Application of Grid Energy Storages in Power Systems

The MAIN JOURNAL for POWER GRID SPECIALISTS in RUSSIA

2014

DIGEST, February, 2014

34

Innovation

Application of Grid Energy Storages 

in Power Systems

Denis Zhuravlev (Денис ЖУРАВЛЕВ),

 Ph.D., VNIIR leading engineer

INTRODUCTION

Development priority of modern intelligent electric 

systems (IES) is to improve reliability of power supply, 
energy ef

fi

ciency and environmental friendliness. 

Ful

fi

 llment of these tasks is often complicated by electrical 

network issues such as high equipment congestion, heavy 
losses and lengthy outages due to network accidents, 
complexity of RES-integrated network control due to 
intermittent power pro

fi

 le they generate.

One of the best ways to solve these problems is the use 

of energy storage systems.

To date, several types of storage devices are used 

with different ways of storing energy and technical 
characteristics: pumped storage power plants, compressed 
air energy storages, 

fl

 ywheel energy, supercapacitor energy 

storage systems etc. This article focuses on one of the most 
rapidly developing and promising directions for energy — 
grid energy storage systems based on batteries (BESS).

The basic structural components of BESS are batteries, 

bidirectional inverter to convert the current during 
battery charging and discharging as well as a system for 
monitoring, control and protection of BESS elements. 

Until recently one of the most studied and practically 
mastered were BESS with lead-acid batteries. However, 
in recent years application of other types of batteries, 
for example, sodium-sulfur, nickel salt, lithium-ion is 
actively developing. Increased interest in such batteries is 
conditioned by the fact that compared with lead-acid they 
usually have higher speci

fi

 c characteristics and longer 

service life.

Depending on the functions performed BESS can 

either be connected directly to the low voltage network 
(0.4 kV) or to a higher voltage network through a power 
transformer. BESS primary modes of operation are: 
•  electric power storage mode in which the storage 

consumes energy from the network for battery 
charging;

•  output mode when BESS supplies previously stored 

power to the grid.

BESS APPLICATION IN POWER GRID SYSTEMS

Currently in Russia and abroad active research and 

practical implementation of BESS for different solutions 
are conducted:

Fig. 1. Daily load profile leveling by BESS

www.eepr.ru

35

•  reduction of peak load, daily load curve leveling;
•  renewable energy power curve balancing;
•  customer and auxiliary systems backup power supply;
•  reduce losses and improve power quality in the 

electrical network;

•  network frequency regulation.

REDUCTION OF PEAK LOAD, DAILY LOAD CURVE LEVELING 

Reducing peak load and daily load curve leveling are 

historically the 

fi

 rst tasks to be solved with the use of 

battery-based ESS.

Back in the 80s several pilot projects in Germany, Japan 

and the United States were implemented where BESS on 
the base of lead-acid batteries were applied for the solution 
of these problems. To level the daily load curve in the 
hours of the low night demand (Fig. 1) BESS enters into 
battery charge mode and operates as a three-phase load, 
during peak demand it goes into a power output mode and 
supplies active and reactive power to the network.

In recent years this area of application is becoming 

increasingly important, as it allows to solve several 
important problems:
• partially unload the substation (SS) overloaded 

transformers, which potentially allows to connect them 
to an additional load

•  to reduce the power and voltage losses in electrical 

network when using BESS as electricity supplier by 
reducing the value of the power transmitted along the 
feeders from substation to the customer by the amount 
of power received by the customer from BESS;

•  maintain customer voltage required by regulatory 

documents during daily peak load.

RENEWABLE ENERGY POWER CURVE

 BALANCING

Renewable energy sources actively implemented 

abroad usually generate intermittent power curve. 
This in turn complicates the tasks of prediction power 
values generated by them and network mode control to 
which they are connected. To balance power generated 
by renewable energy sources BESS are successfully 
used. In excess generation mode BESS goes into 
battery charging mode, with a lack of power generated 
by renewable energy sources BESS outputs power to 
customers. 

In the autonomous power supply systems based on 

renewable energy the use of BESS allows to power the 
customer even when renewable energy sources do not 
produce the amount of power necessary for the customer. 
Fig. 2 shows an example of the daily load curve electric 
network with a high degree of distributed solar generation. 
In this case, the use of renewable energy in the daytime 
allows to unload supply substations.

BESS is used to reduce solar power 

fl

 uctuations while 

the value of power consumption from the network remains 
unchanged.

Fig. 3 shows an example of consumer daily load pro

fi

 le 

powered by independent source based on solar panels, 
wind turbine and BESS. In this case BESS is targeted to 
produce load supply under the shortage of power generated 
by the autonomous power supply system.

To date the leading foreign battery manufacturers 

offer different types of batteries to be used in BESS 
for RES. This is primarily a high capacity sealed 
lead-acid maintenance-free batteries made on GEL 

Fig. 2. Example of daily load curve and power in the network with distributed solar generation

DIGEST, February, 2014

36

Innovation

technology (less AGM) focused on the cycling and 
having compared with lead-acid batteries of other types 
are less self-discharge and having increased resistance 
to deep discharge. In recent years renewable energy 
is increasingly used BESS based on sodium-sulfur, 
nickel-salt and lithium-ion batteries. In comparison with 
lead-acid batteries bene

fi

 ts of its use are higher charge/

discharge cycle, the possibility of deep discharge, the 
best mass and dimension parameters, but their operation 
is conditioned by more complex control system of 
batteries.

