These slides present the basics of different categories of energy storage devices, and their application to power system. Apart from that one control strategy has been presented. Later of the class I will discuss about its control strategies.

1. Physical structure and
characteristics of
energy storage systems
Presented by
Prof. (Dr.) P. K. Rout,
ITER, SOA Deemed to be University
&
Mr. P. Bhowmik,
CSIR, India

2. Introduction
• Grid energy storage is a collection of
methods used to store electrical energy within
an electrical grid.
• Electrical energy is stored during times when
production (especially from renewable energy
sources) exceeds consumption, and returned
to the grid when production falls bellow
consumption.

3. A schematic configuration

4. Different energy storage system categories

5. Benefits of Storage and managing peak load (1/2)
• Electricity production need not be drastically scaled up and down to meet
momentary consumption.
• From the combination of generators and storage facilities, generation can be
maintained at more constant level.
• Fuel based power plants (i.e. coal, oil, gas, nuclear) can be more efficiently
and easily operated at constant production level.
• Peak generation or transmission capacity can be reduced.

6. Benefits of Storage and managing peak load
(2/2)
• More stable pricing can be offered to the bulk power consumers.
• At any emergency condition vital needs can be reliably powered even at no
generation condition (renewable sources concerned).
• The French consulting firm ‘Yole Development’ figures this ‘stationary
storage’ market could be $ 13.5 billion opportunity by 2023, compared
with less than $ 1 billion in 2015

7. Forms of Storage
• Compressed air energy storage (CAES)
• Liquid air energy storage (LAES)
• Super conducting magnetic energy storage (SMES)
• Super capacitor energy storage (SCES)
• Flywheel energy storage (FES)
• Power-to-Gas (P2G)
• Pumped-storage hydroelectricity (PSH)
• Plug-in hybrid electric vehicles
• Thermal storage

8. Compressed air energy storage (CAES)
• Off-peak energy is used to compress air and can be released
to meet peak load demand.
• If the heat generated during compression can be stored and
used during expansion, the efficiency of storage improves
considerably.
• There are three ways in which a CAES can deal with the heat.
1. Adiabatic
2. Diabetic
3. Isothermal

9. A schematic

10. Liquid air energy storage (LAES)
• When it is cheaper (usually at night), electricity is used to cool air
from the atmosphere to -195 degree centigrade where it liquefies.
• Volume of liquid air comes down to 1000 times compared to
ambient air, so can be kept in a large vacuum flask at atmospheric
pressure.
• At time of high demand the liquid air is heated again to turn it
back into the gas.
• The massive increase in volume and pressure is used to drive a
turbine.

11. A schematic

12. Configuration

13. Super conducting magnetic energy
storage (SMES)
• Super Conducting Magnetic Energy Storage (SMES) system stores
energy in the magnetic field created by the flow of direct current in
a super conducting coil.
• A coil when cryogenically cooled to a temperature bellow its super
conducting critical temperature the it becomes a super conducting coil.
• A typical SMES system includes three part-
1. Super conducting coil
2. Power conditioning system
3. Cryogenically cooled refrigerator

14. Configuration

15. A schematic

16. Advantages over other energy storage method
• Time delay during charging and discharging is quite short.
• Power is available almost instantaneously.
• Very high power can be provided for a small period of time.
• Loss of power is less than other storage methods because electric currents
encounter almost no resistance.

17. Configuration of the coil
• Configuration of the coil itself is an important issue from a mechanical
engineering aspect.
• There are three factors which affect the design-
1. Strain tolerance
2. Thermal contraction upon cooling
3. Lorentz forces in a charged coil

18. Current use
• Several 1 MWh units are being used for power quality control where the
ultra clean power is required, such as Microchip fabrication unit.
• These facilities have also been used to provide grid stability in distribution
system in Finland.

19. Super capacitor energy storage (SCES)
• It works same as battery charging and discharging system but offers-
1. High life cycle (>500000 cycled times)
2. Quickly charge/discharge (>1000A)
3. Operating temperature range (-50℃-70 ℃ )
4. Environment friendly

20. Configuration

21. Physical structure

22. Certain Limitations of Supercapacitor
• Low energy density
• Linear discharge voltage prevents use of the full energy spectrum.
• Cells have low voltages
• High self-discharge
• Voltage is limited to 2.7 V only
• We cannot go beyond three series connected capacitor without voltage
balancing system to protect over voltage of individual capacitors.

23. Flywheel energy storage (FES)
• It uses a flywheel for storing off peak energy in the form of kinetic energy.
• It offers comparatively small power with a peak power of up to 20 MW
• It practically used to compensate fluctuation of power in wind or solar
power plant.
2
2
1
= IE

24. Configuration

25. Aspects of efficiency
• The system has very low rotational losses due to the use of magnetic
bearings which prevent the contact between the stationary and rotating
parts, thus decreasing the friction.
• In addition, because the system operates in vacuum, the aerodynamic
resistance of the rotor is outstandingly reduced.
• These features permit the system to reach efficiencies higher than 80%.
• It provides 100% angular stability of grid.

