INTRODUCTION TO ENERGY SCIENCE

Wind for Schools Webinar: August 12th, 2010

Ability to do work or cause changeProduces WarmthProduces LightProduces SoundProduces MovementProduces GrowthPowers Technology

What is energy?

Courtesy of NEED

POTENTIAL

KINETICStored

energy or energy of position Gravitational,

Stored Mechanical,

Nuclear, Chemical

Energy of motion

Motion, Electrical, Sound, Radiant,

Thermal

Classes of Energy

Courtesy of NEED

Gravitational Energy – energy an object or substance has because of its positionAnything “up high”

Potential Energy

Stored Mechanical Energy – stored in an object by the application of forceMust push or pull on an object

Potential Energy

Nuclear Energy – energy stored in the nucleus of an atomHolds the atom together

Nuclear Energy – energy stored in the nucleus of an atomHolds the atom together

Potential Energy

Chemical Energy – energy stored in the bonds between atoms

Holds molecules together

Potential Energy

Mechanical (Motion) Energy – movement of objects or substances from one place to another

Kinetic Energy

 

Electrical Energy – movement of electrons

NOT AN ELECTRON PARADE!

Kinetic Energy

Sound Energy – movement of energy through substances in the form of longitudinal/compression waves

Kinetic Energy

Radiant Energy – electromagnetic energy that travels in transverse waves

Kinetic Energy

Kinetic Energy

Thermal (Heat) Energy – internal energy of a substance due to the vibration of atoms and molecules making up the substance

1 – Energy can not be created nor destroyed, only changed.

Law of Conservation of EnergyFirst Law of Thermodynamics

2 – Energy will always transfer from high to low.3 – No energy transfer is 100% efficient.

Energy Transfers

Conservation of Energy

Units of Energy

Energy requires a force. Each form of energy has it’s own force: gravity, strong & weak nuclear forces, electrical, and kinetic forces.

Kinetic Force = Mass x Acceleration Unit of force = 1 Newton = 1 Kilogram x 1 m/s

Energy is a measurement of work accomplished by a force

Energy = Force x Distance 1 Joule = 1 Newton x 1 Meter

Energy and Power

Energy is a quantity, like distance. 1 kilowatt-hour = 1000 Watts x 1 hour 1 kilowatt-hour = 3.6 x 106 Joules

Power is a rate, like speed, it is the rate that energy is converted from one form to another. 1 Watt = 1 Joule / Second

The Difference Between Energy and Power

  

EnergyEnergy PowerPower  

QuantityQuantity RateRate

UnitUnit kWhkWh kW, MW*kW, MW*

Water analogyWater analogy GallonsGallons Gal / MinGal / Min

Car analogy-Car analogy- - How far?- Gallon of gas- How far?- Gallon of gas

Engine HPEngine HP

Cost exampleCost example 12 ¢/kWh12 ¢/kWh $1,500,000/MW$1,500,000/MW

GridGrid Consumption & productionConsumption & production Installed capacityInstalled capacity

Laws of Thermodynamics

First Law: In any transformation of energy from one form to another, the total quantity of energy remains unchanged. “Energy is neither created nor destroyed, it only changes forms.”

Second Law: In all energy changes, the potential energy of the final state will be less than that of the initial state – (useful energy is always lost.) “Lost” energy is usually energy that has been

converted to heat, but it could be noise (kinetic energy of air), or other forms of wasted energy.

Efficiency

The ratio of the amount of useable energy obtained to the amount of energy input is the efficiency of a process. This is usually expressed as a percent and

it is always less than 100%.

Energy definitions

Primary Energy – amount of energy contained in the initial source of energy

Delivered Energy – amount of useable energy delivered to the customer

Useful Energy – amount of energy attributed to the amount of work accomplished

What is Electricity?

Electricity is energy transported by the motion of electrons

Electricity is energy transported by the motion of electrons

**We do not make electricity, we CONVERT other energy sources into electrical energy**

**We do not make electricity, we CONVERT other energy sources into electrical energy**

Conversion is the name of the gameConversion is the name of the game

Energy Conversion Options for ElectricityNon-Thermal Paths

• Source to Electrical Source ConverterSun Photovoltaic (photon to electron)Chemical Fuel Cell 

• Source to Potential/Kinetic to Mechanical to Electrical Source Converter Kinetic to Mechanical Mech to ElectricalDam Penstocks Turbine (water) GeneratorTides Machine Turbine (air or water) GeneratorWind N/A Turbine (air) Generator

Energy Conversion Options for ElectricityThermal Paths

• Heat to Mechanical to Electrical  Source Heat to Mechanical Mech to ElectricalGeothermal Turbine (vapor) GeneratorOTEC Turbine (vapor) Generator 

