Energy storage technologies

Energy Storage
Technologies In Renewable
Energy

Energy storage technologies

1

Need of Energy Storage In renewable
Energy
The energy storage along with renewable energy
generators/PV is required to increase the
reliability and flexibility.
The intermittent nature of renewable sources like
solar and wind needs storage to deliver the right
amount of power at right quality.
To accommodate the projected high penetration
of solar and wind energy in future grids with
lower grid rejection loss.

2

Services of Energy storage technologies
 Energy Arbitrate: Storing cheap off-peak energy and dispatching
it as peak electricity which requires large storage reservoir
required at large capacity.

o Examples: Compressed air and pumped hydro
 Load Regulation:

 Responding to small changes in demand
 Energy Storage technologies were suitable for
load/frequency regulation due to their high response time
and high partial load efficiency.
 They have to be
Highly reliable
Continuous change in output power
Suitable for frequent on-off
Examples: Flywheel, Ultra capacitors, Batteries

3

Services of Energy storage technologies(cntd.)
Contingency Reserves: Mainly used as
alternatives for generators when there is
transmission line trip or grid failure.
These are categorised into three types:
– Spinning reserve: operates with in 10 min of outage
– Supplemental reserve: Comes into operation when
spinning reserve is fully discharged.
– Back up reserve: Acts as a back up in case of
spinning/supplemental reserve failure.

In all the services the load regulation service
yields more revenue but each storage technology
can participate in more than one market.

4

Other services of Energy storage:
 Load following: To fill the difference or gap between demand and
supply.
– Difference between load following and load regulation is the time
scale.
– The range for load regulation is a few seconds.
– The range for load following is with in minutes.
 Capacity supply: The capacity supply reduces the investment for
new thermal or other conventional generation technologies. The
investor could rent the storage capacity in the market.
 Transmission and distribution loss reduction: With the rise in
demand new transmission lines has to be set up which increases
capital cost and the transmission losses. Energy storage at the load
centres resolves both of the problems.

5

Energy storage technologies-Categories
 Power quality: Main purpose is frequency and voltage
regulation.
 Operating range: Seconds to few minutes
 Examples: Flywheel, Ultra capacitors, SMES,
Batteries
 Bridging power: Main purpose is to act as contingency
reserves and ramping of load.
 Operating range: Few minutes to one/two hour
 Examples: High energy density batteries.
 Energy Management: The main purpose is load
following, Capacity supply, Reduction of transmission
and distribution losses.
 Operating range: Few hours to days
 Examples: CAES, pumped hydro storage
6

Overview
 Technology Types– Batteries, flywheels, electrochemical
capacitors, SMES, Pumped hydro, Compressed air energy storage.
 Theory of Operation– Brief description of the technologies and the
differences between them

 State-of-the-art– Past demonstrations, existing hurdles and
performance targets for commercialization
 Cost and cost projections:– Prototype cost vs. fully commercialized
targets


7

Technology Choice for Discharge Time and Power Rating


8

Available Energy storage Technologies and
Maturity levels







Batteries
SMES
Flywheels
Electrochemical Ultra Capacitors
Conventional pumped hydro
Compressed air


9

Batteries

 Batteries store energy chemically and uses electrochemical reactions to
produce electricity at a fixed voltage
 Pros:
– Convenient voltage Characteristics
– Convenient sizing
– Extensive design history
 Cons:
– Limited cycle life
– Voltage and current limitations, requiring complex series/parallel systems
– Often present environmental hazard
 Battery Application Suitability
– Batteries are suitable for applications that require the supply of relatively large
amounts of energy storage (>1 MWh) over long periods of time (15 minutes or more),
where rapid recharge is not necessary and where maintenance can be reasonably
performed.
– They are not especially suitable for environmentally sensitive sites, remote locations,
or applications that require rapid discharge and absorption of energy.

10

Cycle life


11

Flywheel





Flywheels store energy in the form of momentum in a rotating wheel or cylinder.
Principle:
An electric motor spins the rotor to a high velocity to charge the flywheel.
During discharge, the motor acts as a generator, converting the rotational energy
into electricity.
 Power electronics are used to ensure that output voltage has appropriate voltage
and frequency characteristics
 Pros:
– High power density
– High cycle life
– Quick recharge Independent
– power and Energy sizing

–
–
–

Cons:
Low energy density
Large standby losses
Potentially dangerous failure modes

12

Electro chemical/Super/Ultra capacitors
 Electrochemical capacitors (EC), also known as super capacitors, ultra
capacitors, or electrical double-layer capacitors (EDLC), store energy in the
electrical double layer at an electrode/electrolyte interface.
 Pros:
• High power density
• High cycle life
• Quick recharge
 Cons:
• Low energy density
• Expensive
• Sloped voltage curve requires power electronics
• Energy and Power Density of Electrical Super capacitors:

• The energy and power densities of electrochemical capacitors fall between
those of batteries and conventional capacitors.

