ECS Transactions, 16 (34) 1-16 (2009) / The Electrochemical Society

Transcription

1 / The Electrochemical Society Results of Applying Energy Storage Systems to NEDO New Energy Demonstration Projects S. Morozumi a a New Energy and Industrial Technology Development Organization (NEDO) Kawasaki City, Kanagawa Prefecture , Japan This paper provides an overview of grid connection demonstration projects conducted by the New Energy and Industrial Technology Development Organization (NEDO). One important objective of NEDO s recent R&D is solving problems that arise when distributed and renewable resources are connected to power grids. The author is introducing national grid connection projects promoted by NEDO, especially focusing on energy storage applications in those projects. Overview of Energy Storage Technology Development in Japan and NEDO s Role Development of Energy Storage Technologies in Japan The application of stationary batteries and other energy storage technologies to power grids has been a focus in Japan since the 1970s, when the country was enjoying rapid economic growth. With the need to meet growing demand, pumped hydro storage systems were built as peaking units. After the energy crises, however, the increase in demand growth stalled. However, pumped hydro systems, which provide the ability to adjust pumping speeds, were still important for retaining the ability to regulate load frequency control (LFC) at night. Due to the long construction period for pumped hydro projects, the importance of developing stationary battery technologies became evident, and the New Energy and Industrial Technology Development Organization (NEDO) commenced new battery technology development projects in the 1980s High demand growth Load factor reducing Saturation of demand growth Deregulation Penetration of renewable energy Needs for peaking resources Increasing needs of Pumped hydro Needs capacity for regulation at night time Needs for adjustable speed pumped storage development of Battery in Moonlight and New Sunshine project NAS, Redox, ZnBr, ZnCl Back-up battery, mobile application Lead-acid battery, alkali battery Increased customer service options Demand side energy storage application NAS battery, Redox flow battery, Flywheel, SMES New public welfare use battery Ni-MH, Lithium-ion, Capacitors Increased capability needs for regulation compensating fluctuated renewable energy output Battery for grid connection NAS battery, Leadacid battery Development of stationary battery in NEDO project: Development of an Electric Energy Storage System for Gridconnection with New Energy Resources Figure 1. History of energy storage technology development in Japan 1

2 In the latter part of the 1990s, the deregulation of Japan s electricity market became a new issue for utilities. This led to interest in offering several power quality management options, which utilized energy storage technology to improve quality, as a new business model. Technology development efforts produced NAS batteries and redox flow batteries with load leveling and power quality management capabilities. Since 2000, with our increasing awareness of the serious threats of global warming, power generated from renewable energy sources is being viewed as an important countermeasure. However, because power output from PV and wind power fluctuates and produces a negative impact on power grids, NEDO has been focusing on several energy storage applications for renewable energy and has promoted several demonstration projects since Because the investment recovery period for those energy storage applications is about double the investment recovery period for load leveling applications, NEDO commenced a technology development project in 2006 to develop cheaper, longer-life battery technologies for the future that can reduce renewable energy output fluctuations. NEDO s Role in Promoting the Development Energy Storage Systems NEDO is Japan s largest public research and development management organization for promoting the development of advanced industrial, environmental, new energy and energy conservation technologies. One of the important objectives of NEDO s research and development is solving problems that arise when distributed and renewable energy resources are connected to power grids. Because of the importance of developing energy management and energy storage systems for resolving grid connection issues, NEDO is promoting several grid connection-related projects and one battery technology development project, as shown in Figure 2. Figure 2. NEDO s grid-connection system projects 2

3 Wind Power Stabilization Project The Wind Power Stabilization Technology Development Project (FY ) was undertaken to demonstrate a battery system that could reduce fluctuating output from wind farms. To reduce output fluctuations from a large-scale wind farm, under this project a redox flow battery system (6 MW 4 MWh, Figure 3 & 4) was installed at the Tomamae Winvilla Wind Park in Hokkaido. At the demonstration site, several methods for cost effective operation were examined, as was the reliability of the battery system, in order to reduce short term wind power fluctuations. Also, data on actual wind power output was collected at the facilities of five additional wind farms for the purpose of simulating the potential benefits of introducing the same battery system at those facilities. In addition, a wind power generation forecasting method based on weather forecasts was developed and analyzed for the purpose of forecasting the output from wind farms and utility districts over the short and long-term, using actual data collected from ten additional wind farms since fiscal year Figure 3. Redox flow battery storage facility at Tomamae Figure 4. Redox flow battery cell stacks and storage tanks 3

