All Sections (Spring 2018)

Energy Systems Research Laboratory, FIU

Renewable Energy Utilization

Professor Osama A. Mohammed

Department of Electrical and Computer Engineering

EEL5285 & EEL 4930All Sections (Spring 2018)

Professor O. A. Mohammed, EEL5285 Lecture Notes, Spring 2018


What is Covered

Part I: Renewable Energy Systems

• Introduction

• Electric Systems in Energy Context

• Basic Review of Electric Quantifies and Impact of Power Conditioning

• Energy Efficiency and operational issues

• Energy Generation and operation and control

• Alternate and Renewable Energy Sources and its Economics– Alternate and Renewable Energy Sources

o Wind Energy

o Distributed generation technologies

o Hydro Power

o Wave/ Tidal Power

o Cooling and Heat Pumps

o The Solar Resource

Part II: Renewable Energy Utilization

• Renewable Energy Utilization

• Energy Storage including Electric/Pluggable Hybrid Cars

• Smart Grid Integration Issues



Background on the Electric Utility

Industry

• First real practical uses of electricity began with the

telegraph (around the civil war) and then arc lighting in the

1870’s (Broadway, the “Great White Way”).

• Central stations for lighting began with Edison in 1882,

using a dc system (safety was key), but transitioned to ac

within several years. Chicago World’s fair in 1893 was key

demonstration of electricity

• High voltage ac started being used in the 1890’s with the

Niagara power plant transferring electricity to Buffalo; also

30kV line in Germany

• Frequency standardized in the 1930’s



Regulation and Large Utilities

• Electric usage spread rapidly, particularly in urban areas. Samuel

Insull (originally Edison’s secretary, but later from Chicago)

played a major role in the development of large electric utilities

and their holding companies

– Insull was also instrumental in start of state regulation in 1890’s

• Public Utilities Holding Company Act (PUHCA) of 1935

essentially broke up inter-state holding companies

– This gave rise to electric utilities that only operated in one state

– PUHCA was repealed in 2005

• For most of the last century electric utilities operated as vertical

monopolies



Vertical Monopolies

• Within a particular geographic market, the

electric utility had an exclusive franchise

Generation

Transmission

Distribution

Customer Service

In return for this exclusive

franchise, the utility had the

obligation to serve all

existing and future customers

at rates determined jointly

by utility and regulators

It was a “cost plus” business



Vertical Monopolies

• Within its service territory each utility was the only

game in town

• Neighboring utilities functioned more as colleagues

than competitors

• Utilities gradually interconnected their systems so

by 1970 transmission lines crisscrossed North

America, with voltages up to 765 kV

• Economies of scale keep resulted in decreasing

rates, so most every one was happy



History, cont’d -- 1970’s

• 1970’s brought inflation, increased fossil-fuel

prices, calls for conservation and growing

environmental concerns

• Increasing rates replaced decreasing ones

• As a result, U.S. Congress passed Public Utilities

Regulator Policies Act (PURPA) in 1978, which

mandated utilities must purchase power from

independent generators located in their service

territory (modified 2005)

• PURPA introduced some competition, but its

implementation varied greatly by state



Power System Structure

• 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



LOADS

• 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

– Load variation is very location dependent



Loads- Household Consumption

Source: EIA 2008

Annual Energy

Review



Example: Daily Variation for CA



Example: Weekly Variation



GENERATION

• Large plants predominate, with sizes up to

about 1500 MW.

• Coal is most common source (56%), followed

by nuclear (21%), hydro (10%) and gas

(10%).

• New construction is mostly natural gas, with

economics highly dependent upon the gas

price

• Generated at about 20 kV for large plants



Basic Gas Turbine Efficiency

Brayton Cycle: Working fluid is

always a gas

Most common fuel is natural gas

Maximum Efficiency

550 2731 42%

1150 273

Typical efficiency is around 30 to 35%



Gas Turbine

Source: Masters



Combined Heat and Power

Overall Thermal Efficiency = 33% (Electricity) + 53% (Heat) = 86%



Combined Cycle Power Plants

Efficiencies of up to 60% can be achieved, with even higher values when the steam is used for heating



Determining operating costs

• 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)

• Fuel costs are usually specified as a fuel cost, in $/Mbtu,

times the heat rate, in MBtu/MWh

– Heat rate = 3.412 MBtu/MWh/efficiency

– Example, a 33% efficient plant has a heat rate of 10.24



Heat Rate

• Fuel costs are usually specified as a fuel cost, in

$/Mbtu, times the heat rate, in MBtu/MWh

– Heat rate = 3.412 MBtu/MWh/efficiency

(1 KWh=3.412KBtu)

– 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 balanceProfessor O. A. Mohammed, EEL5285 Lecture Notes, Spring 2018


Historical and Forecasted Heat Rates

http://www.npc.org/Study_Topic_Papers/4-DTG-ElectricEfficiency.pdf



Fixed Charge Rate (FCR)

• 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 below

10%.

