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Chapter11-12 Electricity

LED -The diode has two regions separated by a junction. The p region is

radioactivity by absorbing neutrons), containment structure (with a concrete

Fukushima Daiichi nuclear disaster - A series of equipment failures, nuclear meltdowns,

Electricity is convenient, safe and clean to the end user. The voltage of 220 V in HK

dominated by positive charges (holes), and the n region is dominated by

shell at least 3 feet thick contains the reaction)

and releases of radioactive materials at the Fukushima Nuclear Power Plant, triggered by

reserves direction 50 times a second.

negative charges (electrons). The junction acts as a barrier to the flow of

-LWR – Light Water Reactor; PWR – Pressurized Water Reactor; BWR – Boiling

the Tohoku earthquake and tsunami on 11 March 2011

V (t )=(220 x √ 2)sin ⁡〖(2 π 50t )〗

electrons between the p and the n regions. Only when sufficient V is applied.

Water Reactor; CANDU – Canada Deuterium Uranium reactor; MOX - Mixed-

- The total amount of radioactive materials released into the air:

.

1-Current flows across a diode

Oxide; RU – Recycled Uranium ;DU –Depleted Uranium; NU – Natural Uranium

Basic about electricity The electric charge, q, is an integral multiple of a fundamental

2-Negative electrons move one way and positive holes move the other way

Nuclear fission – Collision of a relatively slow-moving neutron with uranium-235

- The total amount of radioactive material released into the ocean: 2.8×10 18 Bq of iodine-

unit of charge e, thus q = Ne, where e = 1.6*10^-19

3-The holes exist at a lower potential energy level than the free electrons

can split it into two smaller nuclei. Neutrons are also released in the process,

131, 9.4×1017 Bq of cesium-134 and 9.4×1017 Bq of cesium-137

Electrical insulators are material in which all of the electrons are bound to atoms.(cannot

4-Therefore when a free electron falls it losses its potential energy

along with a great deal of energy

- Austrian Meteorological Service estimated the total emissions of iodine-131 ranged from

move freely in the material) Electrical conductors are materials in which some of the

5-This electric potential energy is converted to electromagnetic energy or in a

-During nuclear fission, the nucleus usually divides asymmetrically rather than

1×1016 Bq to 7×1017 Bq, less than 1% to 40% of the release at Chernobyl (17.6×10 17 Bq).

electrons are not bound to the atoms and free to move.(e.g. copper, aluminum, silver,

form of a photon, e.g. light

into two equal parts

- Radiation exposure: ranges from 10^–4 mSv/h to 10^5 mSv/h, over one billions times

gold)

6-The color of the light is determined by the fall of the electron (band-gap

-Moreover, every fission event of a given nuclide does not give the same

Chernobyl nuclear disaster - The world’s worst nuclear accident happened when reactor #4

energy of the semiconductor) and hence energy of the photon.

products; more than 50 different fission modes have been identified for

in the Chernobyl nuclear power plant in Ukraine exploded on 26 April 1986

Applications -brake lights (quicker warm up time), traffic lights, display mon

uranium-235

-For 10 days, the reactor core released radioactive smoke in the air

Ohm’s Law:

R=ρ L ⁄ S Ω

ρ=resistivity, L=length, S=cross-

sectional area.

1.3 ×1017 Bq for iodine-131 and 1.1×1016 Bq for cesium-137

Water system

Electrical System

Function

LED light - the best solid state white light is obtained by using blue LEDs to

-The nuclear energy available per atom is roughly one million times bigger

Chernobyl Forum - 8 United Nations agencies founded the Chernobyl Forum

Pump

Generator

The prime mover. Supplies energy to the

excite yellow phosphors to create white light. lifespan and luminous efficacy

(waste 1000000 smaller)than the chemical energy per atom of typical fuel

2003 to scientifically assess the health effects and environmental consequences of the

system. Converts motion to electrical

better,2-3 times more than fluorescence, 10/20 times than incandescence

Nuclear Chain Reaction – when a uranium nucleus fissions, it breaks up into a

Chernobyl accident and to issue factual, authoritative reports on its environmental and

energy

Life: LED>CFL>ILB, Power: ILB>CFL>LED CO2 emit: ILB>CFL>LED

pair of nuclear fragments and releases energy. At the same time, the nucleus

health effects

Object on which the electrical current flows.

Chapter14 Batteries and Fuel Cells

emits a number of neutrons, the same type of particle that initiated the fission

Long-term effects of Chernobyl nuclear disaster -The number of deaths expected in the

The larger the pipe or conductor the more

Batteries -converts chem energy to elect energy→electrochemical cell

of the uranium nucleus. This makes it possible to achieve a self-sustaining series

future over the lifetime of 600,000 people including emergency workers and residents of

water or current will flow.

of nuclear fissions; the neutrons that are emitted in fission produce a chain

most contaminated areas is estimated to be about 4,000, where 1,000 of them are

The pressure or the push that moves the

reaction, with continuous release of energy.

expected to die from cancer even if they had not been exposed to Chernobyl's radiation.

water or electrical impulse in the system.

Nuclear fuel - 235U and depleted uranium - 0.711% for 235, 99.284% for 238

-Thyroid cancer, one of the big worries at the time of the accident, did not prove as bad as

-natural uranium oxide has to be enriched to contain 3-4% of low-enriched

feared.

uranium for use in nuclear reactors, 90% Highly enriched uranium for use in

Land use - If the nuclear power stations were placed in pairs around the coast, there will

nuclear weapons.

be two every 100 km

-Uranium ore is first processed into yellowcake powder which is in turn purified

Economics of cleanup - Nuclear decommissioning is the dismantling and decontamination

for use in fuel rods in nuclear reactors, the 238U remaining after enrichment is

of a nuclear power plant site after its lifetime (~25 – 60 years) is reached so that it will no

known as depleted uranium and is less radioactive than natural uranium but still

longer require measures for radiation protection

Disposable and Rechargeable Batteries

extremely hazardous

Nuclear Safety

-Zinc-carbon batteries and alkaline batteries are common disposable batteries.

