Bài giảng Green Energy Course Syllabus - Chapter 1: Introduction to Green Energy Technology - Nguyễn Hữu Phúc

ombined
Heat and
Power (CHP)
Renewables
Grid
Source: Masters
Pluggable Hybrid Electric Vehicles (PHEVs) as 
Distributed Generation
Source: www.calcars.org
• Can provide services back to 
the grid
Source: 
• Can charge at night when electricity is 
cheap
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
Reasons for Distributed Generation
• Good for remote locations
• Renewable resources
• Reduced emissions
• Can use the waste heat
• Can sell power back to the grid
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)
HHV and LHV Efficiency
• Find LHV efficiency or HHV efficiency from the heat 
rate:
• Convert to get the other efficiency:
HHV( )
HHV( )
3412 Btu/kWh (3.16)
Heat Rate (Btu/kWh)LHV LHV
 
HHV LHV
LHV (4.1)
HHV
      
Note the LHV is less than the HHV
Microturbines
• Small gas turbines, 500 W to 100s kW 
• Only one moving part 
• Combined heat and power
• High overall efficiency
Source: 
Capstone 65 kW Microturbine
230 kW fuel
80% CHP
Efficiency
120 kW hot 
water output
65 kW electrical 
output
45 kW waste heat
Microturbines
1. Incoming air is 
compressed
2. Moves into cool side 
of recuperator & is 
heated
3. Mixes with fuel in 
combustion chamber
4. Expansion of hot 
gases spins shaft
5. Exhaust leaves
Figure 4.1
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
Four-Stroke Engines
1. Intake
2. Compression
3. Power
4. Exhaust
Figure 4.3
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
Spark-Ignition (Otto-cycle)
• Easily ignitable fuels like gasoline and propane
• Air-fuel mixture enters cylinder during intake
• Combustion initiated by externally-timed 
spark
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
Diesel Engines
• More sudden, explosive ignition – must be 
built stronger and heavier
• Higher efficiencies
• Require more maintenance
• Higher emissions
Charged Aspiration
• Increases efficiency of ICEs 
• Pressurize air before it enters the cylinder
• Turbocharger or supercharger
• Able to lower combustion temperature and 
lower emissions
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: 
Source: 
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
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
Stirling Engines
• Efficiency ~ less than 30% 
• Less than 1 kW to ~25 kW
• Inherently quiet 
• Cogeneration possible with cooling water for 
the cold sink
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 we’ll 
cover later
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 >20%
Source: 
Solar Dish/ Stirling
• 25 kW system in Phoenix, AZ
• Developed by SAIC and STM Corp
Source:
Stirling engine, 
generator, and cooling 
fan
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: 
Source: 
Parabolic Troughs - SEGS
• Mojave Desert, California
• Aerial view of the five 30MW 
parabolic trough plants
• Solar Electric Generation System 
(SEGS)
Source: 
Source: 
Solar Central Receiver 
• Also called Power Towers
• Heliostats – computer 
controlled mirrors
• Reflect sunlight onto 
receiver
Source: 
Solar Central Receiver – Solar Two
• 10 MW
• Two-tank, molten-
salt thermal storage 
system
• Barstow, CA
Source: 
Supplementing CSP
• Hybrid Systems
– Conventional generation as a backup
• Thermal Energy Storage 
– Effectively makes solar power dispatchable
– Storage is still a largely unsolved issue
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
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 -> higher efficiencyAnnual MeasuredEfficiency
Required 
Acres/MW
“Suns” of 
concentration
Dish Stirling 21% 4 3000
Parabolic 
Troughs
14% 5 100
Solar Central 
Receiver
16% 8 1000
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, <20%
• Leads to expensive electricity
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
Cofiring
• Burn biomass and coal
• Modified conventional steam-cycle plants
• Allows use of biomass in plants with higher 
efficiencies
• Reduces overall emissions
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
Biomass plant in Robbins, IL
Fuel Cells
• Convert chemical energy contained in a fuel directly into 
electrical power
• Skip conversion to mechanical energy, not constrained by 
Carnot limits
Chemical energy
Heat
Mechanical energy
Electrical energy
Chemical energy
Electrical energy
Conventional 
Combustion
Fuel Cells
Fuel Cells
• Up to ~65% efficiencies
• No combustion products (SOX,CO) although 
there may be NOX at high temperatures
• Vibration free, almost silent – can be located 
close to the load
• Waste heat can be used for cogeneration
• Byproduct is water
• Modular in nature
Fuel Cells - History
• Developed more than 150 years ago
• Used in NASA’s Gemini earth-orbiting 
missions, 1960s
For more information on the 
history of fuel cells, see the 
Smithsonian project-
u/fuelcells/
Fuel Cells - History
• Residential use – Plug Power’s 7 kW residential fuel cell power plant
• Use at landfills– generate power from methane
• The list goes on
Fuel Cells- Basic Operation
Protons diffuse though electrolyte so cathode is positive 
with respect to anode 
Anode CathodeElectrolyte
2 2 2H H e
  
2 2
1 2 2
2
O H e H O   
2H 
I
Electrical Load
Catalyst
Fuel Cells- Basic Operation
• Combined anode and cathode reactions:
• This reaction is exothermic- it releases heat
• A single cell only produces ~0.5V under normal operating 
conditions, so multiple cells are stacked to build up the 
voltage
2 2 2H H e
  
2 2
1 2 2
2
O H e H O   
2 2 2
1 (4.20)
2
H O H O 
Pluggable Hybrid Electric Vehicles (PHEVs)
• The real driver for widespread implementation of controllable 
electric load could well be
PHEVs.
• Recharging PHEVs when 
their drives return home 
at 5pm would be a really 
bad idea, so some type of 
load control is a must.
• Quick adoption of PHEVs depends on 
gas prices, but will take many years at least
Smart Grid and the Distribution System
• Distribution system automation has been making steady 
advances for many years, a trend that should accelerate with 
smart grid funding
• Self-healing is often
used to refer to
automatic distribution
system reconfiguration
• Some EMSs already
monitor portions of the
distribution system
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