Midterm Flashcards
How much of the energy in burning coal reaches the consumer as electricity?
33%
Roughly the efficiency
causes: waste heat, transmission, Rankine cycle - thermodynamics, machine losses, generation losses/
Are losses higher in transmission or distribution systems?
Distribution
P_loss=i^2r
the transmission we use very high voltage which means a low current - preventing loss. Distribution lines have to use a lower voltage creating a higher current, thus higher loss.
Which state consumes the most energy?
Texas
What state produces the most coal?
Wyoming
What country produces the most coal?
China
What country generates the most electricity from nuclear power?
United States
What country generates the greatest share of its electricity from wind power
Denmark
Most of the energy we use originally came from?
The sun
- everything comes back to nuclear other than nuclear which relies on gravitational pull
primary energy
gross energy - before transmission into more useful forms like electricity
% of total energy utilized to produce electricity
38.1%
overall efficiency of electric power generation
37%
power units
watts (W) or kilowatts (kW - W/1000) or joules/second or ampere*volt
voltage
electrical potential - the energy (E) required to move a unit charge through an element
Electrical Energy (E)
the power multiplied by the time the power is used - usually measure in kWh.
AC
both current and voltage are sinusoidal waveforms
decarbonize the grid
electricity huge demand for energy, tech for other services.
green house gases
carbon (CO2)
Methane (CH4)
Nitrous oxide (N20)
Fluorinated gas (F-gas)
July 2021
1.67F above 20th-century average - the last 7 July's have been the highest temperatures in history. Sea ice concentration species extension increase temperatures water supply
Top 3 CO2 emitting countires
what share of global co2 do they emit
China, US, EU
what percent of GHG emissions worldwide are from electricity and heat generation
what percent of US CO2 emissions are from the power sector?
global - 25%
US electricity 27%
US generation mix
ng 40% renewables 21% coal 19% nuclear 20% other <1%
US electricity generation
renewable 17% (wind - 7.3%, hygro-6.6%, solar-1.8%, biomass 1.4%, geothermal 0.4%)
nuclear 20%
coal 23%
ng 38%
Electricity flow conversion losses
25.22
if the load is purely resistive
current and voltage are in phase and the product of voltage and current is positive or zero
if load is purely reactive
current and voltage at 90 degrees out of phase and for 2 quarter of each cycle, the product voltage and current is positive for the other 2 quarters
electricity loads can be
resistive (heaters)
inductive (motors)
capacitative (capacitors)
Active Power
The power that is dissipated in the resistance of the load
Reactive Power
Power that is exchanged between reactive components. Capacitors generate reactive power and inductors consume it.
Apparent power
Taken into account when designing and operating power systems, because although the current associated with reactive power does not work at the load, it still must be supplied by the power and source.
Frequency Control
Active Power Balance (System Wide)
Voltage control
reactive power balance (local)
Energy
Integration of power over time - what people want from a power system
Energy Units
Joulse = 1 watt-second (J) kWh = kilowatthour (3,6 x 10^6 J) BTU = 1055 J or 1 MBTU = 0.292 MWh
US annual electric energy consumption is about
4000 TWh
1TWh = 10^12Wh=10^Mwh=10^3 GWh
Power in power systems
kW, MW - installed capacity
Capital investments to build power plants
plan and design
Energy in Power Systems
kWh, MW does the actual work
Recover investments by selling energy
Energy in Power Systems
kWh, MW does the actual work
Recover investments by selling energy
power capacity = peak demand
Conventional Power System
- Generation (source)
- Transmission Substaion
- Transmission System
- Distribution Substation
- Distribution System
- Customer (Loads)
3 synchronous grids
east, west, texas
3 largest power plants in the US
Grand Coulee - Washington - hydro - 6.8MW - 35.26%
Palo Verde - Arizona - nuclear - 3.9mw - 90.05%
West county - Flordia - NG-3.7MW - 60.40
PEAKER PLANT
LOWER CAPACITY FACTOR
NUCLEAR
CONTROL ROD
PLANTS
FISSION ABSORBS NEUTRONS-CONTROL THE REACTION OVER 400 PLANTS OPERATING IN 30 COUNTRIES URANIUM 235 Nuclear waste is a problem
NUCLEAR and Grid Intergration
extremely long start-up times and shut-down times (a week or more)
very little ramping
ultra-high minimum generation levels
large capacity plant - 90% of cap.