- small amount can produce a lot of energy( 8000 times more energy than coal)

Death per GWy to quantify the public risk of different power sources. Oil: 4.1, coal: 2.6,

The longest serving and best known rechargeable battery is the lead acid

- the same amount of energy as 16 kg of fossil fuels in a standard nuclear fission

lignite: 2.2, biomass: 1.4, gas: 0.4, wind & nuclear: 0.2

battery invented in 1859. Lithium ion batteries was conceptualized in

reactor is 2 grams. 2g of uranium, 200g of ore have to be mined per day

CO2 emission from Nuclear Power - Building a nuclear power station requires huge

1970s(1990 start to be popular)

Fuel Type

amounts of concrete and steel, materials whose creation involves huge CO2 pollution

Pipe

Water Pressure

Water Flow

Conductor

Voltage

Current

The amount of water or electricity that is

flowing.

Restriction of the

Resistance

water pipe

Rate of work done

-For every 10 degree rise in temp, self discharge rate doubles

The characteristic that restricts water and

current flow.

Power

by the flowing water

The work done provided by the flowing

water per unit of time or the rate at which

electrical energy is changed into useful

work.

“Electromagnetic induction”(N to S) discovered by Michael Faraday

-A steady current through a coil produces a magnetic field.

-increasing current produces an increasing magnetic field in the coil, which in turn

produces or induces an electric field. The voltage (emf) from the induced electric field

opposes the current increase.

-decreasing current produces a decreasing magnetic field in the coil, which in turn

produces an electric field. The voltage from this electric field also opposes the current

decrease.

Lenz’s law: The effects of magnetic induction oppose the changes that produce them.

AC electric Generator – spinning magnet rotor produces an alternating magnetic field.

Produces alternating electric field which induces an alternating voltage in the coil.

Generator (Electromechanical Energy Transfer)

When the turbine turns, the shaft and rotor is turned. As the shaft inside the generator

turns, an electric current is produced in the wire. The electric generator converts

Energy Density(kWh/kg) Number of Times Denser

Electricity produced by batteries

than Coal

- carbon intensity associated with construction

-AC electricity(cheap), some can’t use AC, then need DC(portable devices)

Nuclear fission(100% 235U)

24,513,889

2,715,385

= 300×109g /[106kW(e)× 220,000 h] = 1.4 g / kWh(e)

Hydrogen Fuel Cell Car (efficient and scalable)

Natural uranium (99.3% 238U, 0.7%

6,666,667

738,462

-smaller than the fossil-fuel benchmark of 400 g CO2 / kWh(e)

Hydrogen is used as fuel, transform hydrogen and oxygen into electric

235

power, emitting water as their only waste product. Every fuel cell has an

Enriched Uranium (3.5% 235U) in a

electrolyte which can electrically charge particles from one electrode to the

light water reactor

other, and a catalyst, which speeds the reactions at the electrode.

Type of Fuel Cells

Natural uranium (99.3% 238U, 0.7%

235

Primary

Secondary

Fuel Cells

1) Only acts as galvanic or

1) Acts as galvanic or voltaic

1) a simple galvanic or voltaic cell

voltaic cell (i.e. produce

cell while discharging (produce

(i.e. produces electricity)

-The IPCC (Intergovernmental Panel on Climate Change) estimates that the total carbon

U) in a fast breeder reactor

960,000

106,338

intensity of nuclear power (including construction, fuel processing, and decommissioning)

is less than 40 g CO2 / kWh(e).

123,056

13,631

- The volume of waste from nuclear reactors is rather small. Most of this waste is low-

level waste.

U) in a heavy water reactor

LPG propane

13.8

1.5

LPG butane

13.6

1.5

Gasoline

13.0

1.4

- The high-level waste is stored in pools of water and cooled at the reactor for 40 years.

The level of radioactivity drops 1000-fold in 40 years and then drops to the level of

uranium ore in 1000 years.

mechanical energy into electrical energy.

electricity)

Gas-fired Power Station: Temp.> Coal-fired  efficiency higher. More environmental

elect) and act as electrolytic

Diesel fuel/Residential heating oil

12.7

1.4

Nuclear Waste

cell (consumes electricity)

Biodiesel oil

11.7

1.3

The mass of nuclear waste is about million times less than the waste of coal

friendly (product: Water vapor, carbon). No huge piles of ash to be disposed of.

2) Irreversible

2) Reversible

2) Cell reaction is reversible

Anthracite Coal

9.0

1.0

Combined Cycle Unit – gas turbine and a steam (combined not alone)

3)Can’t be recharged

3)Can be recharged

3)Energy can be withdrawn cont.

Water at 100m dam height

0.0003

N/A

-gas turbine – using hot gases to turn turbine and generate electricity

4)Cam be used as long as the

4)Can be used again by

4)Reactants should be replenished

Sustainable” power from nuclear fission

-waste heat from the gas turbine is used to generate steam, then generate electricity by

active materials are present

recharging

cont. Doesn’t store energy

-The total usable uranium reserve is therefore about 27 million tons

e.g. Leclanche cell or Dry cell,

e.g. Lead storage battery, Ni-Cd

e.g. H2 & O2 Fuel cell

-Sustainable means having resource to last not less than 1000 years.

