should be suppressed within the low levels as specified in Guideline of Higher Harmonics. Clustered PV systems tend to increase the higher harmonics because of interferences between those systems, which tends to give degraded influence on power apparatuses in the power systems and domestic electrifications. In this R&D, analyses and evaluation of higher harmonics are made using the data of relation between number of PV systems and the higher harmonics induced from them. And the limitation of number grid-connected PV systems from the tolerance limits higher harmonics in distribution lines is identified.

3 Analyses of mis-actuation of function to prevent islanding operation A function to avoid islanding operation is activated in PV systems to separate the PV systems from power grid lines in the case of service interruptions. Mis-actuation of the function tends to take place because of interferences between the clustered PV systems. In this R&D, methods preventing the mis-actuation in the clustered PV systems are considered, and the validities of the methods are considered.

4 Development of applied simulations Simulation techniques are developed using those data and results obtained in three subjects. The simulations are designed to contribute to further designs of clustered PV systems as well as to precise evaluation of the data obtained in this R&D.

1. An Evaluation clustered PV system and with battry systems

The SV method has been developed as an evaluation method, which is using monitored data. During converting input energy into output energy, the PV system has numerous kinds of losses, which seem not to be measured. The SV method, however, can estimate system losses from irradiation energy (optical energy) to system electricity output power (AC power). We will evaluate the clustered PV system and PV systems with battry

2. Development of An Evaluation Method of the Fluctuation Characteristics of Photovoltaic Systemsm by Using Frequency Analysis
- an evaluation for smootihng effects -

Photovoltaic (PV) systems are introduced intensively, and they are connected with distribution network more. This is called "Grid-Interconnection of Clustered PV Generation Systems". When PV systems are connected intensively, it tends to be thought that the fluctuation of PV output affords to become a problem because PV output has a short-term fluctuation due to weather fluctuation. However, total of the output of PV system installed in the large space facilitates smoothing the fluctuation due to the fact that fast fluctuation of PV output have a time gap on every point of PV system by drifting of clouds. This phenomenon is called "the smoothing effect" by authors. The purpose of this study is quantitative evaluation of the smoothing effect.

our papers

(1) T.OOZEKI, K.OTANI, H.KOIZUMI and K. KUROKAWA:An Evaluation method of Grid connected photovoitalic with battery systems(1.07[MByte]) (in Japanese) (in Japanese)

(2) T.OOZEKI, H.KOIZUMI, K.OTANI, and K.KUROKAWA:"IDENTIFING OPERATION STATUSES OF GRID CONNECTED PV SYSTEMS WITH BATTERIES UNDER LIMITED DATA ITEMS - APPLYING THE SV METHOD TO EVALUATE GRID CONNECTED PV SYSTEMS WITH BATTERIES -, 19thEuropean Photovoltaic Solar Energy Conference and Exhibition, Palais des Congres Paris, France 7-11 June 2004

(3) Y.UEDA, T.OOZEKI, K.KUROKAWA, T.ITOU, K.KITAMURA, Y.MIYAMOTO, M.YOKOTA, H.SIGIHARA "Evaluation method and data collection method of grid-connected clustered PV system's performance", IEEJ Aug 2004 (in Japanese)

(4) Y.UEDA, T. OOZEKI, K.KUROKAWA, T.ITOU, K.KITAMURA, Y.MIYAMOTO, M.YOKOTA, H.SUGIHARA, S.NISHIKAWA,"ANALYTICAL RESULTS OF OUTPUT RESTRICTION DUE TO THE VOLTAGE INCREASING OF POWER DISTRIBUTION LINE IN GRID-CONNECTED CLUSTERED PV SYSTEMS" , 31th IEEE PVPS, Florida, US, January 2005

(5) N.KAWASAKI, T.OOZEKI, K.OTANI, and K.KUROKAWA:"An Evaluation Method of the Fluctuation Characteristics of Photovoltaic Systems by Using Frequency Analysis", PVSEC-14th, Bangkok, Thailand, 26-30 January 2004 (Poster Award)

(6) N.KAWASAKI, T.OOZEKI, K.OTANI, K.KUROKAWA, "An Evaluation method of the fluctuation characteristics of photovoltaoc systems by using frequency analysis, IEEJ, Aug 2003 (in Japanese)

(7)Y. UEDA, T. OOZEKI, K. KUROKAWA, T. ITOU, K. KITAMURA, Y. MIYAMOTO, M. YOKOTA, H. SIGIHARA, and S. NISHIKAWA, "NALYTICAL RESULTS OF OUTPUT RESTRICTION DUE TO THE VOLTAGE INCREASING OF POWER DISTRIBUTION LINE IN GRID-CONNECTED CLUSTERED PV SYSTEMS", 31st IEEE PVSC, Orland Florida, 2-7 January 2005

other papers

(1) S.NISHIKAWA K.KATO, "DEMONSTRATIVE RESEARCH ON GRID-INTERCONNECTION OF CLUSTERED PHOTOVOLTAIC POWER GENERATION SYSTEMS", WCPEC 3rd, May 2003, Osaka, Japan

(2) Y.MIYAMOTO, M.YOKOTA, S. NISHIKAWA, H. SUGIHARA"DEMONSTRATIVE RESEARCH ON GRID-INTERCONNECTION OF CLUSTERED PHOTOVOLTAIC POWER GENERATION SYSTEMS",19thEuropean Photovoltaic Solar Energy Conference and Exhibition, Palais des Congres Paris, France 7-11 June 2004

(3) S. MIYASHITA, A. NAGAOKA, K. TAKIGAWA, H. SUGIHARA, and Y. OOKUBO "A UNIFIED TEST AND EVALUATION OF PCS ON THE MARKET FOR RESIDENTIAL PV APPLICATION IN JAPAN", 31st IEEE PVSC, Orland Florida, 2-7 January 2005

(4) S. Nishikawa H. Sugihara, "DEMONSTRATIVE RESEARCH ON GRID-INTERCONNECTION OF CLUSTERED PHOTOVOLTAIC POWER GENERATION SYSTEMS", 31st IEEE PVSC, Orland Florida, 2-7 January 2005