Development and Demonstration of Redox Flow Battery System

FEATURED TOPIC

Keiji YANO*, Shuji HAYASHI, Takahiro KUMAMOTO, Toshikazu SHIBATA, Katsuya YAMANISHI and Kazuhiro FUJIKAWA

------High expectations have been placed on rechargeable batteries as a key technology to power system reliability associated with introduction of an increasing volume of renewable energy, as well as efficient power supply and successful business continuity planning. We have developed a redox flow battery system that is safe with a long service life. A demonstration proved its applicability to multiple requirements from electric power companies and other businesses. This paper describes the system, demonstration results, and our effort to reduce the price. ------Keywords: redox flow battery, energy storage, renewable energy, demand response, BCP

1. Introduction 2. Operating Principle and Features of Redox Flow Battery In recent years, an increasing volume of renewable energy sources, such as solar and wind power, has been Figure 1 illustrates the configuration of an RF battery. connected to electrical grids. One of the motivations for Its components include electrolyte flow cells where the cell this is the inauguration of feed-in-tariff program for renew- reaction occurs, positive and negative electrolyte tanks, able energy. In particular, the extent of interconnection is pumps used to circulate the electrolytes between the tanks large in Hokkaido because of the suitability of the region and cells, and a piping system. Sumitomo Electric’s RF for the use of renewable energy. Accordingly, concerns batteries use aqueous solutions of vanadium sulfate as both exist over the impact of the integration of renewable energy positive and negative electrolytes. Charging and into the electrical grid due to the output fluctuations discharging processes of the RF battery are expressed by induced by them. Against this backdrop, the world’s largest the following reactions: redox flow (RF) battery system rated at 60 MWh (15 MW for 4 h) was installed in the Minami-Hayakita substation of (Positive side) Hokkaido Electric Power Co., Inc. (HEPCO) by Sumitomo 2VOSO4 + 2H2O − + Electric Industries, Ltd. In December 2015, a demonstra- ↔ (VO2)2SO4 + H2SO4 + 2e + 2H ...... (1) tion project, subsidized by the Ministry of Economy, Trade and Industry, has been initiated to evaluate the performance (Negative side) − + of the rechargeable battery and to develop a control tech- V2(SO4)3 + 2e + 2H ↔ 2VSO4 + H2SO4 ...... (2) nology with the aim of stabilizing the electrical power grid. However, end users are encountering various chal- While the battery is being charged or discharged, lenges, such as peak shaving, which requires them to these reactions involve changes only in the valence of reduce the maximum demand for utility power and power vanadium ions in the electrolytes. Since there is no phase grid blackout caused by natural disasters. Therefore, these change involved in the reaction, the electrolytes are free end users are increasingly interested in business continuity from degradation in principle and can be used semi-perma- planning (BCP), which enables them to continue their nently. In addition, the RF battery has the following distinct operations at least at the minimum required level even in the instance of any power incident. Moreover, in contrast to the traditional practice of power being supplied unilater- ally by power companies, a new scheme known as the demand response*1 (DR) scheme is emerging, using which electricity can be efficiently used by integrating the distributed power systems and power savings of end users. In order to fulfill these complex requirements of businesses, Sumitomo Electric installed a 3 MWh (500 kW for 6 h) RF battery system at the Technical Research Institute of Obayashi Corporation. The system commenced its operation in February 2015. This paper describes the features of the RF batteries and provides examples of operation of the installed RF battery systems.

Fig. 1. RF battery operating principle

22 · Development and Demonstration of Redox Flow Battery System features: (1) The power output section (cells) is indepen- challenges. Figure 3 schematically illustrates the control dent from the energy section (tanks), allowing for highly system developed for the rechargeable battery systems. flexible output power and energy designs to meet specific Power output information from the solar and wind farms in application requirements; (2) Each cell is naturally in the Hokkaido, information from the weather forecasting uniform state of charge (SOC) because electrolytes of the systems, and load conditions were used as fundamental same SOC are fed from the same tanks; (3) By passing the information to operate the battery system. Based on these electrolytes through a dedicated single cell and measuring sets of information, the demonstration control unit at the its voltage (open-circuit voltage), it is possible to measure load dispatching center has transmitted power charge and the SOC of the cells accurately, even during the charging discharge command values to the rechargeable battery or discharging process; (4) Due to its fast responses in the system. According to these commands, the battery system order of milliseconds, the RF battery, for a short period of carried out charge and discharge operations. time, can be charged or discharged at twice the output power rating.(1),(2) Figure 2 provides an example of the results of a long- term reliability test conducted on the in-house demonstration equipment. This figure shows changes in the cell performance of an RF battery over a period of time. The current efficiency represents the degradation of the membrane, which is a functional component. The cell resistance indicates the degradation of the electrodes. The test results revealed no noticeable degradation in these features, proving that the equipment has high performance as expected from the design. This test is still in progress. 2nd floor: Installed battery cubicles and BMSs