4 Throughout the course of this five-year project, several operating methods were examined at the Tomamae demonstration site. Primary among these was employing first order lag feedback control with the battery system to reduce output fluctuations from the 30.6 MW wind farm. Under this control method, several time constants were tested to determine the relation between the time constants and the required battery capacity (Figure 5). In addition, a comparative simulation using actual output data from other wind farms allowed the required battery capacity to be determined. This information will be useful for developers who intend to use battery systems with new wind farms. Also, several methods for effectively managing batteries were evaluated. Identifying optimum operating modes is important to keeping efficiency levels high, to ensuring a long battery life and to managing the SOC of the battery system. After the demonstration period ended, the battery system was dismantled and the degradation is being examined in fiscal year Wind pow er output MW MW B attery charging and discharging MW MW Stabilized output of wind pow er MW MW Tim e (sec) Smoothing time constant T = 1 minute Tim e (sec) Smoothing time constant T = 10 minutes Figure 5. Typical operation of Tomamae energy storage system Clustered PV Project In the Demonstrative Project on Grid-interconnection of Clustered Photovoltaic Power Generation Systems (FY ), more than 550 residential PV power generation systems were installed in Ota City, Gunma Prefecture (Figure 6), and technologies related to voltage control and islanding prevention on the distribution network were demonstrated. The main purposes of this project were to develop: 1) technology to counter PV system output restrictions, 2) functions to prevent unintentional islanding, and 3) applied simulation technologies. In order to avoid PV system output restrictions, an external storage enclosure, housing an inverter, battery and monitoring equipment, was installed with each PV system. When power output from the PV systems caused voltage levels on the distribution line to exceed the maximum nominal voltage level, the excess power was used to charge the batteries, thereby maintaining line voltage within the nominal operational range (101±6V, 202±20V). 4

5 Figure 6. Clustered PV project in Ota City Single-Family houses External storage box (PCS, batteries) Figure 7. Illustration of systems installed in Ota City project In this project, a new islanding detection method was developed. A PV system must disconnect from the power grid in the event of service interruptions to prevent islanding. However, interference among the equipment used to prevent islanding can occur when many PV systems are installed on the same feeder line. To avoid this problem, a new type of equipment needed to be developed and verified through demonstration testing. A method based on synchronizing reactive power signals to avoid islanding for clustered PV systems was developed. 5

6 Inverter for P V Inverter for battery Islanding detection equipm ent battery Figure 8. External battery storage and inverter enclosure 6 4 P V output (K W ) PV アレイ出力 (kw) 負荷電力 D em and (kw ) (K W ) R everced pow er flow (KW ) 受電点電力 (kw ) B attery output (K W ) 蓄電池充放電電力 (K W ) 電力 (kw ) :00 3:00 6:00 9:00 12:00 15:00 18:00 21:00 0:00 In this exam ple, the battery started to receive a charge at 10 a.m. Figure 9. Example of battery charging and discharging in Ota City project Large-Scale PV Power Generation System In autumn, 2006, NEDO kicked-off a new project called Verification of Grid Stabilization with Large-scale PV Power Generation Systems (FY ). Under this project, a 5 MW-class PV power plant in Wakkanai City, Hokkaido and a 2 MW-class PV power plant in Hokuto City, Yamanashi Prefecture, are being built to test several technologies for connecting mega solar power plants to a utility transmission system. In 6

