Electric Power Operations

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ECE 333 Green Electric Energy

• Lecture 10
• Electric Power Operations
• Professor Tom Overbye
• Department of Electrical andComputer Engineering

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Announcements

• Be reading Chapter 4
• First exam is Oct 8 in class (as specified on
  syllabus
• Homework 4 is due now
• Homework 5 is 4.2, 4.4, 4.5, special problems 3
  and 4 it is due on Thursday Oct 1.
• Special Problem 3 As presented in class, explain
  how the area control error is calculated (note
  the definition presented in class is a
  simplification of what occurs in practice).
• Special Problem 4 Briefly discuss the advantages
  and disadvantages of one method presented in
  class for charging for electric power transfers.

3
In the News DOE Secretrary Chu Presentation at
Grid Week, 9/21/09
DOE Secretary Chu Grid Week Presentation, Sept
21, 2009, Slide 11
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In the News DOE Secretrary Chu Presentation at
Grid Week, 9/21/09
Note, in 2007total electricgeneration inthe US
was4,156 billion kWh
DOE Secretary Chu Grid Week Presentation, Sept
21, 2009, Slide 5
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Pricing Electricity

• Cost to supply electricity to bus is called the
  locational marginal price (LMP)
• Presently PJM and MISO post LMPs on the web
• In an ideal electricity market with no
  transmission limitations the LMPs are equal
• Transmission constraints can segment a market,
  resulting in differing LMP
• Determination of LMPs requires the solution on an
  Optimal Power Flow (OPF)

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Three Bus Case LMPs Line Limit NOT Enforced
Gen 2s cost is 12 per MWh
Gen 1s cost is 10 per MWh
Line from Bus 1 to Bus 3 is over-loaded all
buses have same marginal cost
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Three Bus Case LMPS Line Limits Enforced
Line from 1 to 3 is no longer overloaded, but
now the marginal cost of electricity at 3 is 14
/ MWh
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Generation Supply Curve
As the load goes up so does the price
Natural Gas Generation
Base Load Coal and Nuclear Generation
Renewable Sources Such as Wind Have Low Marginal
Cost, but they are Intermittent
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MISO LMPs on Feb 24, 2009 (835am)
Prices were lt -30/MWh in Minnesota (paid to use
electricity)
Available on-line at www.midwestmarket.org
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Frequency Control

• Steady-state operation only occurs when the total
  generation exactly matches the total load plus
  the total losses
• too much generation causes the system frequency
  to increase
• too little generation causes the system frequency
  to decrease (e.g., loss of a generator)
• AGC is used to control system frequency

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April 23, 2002 Frequency Response Following Loss
of 2600 MW
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Distributed Generation (DG)

• Small-scale, up to about 50 MW
• Includes renewable and non-renewable sources
• May be isolated from the grid or grid-connected
• Near the end user

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Integrated Generation, Transmission, Buildings,
Vehicles
Renewables
Grid
kWh
kWh
PHEV
Smart meters
Vehicle-to-Grid
Heat kWh
Combined Heat and Power (CHP)
N. Gas
Source Masters
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Pluggable Hybrid Electric Vehicles (PHEVs) as
Distributed Generation

• Can charge at night when electricity is cheap

Source http//www.popularmechanics.com/automotive
/new_cars/4215489.html

• Can provide services back to the grid

Source www.calcars.org
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DG Technologies

• Microturbines
• Reciprocating Internal Combustion Engines
• Stirling-Cycle Engine
• Concentrating Solar Power (CSP)
• Solar Dish/Sterling
• Parabolic Troughs
• Solar Central Receiver
• Biomass
• Micro-Hydro
• Fuel Cells

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Reasons for Distributed Generation

• Good for remote locations
• Renewable resources
• Reduced emissions
• Can use the waste heat
• Can sell power back to the grid