• Stored Energy to Heat to Mechanical to Electrical  Source Reactor Heat to Mechanical Mech to ElectricalFuel Combustor Turbine (gas or vapor) GeneratorU, Pu Reactor Turbine (gas or vapor) GeneratorSun Collector* Turbine (gas or vapor) GeneratorH, H2, H3Reactor Turbine (gas or vapor) Generator

 * More a modifier or concentrator than a reactor

Faraday Effect

• Faraday Effect

• Basic Concepts• Voltage – V – Potential to Move Charge (volts)• Current – I – Charge Movement (amperes or amps)• Resistance – R – V = IxR (R in =ohms)• Power – P = IxV = I2xR (watts)

Electric Motor

MElectricalEnergy

MechanicalEnergy

DC MotorDC Motor

Model Electric Motor

Beakman MotorBeakman Motor

What do you need?What do you need?1. Electric Energy2. Coil3. Magnetic Field

1. Electric Energy2. Coil3. Magnetic Field

Electric Generator

GMechanicalEnergy

ElectricalEnergy

Stationary magnets - rotating magnets - electromagnetsStationary magnets - rotating magnets - electromagnets

AC/DC (not the band)

Alternating Current Large-scale

generators produce AC

Follows sine wave with n cycles per second

1, 2, 3-phase? US:120 V,60 Hz Europe: 240 V,50Hz Transforming ability

Direct Current Batteries,

Photovoltaics, fuel cells, small DC generators

Charge in ONE direction

Negative, Positive terminals

Easy conversion AC to DC, not DC to AC

Generator Phases 1 Phase – 2 Phase – 3 Phase…Smooth Power

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035150

100

50

0

50

100

150

200

250220

110

V t( )

V 1 t( )

V 2 t( )

V 3 t( )

0.0330 t

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035150

100

50

0

50

100

150110

110

V t( )

V 1 t( )

V 2 t( )

V 3 t( )

0.0330 t

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035150

100

50

0

50

100

150

200155.563

110

V t( )

V 1 t( )

V 2 t( )

V 3 t( )

0.0330 t

Polyphase Systems 3 phases for smoother torque delivery

Force Driving Motor (Red)

Single Phase Two Phase Three Phase

WHERE DO WE GET ENERGY FROM AND WHAT DO WE USE IT FOR?

Energy Sources

Non Renewable Fossil Fuels Natural Gas Shale Oil Tar Sands Nuclear Fusion Fuel

Renewable Solar Geothermal Tidal

Solar

Direct Sunlight Wind Hydroelectric Ocean Currents Ocean Thermal Gradients Biomass

World Primary Energy Consumption

Energy Consumption Versus GDP

2008 US Energy Flow

US Energy Consumption

Alaska Energy Consumption

Alaska Energy Consumption

The United States uses more energy per capita than any other country in the world, and Alaska as a state has the highest energy per capita energy use in the narration at 1112 MMBtu per person. This is three times higher than the national average of 333 MMBtu.

This is due to our cold harsh winters, high level of air travel

43% of total energy is from jet fuel most of which is for international flights.

Alaska Energy Consumption

Climate Change Logic

1. The Burning of fossil fuels cause carbon dioxide concentrations to rise.

2. Carbon dioxide is a greenhouse gas.3. Increasing the greenhouse effect

increases average global temperatures (among other impacts)

“Does Skeptic mean a person who has not looked at the data?”

1000 years of CO2 Concentration

1000 Years of Temperature Changes

Every Year an Average Coal Plant Releases

3,700,000 tons of CO2 10,000 tons of SO2. 500 tons of particulates 10,200 tons NOx 720 tons of CO 220 tons of volatile organic

compounds (VOC) 170 pounds of mercury 225 pounds of arsenic 114 pounds of lead

And there are over 600 of them in the US.Source: Union of Concerned Scientists: www.ucsusa.org

Types of Pollutants

CO2 – Global Warming CO – Health problem PM –Respiratory and

heart disease, haze SOx – Acid Rain,

respiratory illness, haze

NOx – Ozone formation, acid rain, smog, nutrient loading, global warming

Mercury – Neurotoxin

Lead – Neurotoxin Arsenic - Poison VOCs – Numerous

health problems Ozone – Health

problems, damage to flora & fauna

Hundreds of other toxic chemicals

Power in the Wind

Power = Work / t

= Kinetic Energy / t

= ½mV2 / t= ½(ρAd)V2/t= ½ρAV2(d/t)= ½ρAV3

d/t = V

Power in the Wind = ½ρAV3

A couple things to remember…

Swept Area – A = πR2 (m2) Area of the circle swept by the rotor.