7 the Wakkanai subproject, a battery system and other technology to reduce voltage fluctuations caused by the output of a mega PV power plant will be demonstrated through the system illustrated. Also, an inverter system that compensates for overvoltage and suppresses harmonics will be developed and demonstrated in the Hokuto subproject. The two project sites have unique solar irradiation conditions; Wakkanai City is Japan s northernmost city, and, as such, the variance in daylight hours is greater than anywhere else in Japan, whereas Hokuto City receives more solar irradiation throughout the year than any other city in Japan. By the end of fiscal year 2007, 2 MW of PV were installed in Wakkanai City (Figure 10), and 0.6 MW were installed in Hokuto City (Figure 11). Fiscal year 2008 will be the third year of the project and most of the PV panels and related facilities will have been installed by the end of this fiscal year. At the halfway stage of the project, several things have been learned through simulations. For example, sodium-sulfur batteries (Figure 13) have enough output capacity to almost completely compensate for PV system output fluctuations (Figure 14). In addition, the discharge rate of the batteries can keep pace with the speed of large-scale PV system output fluctuations. In the Hokuto subproject, a reactive power compensating inverter system is being developed. This inverter technology and battery application will help stabilize voltage levels on lines connected to fragile rural power systems. Figure 10. PV arrays installed at Wakkanai site 7

8 Figure 11. PV arrays installed at Hokuto site Figure 12. NAS battery building and facilities at Wakkanai site 8

9 受電点 Flow at grid-connection point PV NAS 受電点電力一定制御 T arget flow at 受電点電力目標値 connecting point :600kW:600kW 電力 [kw ] Start of battery 制御開始 operation -300 PV Battery :00 13:30 14:00 14:30 15:00 Figure 13. Use of batteries to produce consistent power flows in Wakkanai Micro Grid Related Projects The Demonstrative Project of Regional Power Grids with Various New Energies is one of the most notable projects in the history of NEDO, and it included the three following subprojects: (1) Demonstrative Project of Regional Power Grids with Various New Energies at Expo 2005 Aichi and Central Japan Airport City (Aichi subproject) (2) Kyoto Eco-Energy Project (Kyotango subproject) (3) Regional Power Grid with Renewable Energy Resources; a Demonstrative Project in Hachinohe City (Hachinohe subproject) In the Aichi subproject, a power supply system utilizing fuel cells, photovoltaic cells and a battery system, all equipped with inverters, was constructed. A diagram of the supply system for the project is shown in Figure 14. The primary power generation sources for this micro grid system were the fuel cells and the PV systems. The fuel cells (Figure 15) included two molten carbonate fuel cells (MCFCs) with capacities of 270 kw and 300 kw, one 25 kw solid oxide fuel cell (SOFC) and four 200 kw phosphoric acid fuel cells (PAFCs). Although city gas was the primary fuel for the fuel cells, some of the fuel for the MCFCs was supplied by a methane fermentation system and a gasification system. The total capacity of the installed PV systems was 330 kw and multi-crystalline silicon, amorphous silicon and single crystalline silicon bifacial cells were used. Also, a sodium-sulfur (NaS) battery was used to store energy within the supply system and it played an important role in balancing supply and demand, as shown in Figure 16. This demonstrative power plant was installed at the site of The 2005 World Exposition, Aichi, Japan (EXPO 2005) and operated from December 2004 to September During the demonstration period, a total of 3,716MWh of electricity was supplied by the power plant to two major pavilions. After EXPO 2005, the power plant was 9

10 relocated to a site (Figure 17) in Tokoname City, near the Chubu International Airport, and demonstrative operation was restarted in August 2006 and concluded in December Figure 14. Micro grid system installed in Aichi Prefecture M C FC 270kW * 2 PA FC 200kW * 4 SO FC 25kW N A S battery 500kW Figure 15. Fuel cells and battery technologies adopted in Aichi subproject 10

11 Output from NAS battery 1,200 Output from PVs 1,000 Demand 800 Power [kw ] Output from MCFCs and SOFC Output from PAFCs Purchased from utility 0 Charge to NAS battery :30 3:30 6:30 9:30 12:30 15:30 18:30 21:30 Time Figure 16. Typical daily operation of the micro grid in Aichi subproject Gasification system M ethane ferm entation system PV systems MCFC building Figure 17. Micro grid installed near Chubu international airport in Aichi Prefecture One of the unique elements of the micro grid system constructed in the Hachinohe subproject was a private distribution line measuring more than five kilometers. The private distribution line was constructed to transmit electricity, primarily generated by a gas engine. Three 170 kw gas engines and a 100 kw PV system were installed at a sewage plant (Figure 18). Because thermal heat was in short supply and was necessary to safeguard the microorganisms that produced digestion gas in the sewage plant, a wood waste steam boiler was also installed. Between the sewage plant and city office, four 11