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Terminology

• Cogeneration and Combined Heat and Power (CHP)
• capturing and using waste heat while generating
  electricity
• When fuel is burned one product is water if
  water vapor exits stack then its energy is lost
  (about 1060 Btu per pound of water vapor)
• Heat of Combustion for fuels
• Higher Heating Value (HHV) gross heat, accounts
  for latent heat in water vapor
• Lower Heating Value (LHV) net heat, assumes
  latent heat in water vapor is not recovered
• Both are used - Conversion factors (LHV/HHV) in
  Table 4.2

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HHV and LHV Efficiency

• Find LHV efficiency or HHV efficiency from the
  heat rate
• Convert to get the other efficiency

Note the LHV is less than the HHV
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Microturbines

• Small gas turbines, 500 W to 100s kW
• Only one moving part
• Combined heat and power
• High overall efficiency

230 kW fuel
120 kW hot water output
80 CHP Efficiency
65 kW electrical output
45 kW waste heat
Capstone 65 kW Microturbine
Source http//www.capstoneturbine.com
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Microturbines

• Incoming air is compressed
• Moves into cool side of recuperator is heated
• Mixes with fuel in combustion chamber
• Expansion of hot gases spins shaft
• Exhaust leaves

Figure 4.1
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Reciprocating Internal Combustion Engines (ICEs)

• Piston-driven
• Make up a large fraction of the DGs and CHP today
• From 0.5 kW to 6.5 MW
• Electrical efficiencies 37-40
• Can run on gasoline, natural gas, kerosene,
  propane, fuel oil, alcohol, and more
• Relatively clean for burning natural gas
• Most are four-stroke engines
• Waste heat for cogeneration

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Four-Stroke Engines

• Intake
• Compression
• Power
• Exhaust

Figure 4.3
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Two-Stroke Engines

• A compression stroke and a power stroke
• Intake and exhaust open at end of power stroke,
  close at start of compression stroke
• Greater power for their size
• Less efficient
• Produce higher emissions

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Spark-Ignition (Otto-cycle)

• Easily ignitable fuels like gasoline and propane
• Air-fuel mixture enters cylinder during intake
• Combustion initiated by externally-timed spark

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Compression-Ignition (Diesel-cycle)

• Diesel or fuel oil
• Fuels not premixed with air
• Fuel injected under high pressure into cylinder
  towards end of compression cycle
• Increase in pressure causes temperature to rise
  until spontaneous combustion occurs, initiates
  power stroke

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Diesel Engines

• More sudden, explosive ignition must be built
  stronger and heavier
• Higher efficiencies
• Require more maintenance
• Higher emissions

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Charged Aspiration

• Increases efficiency of ICEs
• Pressurize air before it enters the cylinder
• Turbocharger or supercharger
• Able to lower combustion temperature and lower
  emissions

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Advanced Reciprocating Engines Systems (ARES)
Project

• US Department of Energy
• Goals
• 50 (LHV) electrical efficiency by 2010
• Available, reliable, and maintainable
• Reduce NOX emissions
• Fuel flexibility
• Lower cost

Check it out online http//www.eere.energy.gov/de
/gas_fired/
Source http//www.ornl.gov/sci/de_materials/docum
ents/posters/ARESOverview.pdf
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Stirling Engines

• An external combustion engine
• Energy is supplied to working fluid from a source
  outside the engine
• Poor-quality steam engines used to explode, and
  Stirling engines operate at low pressures
• Used extensively until early 1900s
• Now can convert concentrated sunlight into
  electricity

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Stirling Engines

• Two pistons in same cylinder- left side hot,
  right side cold
• Regenerator short term energy storage device
  between the pistons
• Working fluid permanently contained in the
  cylinder
• Four states, four transitions

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Stirling Engines State 1

• State 1
• Cool gas
• Max volume
• Min pressure
• 1 to 2
• Cold piston moves left
• Gas compresses

Figure 4.6
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Stirling Engines State 2

• State 2
• Compressed gas rejects heat to cold sink
• Min volume
• 2 to 3
• Both pistons move left
• Gas flows through regenerator warms up

Figure 4.6
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Stirling Engines State 3

• State 3
• Hot gas
• Min volume
• Max pressure
• 3 to 4
• Gas heats
• Hot gas drives hot piston to left in power stroke