Lithium cell

battery, Lithium ion cell

CH3OH & O2 Fuel cell

2 ways to use uranium in a reactor

Uses: Pace makers, watchers,

Uses: electronic equipment,

Uses: Space vehicles due to its light

-widely-used once-through reactor gets energy from 235U

Transistors, radios

automobile equipment

weight (for astronauts)

-fast breeder reactor gets roughly 60 times more energy from 238U.

steam turbine - more efficient, 50-60%

Steam turbine (generates 80% electricity in the world)

– magnetic rotor is rotated by a steam turbine(coal, oil, natural gas, nuclear)

-converts energy of fluid into mechanical energy. steam driven rotary engine.

- prime-mover in which pressure energy of steam is transformed into kinetic energy, and

later in its turn is transformed into the mechanical energy of rotation of turbine shaft.

-contains a rotor assembly, which is the moving part, having shaft or drums with blades

attached to them. The movement of the blades, which is caused by the flow of steam,

creates rotational energy which is imparted to the rotor.

-maximize the efficiency of steam turbine the steam is expanded, generating work in a

number of stages. Multiple stages turbine is highly efficient.

Principle of steam turbine:

-steam energy is converted to mechanical work by expansion through the turbine.

-two basic types according to the mode of steam: Impulse turbine &Reaction turbine

-Most steam turbines use a mixture of both impulse and reaction design.

-Higher pressure sections are impulse type and lower pressure sections are reaction type.

Step-up and step-down transformers; Electric power grid

-grid – generation, transmission, distribution and load

-power plant produces electrical energy in medium voltage to step-up transformer

-step-up transformer elevate to high voltage, transmitted along high-tension power lines,

convert to medium or low voltage by step-down transformers.

-to get power to our home, high resistance(far, long power line)

P Plant=Pload + Pwire ↑transmission efficiency: ↓I , ↑V High voltage may cause sparks, fire

AC (Alternating current) vs DC (Direct current) transmission system

AC – frequency of 50 or 60 Hz; current changes direction 100 or 120 times a sec

– line voltages can be easily and economically transformed up and down

-does not use the whole conductor due to ‘skin effect’. AC conductors have larger

diameter than adequate DC

-cheaper transformation between voltages, easy to switch off, less equipment needed,

known and reliable technology, more economical in general, could provide rotating

field

DC – current flows in one direction

-conductor cross-section fully used. No skin effect, no reactance, low loss

-requires DC-AC converters to control the voltage level – expensive

-switching of higher voltage DC is more difficult

-long distance and higher power point to point transmission – higher investment costs

offset by lower losses

Alkaline, Phosphoric Acid, Solid Polymer, Moltan Carbonate, Solid Oxide,

Once-through reactor

The Future of Nuclear Energy – Travelling Wave Reactor

A travelling wave reactor could use widely available depleted uranium and operate for 60

years without refueling.

-a breeding zone preceded the fission zone; very little nuclear waste and zero emission;

nuclear proliferation very unlikely

-once started with a small amount of low-enriched uranium, TWR can run for 60 years on

depleted uranium

-an 8 metric-ton canister of depleted uranium could generate 25e+9 kWh of electricity,

Direct Methanol

there are currently 700,000 metric tons of depleted uranium in the US

Energy for home heating and cooling

Heat Transfer in Buildings: When the temperature in a building is higher (lower)

-The fast neutrons produced in fission do not cause fission as efficiently as

than the temperature outside, heat will flow out (in). There are two ways heat

slower-moving ones so they are slowed down in once-through reactors by light

can leave or enter a house.

water, or heavy water, or graphite, which cools the neutrons to optimum

Conduction: heat flowing directly through walls, windows & doors

energies for causing fission.

Convection: hot/cold air passing through cracks, openings or ventilation ducts

Fast breeder reactor

Chapter 18 Water Power

Hydro-Power - Water-wheels : direct conversion to mechanical work

-Modern use of hydropower: hydro-electricity, the first hydro-electric power plant:

installed in Rothbury, England, completed in 1870

Hydroelectricity - Hydro-electric power plants convert the energy contained in falling water

and running water into electricity – World’s largest renewable source of electricity:

Conduction loss: conduction loss = A U ΔT, U-value is the thermal conductance,

Accounting for 6% of worldwide energy supply, or about 16% of the world’s electricity

W/m2 OC

Hydropower is Renewable - The Sun evaporates water from the sea, lakes and land, which

-Bigger U means bigger power losses, U of a wall is inversely proportional to its

forms clouds and falls as rain in the mountains, keeping the dam supplied with water.

thickness, -double-glazed window is as good as a solid thick wall. Keep cold

temp on the outside

-Natural uranium consists primarily of 238U, which does not fission readily. In a

Convection loss: Convection loss = N V ΔT C = ⅓ N V ΔT, N = no. of air

fast breeder reactor, the fast neutrons are captured by 238U, which then

change per hour, v = volume of the space, C = specific heat factor of air =

becomes fissionable plutonium (239Pu). This plutonium isotope can be

1.2kJ/m3K

reprocessed and used as more reactor fuel. It is usually said that 238U is used to

Power loss = (AU + ⅓ NV) ΔT , energy loss = (AU + ⅓ NV) (ΔT Δt) first factor(AU

breed 239Pu.

+ ⅓ NV), leakiness of the house, second factor(ΔT Δt), temp demand -> reflect

Once-through reactors, using uranium from the ground

the need of energy to achieve heating and cooling during a period -> year basis

-1 GW nuclear power station uses 162 tons of uranium per year

-> The sum of the product of [(ΔT)i*day] of the i th day over a year.