12 schools and a water supply authority office were connected to the private distribution line. At the school sites, renewable energy resources were used to create a power supply that fluctuated according to weather conditions in order to verify the micro grid control system s capabilities to match demand and supply. In the Hachinohe subproject, the control system used to balance supply and demand consisted of three facets: weekly supply and demand planning, economic dispatch control once every three minutes, and second-by-second power flow control at interconnection points. The control target was a power imbalance of less than 3% for moving average six minute intervals. From October to November 2006, a margin of error rate of less than 3% was achieved during 99.99% of the system s operational time. Figure 18. Power plant constructed within sewage plant in Hachinohe City In the Hachinohe subproject, completely independent operation was tested for one week in November Power imbalances among the three phases were a serious problem with the Hachinohe system; therefore, a new PV inverter that could compensate for the imbalances among the three phases was installed and operated (Figure 19). Power quality during independent operation was very stable, and voltage (6600V ±5%) and frequency (50Hz ±0.3Hz) were maintained within operating standards. Electricity consumed in the City Hall s main office building was supplied only by the micro grid. No one recognized a difference between electricity from the micro grid and electricity from the utility. When operated independently, most PV output fluctuations could be offset by a gas engine. Rapid and large demand spikes, such as the start-up of a compressor or motor, were compensated for by a battery system. 12

13 Compensating for imbalances am ong the three phases 3 170kW GE 50kW Control System Inverter AC DC CB7 CB4 CB3 Schools City Office Utility Network 50kW Inverter Figure19. Independent operation of micro grid in Hachinohe subproject 電力 [kw ] 50 0 Gas ガスエンジン engine Demand 需要 PV Frequency 周波数 二次電池 battery :00 12:02 12:04 12:06 12:08 12:10 時刻 周波数 [H z} P V output fluctuations w ere mainly com pensated for by a gas engine.. Batteries m ainly com pensated for rapid frequency changes caused by dem and fluctuations Figure 20. Sample data from independent operation of Hachinohe micro grid Battery Development Project and Future Network - Transmission Research Battery Storage Technology Development NEDO has been promoting a battery technology development project called Development of an Electric Energy Storage System for Grid-connection with New Energy Resources since fiscal year This project includes the following four themes: (1) Establishing technologies for large-scale (MW) storage systems (2) Establishing module level technologies for cost reduction and scaling-up (48,000 yen/kwh if commercialized, 10-year life cycle, 1 MW-scale) 13

14 (3) Developing low cost next-generation storage technologies (15,000 yen/kwh, 20-year life cycle, 30 MW-scale) to be commercialized by 2030 (4) Conducting fundamental study to evaluate safety, economy and life cycle NEDO has sponsored several research projects and collaborative studies to promote the development of various technologies, including lithium-ion batteries, nickel-metal hydride batteries, and capacitors, in order to establish battery technologies that will be economically feasible by Pre-Feasibility Study for Next-Generation Power Systems In fiscal year 2007, NEDO promoted a pre-feasibility study of future network technologies, in anticipation of the installation of many renewable energy systems. In the study, we recognized the potential for the rapid penetration of PV systems, as shown in Figure 21. This penetration scenario was created based on national long-term energy supply and demand forecast and the PV Roadmap toward 2030, created by NEDO. Under this scenario, that rate of installation of PV systems will accelerate rapidly after 2010, when the cost of residential PV systems will be one-half of current costs. If PV capacity were to begin accelerating rapidly, it is thought that managing the voltage on the distribution lines will soon become difficult. Within ten years of the accelerated installation of PV systems, it is also thought that the transmission system may experience stability problems. As shown in Figure 22, instability occurs when power flows increase due to differences in solar radiation within a grid area, or when many PV systems are suddenly disconnected from the distribution network. G W Totalcapacity of utility ow ned generation (low scenario) Totalcapacity of utility ow ned generation (high scenario) N uclear (long-term forecast by M ETI) P V (based on N ED O s P V 2030 roadm ap) W ind pow er (long-term forecast by M ETI) Figure 21. Estimated future growth of renewable energy 14

