Sustainable Energy Science and Engineering...

Sustainable Energy Science and Engineering Center

Energy Storage

Storage modes are determined by the particular end-use

applications

Anjane Krothapalli, September 20, 2006

http://www.sesec.fsu.edu


Main Parameters

Energy density: The amount of energy that can be stored.

Recovery rate: The efficiency at which the energy can be recovered.

Hydrogen has for example has one of the highest storage densities (kWh/kg) of 38 as compared to that of lead acid batteries, 0.04.

The efficiency of work exchange processes:

ηcycle ≡Wre cov ered

Win

= ηinηout


Electrochemical systemsbatteries and flow cells

Mechanical systemsfly-wheels and compressed air energy storage (CAES)

Electrical systemssuper-capacitors and super-conducting magnetic energystorage (SMES)

Chemical systemshydrogen cycle (electrolysis -> storage -> power conversion)

Thermal systemssensible heat (storage heaters) and phase change

Generic Storage Systems


Ragone Plot

Source: Tester et. al. Sustainable energy, MIT Press


Energy Density

2/m3Compressed Air38Hydrogen0.9Flywheel, Fused Silica0.2Flywheel, Carbon Fiber0.05Flywheel, Steel0.3/m3Hydrostorage0.04Lead Acid Batteries14GasolinekWh/kgMethod


Battery Storage

Designed for load leveling

Large number of batteries charged during low demand periods

One acre could store 400 MWh of energy, deliver 40 MW for 10 hours

Batteries require environmentally damaging chemicals

Typical installation: Southern California Edison

8000 lead acid battery modules to deliver up to 10 MW of power for four hours of continuous discahrge


1. Life time (maximum number of charge and discharge cycles)

2. Overall cycle efficiency

3. Depth of discharge per cycle (deep cycle - less instant energy but longer term energy delivery: e.g.: Golf cart battery)

4. Cost of unit of power or energy stored

Performance Factors


Rechargeable Battery Characteristics

http://www.afrlhorizons.com/Briefs/Feb04/PR0306.html

>2,000>3.6300150Lithium

>10,0001.20.0655Nickel hydrogen

>10001.20.0835Nickel Cadmium

40020.0835Lead acid

Cycle LifeVoltageWh/m3Wh/kgProperties


400 Wh/kg Goal


Typical compact automobile power requirement: 50 KW

Typical driving distance: 500 km

Average speed: 100 km/hr

Required stored energy: 250 kWh

Battery capacity: 400 Wh/kg

Batteries weight: 625 kg; Cost: $50,000

Battery Storage Requirement

Individual Americans use about 1.5 kWh of electricity every hour

Typical storage requirement: 15 kWh

Battery capacity: 400 Wh/kg

Batteries weight: 37.5 kg; Cost: $3000


Potential Energy Storage

Use excess energy to pump water uphill from a lower reservoir to higher reservoir:

Energy recovery depends on total volume of water and its height above the turbine location

The efficiency of pumping: 80%

Net efficiency: 0.8 x 0.8 = 0.64

The typical coal power plant efficiency ~ 40%

The efficiency of the recovered energy =

0.64 x 0.4 ~ 0.25 (25%)

Pumped hydropower:


Pumped-Storage Plant

Source: NREL


Hydropower Storage Facility


Pumped Stored Energy

Energy stored is predominantly Nuclear Power

The water head ranges widely: 25 - 600m

Large range in capacity: 4 MW - 2100 MW

USA storage capacity: 20 GW

Europe: 32 GW

Others: 34 GW

Opportunity to store renewable energy (especially wind) when it is produced and deliver when needed.

Ideally suited in mountainous regions.

Total hydro capacity: 420 GW

Typical pumping up cost: $14 ~ $21/MWh


Source: Toshiba

Pump Turbine Progress


Compressor train Expander/generator train

Fuel (e.g. natural gas, distillate)

Intercoolers

Heat recuperator

PC PG

AirExhaust

AirStorage

Aquifer,salt cavern,

or hard mine

hS = Hours ofStorage (at PC)

PC = Compressorpower in

PG = Generatorpower out

Compressed Air Energy Storage SystemPotential Energy Storage


Wind capacity factor can be significantly improved

Wind farm Transmission

CAES plant

Undergroundair storage

PWF = Wind Farm max.power out(rated power)

PT = Transmission linemax. power

PWF PT

Wind/CAES

Source: Toward optimization of a wind/ compressed air energy stoSource: Toward optimization of a wind/ compressed air energy storage (CAES) power system rage (CAES) power system Jeffery B. Jeffery B. GreenblattGreenblatt, , Samir SuccarSamir Succar, David C. , David C. DenkenbergerDenkenberger, Robert H. Williams, , Robert H. Williams,

Princeton UniversityPrinceton University


Compressed Air Energy Storage

Huntorf plant



Energy needed to compress gases: the adiabatic compression work

W: specific compression work (J/kg); po: initial pressure; p1: final pressure; Vo: initial specific volume (m3/kg); γ: ratio of specific heats

Net work = Wnet= Wturbine - Wcompressor

ηoverall = ηturbineηcompressor

W =γ

γ −1poVo

p1

po

⎛

⎝ ⎜

⎞

⎠ ⎟

γ −1( )γ

−1⎡

⎣

⎢ ⎢ ⎢

⎤

⎦

⎥ ⎥ ⎥


Flywheels

A flywheel is a mechanical battery storing energy mechanically in the form of kinetic energy. It uses an electric motor to accelerate the rotor up to a high speed and return the electrical energy by using the same motor as a generator. The rotational energy is delivered until friction overcomes it.