100 ) Ω m

( 90

c e

n 80 a s t

s i 70

e Current eﬃciency r

l l 60 c e

d 50 n a

) 40 % (

c y 30 n

e Cell resistance c i

i 20 f f 1st floor: Installed PCSs, tanks, and pumps e

t 10 n e r r

u 0

C Photo 1. Large rechargeable battery system

Load dispatching center Fig. 2. Changes in cell performance over a period of time (Demonstration control unit)

Wind power output

Photovoltaic power output 3. Large Rechargeable Battery System for Electrical Grids Control command A rechargeable battery system rated at an output power of 15 MW (30 MW max.) with a discharge energy ■ Frequency fluctuations (3)-(6) controlled by charging of 60 MWh has been installed to the Minami-Hayakita and discharging rechargeable battery substation of HEPCO by Sumitomo Electric. This system Discharge was placed in a dedicated two-story building since its Frequency installation took place in a cold region. Photo 1 depicts the Large Rechargeable Battery Charge equipment. (Redox Flow Battery) 3-1 Objective of the demonstration project Challenges associated with integrating a renewable Fig. 3. Schematic image of rechargeable battery control energy source into an electrical grid include short- or long- period frequency fluctuations and surplus electricity. By developing a control methodology and by evaluating the performance of the large rechargeable battery system, the 3-2 System configuration demonstration project is targeted to examine the function- Figure 4 shows the configuration of the battery ality of the battery system to solve the aforementioned system. One set of electrolyte circulation lines consisting

SEI TECHNICAL REVIEW · NUMBER 84 · APRIL 2017 · 23 of tanks, pumps, and cell stacks is called as a module. A 20 15 group of modules connected to a PCS as a unit that enables 10 independent charge and discharge control is called a bank. 5 0 The entire system is comprised of 13 banks, with each bank -5 -10 Active power (MW) (output rating: 1,250 kW; max. output: 2,500 kW) -15 consisting of five modules. Accordingly, the battery system -20 11:00 12:00 13:00 14:00 15:00 16:00 17:00 had a total of 520 cell stacks and a discharge energy of 60 Time

3 ) 800 3500 %

MWh with 5,200 m of electrolyte. These specifications ( 700 3000 C DC voltage O 600 2500 made the system the largest RF battery system and the S 500 2000 and

DC current largest rechargeable battery system in the world. ) 400 1500 V ( 300 1000 ag e t l 200 500 DC current (A) o v 100 SOC (remaining energy) 0 DC 0 -500 11:00 12:00 13:00 14:00 15:00 16:00 17:00 66 kV bus Time O 66 kV yard, Minami-Hayakita Incoming switchgear substation External Fig. 5. Energy test Internal 6.6 kV bus x x x

PCS d a

1 (2) High-power charge and discharge test o l k g n n

a Cells can be charged and discharged to excess of the i

BMS Inverter k1 3 B n il d a output rating for a short period of time. This feature is B Module A B u useful for the purpose of short-period fluctuation control (output fluctuation control in a relatively short time in the Tank Tank Battery Heat order of few milliseconds to seconds), making it possible (+) (-) cubicle exchanger x 2 x 2 to reduce the number of installed cell stacks. The battery system incorporated a PCS with twice the output rating of Module B the rechargeable battery. Figure 6 shows an example of the

Module C test results. The battery was charged and discharged at 120% (1,500 kW), 160% (2,000 kW), and 200% (2,500 Module D kW) of the battery output rating (continuous charging and Module E discharging for 60 s). Under any of these conditions, the system proved itself to be capable of being charged and discharged at high power. Fig. 4. System configuration diagram

《High-power discharging property》《High-power charging property》 3000 3000 Testing from 0% SOC 3-3 Initial performance evaluation 2500 2500 After installation, the system was subjected to 2000 2000 ban k)

ban k) 1500 1500

completion testing for initial performance evaluation. / / (5),(6) 1000 1000 Charging power rating k W k W (

Shown below are the representative test results. ( (-1250 kW)