CUSTOMER AND AUXILIARY SYSTEMS BACKUP 

POWER SUPPLY

Nowadays to provide backup power to consumers 

of low energy needs battery-based BESS are used very 
widely. The market offers a number of solutions, mainly 
on the basis of lead-acid batteries, allowing autonomous 
electricity supply to consumers with relatively low load 
by earlier charged batteries from the network.

Application of BESS to provide backup power to 

consumer groups of high equivalent wattage is currently 
implemented in a number of projects abroad. This 
direction is promising, but the high cost of batteries 
restricts mass use of battery-based BESS to solve this 
problem. An example of a successful implementation 
of BESS in the distribution networks are projects of the 
U.S. company American Electric Power (AEP) carried 
out with the 

fi

 nancial support of the U.S. Department 

of Energy. Within the framework of these projects by 
2010 in Texas and West Virginia 

fi

 ve large BESS of total 

power 11 MW and 75.4 MWh energy storage capacity are 
used for backup power applications as well as maintain 

a stable level of power at sharp increase in electricity 
demand. Also as part of the project “Community 
Energy Storage” 80 BESS of 25 kW/25 kWh each on 
the basis of lithium-ion rechargeable batteries are under 
construction and targeted to provide backup power for 
consumers.

BESS application for auxiliary systems backup power 

supply at a complete loss of the external power supply 
is an important direction of energy storage devices 
utilization that will improve the reliability of electricity 
supply to customers. This direction is successfully 
developed abroad and since recently — in Russia. One 
of the 

fi

 rst BESSs in our country to provide backup 

power for substation auxiliary power supply were 
installed by JSC UES FGC in 2010 at 220 kV “Psou” 
SS (Sochi) and in 2011 at  SS “Volkhov-Severnaya” 
(St. Petersburg).

REDUCE LOSSES AND IMPROVE POWER QUALITY IN THE 

ELECTRICAL NETWORK 

Utilities are facing a number of challenges such as 

equipment congestion, assets degradation, non-optimal 
con

fi

 guration of the distribution networks, etc. which 

lead to increased losses in electric networks and reduce 
the quality of electricity. To improve the situation various 
technical measures usually requiring signi

fi

 cant time and 

material costs are taken: disaggregation of existing power 
networks, construction and commissioning of new supply 
substations and adjacent sections of the network, the use 
of booster transformers, reactive power compensation 
devices, etc. One of the operational decisions to 
these issues is to integrate BESS into distribution 
networks.

Fig. 3. Example of daily load curve and power when customers are supplied from a BESS autonomous RES

www.eepr.ru

37

16 MW lithium-ion energy storage used to regulate network frequency. BESS is installed by AES Energy Storage in 
Jonson -city, New York.

Control system used in BESS bidirectional inverters 

allows to adjust BESS input and output power factors. 
Due to this the storage can be used as a reactive power 
compensation device. BESS application for reactive 
power control helps to maintain voltages at electrical 
network nodes speci

fi

 ed by regulatory requirements, to 

reduce the voltage and power loss in the power grid as 
well as improve the load power factor.

When BESS is used to output energy to network 

the active power transmitted from substation to BESS 
site decreases also leading to power losses and voltage 
reduction in these parts of the network. 

Thus, application of the BESS in distribution networks 

can improve the quality of voltage, to provide the 
required voltage to consumers in daily peak load and 
delay the necessary measures for the reconstruction and 
modernization of electrical networks.

NETWORK FREQUENCY REGULATION 

Another important area of BESS application is to 

regulate frequency of the network. In this case BESSs 
connected to the mains can be used as active power 
spinning reserve or as an additional load. In case of network 
frequency reduction BESSs can be automatically or by the 
system operator transferred to output active power into 
the network until the frequency returns to the speci

fi

 ed 

range or BESS is discharged to an acceptable value. With 
frequency increasing BESS can be switched into charge 
mode to increase the power load on the network. Abroad 

pilot projects on the use of BESS for frequency regulation 
have been implemented since the 80s. Currently this area 
is becoming increasingly important due to the increasing 
share of distributed generation based on renewable energy 
which  power curve is often intermittent and dif

fi

 cult to 

forecast, and limited control under the deviations at mains 
frequency.

CONCLUSIONS

Abroad BESSs are considered as one of the key 

components of modern IPS. With more sophisticated 
network topology, increasing power load, growth 
of distributed generation and renewable energy the 
implementation of BESS is becoming increasingly 
important. Today BESSs are successfully applied to 
solve a number of problems: reduce maximum and daily 
load curve leveling, balance power curve generated by 
renewables, backup power service to consumers and 
auxiliary systems, reduce losses and improve power 
quality in the electrical network, regulate frequency in the 
electric networks etc.

Modern energy storage technology and power 

electronics allow to develop BESS with high speci

fi

 c 

characteristics and long life. One of the major factors 
hindering the implementation of BESS remains their 
high cost, which is primarily determined by the cost of 
battery. Despite this, thanks to wide functionality, the use 
of network energy storages to address energy challenges 
is very promising.