Verification of Grid Stabilization with Large-scale PV Power Generation Systems

The project named "Verification of Grid Stabilization with Large-scale PV Power Generation systems" has been started in 2006 at Wakkanai, northernmost city of Japan. This project is a five-year demonstration project that will continue until 2011. NEDO, New Energy and Industrial Technology Development Organization of Japan conducts this project and HEPCO manages the overall project. The major objectives of this project are to evaluate adverse impacts of large-scale PV power generation systems connected to the power grid and develop output control technologies with integrated battery storage.

In the process of rapid expansion of the photovoltaic generation system (PV system), the constructions of large-scale PV systems are expected. If a number of large-scale PV systems are connected to power grids, there is a concern that the fluctuating output of PV could affect the quality in voltage and frequency of power grids and result in restriction that limit the further implementation and application of PV systems. To investigate these technological issues, the following activities are being carried out.

Construct a large-scale (megawatt) PV power generation system: Some 4 MW of PV modules and a 1.5-MW sodium-sulfur (NAS) battery system have already been constructed and are in operation. This system connects to HEPCO's 33-kV power grid. Each performance data (for example, determination of PV output characteristics, the power decrease effect of PV array due to another array's shadow and impacts of snow accumulation on PV arrays) is being collected and analyzed in this project.

Develop a harmonic suppression technology: Large-scale PV power systems may possibly adversely impact smaller or weaker electric power system because the PV generation output may fluctuate greatly. For more efficient and effective operation of the NAS battery, several control algorithms of battery system for smoothing PV output are developed and examined in field test. It is expected to achieve the target of this project, more than 80% of fluctuation reduction.

Scheduled operation of PV power station: The station output is determined based on the PV output power estimated from the solar radiation forecast data. Mismatch between the scheduled station output and actual PV output are absorbed by the NAS battery. Therefore, accuracy of the solar radiation forecast plays very important role in the scheduled operation. In this project, various forecast techniques and meteorological observation data are applied to sophisticate the accuracy of solar radiation forecasts.

Photo-1 Overview of Wakkanai PS

Fig.1 Field test result of fluctuation suppression