Energy per person = 0.57 kWh/d-p (share among 7 billion ppl for 1000 years)

The power used to heat a building:

-This is much less than the 18 kWh/d-p of electricity generated by burning 45

- reduce the temp demand or average temp diff

kWh/d-p of fossil fuels

- reduce the leakiness or the heat-loss coefficient of the buildings

Fast breeder reactors, using uranium from the ground (More sustainable) 40

- double glazing, cavity insulation, fiberglass insulation, draft excluders

kWh/d-p

- increasing the COP of the heating/cooling system

-Uranium can be used 60 times more efficiently in fast breeder reactors, which

- the temp difference between evaporation temp and condensation temp

burn up both 235U and 238U

Smart Green Building Benefits

-The depleted uranium from the once-through reactors can be used in fast

- smart green building (low carbon, renewable energy gen, waste treatment)

breeder reactors

25% - 60% energy savings: 30% - 50% water savings; Improved worker

Once-through, using uranium from the oceans

productivity due to improved lighting and thermal comfort; reduced sick time;

-4.5 billion tons/162 tons per GW-yr = 28 million GW-yr

lower life-cycle costs

-The ocean circulation is slow, and deep Pacific waters circulate to the surface

Chapter15 Stuff and RPUD Phases

every 1600 years. Assuming 10% of the uranium is extracted over a period of

Embodied energy in “stuff”

1600 year, the power is delivered in

Stuff –a main sink of energy

once-through reactors at a rate of -2.8 million GW-yr / 1600 yr = 1750 GW

-Renewable: the Sun provides the water by evaporation from the sea, and will keep on

doing so. Three primary types of hydropower facilities:

Impoundment System - An impoundment is simply a dam that holds water in a reservoir

-The water is released when needed through a penstock, to drive the turbine.

-Most large, high-head hydropower facilities use impoundments.

-head = the height from which the water falls.

Run-of-the-River Hydropower System(often low-head) - uses the river’s natural flow and

requires little or no impoundment

- involve a diversion of a portion of the stream through a canal or penstock, or it may

involve placement of a turbine right in the stream channel.

Pumped Storage System - operate as a closed circuit. Their operation is based on two

water reservoirs: upper and lower.

- When the demand for electricity is low, the pumped storage facility stores energy by

pumping water from the lower reservoir to the upper reservoir.

-During periods of high electrical demand, water from the upper reservoir is passed

through the turbines to generate electricity and then collected into the lower reservoirs.

-The upper reservoir provides a reserve of energy. The capacity of the pump storage power

station depends on the flow through it and the head of water between the two reservoirs

- It takes fossil fuel power stations about half an hour to increase their output to full

power, but pumped storage reservoirs can generate electricity almost immediately

- evaporation losses and conversion losses, approximately 70% to 85% of the electrical

energy used to pump the water into the elevated reservoir can be regained

-undersea and underground transmission –no reactive power problem

The Four Phases

-(1750 GW/ 7 billion people) ×24 h/d = 6 kWh/d-p

Hydropower Plants Also Vary in Size - . The United States Department of Energy classifies

-connection of separate asynchronous power systems – with different frequencies,

RPUD – raw materials (R) phase; production (P) phase; use (U) phase and

Fast breeder reactors, using uranium from the oceans (More sustainable)

power plants by how much energy they are able to produce

disposal (D) phase.

-If fast breeder reactors are 60 times more efficient, the same extraction of

-focuses on the energy costs of the R and P phases which are called the

uranium could deliver 360 kWh/d-p.

Transformer -use induction, transfer power (X transfer charge) between two circuits

“embedded” or “embodied” energy of the stuff

-The sustainability depends on the extraction of uranium in oceans and building

-transformer must obey energy conservation

Energy for the making of stuff & transporting of stuff

fast breeder reactors. The former is not yet developed and the latter is

Load Factor

control area

-less space required for transmission line

-power arriving in the primary circuit must equal

Energy for making stuff

48+ kWh/d-p

controversial.

The output of a power plant divided by the max. possible output of the power plant

Power leaving the secondary circuit

-imported stuff

40 kWh/d-p

Radioactive decay - Radioactive decay is the process by which an atomic

Advantages

-P = VI – transformer can exchange V for current or current for voltage

-Packaging

3+ kWh/d-p

nucleus of an unstable atom loses energy by emitting ionizing radiation or

-Once the dam is built, the energy is virtually free. -No waste or pollution produced

-Daily newspaper

2 kWh/d-p

particles.

(directly). - -Much more reliable than wind, solar or wave power. - Water can be stored

-Road-making

2 kWh/d-p

- Common types of decay include α(He nucleus), β(electron) and γ decay, x-ray

above the dam ready to cope with peaks in demand. - Hydro-electric power stations can

-House-making

1 kWh/d-p

and neutron emission.

reach full power in a minute or two while fossil-fuel power stations in hours. - Electricity

Energy for transporting stuff

12 kWh/d-p

The decay rate of a radioactive substance is characterized by its half-life

can be generated constantly. - Dams are also used for flood control or irrigation

Disadvantages

7 kWh/d-p

-the average time it takes for the number of parent radioactive atoms in a -By road

sample to halve; -equivalently, it is the time it takes for the count rate from the

-Flooding of land, much of it previously forested or used for agriculture. The size of

-By sea

4 kWh/d-p original substance to fall to half its initial level

reservoirs created can be extremely large. Relocation of population (human right issues)

-By pipe

0.4 kWh/d-p -The activity of a quantity of radioactive material is measured by the number of

-Damming a river can alter the amount and quality of water in the river downstream of the

-Storing food in supermarkets

0.5 kWh/d-p nucleus decays it undergoes per second. One decay per second is one Becquerel

dam, as well as preventing fish from migrating upstream to breed.

Absorbed dose of radiation

-Decaying vegetation, submerged by flooding, may give off greenhouse gases.