ρ = air density – in Colorado its about 1-kg/m3

Power in the Wind = ½ρAV3

R

Example – Calculating Power in the Wind

V = 5 meters (m) per second (s) m/sρ = 1.0 kg/m3

R = .2 m >>>> A = .125 m2

Power in the Wind = ½ρAV3

= (.5)(1.0)(.125)(5)3

= 7.85 WattsUnits = (kg/m3)x (m2)x (m3/s3)

= (kg-m)/s2 x m/s= N-m/s = Watt

Power in the Wind = ½ρAV3

(kg-m)/s2 = Newton

Wind Turbine Power

Power from a Wind Turbine Rotor = Cp½ρAV3

Cp is called the power coefficient. Cp is the percentage of power in the wind that

is converted into mechanical energy.

What is the maximum amount of energy that can be extracted from the wind?

Betz Limit when a = 1/3 Vax = 2/3V1

V2 = V1/3

Actuator Disk Model of a Wind Turbine

V1

(1) (2)

Where

Free stream velocity, V1

Wake velocity, V2=(1 2a)

Velocity at rotor, Vax = V1(1-a)

Induction factor, a

5926.27

16C max,p

Rotor Wake

Rotor Disc

Tip Speed Ratio

Capacity Factor

Reality Check

What’s the most power the .6 ft turbine in the example can produce in a 5 m/s wind?

7.85 Watts x .5926 (Betz Limit) = 4.65 Watts

Maximum Possible Power Coefficient0.60

0.50

0.40

0.30

0.20

0.10

0.00

Cp

109876543210Tip Speed Ratio

Betz - Without Wake Rotation With Wake Rotation

Tip-Speed Ratio

Tip-speed ratio is the ratio of the speed of the rotating blade tip to the speed of the free stream wind.

ΩRV

=

ΩR

R

Where,

Ω = rotational speed in radians /sec

R = Rotor Radius

V = Free Stream Velocity

Blade Planform Types Which should work the best??

Rectangular Reverse Linear Taper

Linear Taper

Parabolic Taper

Airfoil Nomenclaturewind turbines use the same aerodynamic principals as aircraft

α

VR = Relative Wind

α = angle of attack = angle between the chord line and the direction of the relative wind, VR .

VR = wind speed seen by the airfoil – vector sum of V (free stream wind) and ΩR (tip speed).

V

ΩR Ωr

V

Airfoil Behavior

The Lift Force is perpendicular to the direction of motion. We want to make this force BIG.

The Drag Force is parallel to the direction of motion. We want to make this force small.

α = low

α = medium<10 degrees

α = HighStall!!

Airfoil in stall (with flow separation)

• Stall arises due to separation of flow from airfoil• Stall results in decreasing lift coefficient with

increasing angle of attack• Stall behavior complicated due to blade rotation

Gradual curves Sharp trailing edge Round leading edge Low thickness to

chord ratio Smooth surfaces

Making Good Airfoils

Good

Not so good

Energy Production Terms• Power in the Wind = 1/2AV3

• Betz Limit - 59% Max

• Power Coefficient - Cp

• Rated Power – Maximum power generator can produce.

• Capacity factor– Actual energy/maximum

energy

• Cut-in wind speed where energy production begins

• Cut-out wind speed where energy production ends.

Typical Power Curve

Performance Over Range of Tip Speed Ratios

• Power Coefficient Varies with Tip Speed Ratio• Characterized by Cp vs Tip Speed Ratio Curve

0.4

0.3

0.2

0.1

0.0

Cp

121086420Tip Speed Ratio

Considerations for Optimum Blade

• Optimum blade will have low solidity (10%) and tip speed

ratio, λ, about 5-7. (match speed to generator)

• High λ means lower pitch angle (blade tip is flat to the

plane of rotation).

• Lower λ means higher pitch angle (feathered).

• Pitch angles should be equal for all blades.

• Optimum blade has large chord and large twist near hub

and gets thinner near the tip.

• Optimum blade is only "optimum" for one tip speed ratio.

• The optimum blade will have smooth streamlined airfoils.

Number of Blades – One Rotor must move more

rapidly to capture same amount of wind Gearbox ratio reduced Added weight of

counterbalance negates some benefits of lighter design

Higher speed means more noise, visual, and wildlife impacts

Blades easier to install because entire rotor can be assembled on ground

Captures 10% less energy than two blade design

Ultimately provide no cost savings

Number of Blades - Two

Advantages & disadvantages similar to one blade

Need teetering hub and or shock absorbers because of gyroscopic imbalances

Capture 5% less energy than three blade designs

Number of Blades - Three Balance of

gyroscopic forces Slower rotation

increases gearbox & transmission costs

More aesthetic, less noise, fewer bird strikes