500 r 500 r e e (1) Energy test 0 0 po w po w

-500 -500 e The energy test was intended to check whether the e v v Discharge power rating i i -1000 -1000 c t c t (1250 kW) A battery met the applicable discharge duration requirement A -1500 -1500 when set to discharge at the rated output from fully charged -2000 -2000 state. The energy test examined the banks on a bank-by- -2500 Testing from 100% SOC -2500 -3000 -3000 bank basis and as an integrated unit. In both the tests, the 0 60 120 180 240 0 60 120 180 240 system marked a discharge duration of at least 4 h, as spec- Time (s) Time (s) ified. Figure 5 represents the test waveforms exhibited by the banks when they were integrated as a whole and oper- Fig. 6. High-power charge and discharge test ated at the fixed discharge rate. The upper graph indicates active power waveforms of all banks, whereas the lower graph shows the waveforms of a representative bank (DC voltage, DC current, and SOC). In total, the discharge (3) Response time test energy of all banks reached approximately 75 MWh. The response time of the battery system from the An efficiency test was conducted in an operation that instant it receives a power charge or discharge command simulated a short-period fluctuation control. The system from the demonstration control unit and till it reaches the efficiency reached 70.8% as an average of all the 13 banks. specified output power has been measured. The test results are shown in Fig. 7. The system required a duration of approximately 60 ms (time required to reach 98% of the

24 · Development and Demonstration of Redox Flow Battery System command value) for a transition from +2,500 kW or twice fluctuations without delay, as shown by the test waveforms the output power rating to −2,500 kW, and vice versa. Its in Fig. 8. response was noticed to be suitably high for short-period fluctuation control operation. 4. Rechargeable Battery System for End Users 4-1 System objective 3000 2500 Time required for output power to reach The battery system was installed at the Technical ) 2000 k 90% of output command value n

a 1500 ( -2,500 kW × 90% = -2,250 kW ): 27 ms Research Institute of Obayashi Corporation to serve as a b

1000 W

k 500 smart energy system. The purposes of this system were to (

r 0 e

w -500 make the maximal use of renewable energy in order to o Time required for output power to reach p -1000 98% of output command value e

v 2 i -1500 ( -2,500 kW × 98% = -2,450 kW ): 60 ms reduce CO emissions, to reduce utility power demand

c t Output command value Output

A -2000 -2500 peaks for a lowered base rate, to cut electricity demand for -3000 energy savings, and to improve BCP capabilities. -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 400 450 500 Time (ms) This paper reports the results of a DR test and an 3000 3 2500 Output command value Output island operation* test. The DR test was conducted with an

) 2000 k

n Time required for output power to reach a 1500 aim of reducing import from a utility. The purpose of the b

98% of output command value /

1000 ( 2,500 kW × 98% = 2,450 kW ): 56 ms (7) W islanding operation test was to improve BCP capabilities.

k 500 (

r 0 e

w 4-2 System configuration

o -500 p

Time required for output power to reach

e -1000

v 90% of output command value

i In addition to the RF battery installed from Sumitomo -1500 c t ( 2,500 kW × 90% = 2,250 kW ): 34 ms A -2000 Electric, which is rated at an output power of 500 kW and a -2500 -3000 discharge energy of 3 MWh, the system included photovol- -500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350 400 450 500 Time (ms) taic power generation equipment (PV, 820 kW in total) and generators (445 kW in total), all of which were controlled Fig. 7. Response time test and managed by an energy management system (EMS). Figure 9 presents the configuration of the system.

3-4 Results of governor-free mode equivalent control test As an example of the demonstration test results, this Utility PV power Micro-combined Redox flow PV power power power battery section presents the test results of governor-free mode 6.6 kV 120 kW 445 kW 500 kW×6 h 700 kW equivalent control.*2 This islanding control allows the rechargeable battery system to detect the frequency, computes required power accordingly, and subsequently charge or discharge the battery. This control provides fast responses because it does not involve the time required to Bus tie circuit breaker transmit command signals from the demonstration control unit. In general, the grid frequency increases or decreases Power Power when an imbalance occurs between the supply (generated load load power) and the demand (load). One of the possible conse- Dynamics laboratory Main office quences for the grid frequency to go beyond certain limits and others is the stoppage of production lines to the end user. Therefore, rechargeable battery systems need to ensure fast Fig. 9. System configuration responses in order to reduce frequency fluctuations. The test results showed that the system could follow frequency

4-3 Demand response functionality test (1) Test overview 8,000 50.05

Frequency In a DR scheme, in response to a request from a

6,000 50.00 power company, the system computes the negawatt power (command value)*4 that the system could offer and W ) ) z ( k