-The risk posed to a human being by any radiation exposure depends partly

-Catastrophic risks: what if dam fails?

upon the absorbed dose, the amount of energy absorbed per kg of tissue. The

Physics of Impoundment Hydroelectric Power

absorption of 1 J of energy in 1 kg of tissue is one gray (Gy)

-Mechanical Power = change of potential energy/ time = MgΔh/t = g Δh(M/t)

Equivalent dose (sievert (Sv)) - biological effect of the same amount of absorbed

-M/t = mass /time = density ×volume /time

energy is different for different types of radioactivity

-density of water ≈ 1000 kg/m3, g ≈ 10 m/s2

-biological effect is computed by multiplying the absorbed dose (in gray) by a

-Mechanical Power (W) = density×g×Δh×volume /time = 104×FLOW×HEAD

number indicating the quality factor of the particular type of radiation

-volume /time = FLOW (m^3/s) , Δh = HEAD (m)

-while keeping the power unchanged

Step-up Transformer (Step-down is reversed)

-has more turns in secondary circuit -so charge is pushed a longer distance

-and experience a larger distance -smaller current at high voltage flows in 2nd circuit

n=N P /N S=V P /V s =I P / I S n1→step-down

Step-up for efficient long-distance transmission, step-down for safe delivery

The need of electric power grid

-electricity once generated and transmitted, must all be used instantly Food and farming -Modern agriculture is the use of land to convert petroleum -electricity cannot be stored in large quantity. Capacitors and batteries, the amount is into food, modest -for a person, consume 3kWh/d -this means that the generation and consumption of electricity must be matched all the -Most of the absorbed energy from food eventually escapes from the body as time heat. - achieved by electric power grid – interconnected network for delivering electricity, -One person thus functions like a space heater with an output of a little over includes, generators, switches that controls the flow of electricity, sub-stations, power 100 W lines, transformers -It takes 15 kWh of energy to produce 3 kWh of food -Generation, transmission, commercial & industrial business consumers, distribution, High-tech gadgets - The energy used to produce electronic gadgets is distribution automation devices, residential consumers

- For photons and electrons the quality factor is 1; for neutrons it ranges from considerably higher than the energy used during their operation

Benefits of Smart Grid

5 to 20 depending on the energy of the neutron. This product is called the -Embodied energy in 1 g of microchip electronics: 36MJ = 10 kWh (per g)

-more reliable electric service

equivalent dose. -Toxic chemicals and materials are used and hazardous to health and envi.

-faster power restoration following an outage 2015

Smart

Tablet

Laptop

Mobile

-more information about power usage to better manage electric bills phone

Effective dose - biological effect also depends on the type of tissue being

-Mechanical Power (kW) = 10×FLOW×HEAD

irradiated. As with different types of radioactivity, another quality factor is

-Electric Power (kW) = efficiency ×10×FLOW×HEAD

introduced depending on the type of tissue. The more sensitive the tissue is to

-The efficiency of large water turbines and generators usually exceeds 90%

radiation, the higher the factor

-We want a big and high dam in order to have big FLOW and high HEAD

- effective dose is the sum of the equivalent doses of the various types of

Physics of Run-of-the-river Hydroelectric Power

irradiated tissue, each weighted for its sensitivity to the radioactivity

-Power = change of kinetic energy /time = ½ M v^2/ t

Car

device

Chapter13 Lighting Total sales

1.9*10^9

2.3*10^8

6*10^7

7.2*10^7

Embodied

0.25

1.0

4.5

100

Types of electric lighting

incandescent light bulbs(ILB) - produces light with a filament wire heated to a high Energy per temperature by an electric current passing through it, until it glows. device (GJ) arc lamps -produces light by an electric arc between two electrodes separated by a gas.

M/t = mass /time = density ×volume /time = density ×area ×speed = ρ A v Total

0.475

0.23

0.27

1

7.2

The type of lamp is often named by the gas contained in the bulb; including neon, argon,

-Power (W)= ½ ρ A v^3; Power (kW) = ½ A v^3 Embodied

xenon, krypton, sodium, metal halide, and mercury.

(as ρ≈ 1000 kg/m3) A = the area the water flows through energy(10^18)

gas-discharge lamps -a family of artificial light sources that generate light by sending an

Three Gorges Dam - A dam across the Yangtze river (first suggested by Dr. Sun Yat Sen) Weight per

0.14

0.7

2.0

1400

electrical discharge through an ionized gas, a plasma

-flood control – electricity generation - Supply power mainly to Shanghai and Guangdong device (kg)

light-emitting diodes -a family of artificial light sources that generate light by sending an

and also to Hubei, Hunan, Jiangsu, and Anhui. Total weight

2.66

1.6

1.2

5.5

1008

electrical discharge through an ionized gas, a plasma

- World's biggest hydroelectric power station by total capacity (10^8)

General lighting information- Good lighting focuses on light quality as well as light

- Total installed capacity is 22,500 MW, and account for 14% of China’s total hydroelec. gen Disposal of electronic gadgets United Nations Environment Program (UNEP)

quantity. The environment is lit for people so lighting should be both functional and

- has 32 main water turbines in total, each with a capacity of 700 MW, together with two in 2006 estimated the amount of worldwide electronic waste discarded each

attractive.

year to be 50 million metric tons

smaller generators (50 MW each) to power the plant itself

– luminous flux(lm) – the total light output of a light source

-WEEE (waste from electronic & electrical equipment), is classified as hazardous

Power from tides

-light intensity(cd)– the light output in a specified direction

waste due to the many toxic ingredients it contains, including heavy metals and

-Tides arise from the different gravitational pull of the Moon & the Sun at the surfaces and

- illuminance – amount of light falling onto a surface. Luminous flux per area

harmful, persistent chemicals, with the potential to pollute the environment

at the center of the Earth. (Earth, 2 high tides a day)

- visible surface – surface brightness. Cd per square meter

and damage human health when it is processed, recycled or disposed of.

Tidal Influence

Efficacy of light sources – efficacy – ratio of input to light output, lm/watts.