26. Power-to-Gas (P2G)
• It converts off-peak electrical power to a gas fuel, again which is used to
generate electrical power during peak hours.
• Typically the electrical power is used to split water into hydrogen and
oxygen by means of electrolysis.
• Hydrogen and Oxygen separately used to drive gas turbine.
• The storage capacity of German natural gas network is more than 200,000
GWh which is enough for several months of energy requirement of
German.

27. Configuration

28. Efficiency
• In 2013 the round trip efficiency of P2G storage was bellow 50%
• In 2015 a study published in ‘Energy and Environmental Science’ claims that
efficiency can be reached up to 70% cost effectively.

29. Pumped-storage hydroelectricity
• The method stores energy in the form of gravitational potential energy
of water during off-peak hours.
• During peak hours that potential energy of water is converted to electrical
energy.
• The same turbine is used as a pump when lifts water to high level reservoir
from low level reservoir.

30. Configuration

31. Plug-in hybrid electric vehicles
• Daily load leveling
• Frequency regulation
• Reserved power
• Large-scale use: reduce battery costs
through competition and mass
production

32. Inside the campus of University of
Delaware, United States

33. Thermal storage
• Thermal Storage is mainly divided into two parts-
1. Hot thermal storage
2. Cold thermal storage

34. A schematic overview

35. Hot thermal storage
• Hot thermal storage is
generally used with solar
collectors.
• Store heat energy in hot
water for later use.
• Reduce electricity
demand for hot water

36. Cold thermal storage
• A cold storage system generates ice to chill water for air conditioning.
• Shift electricity demand for air conditioning from day to night.

37. Construction

38. State of Charge management between BES &
CAES
PCC
computing
state of
charge
K
local parameter
rtdv
PI PWMPI
n
DESU
−
+
vscV vscI
current regulationvoltage regulation
+
−
+
−+
− 1errorv
*
1errorv 2errorv
*
vscv
errorirefi *
i

39. SoC management during discharging

40. Evaluation of performance
Management scheme Controller
SoC equalization time
(Sec)
Mean equalization error
(%)
State of charge
Proposed STDE 4.82 0.0250
Conventional PMS 9.34 (quasi) 1.8724

41. Parameters of an Energy Storage Device
• Power Capacity: is the maximum instantaneous output that an energy
storage device can provide, usually measured in kilowatts (kW) or megawatts
(MW).
• Energy Storage Capacity: is the amount of electrical energy the device can
store usually measured in kilowatt‐hours (kWh) or megawatt‐hours (MWh).
• Efficiency: indicates the quantity of electricity which can be recovered as a
percentage of the electricity used to charge the device.
• Response Time: is the length of time it takes the storage device to start
releasing power.
• Round‐Trip Efficiency: indicates the quantity of electricity which can be
recovered as a percentage of the electricity used to charge and discharge the
device.

42. Energy Storage Applications 1/11

43. Energy Storage Applications 2/11
Energy storage devices can accommodate a number of network requirements. These are:
• Load management
• Spinning reserve
• Transmission and distribution stabilisation
• Transmission upgrade deferral
• Peak generation
• Renewable energy integration
• End‐use applications
• Emergency back‐up
• Demand Side Management (DSM)

44. 1: Load management 3/11
There are two different aspects to load management:
1. Load levelling: using off‐peak power to charge the energy storage device and
subsequently allowing it to discharge during peak demand. As a result, the overall
power production requirements become flatter and thus cheaper base load power
production can be increased.
2. Load following: energy storage device acts as a sink when power required
falls below production levels and acts as a source when power required is above
production levels. Energy devices required for load management must be in the 1
MW to 100+ MW range as well as possessing fast response characteristics.

45. 2: Spinning reserve 4/11
Once again spinning reserve is classified under two categories:
1. Fast response spinning reserve: power capacity that is kept in the state of
‘hot‐stand‐by’. As a result it is capable of responding to network abnormalities
quickly.
2. Conventional spinning reserve: power capacity that requires a slower response.
Energy storage devices used for spinning reserve usually require power ratings of 10
MW to 400 MW and are required between 20 to 50 times per year.

46. 3: Transmission and distribution stabilisation
5/11
Energy storage devices are required to stabilise the system after a fault occurs on the
network by absorbing or delivering power to generators when needed to keep
them turning at the same speed.
These faults induce phase angle, voltage and frequency irregularities that are corrected by
the storage device.
Consequently, fast response and very high power ratings (1 MW to 10 MW) are essential.

47. 4: Transmission upgrade deferral 6/11
✓Typically, transmission lines must be built to handle the maximum load required
and hence it is only partially loaded for the majority of each day.
✓Therefore, by installing a storage device, the power across the transmission line can
maintained a constant even during periods of low demand. Then when demand
increases, the storage device is discharge preventing the need for extra capacity on
the transmission line to supply the required power. Therefore, upgrades in
transmission line capacities can be avoided.
✓Storage devices for this application must have a power capacity of kW to
several hundreds of megawatts and a storage capacity of 1 to 3 hours.
Currently the most common alternative is portable generators; with diesel and
fossil fuel power generators as long term solutions and biodiesel generators as a
short term solution.

