Download Lecture #2

ECE 333
Renewable Energy Systems
Lecture 2: Introduction,
Power Grid Components
Prof. Tom Overbye
Dept. of Electrical and Computer Engineering
University of Illinois at Urbana-Champaign
[email protected]
Announcements
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Be reading Chapters 1 and 2 from the book
Homework 1 is 1.1, 1.11, 2.6, 2.8, 2.14. It will be
covered by the first in-class quiz on Thursday Jan
29.
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Energy Economics
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Electric generating technologies involve a tradeoff
between fixed costs (costs to build them) and operating
costs
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Nuclear and solar high fixed costs, but low operating costs
(though cost of solar has decreased substantially recently)
Natural gas/oil have low fixed costs but can have higher
operating costs (dependent upon fuel prices)
Coal, wind, hydro are in between
Also the units capacity factor is important to
determining ultimate cost of electricity
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Ball park Energy Costs
Energy costs depend
upon the capacity factor
for the generator.
The capacity factor is the
ratio of the electricity
actually produced,
divided by its maximum
potential output. It is
usually expressed on an
annual basis.
Source: Steve Chu and Arun Majumdar, “Opportunities and challenges for a
sustainable energy future,” Nature, August 2012, Figure 6
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Natural Gas Prices 1997 to 2015
Marginal cost for natural gas fired electricity price
in $/MWh is about 7-10 times gas price
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Coal Prices have Fallen Substantially
from Four Years Ago
Jan 2015 prices
per ton range
from $11.55 to
$62.15
BTU content per pound varies between about 8000
and 15,000 Btu/lb, giving costs of around $1 to 2/Mbtu
Source: http://www.eia.gov/Ftproot/coal/newsmarket/coalmar110805.pdf
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Power System Structure
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All power systems have three major components:
Load, Generation, and Transmission/Distribution.
Load: Consumes electric power
Generation: Creates electric power.
Transmission/Distribution: Transmits electric
power from generation to load.
A key constraint is since electricity can’t be
effectively stored, at any moment in time the net
generation must equal the net load plus losses
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Electric Power Systems
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Electric utility: can range from quite small, such as
an island, to one covering half the continent
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there are four major interconnected ac power systems in
North American, each operating at 60 Hz
Smaller systems: microgrids, stand-alone, backup
systems
Transportation
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Airplanes and Spaceships: reduction in weight is primary
consideration; frequency is 400 Hz.
Ships and submarines
Automobiles: dc with 12 volts standard
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Large-Scale Power Grid Overview
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Notation and Voltages
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The IEEE standard is to write ac and dc in smaller case,
but it is often written in upper case as AC and DC.
North American grid is 60 Hz (ac), whereas most of the
rest of the world is 50 Hz.
In the US the standard household voltage is 120/240,
+/- 5%. Edison actually started at 110V dc. Other
countries have other standards, with the European Union
recently standardizing at 230V. Japan’s voltage is just
100V
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A higher standard voltage allows for more power, but is more
of a safety hazard
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Loads
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Can range in size from less than one watt to 10’s of
MW
Loads are usually aggregated for system analysis
The aggregate load changes with time, with strong
daily, weekly and seasonal cycles
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Load variation is very location dependent
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Example: Daily Variation for CA
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Example: Weekly Variation
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8273
7756
7239
6722
6205
5688
5171
4654
4137
3620
3103
2586
2069
1552
1035
518
1
MW Load
Example: Annual System Load
25000
20000
15000
10000
5000
0
Hour of Year
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Load Duration Curve
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A very common way of representing the annual load is
to sort the one hour values, from highest to lowest. This
representation is known as a “load duration curve.”
6000
DEMAND (MW)
5000
4000
3000
2000
1000
0
0
1000
HRS
7000
8760
Load duration curve tells how much generation is needed
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GENERATION
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Large plants predominate, with sizes up to about 1500
MW with wind a rapidly growing source.
Coal is still the most common source but with a value
falling from 56% a few years ago to 39% now.
Natural gas has rapidly grown due to low costs, now
making 27% of total. Nuclear (20%), hydro (6%),
wind (4.3%), wood (1.0%), solar (0.4%, high growth)
New construction is mostly natural gas and wind with
economics highly dependent upon the gas price
Generated at about 20 kV for large plants, around 600
V for many wind turbines; solar PV is dc.