Chapter16-17 Nuclear Energy

Air Quality in HK street canyon-presence of numerous tall buildings prevents

- high tide on the side nearest the Moon because the Moon pulls the water away from the

Solar spectrum and human eye color response The white sunlight we see is a continuous

Nuclear power plant

free circulation of air and traps pollutants at ground level Air Quality Health

Earth; high tide on the far side because the Moon pulls the Earth away from the water on

spectrum spanning from violet to red. The evolution of vision in human is optimized with

In 2016, ~10.5% of electricity worldwide is produced by nuclear power plants,

Index- reported hourly at each ambient and roadside station, informs you of

the far side

respect to the solar radiation such that the human spectral response peaks at the peak of

but in some countries like France, over 70% of their electricity is produced by

short-term health risk of air pollution and help u take precautionary measures

Sun’s effect on Tides

the solar spectrum.

nuclear power. In China, nuclear power is about 3.6%.

to protect your health

- regular rise and fall of the tides around our coasts are caused mainly by the gravitational

Eyes perception of colors three kinds of color receptors or cone cells (short (S), medium

Pressurized water reactor (PWR)

pull of the moon on the oceans. The sun also contributes a small additional effect.

(M), and long (L), with peak spectral sensitivities at 420-440 nm (blue), 534-545 nm

-Nuclear Reactor device built to sustain a controlled nuclear fission chain

Tidal energy

(green) and 564-580 nm

reaction

-The technology for harnessing tidal energy involves building a low dam, or barrage, across

Color Rendering Index (CRI)-The accuracy can be measured by the color rendering index

-Pressurized Water Reactor (PWR) keeps water under pressure so that it heats

the estuary (河口) of a suitable river

or CRI. -100 represents the most true to life color rendering, 70 or above is generally

up but doesn’t boil.

-The river behind the barrage is filled up during high tide forming a pool. After the tide has

required for most lighting applications. -is a quantitative measure of the ability of a light

-Water from the reactor and water that is turned into steam are in separate

reached maximum height, the water inlets are closed and at low tide the impounded water

source to reveal the colors of various objects in comparison with natural light source.

pipes

is allowed to flow back to the sea through a turbine-generator system to generate

Correlated Color Temperature (CCT)(unit K) the relative color appearance of a white light

- main components: reactor vessel, tubes of uranium, control rods(control

Chapter22 Climate Change

electricity

source, indicating whether it appears more yellow/gold or more blue, in terms of the

Solar thermal power or Concentrated solar power (CSP)

Surface temperature of the Earth

over a contract period of two years at 3000 minutes per month. (a) Find the embodied

681 W/m^2

range of available shades of white. The higher the CCT the ‘cooler’ or bluer the light is –

2500 K has a very warm or yellow appearance where is 4000 K is a cool blueish light

energy of the iPhone’s microchip in kWhe, assuming the electricity generated by one kg of

fossil fuel is 12.5 kWhe. (b) Find the embodied energy per hour used for the iPhone. (c) 129 W/m^2

Fluorescent lamp (Gas discharge lamp) -A fluorescent lamp is a sealed glass tube

How many 100 W light bulbs per hour can the equivalent embodied energy per hour

341 W/m^2

containing a small amount of mercury and an inert gas, typically argon, kept under very

low pressure.

support? How long can the equivalent embodied energy support a 40 W light bulb?

Solution: (a) The embodied fossil fuel in an iPhone is 0.065×800 kg =52 kg, which is

-The inside of the glass tube is coated with a phosphor powder

Solar photovoltaic: Photovoltaic (PV) panels convert sunlight into elec. Typical

The earth to maintain constant average temperature, the amount of energy it

equivalent to 52×12.5 kWhe =650 kWhe. (b) The time used in the two year period = 3000

-The tube has two electrodes, one at each end, which are wired to AC electrical circuit.

solar panels have an efficiency of about 10%; expensive ones perform at 20%

radiates must equal to the amount of solar energy radiation it absorbs.

min per month ×24 month =1200 hr. The embodied energy used per hour = 650/1200

a1.Free electrons (E) from the heated filaments are introduced to ionize the gas (A).

-The average power delivered by south-facing 20%-efficient photovoltaic panels

Save(1-α)=σTE4 , Save~341W/m^2 – averaged on day and night

=0.54 kWhe per hour. (c) 1 kWhe per hour can support ten 100 W bulbs per hour, or one

a2.An electric current is passed through the ionized gas; electrons and gas move quickly

in Britain would be

α ~30% - reflected solar radiation by the earth→TE=255K

40 W bulb for 25 hours, or roughly one day. The embodied energy of 650 kWhe can

from one end of the tube to the other.

20%×10 m^2/p× 110 W/m^2= 220 W/p → 5 kWh/d-p

Greenhouse effect and Greenhouse gases

support one 40 W bulb for 650x103 /(40x24) = 677 day1. According to World Nuclear

a3.The energy of the electrical current changes the mercury from liquid to gas (M).

For Hong Kong: 20%×10 m^2/p× 148 W/m^2= 296 W/p → 7 kWh/d-p

The glass lets in short wavelength light, and blocks long wavelength light.

Association, 2600 × 109 kWhe of electricity were generated in the year of 2008 using

b1.Collisions with moving particles (electrons and ions) excite the mercury gas atoms.

-The present cost of installing such photovoltaic panels is about four times the

65,000 tons of natural uranium. (a) Find the average electric energy obtained from 1 ton of

b2.In an excited mercury atom, an electron jumps to a higher energy level.

cost of installing solar thermal panels, but they deliver less than half as much

uranium. (b) How much coal is needed to generate the electrical energy of 1 ton of

b3. When the electron at a certain high energy level falls back to its original level, the

energy, albeit high-grade energy (electricity)

uranium? (Energy density of coal is 30 MJ/kg) (c) How much less coal was used in the year

atom releases the extra energy in the form of an ultraviolet (UV) photon.