13

Electrochemical Capacitor Technology Status


Currently viable for bridging power (seconds) in the hundreds of kW power
range.



Smaller (several kW) power range, long term energy storage (hours)
application of electrochemical capacitors for residential peak shaving is
another application that is currently under consideration.



Use of ECs for multi-MW utility T&D applications that require several hours
of energy storage (peak shaving, load levelling, etc.) is not feasible at present.


14

Superconducting Magnetic Energy storage(SMES)
 SMES systems store energy in the magnetic field produced by current flowing through a superconducting
coil.
 The SMES energy-storage principle is based on inductive energy storage in the magnetic field produced
by current flowing through a superconducting coil.
 The DC current is converted to three-phase AC output using a solid-state power-conditioning system.
 Pros:
– High Power
– Quick recharge
 Cons:
– Low energy density
– Large parasitic losses
– Expensive
 SMES Technology Status
– Currently viable for short-term power (seconds) in the 1-10 MW power range
– Proposed applications are in PQ and transmission support
– Several demonstration projects have shown the capability of the technology in these applications.
– High initial cost is the major obstacle for the technology


15

Compressed Air Energy Storage (CAES)
 Air is compressed and stored in large underground spaces, and is
later used in gas turbine generators.
 Smaller Hybrid Systems (<50 MW)
 Above Ground
 Pros:
– Huge energy and power capacity
 Cons:
– Requires special location
– Expensive to build and maintain
– Slow start –an unlikely candidate
for distributed resources.


16

Pumped Hydroelectric Storage
 Water is pumped from low elevations to higher elevations
to store energy as gravitational energy, and run down
through hydroelectric turbines to generate electricity.
 Pros:
– Huge energy and power capacity
 Cons:
– Requires special locations
– Expensive to build
– Not suitable for DER


17

Technology Comparison


18

Proposed Models


19

Heterogeneous Energy Storage System(HESS)
 Since all the storage technologies have their own
merits and demerits a composite system has to be
designed to enjoy all the storages to maximum possible
efficient way.
 The proposed model contains heterogeneous storage
systems each of which includes several units of
homogenous units.
 The charge allocated for each type of storage system is
decided instantaneously depending upon the load
requirements.
 Each type of storage bank is connected to the common
charge transfer interface through a converter whose
output current(charging current) is regulated to achieve
the maximum possible efficiency of whole system.

20


21

Distributed Micro-Energy storage
• Distributed Battery Micro-Storage Systems Design and
Operation in a Deregulated Electricity Market
• The deregulation of electricity market is evident from the
entry of renewable Energy so the distributed energy
storage or micro storage which is not the storage at the
grid level but at the lower/load level.
• The off peak energy is been stored and it is dispatched at
the peak hours to shave the peak demand and power
regulations.
• The paper suggests the hardware design considering the
DOD and health of the battery and static, dynamic
economic model to maximise the return keeping the
battery conditions in mind.

22

Flowchart of the day-ahead operation
scheduling of the MSS


23

Li-Ion Battery-Super capacitor Hybrid
Storage System
• The energy storage has to address the two types of
discharge/charging i.e faster rates of discharging/charging for short
time periods for ramping up the load or regulating the voltage,
frequency etc. and discharging/charging at slower rates for long
hours for load following.
• But if the batteries were discharged at rapid rates the life time will
gets reduced drastically. So there has to be an integration of storage
devices to cope up with the charging and discharging conditions.
• This paper describes the integration of super capacitors which suits
the faster charging and discharging and the Li-ion batteries which
charges and discharges slowly thus giving the power output for long
time.

24

Power management block diagram


25

Optimal Charging/Discharging Scheduling of BSS
 Traditionally, the BSSs are charged and discharged in off-peak load
and peak load hours, respectively.
 However, to cope with the intermittent output of PVGSs, the
charging/discharging scheduling of BSSs should be arranged at
least hourly with respect to the load variations and intermittent
outputs of PVGSs.


26

Charging and discharging limits

Proposed piecewise CC charging
for CV stage.


27

Thank you


28

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