4,000 49.95 responds to the request for reduced power demand. The test t ( H

u In response to the decreasing trend of frequency, y p c t n u the battery output compensated for the decrease, was run based on an assumption that Waseda University’s e o

u y

operating in the direction of discharge (+). q r e e 2,000 49.90 r F

tt EMS Shinjuku R&D Center, which held the only DR

a Battery output B demonstration facility in Japan, was a power company and 5 0 49.85 an aggregator* and the Technical Research Institute, which had the rechargeable battery system, was an end user. -2,000 49.80 (2) Test description 10:00 10:30 11:00 Time The testing can be categorized into two types: one with receiving a DR request with a one-day advance notice Fig. 8. Example results of testing governor-free mode equivalent control and the other with a one-hour advance notice. The DR with

SEI TECHNICAL REVIEW · NUMBER 84 · APRIL 2017 · 25 a one-day advance notice is described below. Demand power in excess of demand during high solar radiation response target hours were 2 h in the morning (9:00‒11:00) hours, generators cannot accommodate for the surplus and another 2 h in the evening (17:00‒19:00). Table 1 power. As a solution to this problem, the tested islanding provides the negawatt power required during these hours. operation system was configured to ensure balanced supply and demand during islanding operation without PV output control. This was achieved by using the RF battery as the Table 1. DR requested hours and negawatt power voltage source, which was charged when PV generated DR requested hour Negawatt power surplus power and was discharged when demand exceeded 9:00 ~ 10:00 200 kW the power supplied by PV and generators. Morning 10:00 ~ 11:00 400 kW 17:00 ~ 18:00 200 kW Evening In-house bus (6.6 kV) 18:00 ~ 19:00 200 kW → 400 kW Bus tie circuit breaker (VCB) Island operation system

Measuring point 3φ750kVA for line voltage It was planned that for the morning hours, the required and phase 1φ200kVA negawatt power will be supplied by discharging the RF current of high- voltage bus battery. For the evening hours, the negawatt power was planned to be increased by 200 kW 1 h prior to the DR ~/- target hour (18:00‒19:00) and to have generators operating in addition to the RF battery. These operations were exam- G G ined in the test. Power PV power Lighting RF battery Gas engine generator (3) Test results load (700 kW) load (500 kW x 6 H) (200 kW x 2) Figure 10 presents the test results, which reveal that in the morning, the RF battery was discharged in order to Fig. 11. System configuration (island operation system) reduce the demand for utility power and in the evening, the demand for utility power was reduced by using generators in addition to the RF battery, as originally planned. Throughout the testing, which included the DR with one- (2) Test description hour advance notice, the ratio of actual performance to the During the island operation test, the bus tie circuit command value varied from 71.5% to 349.0%. Thus, the breaker was opened and the island operation system was test using the RF battery is considered to be successful subjected to a simulated power outage in the area defined since success in DR is defined to be the ratio being at least by dashed lines, as shown in Fig. 11. Following the power 70%. outage, island operation was established by starting up the RF battery and using it as a voltage source, which was subsequently followed by a sequence of connections estab-

PV power RF battery charged RF battery discharged lished between the RF battery and PV and the generators. Micro-combined power Utility power SOC 1000 100% (3) Test results The test induced changes in the operating status of the 750 75% distributed power system by making in-house load adjust- ments and by varying control settings. Conditions that ) W

k 500 50% ensured stable operation and output power were examined (

r C e in instances such as PV disconnection, reconnection, and w S O o P 250 25% generator startup and shutdown. In this paper, we explain the behaviors of the system at the time of PV disconnec-

0 0% tion. The test results are plotted in Fig. 12. Sequential disconnections of PV caused rapid changes in the output.

-250 -25% 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 : : : : : : : : : : : : : : : : : : : : : : : : 3 2 1 0 9 8 7 6 5 9 4 8 3 7 2 6 1 5 0 4 3 2 1 0 2 2 2 2 1 1 1 1 1 1 1 1 1 1 Time

( V ) 10000 5000 a g e 0 o l t Fig. 10. Power log for DR operation day v -5000

L i n e -10000 60

e 30 0

P h a s -30 u r e n t ( A ) c -60 0 )

r o m PV disconnection point W f

4-4 Island operation test ( k

e r -200 e r y t p o w (1) Test overview -400 b a t

p u t F R

Figure 11 shows the configuration of the tested O u t -600 10:45:00.0 10:45:00.5 10:45:01.0 10:45:01.5 10:45:02.0 islanding operation system. In many cases of islanding Time operation, generators serve as the voltage source. However, where PV accounts for a high percentage and provides Fig. 12. Behaviors at PV disconnections