-huge subsidy from the government supports their growth

of 2008? (d) The nuclear plant generating capacity in the USA is 101 GW. The actual

c1.UV photons released by the mercury excite atoms in the tube’s phosphor coating.

How it works: Absorption of light generating electron-hole pairs→ Separation of

electricity generated is 809x109 kWh. What is the average load factor of the nuclear

c2.In each phosphor atom, the energy of the UV photon boots an electron to a higher

the charge carriers→ Extraction of those carriers to an external circuit.

Water – H2O -About 30% of the radiation from the sun falling on the earth is

reactors? Solution: (a) The average electric energy obtained from 1 ton U = 2600×109

energy level.

(1) 1st generation: crystalline Si solar cell, efficiency 19.5-24.7% (2)2nd: thin

REFLECTED, mainly by the clouds, ice and snow

kWhe / 65000 tons =40 ×106 kWhe/ton (b) Assuming an efficiency of one third, the

c3.When the electron falls back to its original energy level, the atom releases energy as a

film solar cell, reduce amount of material used, CdTe, CulnGaS(Se)(CIGS),

- Up to 85%of the radiation from the earth is ABSORBED in the ATMOSPHERE

equivalent thermal energy per ton = 40 ×106 kWhe ×3 = 120×106 kWh. The energy density

visible light photon.

amorphous Si are main types, efficiency 7.3-20.3% (3)3rd: QDSCs: use quantum

, mainly by clouds and water vapor.

of coal is 30 MJ/kg. The amount of coal needed replace 1 ton U = (120×106 kWh × 3.6×106

CFL and mercury -75% less energy than conventional incandescent light bulbs, contain

dots as absorbing PV material, Organic solar cell: can be processed from liquid

- Water modifies the radiation balance and temperature of the earth directly

) J / 30 ×106 J/kg = 14,400 tons. 14,400 tons less coal is used for each ton U used. (c) The

extremely low levels of mercury(3mg per bulb)

solution, possibility of simply roll-to-roll printing process leading to inexpensive,

- Water AMPLIFY the radiation balance and temperature of the earth indirectly

amount of coal is not used due to the use of 65,000 tons U = 14,400×65,000 = 936×106

- The world’s largest tidal power installation is the Sihwa Lake Tidal Power Station in

large scale production & Perovskite solar cell: use perovskite structured hybrid

Milankovitch Cycles (100,000 year time scale) -Natural global warming, and

tons. (d) The maximum possible energy generation = 101 ×109 × 365 ×24 Wh = 885 ×109

South Korea (opened in 2011 with installed capacity 254MW coming from 10 25.4MW

organic-inorganic lead/tin halide-based material as light-harvesting active layer,

cooling, is considered to be initiated by Milankovitch cycles.

kWh The load factor is thus 809/885 = 91.4%. 6. The 15 m × 15 m Amonix

turbines)

efficiency 22.1%- fastest advancing solar tech

- These orbital and axial variations influence the initiation of climate change in

concentrated pv collector or module with a peak power of 25 kWp generates 138 kWh of

Power density of tidal pool

Issues about solar cells Temperature dependent output power: The output

long-term natural cycles of 'ice ages' and 'warm periods' known as 'glacial' and

electricity per day. The world’s pv power capacity at the end of 2012 is about 101 GWp. (a)

-PE = mgh

power will decrease as the module temperature increases once the module

'interglacial' periods. - The Milankovitch cycles are caused by changes in the

How many Amonix concentrated pv modules are need to provide 101GWp? (b) How much

- power per unit area generated by a tide-pool is (2ρh)gh /6 hours

reaches about 40°C. Power loss when power is converted into AC (About 20%)

shape of the Earth's orbit around the sun (E), the tilt of the Earth's rotation axis

electricity is generated each day using such modules? (c) Assuming a consumption rate of

Tidal Stream Generators -Barrage is not needed, limiting total costs. Tidal stream systems

Manufacturing Solar Panel Will Not Consumes More Energy than It Will Ever

(T), and the wobble of our axis (P). The mass and movement of the other

20 kWh per person per day, what percentage of the world’s population of 7 billion can be

make use of the kinetic energy from the moving water currents to power turbines, in a

Deliver: energy yield ratio (energy delivered over lifetime to energy required to

planets in our solar system actually affect the Earth orbit just as our planetary

provided for using such modules? (a) The peak power of the Amonix pv module is 25 kWp.

similar way to wind mills use moving air

make it) of solar system in central northern Europe is 4, with lifetime 20 years

mass similarly affects their orbits.

The number of such modules needed to generate 101 GWp = 101×106 kWp /25kWp =

-lower cost and lower ecological impact

Efficiency is Not likely to improve much when PV panels become cheaper and

Recent Warming Reverse Long-Term Arctic Cooling

4.04×106 . (b) The electricity generation per day = 138 kWh × 4.04×106 /d = 557.5×106

Power density of tidal stream farm

energy ratio improve

- From 1 to 1900 there has been a general cooling trend, consistent with

kWh /d. (c) The number of people per day that the electricity generated can be provided

Chapter21 Air Pollution

the idea that on a 100,000 year time scale we’re heading into an ice age.

for = 557.5×106 kWh / 20 kWh = 27.9×106 or 28 million. The world population is 7 billion,

Air pollution killed - the London Smog Disaster of 1952

- But, suddenly, in the 1900’s, the temperature starts to shoot up.

this is 28 /7000 = 0.4%.3. When China reaches the target of 200 GW of nuclear power

-the weather was considerably colder than usual. burning large amounts of

- All find the same result -that the last few decades are the hottest in the last

capacity in 2030, how much uranium per year is needed to generate electricity using

Tidal lagoons - are created by building walls in the sea; can then be used like artificial

coal and smoke bellowed from the chimneys leading to the formation of smog

500 to 2000 years

nuclear reactors with an average load factor of 0.9. Find also the kWh of electricity

estuaries. The required conditions for building lagoons are that the water must be

-fog that has soot in it

Circulation of Deep Waters and Surface Waters

obtained from nuclear reactors per day per Chinese. The world’s reactors with a capacity

shallow and the tidal range must be large.