Flywheel has a higher energy density over chemical energy storage. The rate at which energy can be exchanged into or out of the flywheel is limited only by the motor-generator design. Hence, it is possible to withdraw large amounts of energy in a far shorter time than with traditional chemical batteries. As such they are widely used in automobile applications.

Flywheels store energy very efficiently and can provide high specific power (kWh/kg) compared with batteries.

Flywheel purchase costs: $100/kW - $300/kW

Installation costs: $20/kW - $40/kW


Flywheel ParametersStored energy:

ω = rotational velocity

I = moment of inertia (ability of an object to resist changes in its rotational velocity)

= kmR2

k: inertial constant depends on shape; m: mass; R: radius

Wheel loaded at rim (bike tire); k = 1: solid disk of uniform thickness; k = 1/2 solid sphere; k = 2/5; spherical shell; k = 2/3; thin rectangular rod; k = 1/2

KE =12

Iω 2 =12

kmR2ω 2


In order to optimize the energy-to-mass ratio, the flywheel needs to spin at the maximum possible speed.

Rapidly rotating objects are subject to centrifugal forces that can rip them apart.

Centrifugal force =

While dense material can store more energy it is also subject to higher centrifugal force and thus fails at lower rotational speeds than low density material. Therefore the tensile strength is more important than the density of the material.

Efficiency ~ 80%

Flywheel Parameters

mRω 2


Technical Challenges: Light weight high tensile strength rotors (e.g. Fused Silica or composite material rotors) , low density and reduced

friction using evacuated housing with magnetic bearings

Specific Energy Density

Specific energy density =KErotational,max

m=

kσ max

ρm

σmax= maximum allowable tensile stress of the material

ρm = volumetric mass density (kg/m3)


3600-300Ultracapacitors

1500-650SMES

12750CAES

500350Flywheels

200300Li-Ion

12800Pumped Hydro

US$/kWhUS$/kWStorage Type

Estimated Costs


Alternative Ragone Plot


Supercapacitors

Electrical energy storage in the form of confined electrostatic charges in a device consisting of conductive plates separated by dielectric medium.

Power Density =

V: applied voltage; R: total effective resistance of the capacitor, A: nominal surface area of the conducting plate or electrode

Very high surface area activated carbon (nanopores) electrodes and charge separation distances in nanometers.

Attractive for Regenerative breaking and other power needs in electric and hybrid vehicles.

0.5V2

RA2


Supercapacitors - State of the Art

Source: CAP-XX Pty Ltd, Australia, 2005


Superconducting Magnetic Energy Storage (SMES)

A device for storing and instantaneously discharging large quantities of power. It stores energy in the magnetic field created by the flow of DC in a coil of superconducting material that has been cryogenically cooled. The SMES recharges within minutes and can repeat the charge/discharge sequence thousands of times without any degradation of the magnet. Recharge time can be accelerated to meet specific requirements, depending on system capacity.

In low-temperature superconducting materials, electric currents encounter almost no

resistance.


Storage Technology Costs

Source: iti Scotland Ltd, 2005


Hydrogen Storage


Energy Sources Typical Chemical Energy Density

Hydrogen 142.0 MJ/kgEthanol 29.7 MJ/kgAmmonia 17.0 MJ/kgAutomotive Gasoline 45.8 MJ/kgMethane 55.5 MJ/kgMethanol 22.7 MJ/kg

(Source: Chemical Energy, The Physics Hyper text Book)

Potential Fuel


Fuel Typical Stored ChemicalEnergy Density

Hydrogen 7.1 MJ/kg @ 5wt%Ethanol 26.7 MJ/kg @ 90wt%Ammonia 13.6 MJ/kg @ 80wt%Automotive Gasoline 41.2 MJ/kg @ 90wt%Methane 44.5 MJ/kg @ 80wt%Methanol 20.4 MJ/kg @ 90wt%

Energy Density


ObjectiveTo achieve adequate stored energy in an efficient, safe and

cost effective system.