48. 5: Peak generation 7/11
Energy storage devices can be charged during off‐peak hours and then used to
provide electricity when it is the most expensive, during short peak
production periods.

49. 6: Renewable energy integration 8/11
In order to aid the integration of renewable resources, energy storage could be used
to:
1. Match the output from renewable resources to the load required
2. Store renewable energy during off‐peak time periods for use during peak
hours
3. Act as ‘renewable back‐up’ by storing enough electricity when it is available
to supply electricity when it isn’t available
4. Smooth output fluctuations from a renewable resource
A storage system used with renewable technology must have a power capacity of 10
kW to 100 MW, have fast response times (less than a second), excellent
cycling characteristics and a good lifespan (100 to 1,000 cycles per year).

50. 7: End‐use applications 9/11
✓ The most common end‐use application is power quality which primarily
consists of voltage and frequency control.
✓Transit and end‐use ride‐through are applications requiring short power
durations and fast response times, in order to level fluctuations, prevent
voltage irregularities and provide frequency regulation.
✓This is primarily used on sensitive processing equipment.

51. 8: Emergency back‐up 10/11
✓ This is a type of UPS except the units must have longer energy storage
capacities.
✓The energy storage device must be able to provide power while generation is
cut altogether.
✓Power ratings of 1 MW for durations up to one day are most common.

52. 9: Demand Side Management (DSM) 11/11
DSM involves actions that encourage end‐users to modify their level and
pattern of energy usage.
Energy storage can be used to provide a suitable sink or source in order to
facilitate the integration of DSM. Conversely, DSM can be used to reduce
the amount of energy storage capacity required in order to improve the
network.

53. Energy Storage Plant Components
Before discussing the technologies, a brief explanation of the components
required to have an energy storage device are discussed. Every energy storage
facility is comprised of three primary components:
1. Storage Medium
2. Power Conversion System (PCS)
3. Balance of Plant (BOP)

54. Storage Medium
✓The storage medium is the ‘energy reservoir’ that retains the potential energy
within a storage device.
✓It ranges from mechanical (Pumped‐Hydroelectric Energy Storage), chemical
(Battery Energy Storage) and electrical (Superconducting Magnetic Energy
Storage) potential energy.

55. Power Conversion System (PCS)
✓It is necessary to convert from alternating current (AC) to direct current (DC)
and vice versa, for all storage devices except mechanical storage devices e.g.
Pumped‐Hydroelectric and Compressed Air energy storage. Consequently, a PCS is
required that acts as a rectifier while the energy device is charged (AC to DC)
and as an inverter when the device is discharged (DC to AC).
✓The customization of the PCS for individual storage systems has been identified as
one of the primary sources of improvement for energy storage facilities, as each
storage device operates differently during charging, standing and discharging
✓Development of PCSs has been slow due to the limited growth in distributed
energy resources e.g. small scale power generation technologies ranging from 3 to
10,000 kW.

56. Balance of Plant (BOP)
These are all the devices that:
✓ Are used to house the equipment
✓ Control the environment of the storage facility
✓ Provide the electrical connection between the PCS and the power grid
• It is the most variable cost component within an energy storage device due to the various
requirements for each facility. The BOP “typically includes electrical interconnections, surge
protection devices, a support rack for the storage medium, the facility shelter and
environmental control systems” .

57. Typical Suitability of Storage Technologies to
Different Applications

58. Comparison of Energy Storage Technologies
• PHES: Pumped‐Hydroelectric Energy Storage
• UPHES:
• CAES:Compressed Air Energy Storage
• BES: Battery Energy Storage
• FBES:Flow Battery Energy Storage
• FES:Flywheel Energy Storage
• SCES:Supercapacitor Energy Storage
• SMES:Superconducting Magnetic Energy Storage
• HESS:Hydrogen Energy Storage System
• TESS:Thermal Energy Storage System
• Evs:

59. Comparison of Energy Storage Technologies

60. Comparison of Energy Storage Technologies

62. Conclusion
• Current renewable technologies
require storage possibilities
• Pumped-storage hydroelectricity
is currently the only viable
solution
• Flywheels, SMES, SCES and batteries
possess small potential
• CAES shows the greatest
potential

63. References
• Arani, AA Khodadoost, G. B. Gharehpetian, and M. Abedi. "Review on
energy storage systems control methods in microgrids." International journal
of electrical power & energy systems 107 (2019): 745-757.
• Aneke, Mathew, and Meihong Wang. "Energy storage technologies and real
life applications–A state of the art review." Applied Energy 179 (2016): 350-
377.

64. Question?
• What are the major parameters of an energy storage device?
• What are the energy storage applications?