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US Generator Capacity Additions
Total US Generation Capacity is about 1000 GW
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Basic Steam Power Plant
Rankine Cycle: Working fluid (water) changes
between gas and liquid
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Carnot Efficiency of Heat Engines
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Heat engines use differences in temperature to convert
part of the heat from a high temperature source, QH,
into work, W, with output heat QC
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Examples are fossil fuel generators, nuclear generators,
concentrated solar generators and geothermal generator
Thermal Efficiency =  =
Net work output W

Total heat input QH
QH  W  QC
Carnot Maximum Efficiency = 1 -
TC
TH
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Modern Coal Power Plant
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Basic Gas Turbine
Brayton Cycle: Working fluid is
always a gas
Most common fuel is natural gas
Maximum Efficiency
550  273
 1
 42%
1150  273
Typical efficiency is around 30 to 35%
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Gas Turbine
Source: Masters
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Combined Heat and Power
Overall Thermal Efficiency = 33% (Electricity) + 53% (Heat) = 86%
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Combined Cycle Power Plants
Efficiencies of up to 60% can be achieved, with even higher
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values when the steam is used for heating
Determining operating costs
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In determining whether to build a plant, both the fixed
costs and the operating (variable) costs need to be
considered.
Once a plant is build, then the decision of whether or not
to operate the plant depends only upon the variable costs
Variable costs are often broken down into the fuel costs
and the O&M costs (operations and maintenance)
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Heat Rate
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Fuel costs are usually specified as a fuel cost, in
$/Mbtu, times the heat rate, in MBtu/MWh
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Heat rate = 3.412 MBtu/MWh/efficiency
Example, a 33% efficient plant has a heat rate of 10.24
Mbtu/MWh
About 1055 Joules = 1 Btu
3600 kJ in a kWh
The heat rate is an average value that can change as
the output of a power plant varies.
Do Example 3.5, material balance
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Fixed Charge Rate (FCR)
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The capital costs for a power plant can be annualized by
multiplying the total amount by a value known as the
fixed charge rate (FCR)
The FCR accounts for fixed costs such as interest on
loans, returns to investors, fixed operation and
maintenance costs, and taxes.
The FCR varies with interest rates, and is now typically
below 10%
For comparison this value is often expressed as
$/yr-kW
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Annualized Operating Costs
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The operating costs can also be annualized by
including the number of hours a plant is actually
operated
Assuming full output the value is
Variable ($/yr-kW) =
[Fuel($/Btu) * Heat rate (Btu/kWh) +
O&M($/Kwh)]*(operating hours/hours in year)
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Coal Plant Example
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Assume capital costs of $4 billion for a 1600 MW coal
plant with a FCR of 10% and operation time of 8000
hours per year. Assume a heat rate of 10 Mbtu/MWh,
fuel costs of 1.5 $/Mbtu, and variable O&M of
$4.3/MWh. What is annualized cost per kWh?
Fixed Cost($/kW) = $4 billion/1.6 million kW=2500 $/kW
Annualized capital cost = $250/kW-yr
Annualized operating cost = (1.5*10+4.3)*8000/1000
= $154.4/kW-yr
Cost = $(250 + 154.4)/kW-yr/(8000h/yr) = $0.051/kWh
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Capacity Factor (CF)
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The term capacity factor (CF) is used to provide a
measure of how much energy an plant actually produces
compared to the amount assuming it ran at rated
capacity for the entire year
CF = Actual yearly energy output/(Rated Power * 8760)
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The CF varies widely between generation technologies,
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Generator Capacity Factors
The capacity factor for solar is usually less than 25%
(sometimes substantially less), while for wind it is usually
between 20 to 40%). A lower capacity factor means a
higher cost per kWh
Source: EIA Electric Power Annual, 2007
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In the News
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UI is building a new "solar farm" on 21 acres just south
of Windsor and west of First Street
Farm has a 5.9 MW peak capacity, and is estimated to
produce 7860 MWh per year
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This gives it a capacity factor of 7860/(5.9*8760) = 15.2%
Will supply about 2% of the campus electric load
Project will be built and operated by Phoenix Solar for
ten years, with UI buying all the output for about $1.5
million per year
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Energy cost is $1.5million/7860MWh = $0.19/kWh
But after ten years UI takes ownership with no additional cost
Source: News-Gazette, January 21, 2015
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