Figure 4.6
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Stirling Engines State 4

• State 4
• Hot gas
• Max volume
• 4 to 1
• Both pistons move right
• Gas flows through regenerator cools off
• Back to State 1

Figure 4.6
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Stirling Engines

• Efficiency less than 30
• Less than 1 kW to 25 kW
• Inherently quiet
• Cogeneration possible with cooling water for the
  cold sink

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Concentrating Solar Power Technologies (CSP)

• Basic idea Convert sunlight into thermal energy,
  use that energy to get electricity
• Concentration is needed to get a hot enough
  temperature
• Three successfully demonstrated technologies
• Parabolic Trough
• Solar Central Receiver
• Solar Dish/ Sterling
• This is a different topic than photovoltaic (PV)
  cells which well cover later

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Solar Dish/ Sterling

• Multiple mirrors that approximate a parabolic
  dish
• Receiver absorbs solar energy converts to
  heat
• Heat is delivered to Stirling engine
• Average efficiencies gt20

Source http//www.eere.energy.gov/de/csp.html
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Solar Dish/ Stirling

• 25 kW system in Phoenix, AZ
• Developed by SAIC and STM Corp

Stirling engine, generator, and cooling fan
Sourcehttp//commons.wikimedia.org
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Parabolic Troughs

• Receivers are tubes - Heat collection elements
  (HCE)
• Heat transfer fluid circulates in the tubes
• Delivers collected energy to steam
  turbine/generator
• Parabolic mirrors rotate east to west to track
  the sun

Source http//www.eere.energy.gov/de/csp.html
Source http//www.nrel.gov/csp/troughnet/solar_fi
eld.html
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Parabolic Troughs - SEGS
Source http//www.flagsol.com/SEGS_tech.htm

• Mojave Desert, California
• Aerial view of the five 30MW parabolic trough
  plants
• Solar Electric Generation System (SEGS)

Source http//www.flagsol.com/SEGS_tech.htm
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Solar Central Receiver

• Also called Power Towers
• Heliostats computer controlled mirrors
• Reflect sunlight onto receiver

Source http//www.eere.energy.gov/de/csp.html
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Solar Central Receiver Solar Two

• 10 MW
• Two-tank, molten-salt thermal storage system
• Barstow, CA

Source http//www.trec-uk.org.uk/csp.htm
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Supplementing CSP

• Hybrid Systems
• Conventional generation as a backup
• Thermal Energy Storage
• Effectively makes solar power dispatchable
• Storage is still a largely unsolved issue

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CSP Thermal Energy Storage

• SEGS I (operated 1985-1999)
• two tank energy storage system
• mineral oil heat transfer fluid to store energy
• German Aerospace Center
• High-temperature concrete or ceramics
• Pipes are embedded, transfer energy to media
• Solar Two
• Molten-Salt Heat Transfer Fluid

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CSP Comparisons

• All use mirrored surfaces to concentrate sunlight
  onto a receiver to run a heat engine
• All can be hybridized with auxiliary fuel sources
• Higher temperature -gt higher efficiency

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Biomass

• Use energy stored in plant material
• 14 GW around the world, half in US
• 2/3 of biomass in US is cogeneration
• Little to no fuel cost
• High transportation costs
• Low efficiencies, lt20
• Leads to expensive electricity

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Gas Turbines and Biomass

• Cannot run directly on biomass without causing
  damage
• Gassify the fuel first and clean the gas before
  combustion
• Coal-integrated gasifier/gas turbine (CIG/GT)
  systems
• Biomass-integrated gasifier/gas turbine (BIG/GT)
  systems

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Cofiring

• Burn biomass and coal
• Modified conventional steam-cycle plants
• Allows use of biomass in plants with higher
  efficiencies
• Reduces overall emissions

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Biomass plant in Robbins, IL

• GE is converting the plant to generate power from
  3 wood chips made from scrap lumber
• Photos from PES field trip last year

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Biomass plant in Robbins, IL