energy storage technologies

Energy storage technologies 1

Energy Storage Technologies In Renewable Energy


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.


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 beHighly reliableContinuous change in output powerSuitable for frequent on-offExamples: Flywheel, Ultra capacitors, Batteries


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.


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.

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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 storageEnergy storage technologies


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


Technology Choice for Discharge Time and Power Rating


Available Energy storage Technologies and Maturity levels

Batteries SMES Flywheels Electrochemical Ultra Capacitors Conventional pumped hydro Compressed air


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.


Cycle life


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 characteristicsPros:– High power density

– High cycle life

– Quick recharge Independent

– power and Energy sizingCons:– Low energy density– Large standby losses– Potentially dangerous failure modes


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.


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.

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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 technologyEnergy storage technologies


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.


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


Technology Comparison


Proposed Models

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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.Energy storage technologies


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.


Flowchart of the day-ahead operation scheduling of the MSS


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.


Power management block diagram


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.


Charging and discharging limits

Proposed piecewise CC charging for CV stage.


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