26 · Development and Demonstration of Redox Flow Battery System Despite these changes, the power used to charge the RF Technical Terms battery underwent instant change with the corresponding ＊1 Demand response: Demand response is a change made time, thus maintaining an appropriate balance between the by end users in their power consumption pattern as supply and the demand. Even in the event of a rapid change required by the utility. This is done in response to in the generated power, the line voltage was observed to be certain electricity rate settings or incentive payments at stable, thus establishing the functionality of the RF battery the instance of soaring market electricity prices or as a voltage source to be satisfactory. declining reliability of electric power grids. ＊2 Governor-free mode equivalent control: In the governor-free mode of operation, the governor (a device that maintains uniform speed and is used along 5. Cost Reduction Efforts with a water wheel or steam turbine) operates free of While the RF battery has proved itself to offer excel- restrictions imposed by load controller and responds lent functionality as explained above, the greatest challenge directly to the frequency fluctuations. Rechargeable facing its widespread usage is its cost. In order to reduce batteries have no governor. However, they have a the transportation and construction expenses of the RF similar function (to detect and independently control battery, Sumitomo Electric is striving to improve the output the frequency); and hence the term “equivalent power of cell stacks and build the system into a package, control.” key design points of which are: i) output rating to be at ＊3 Island operation: In this mode, when a blackout of a least twice as high as the current system and ii) packaging utility power grid occurs, the distributed power of all principal devices including cell stacks, pumps, tanks, sources including rechargeable batteries serve as and piping entirely into a standard shipping container. A voltage sources to supply power to important loads prototype system has been installed in-house for demon- connected. stration and testing purposes. Photo 2 shows the exterior of ＊4 Negawatt power: The power demand is reduced in the the container system. instance of tight supply of electricity. Reduced demand is viewed as negative power in contrast with usual positive power, and is termed as “negawatt power” (negative watt power). ＊5 Aggregator: It is an entity in charge of carrying out efficient energy management between power companies and end users. Aggregators buy and sell electricity, by collecting some negawatt power from end users.

References Photo 2. Exterior of container system (1) T. Shigematsu, “Redox Flow Battery for Energy Storage,” SEI Technical Review No. 73, pp.4-11 (2011) (2) T. Shibata et al., “Redox Flow Battery for the Stable Supply of Renewable Energy,” SEI Technical Review No. 76, pp.14-22 (2013) 6. Conclusion (3) K. Tada et al., “Minami-Hayakita Substation Large-scale Storage Battery System Demonstration Project (1) - Overview of the Demonstration Redox flow battery systems have been developed in Project - ,” Annual Conference of Power & Energy Society, 225, pp.4-5- order to stabilize the electric power grids against the inte- 17-18 (September 2016) (4) A. Inoue et al., “Minami-Hayakita Substation Large-scale Storage gration of an increasing bulk of renewable energy and to Battery System Demonstration Project (3) - Development of the wind meet the emerging electricity needs of the end users. These power generation and photovoltaic power generation forecast system -,” systems are safe and long lasting and fulfill their respective Annual Conference of Power & Energy Society, 227, pp.4-5-21-22 performance requirements. Future goals include improve- (September 2016) (5) T. Shibata et al., “60MWh vanadium flow battery system for grid control,” ment in the operating efficiency, further technology devel- IFBF2016 (June 2016) opment, and cost reduction. Sumitomo Electric is (6) K. Yano et al., “Minami-Hayakita Substation Large-scale Storage committed to contributing to the wider introduction of Battery System Demonstration Project (2) - Evaluation of the 60MWh renewable energy and the efforts towards building a society Redox Flow Battery System Performance -,” Annual Conference of inclined to saving more energy. Power & Energy Society, 226, pp.4-5-19-20 (September 2016) (7) K. Kojima et al., “Research on the Smart Energy System for Large R&D Facility Part5 Demand Response and Isolated Operation Test,” Annual Conference of Power & Energy Society, 28, pp.7-2-13-7-2-18 (September 2016)

SEI TECHNICAL REVIEW · NUMBER 84 · APRIL 2017 · 27 Contributors The lead author is indicated by an asterisk (*).

K. YANO* • ‌Energy System Division

S. HAYASHI • ‌Senior Assistant General Manager, Energy System Division

T. KUMAMOTO • ‌Assistant General Manager, Energy System Division

T. SHIBATA • ‌Group Manager, Energy System Division

K. YAMANISHI • ‌Group Manager, Energy System Division

K. FUJIKAWA • ‌Ph.D. Assistant General Manager, Energy System Division

28 · Development and Demonstration of Redox Flow Battery System