Nuclear in the US
61 plant and generate 20% of the nation’s electricity
Coal grid intergration
plants tend to have long start-up and shutdown times
-24 hours or more
slow ramping up and down
long min run times
high minimum generation levels
400 coal plants in US and generate 30% of nations electricity
Natural Gas: Steam
efficiency 32-35%
Nature Gas Turbine
compressor - combustion system - turbine historically peaker plants start up and shut down faster 20-35% conversion effieicnt fuel flexiable
increase ng turbines
utilize waste heat - cogeneration plant (turbine +steam plant) combined cycle plant
run all the time
ng combined cycle plants
increase efficiency to 50-60%
startup time -2-4 hours
mid-range units
gas power plants
open cycle gas turbines
combined cycle gas turbines - most effieicnt
internal combustion engines and steam turbines
high ramp rates
thermal efficiencies 20-60%
gas in US
1793 plants-34% of nations electricity
oil
similar to gas plants
peaker plants
most polluating
diesel in isalnds and remote
conventional systems
nuclear natural gas gas oil coal
what is renewable energy
renewable energy is energy from sources that are naturally occurring replenishing but flow-limited. They are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time.
hydropower turbines
francis - larger
pelton
Hydropower
80-95%
6-10% US generation
Geothermal
the heat from the earth’s core is used to heat water or another working fluid to turn an electricity generator turbine
baseload power - similar to nuclear and coal
Geothermal Power Plants
Dry steam - simple -oldest - most efficient - 150 C or greater
Flash steam - most common - fluid temp 180 C
Binary Cycle - most recent development - temp as low as 57
secondary fluid with a much lower boiling point than water flash vaporizes
Biomass
is organic material that comes from plants and animals, and it is a renewable source of energy.
Contains stored energy from the sun. Plants absorb the sun’s energy in a process called photosynthesis when biomass is burned. the chemical energy in biomass is released as heat. can be burned directly or converted to liquid biofuels or biogas that can be burned as fuel.
Biomass types
wood and wood processing waste:
burned to heat buildings, to produce process heat in industry, and to generate electricity.
agricultural crops and waste materials:
burned as a fuel or converted to liquid biofuels
food, yard, and wood waste in the garbage:
burned to generate electricity in power plants or converted to biogas in landfills
animal manure and human sewage-converted to biogas which can be burned to fuel
Biomass Power Generation
similar to fossil fuel power plants, fuel sources can be stored and used for electricity generation when needed.
Energy density of biomass is limited, mostly needs to be consumed locally. small plants.
usually combined heat and power (CHP) plants
power plant types - steam turbine, gas turbine, internal combustion engine
Offshore wind pros and cons
pros: generally higher capacity factor
less visual impact
often closer to load centers
better correlation with load in some locations
cons: higher installation cost
maintenance issues
Power in the wind equation
P = K0.5densityAV^3
V = wind speed A = Swept Area Density = Air density K = Efficiency constant 0.45 efficiency for modern machines
Wind axis types
the vertical and horizontal axis
Wind Turbine Types
4 Types
GHI
Global Horizontal Irradiance (GHI)
Direct Normal Irradiance
(DNI)
Solar Energy Technologies
Photovoltaic (light -> electricity)
Concentrated Solar Power (heat -> electricity)
Solar Heating (heat -> heat)
Solar Lighting (light -> light)
Energy
ability to do work
toe
ton of oil equivalent
Exergy
energy content of an energy carrier is the max. amount of work that can be extracted from it
heat rate
measures the amount of heat input in BTU’s per hour for each kilowatt-hour of electricity produced
mmBTU/MWh = BTU/kwh
the efficiency is 1/(BTU/KWH))
Manufacturers typically provide the following operational data on PV panels:
the shortcircuit current, the open circuit voltage, the maximum power point current and voltage, the
temperature coefficients of short-circuit current and open circuit voltage, and the efficiency
PV module in Series
In a series PV module, the voltage drop across each individual solar cell adds up to the total module voltage, whereas the current flow through each solar cell is the same and is equal to the total module current:
PV module in Parallel
In a parallel PV module, the voltage drop across the cells remains constant and equal to the total module voltage, whereas the current flowing through each individual solar cell, adds up to the total module current
run of river vs humped hydro
In the case of a hydroelectric dam, the potential energy of water is converted into
mechanical energy during the water fall, which is then converted into electric energy, while
in the case of a run-of-river plant, the kinetic energy of water flow is converted into
mechanical energy, which is then converted into electric energy. The energy that is
converted into mechanical energy is different for these two hydropower plants, and
consequently, the types of hydro turbines employed needs to be adequate and differs for
these two hydropower plant types.