15 T IM E ( S E C ) TIME(SEC) T im e [sec ] ECS Transactions, 16 (34) 1-16 (2009) Fault point Fault point Increasing 潮流大 power ( 不安定 flow ) substation 変電所 substation 変電所 substation 変電所 Sudden cut off 発電機内部相差角 [deg] G E N. IN T E R Fault 系統事故発生 occurs 系統電圧 [p.u] 一斉脱落 Fault 系統事故発生 occurs NO DE VO LTAGE (PU) PV 脱落量 (GW ) 7.2GW 脱落 4.8GW 脱落 4.7GW 脱落 Unstable 脱調する ( 不安定 ) 時間 [s] 2 [s] 時間 [s] 事故近辺の Sudden PV PV が脱落 cut off 系統動揺で他のPV も脱落 最終的に供給力不足 Supply shortfall 全停 Blackout Figure 22. Instability caused by variances in solar radiation within a grid area Around 2030, utility energy management systems (EMS) may need to control each PV system directly or indirectly in order to balance demand and supply. By that time, the output from PV, run of river hydro and nuclear power (Figure 23), which are unable to be balanced, may exceed the weekend demand during the low demand season. Under that scenario, it is estimated that a large number of battery systems will need to be installed on utility networks. 発電量 ( 春季休日 : 晴天 ) の推移 Demand and supply (GW) 電力需要 (GW) Total 太陽光発電分 PV output 電力貯蔵あるいは出力抑制 Controllable resources 石炭 LNG 石油 (Thermal 貯水式 揚水式 and reservoir hydro) Run of 自流式水力 river hydro 80GW 50 Nuclear 原子力 120GW 30GW 時間 Time of day Figure 23. Difficulty of balancing when large amount of PV systems are installed 15

16 Conclusion Through its demonstration projects and pre-feasibility study, NEDO came to the following conclusions: (1) NEDO recognized the importance of developing battery technology, and the need to cut battery costs in half, relative to recent NAS battery costs. Also, the life cycle of batteries should be extended to 20 years to be commensurate with the life cycle of renewable energy systems. (2) Although the potential of battery-related and micro grid technologies were demonstrated in several projects, creating a roadmap or future vision of a new generation network and grid connection technologies will be important, as policy decisions will be needed to invest in such new power systems. (3) Micro grid technology and battery applications for renewable energy may be useful for local energy supply systems. However, in the future those technologies will experience a paradigm shift vis-à-vis utility network systems, as many PV and other renewable energy systems are connected to networks and power flows are reversed. References 1. Outline of NEDO , New Energy and Industrial Technology Development Organization (2007) 2. PV Roadmap toward 2030 (PV2030), New Energy and Industrial Technology Development Organization, (2004) 3. Technology development for grid-connection issues, S. Morozumi, Renewable Energy 2006, Makuhari, Japan (2006) 4. Micro-grid demonstration projects in Japan, S. Morozumi, PCC-Nagoya 2007, Nagoya, Japan (2007) 5. Recent trend of new type power delivery system and its demonstrative project in Japan, S. Morozumi, K. Nara, IEEJ Trans. PE, Vol. 127 No. 7 (2007) 6. Large-scale PV demonstration projects promoted by NEDO, S. Morozumi, Y. Arashiro and N. Inoue, PVSEC-17, Fukuoka, Japan (2007) 7. Strategies and status of grid-connection technology development in NEDO, S. Morozumi, N. Inoue, Y. Arashiro, Y. Chiba and T. Iwasaki, IEEE PES general meeting, Pittsburgh, USA (2008) 8. Distribution Technology Development and Demonstration Projects in Japan, S. Morozumi, S. Kikuchi, Y. Chiba, J. Kishida, S. Uesaka and Y. Arashiro, IEEE PES general meeting, Pittsburgh, USA (2008) 16