Source: Oak Ridge National Laboratory Hydrogen Storage Work Shop, May 2003


Source: Ian Edwards, ITI Energy, May 24th, 2005

Energy Storage


Hydrogen pellets

Mg(NH3)6Cl2

Hydrogen Storage


Technology Status


Storage Methods


14 13 13 13 13 12 12 11 12 13 12 129

1113

2018 18 17 16 15

1212 9 8

4

0

10

20

30

40

cetan

e (dies

el)

octane (

gasolin

e)hep

tane

hexan

epen

tane

butane

ethan

epro

pane

ethan

olmeth

ane

methan

olam

monialiq

. hyd

rogen

hydrid

ewate

rEn

ergy

Den

sity

(MJ/

liter

)

carbon

hydrogen

Hydrogen density range

Energy Densities (LHV) in Liquid state


Compressed Gas Storage Density (300 K, LHV)

0

1

2

3

4

5

0 2000 4000 6000 8000 10000

Pressure (psi)

Ener

gy D

ensi

ty (M

J/lit

er)

350 bar 700 bar

Gasoline: 13 MJ/L

Compressed Gas


• increased pressure (>700 bar)– stronger, lighter composite tanks (cost)– hydrogen permeation– non-ideal gas behavior

• conformable tanks– maximum volume gain ~20% (cylind./rect. volumes)– some increase in weight

• microspheres– multiple shell volumes– close-packed packing density ~60% of volume– hydrogen release/reload mechanism

Compressed Gas


Carbon fiber wrap/polymer liner tanks are lightweight and commercially available.

weight specific energy6 wt.% 7.2 MJ/kg7.5 wt.% 9.0 MJ/kg10 wt.% 12 MJ/kg

Energy density is the issue:

Pressure Gas density System density350 bar 2.7 MJ/L 1.95 MJ/L700 bar 4.7 MJ/L 3.4 MJ/L

Compressed Gas Cylinders


Liquid Hydrogen EOS

0

100

200

300

400

500

600

20 30 40 50 60 70 80 90 100

Temperature K

Pres

sure

bar

High Pressure Cryogenic Tank

• reduces temperature requirements• eliminates liquifaction requirement• essentially eliminates latency issue

S. Aceves, et al 2002

Estimated energy density: 4.9 MJ/L (Berry 1998)


Requires cryogenic systems

• Equilibrium temperature at 1 bar for liquid hydrogen is ~20 K.• Estimated storage densities1

Berry (1998) 4.4 MJ/literDillon (1997) 4.2 MJ/literKlos (1998) 5.6 MJ/liter

• Issues with this approach are:– dormancy.– energy cost of liquifaction.

1 J. Pettersson and O Hjortsberg, KFB-Meddelande 1999:27

Liquid Storage


Gaseous Hydrogen Storage

Higher Heating value of Hydrogen: 142 MJ/kg

Hydride storage of hydrogen may be compared to the compression of

hydrogen

Source: The Future of Hydrogen Economy: Bright or Bleak? Baldur Eliasson and Ulf Bossel, ABB Switzerland Ltd.


Hydrogen Storage - Liquefaction

Total energy requirement for liquefaction of 1 kg of H2



Hydrogen Delivery - Pipelines



Hydrides

Chemically bond hydrogen in a solid material• This storage approach should have the highest hydrogen packing

density.• However, the storage media must meet certain requirements:

– reversible hydrogen uptake/release– lightweight with high capacity for hydrogen– rapid kinetic properties– equilibrium properties (P,T) consistent with near ambient

conditions.• Two solid state approaches

– hydrogen absorption (bulk hydrogen)– hydrogen adsorption (surface hydrogen)

including cage structures


Alanates


Complex Hydrides


Hydrogen Storage Volume


Hydrogen System Weight


Future


US DOE Strategy


Complex Hydrides


Source: Ali T. Raissi, FSEC

Complex Hydrides


Fuel Tank Problem


Current Status


Compressed Gas System Requirements


Improvements


US DOE Targets


Comparative Volumes and WeightsComparative Volumes and Weightsof a FCEV Hydrogen Storage Systemof a FCEV Hydrogen Storage System

(Capable of 560 km (350 mi) Range (Capable of 560 km (350 mi) Range –– Compact Sedan)Compact Sedan)

0

100

200

300

400

500

600

700

800

ICE Case (Reference)248 bar H2

Compressed Hydrogen (345 bar)

Liquid H2(< 300 mm dia.)

Liquid H2 (>540 mm dia.)

Metal Hydride (Mg)Sodium Borohydride

Lite

rs

kg

Lite rskg

FCEV Storage System


LH2 Tank Configuration

filling port

inner vessel

gaseous hydrogen(+20°C up to +80°C)

liquefied hydrogen253°C)

suspension

safety valve

outer vessel

shut off valve

cooling waterheat exchanger

electrical heater

reversing valve(gaseous / liquid)

liquid extractiongas extraction

filling line

level probe

super insulation


Storage Systems

CompressedGas (5,000 psi)

Cryogenic Liquid H2

Cryo - LiquidCompressed H2

RechargeableMetal Hydride

Carbon Adsorbtion

Chemical Hydride

SystemWeight

SystemVolume

ExtractionComplexity

SystemCost

FuelCost

Dormancy Safety

Good Acceptable Problem

Sustainable Energy Science and Engineering...

Documents

Transcript of Sustainable Energy Science and Engineering...