• For comparison this value is often expressed as

$/yr-kW



Annualized Operating Costs

• 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)



Coal Plant Example

• 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



Capacity Factor (CF)

• The term capacity factor (CF) is used to provide a

measure of how much energy a 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)

• The CF varies widely between generation technologies,



Generator Capacity Factors

Source: EIA Electric Power Annual, 2007

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


Energy Systems Research Laboratory, FIUProfessor O. A. Mohammed, EEL5285 Lecture Notes, Spring 2018

Alternate and Renewable Energy Sources


Wind Power Systems



Historical Development of Wind Power

• In the US - first wind-electric systems built in the late

1890’s

• By 1930s and 1940s, hundreds of thousands were in

use in rural areas not yet served by the grid

• Interest in wind power declined as the utility grid

expanded and as reliable, inexpensive electricity could

be purchased

• Oil crisis in 1970s created a renewed interest in wind

until US government stopped giving tax credits

• Renewed interest again since the 1990s



US Wind Resources

http://www.windpower.org/en/pictures/lacour.htmhttp://www.windpoweringamerica.gov/pdfs/wind_maps/us_windmap.pdf

50 meters



Cape Wind

off-shore wind farm

• For about 10 years Cape Wind Associates has been attempting to

build an off-shore 170 MW wind farm in Nantucket Sound,

Massachusetts. Because the closest turbine would be more than

three miles from shore (4.8 miles) it is subject to federal, as

opposed to state, jurisdiction.

– Federal approval was given on May 17, 2010

– Cape Wind would be the first US off-shore wind farm

• There has been significant opposition to this project, mostly out

of concern that the wind farm would ruin the views from private

property, decreasing property values.



Massachusetts Wind Resources


http://upload.wikimedia.org/wikipedia/commons/c/c1/Massachusetts_wind_resource_map_50m_800.jpg


Cape Wind Simulated View,

Nantucket Sound, 6.5 miles Distant

Source: www.capewind.org



Types of Wind Turbines

• “Windmill”- used to grind grain into flour

• Many different names - “wind-driven generator”,

“wind generator”, “wind turbine”, “wind-turbine

generator (WTG)”, “wind energy conversion system

(WECS)”

• Can have be horizontal axis wind turbines (HAWT)

or vertical axis wind turbines (VAWT)

• Groups of wind turbines are located in what is

called either a “wind farm” or a “wind park”



Vertical Axis Wind Turbines

• Darrieus rotor - the only vertical axis

machine with any commercial success

• Wind hitting the vertical blades, called

aerofoils, generates lift to create rotation

http://www.reuk.co.uk/Darrieus-Wind-Turbines.htm

• No yaw (rotation about vertical axis)

control needed to keep them facing into

the wind

• Heavy machinery in the nacelle is located

on the ground

• Blades are closer to ground where

windspeeds are lower

http://www.absoluteastronomy.com/topics/Darrieus_wind_turbineProfessor O. A. Mohammed, EEL5285 Lecture Notes, Spring 2018


Horizontal Axis Wind Turbines

• “Downwind” HAWT – a turbine

with the blades behind (downwind

from) the tower

• No yaw control needed- they

naturally orient themselves in line

with the wind

• Shadowing effect – when a blade

swings behind the tower, the wind it

encounters is briefly reduced and

the blade flexes



Horizontal Axis Wind Turbines

• “Upwind” HAWT – blades are in

front of (upwind of) the tower

• Most modern wind turbines are

this type

• Blades are “upwind” of the tower

• Require somewhat complex yaw

control to keep them facing into

the wind

• Operate more smoothly and

deliver more power



Number of Rotating Blades

• Windmills have multiple blades

– need to provide high starting torque to overcome weight

of the pumping rod

– must be able to operate at low wind speeds to provide

nearly continuous water pumping

– a larger area of the rotor faces the wind

• Turbines with many blades operate at much lower rotational

speeds - as the speed increases, the turbulence caused by one

blade impacts the other blades

• Most modern wind turbines have two or three blades



Power in the Wind

• Consider the kinetic energy of a “packet” of air with

mass m moving at velocity v

• Divide by time and get power

• The mass flow rate is (r is air density)

21KE (6.1)

2mv

21 passing though APower through area A (6.2)

2

mv

t

passing though A= = A (6.3)

mm v

t



Power in the Wind

Combining (6.2) and (6.3),

21Power through area A A

2v v

31P A (6.4)

2W v Power in the wind

PW (Watts) = power in the wind

ρ (kg/m3)= air density (1.225kg/m3 at 15˚C and 1 atm)

A (m2)= the cross-sectional area that wind passes through

v (m/s)= windspeed normal to A (1 m/s = 2.237 mph)



Power in the Wind (for reference solar is

about 600 w/m2 in summer)

• Power increases like the

cube of wind speed

• Doubling the wind

speed increases the

power by eight

• Energy in 1 hour of 20

mph winds is the same

as energy in 8 hours of

10 mph winds

• Nonlinear, so we cannot

use average wind speedFigure 6.5



Power in the Wind

• Power in the wind is also proportional to A

• For a conventional HAWT, A = (π/4)D2, so wind

power is proportional to the blade diameter squared

• Cost is roughly proportional to blade diameter

• This explains why larger wind turbines are more

cost effective

31P A (6.4)

2W v



Nikola Tesla: Inventor of Induction

Motor (and many other things)

• Nikola Tesla (1856 to 1943) is one of the key inventors associated with the development of today’s three phase ac system. His contributions include the induction motor and polyphase ac systems.– Unit of flux density is named after him

• Tesla conceived of the induction

motor while walking through a park in

Budapest in 1882.