the typical capacity factor for hydro
30-40%
typical efficiency for hydro
80-95% effiency
wind blade materials
strong and light - fiberglass for max amount of energy + hold up in high wind speeds
the vertical and horizontal axis
the horizontal axis has a higher efficiency, reach higher and more consistent wind speeds, typically 3 blades.
vertical axis needs more support
parts of a horizontal axis
Tower, nacelle + gear box, rotor blade.
how does a wind turbine produce eletricity
kinetic energy (wind) is captured by the blades which turn due to their profile (lift) which creates thrust through the sweep of the blades which turns a shaft into kinetic energy to a generator to electricity
Pitch in wind turbine
a wind turbine can move in 2 directions: deals with the blades can also be called feathering, shifts the angle to capture more or less energy. why capture less? to high wind speed
Yaw in wind turbine
a wind turbine can move in 2 directions: the gear box turning generally to capture the most wind. Yaw drive rotates the gearbox.
changes in wind turbine design
higher hub height
larger rotor diameter
higher capacity factor averaging around 40 or above
type 1 and 2 wind turbines
limited operating - they want to operate at a fixed speed. Bad power quality and low capacity factor.
does not provide reactive power to grid pf = 1
1st law of thermo
energy cannot be created or destroyed but can only convert from one form to another
746 W
1 hp
m2 to ft2
m2 * 10.7 = ft2
what are power electronics
semi-conductor devices used for power conversion
dioide
controls the flow of current in one direction
transistor operations
control and switch speeds
4 basic topologies for power electronics
bridge the gap
rectifier = AC to DC Inverter = DC to AC Converter = DC to DC Cycloconverter = AC to AC
is it adequate for an inverter to just create a steady sinusoidal waveform (60hz) in order to interface with the power system?
No, relative phase, between the interfacing device and point of interconnection, dictates power export.
power equiv, sin(phase angle)
3-phase grid-following power electronic converter
changes the ouput for the phase angle difference
adjust the sinusoidal voltage at the connection point
it maps the generation output (solar/wind) to the grid signal
this is historically created by a synchronous convertor.
maintaining ____ is one of the fundamental drivers of power system reaila
system frequency.
frequncy is global-transmisson
voltage 0local - distribtuin
unit commitment
which generation sources will be on
synchronous machine convertors (generators)
large mass electromagetically coupled to AC system - embeds interia in power system
protection system - such as protection against overcurrent
are inverters the only type (4 basic types) of power electronics devices used for integrating renewables?
rectifiers may be used in type 3 and 4 turbines
dc/dc converters -charge controllers (manage output voltage)
resistive loads
PF = 1 requires only real power incandaescent light bulbs kettles irons electric water heater
partially reactive loads
the wave offsets require the supply of reactive power
washing machine
refrigerator
freezers
importance of reactive power
provides voltage control to ensure proper operations.
voltage control is important for preventing damage to generators and motors. reducing line voltage.
Preventing voltage collapse (more load than voltage can support) local
Reactive power sinks
transformers - reactive losses
shunt reactors
overhead AC lines
Load
Reactive power sources
shunt capacitors
underground AC lines (high capacitance)
overhead AC lines (light loading)
capacitance exceeds reactive due to impedajce
vertical integrated
control transmission, generation, distribution
Reactive power sources
shunt capacitors
underground AC lines (high capacitance)
overhead AC lines (light loading)
capacitance exceeds reactive due to impedance
Investor-owned utilities (IOUs)
privately owned and publicly traded stocks. can be vertically integrated or participate in electricity markets
Federally owned utilities
produced power at facilities run by federal entities
Public owned utilities
state and local government agencies which may generate power but are mostly distribution utilities
Rural electric cooperatives
owned by groups of residents
Independent Power Producers and merchant Power pants
privately owned entities that generate power
do not operate transmission or distribution networks
IPPS- have prenegotiated contracts with customers. Specified by a power purchase agreement (PPAs).
Merchants do not have predined customers and sell power in wholesale electricity markets
about 40% of electricity in the US is generated by IPPs and merchant power plants.
RTO
RUNS TRANSMISSION GRID IN AREA MAY OVERLAP WITH ISO WITH OPERATES A MARKET/
SUPPLY MEETS DEMAND
m to ft
m*3.28 = ft
gallon to m3
gall*0.0037=m3
gallon to m3
gall/264=m3
transformer
v_s/v_p = N_s/N_p
cells in series
voltage is summed
current same throughout the module
cells in par
voltdrop is same
current is summed
ISO VS RTO
Both provide transmission and reliabilty however and RTO does not have a market.
BA’s are the smallest.
btu to kwh
btu/3412 = kwh