• He emigrated to the US in 1884


http://upload.wikimedia.org/wikipedia/commons/5/56/Tesla3.jpg


World’s Largest Offshore Wind Farm Opens

• “Thanet” located off British coast in English Channel

• 100 Vestas V90 turbines, 300 MW capacity

http://edition.cnn.com/2010/WORLD/europe/09/23/uk.largest.wind.farm/?hpt=Sbinhttp://www.vattenfall.co.uk/en/thanet-offshore-wind-farm.htm

Turbines

are

located

in water

depth

of

20-25m.

Rows

are

800m

apart; 500m

between

turbines



Off-shore Wind

• Offshore wind turbines currently need to be in

relatively shallow water, so maximum distance from

shore depends on the seabed

• Capacity

factors tend

to increase

as turbines

move further

off-shore

Image Source: National Renewable Energy Laboratory



Maximum Rotor Efficiency

Figure 6.10

Rotor efficiency CP vs.

wind speed ratio λ



Tip-Speed Ratio (TSR)

• Efficiency is a function of how fast the rotor turns

• Tip-Speed Ratio (TSR) is the speed of the outer tip

of the blade divided by wind speed

Rotor tip speed rpm DTip-Speed-Ratio (TSR) = (6.27)

Wind speed 60v

• D = rotor diameter (m)

• v = upwind undisturbed windspeed (m/s)

• rpm = rotor speed, (revolutions/min)

• One meter per second = 2.24 miles per hour



Tip-Speed Ratio (TSR)

• TSR for various

rotor types

• Rotors with fewer

blades reach their

maximum

efficiency at higher

tip-speed ratios

Figure 6.11



Synchronous Machines

• Spin at a rotational speed determined by the number

of poles and by the frequency

• The magnetic field is created on their rotors

• Create the magnetic field by running DC through

windings around the core

• A gear box is needed between the blades and the

generator

• 2 complications – need to provide DC, need to have

slip rings on the rotor shaft and brushes



Asynchronous Induction Machines

• Do not turn at a fixed speed

• Acts as a motor during start up as well as a

generator

• Do not require exciter, brushes, and slip rings

• The magnetic field is created on the stator

instead of the rotor

• Less expensive, require less maintenance

• Most wind turbines are induction machines



The Induction Machine as a Generator

• Slip is negative because the rotor spins faster

than synchronous speed

• Slip is normally less than 1% for grid-

connected generator

• Typical rotor speed

(1 ) [1 ( 0.01)] 3600 3636 rpmR SN s N



Speed Control

• Necessary to be able to shed wind in high-speed

winds

• Rotor efficiency changes for different Tip-Speed

Ratios (TSR), and TSR is a function of windspeed

• To maintain a constant TSR, blade speed should

change as windspeed changes

• A challenge is to design machines that can

accommodate variable rotor speed and fixed

generator speed



Blade Efficiency vs. Windspeed

Figure 6.19

At lower windspeeds, the best efficiency is achieved at a lower rotational speed



Power Delivered vs. Windspeed

Figure 6.20

Impact of rotational speed adjustment on delivered power, assuming gear and generator

efficiency is 70%



Variable Slip Example: Vestas

V80, 1.8 MW

• The Vestas V80, 1.8 MW turbine is

an example in which an induction

generator is operated with variable

rotor resistance (opti-slip).

• Adjusting the rotor resistance

changes the torque-speed curve

• Operates between 9 and 19 rpm

Source: Vestas V80 brochure



Vestas

V80 1.8 MW



Doubly-Fed Induction Generators

• Another common approach is to use what is

called a doubly-fed induction generator in which

there is an electrical connection between the

rotor and supply electrical system using an ac-ac

converter

• This allows operation over a wide-range of

speed, for example 30% with the GE 1.5 MW

and 3.6 MW machines



GE 1.5 MW and 3.6 MW

DFIG Examples

Source: GE Brochure/manual

GE 1.5 MW turbines are the

best selling wind turbines

in the US with 43% market share in 2008



Indirect Grid Connection Systems

• Wind turbine is allowed to spin at any speed

• Variable frequency AC from the generator goes

through a rectifier (AC-DC) and an inverter (DC-

AC) to 60 Hz for grid-connection

• Good for handling rapidly changing wind speeds

Figure 6.21



Example: GE 2.5 MW Turbines


Documents

All Sections (Spring 2018)