-The London smog was especially lethal because it contained high quantities of

- Since the amount of extra carbon from burning fossil fuels is so much smaller

of about 400 GW generate about 10,000 tons of high-level spent nuclear waste each year.

-If two lagoons are built in one location, a neat trick can be used to boost the power

SO2

than the total in the oceans, “in the long term” (thousands of years) the extra

Find the high-level nuclear waste per Chinese within an average lifetime of 80 years,

delivered and to enable the lagoons to deliver power on demand at any time,

(exceeded 2.0 mg/m^3, a 7 fold increase; from the cheap sulphurous coal)

carbon will make its way into the ocean, and the amounts of carbon in the

assuming the population of China is 1.3 billion. (Use the value of the electr ic energy

independent of the state of the tide

-SO2 reacted with moisture in the air to produce a dilute, but lung-corrosive,

atmosphere, vegetation, and soil will return to normal.

obtained from 1 ton of uranium from Q1) Solution: The amount of electric energy

-At low tide, electricity using other sources can be used to pump water out of the low

sulphuric acid mist triggering a massive inflammation of the lung, suffocating

- The average depth of the oceans is about 4000m.

generated per year with a capacity of 200 GW and a load factor of 0.9 =

lagoon, making its level even lower than low water. The energy required to pump down

thousands of people to death.

- The oceans circulate slowly: a chunk of deep-ocean water takes about 1000

0.9×200×109×365×24 Wh = 157680 ×107 kWh. From Q1, the average electric energy

the level of the low lagoon is then repaid with interest at high tide, when power is

-Smoke and sulphur dioxide peaks coincide with the peak in death rate

years to roll up to the surface and down again.

obtained from 1 ton U = 40 ×106 kWhe/ton. The amount of uranium needed to generate

generated by letting water into the low lagoon.

-These Acts banned emissions of black smoke and decreed that residents of

- The circulation of the deep waters is driven by a combination of temperature

157680 ×107 kWh of electricity = 157680×107 /40×106 = 39,420 tons. The nuclear

urban areas and operators of factories must convert to smokeless fuels

gradients and salinity gradients, so it is called the thermohaline circulation

electricity per day per person in China = 157680×107 /365×1.3×109= 3.3 kWh The high-

-Recent Urban Air Quality in UK – the main pollutants – NOx (nitrogen oxides),

whereas the circulations of the surface waters are driven by winds.

level nuclear waste generated per year with a capacity of 200GW is 5,000 tons. The total

Advantages of Tidal Power

VOCs(volatile organic compounds), CO(Carbon Monoxide), PM10 particulates

Unbalanced Carbon flow

lifetime waste in 80 years = 400,000 tons The high-level nuclear waste per Chinese within

-Tidal power is completely predictable; unlike wind and sun, tidal power is a renewable

Air Pollutants and their health effects

Fossil fuels burning rate: 1Gt C in 1920→2 Gt C in 1955→8.4 Gt C in 2006→↑

an average lifetime of 80 years = 4×105×103 kg /1.3×109 = 0.3 kg. 4. Assuming the total

on which one could depend; it works day and night all year round; using tidal lagoons,

Oxides of Nitrogen: released to the air from the exhaust of motor vehicles, the

+slow circulation of the ocean’s surface water and deep water, It leads to CO2

amount of radioactive iodine-131 from Fukushima accident released into the air in 25 days

energy can be stored so that power can be delivered on demand.

burning of coal, oil, and natural gas. react with other substances commonly

stays in the atmosphere, double their pre-industrial levels in ~ 50 years,

(11 March to 5 April) is 1.3×1017 Bq (see lecture notes of L17). When this amount is

- Once the barrage is built, tidal power is free. It needs no fuel.

found in the air leading to the formation of nitric acid -> acid rain, and to the

CO2GHG, HOLD IN HEAT, temperature rise or global warming

dispersed into a circular region of radius 30 km and height of 10 km. (a) What is the

-The power density of a typical tidal flow is greater than the power density of a typical

formation of ozone and smog conditions in the air we breathe

Individual Actions

average radioactivity in Bq/m3 in this region? In any one day, the amount of iodine-131 is

wind, a 1 MW tide turbine is smaller in size than a 1 MW wind turbine; perhaps tide

-Inhaled NOx lead to formation of nitric and nitrous acids on the moist surfaces

less than the total. How does the half-life of iodine-131 affect the amount staying in the

turbines could therefore be cheaper than wind turbines.

of the airways.

air? (b) Hong Kong is more than 3,000 km from Fukushima. Assume the iodine-131 has

-Life below the waves is peaceful; there is no such thing as a freak tidal storm; so, unlike

-2NO2 +H2O -> HNO2 +HNO3

spread to a height of 30 km. Find the average radioactivity due to the Fukushima iodine-

wind turbines, which require costly engineering to withstand rare windstorms,

-Low levels of nitrogen oxides in the air can irritate your eyes, nose, throat, and

131 in Hong Kong. (c) How does the result of (a) compare with the radioactivity standing

underwater tide turbines will not require big safety factors in their design.

lungs, possibly causing you to cough and experience shortness of breath,

on 10 kg of coal ash assuming 10% of the radioactivity from the coal is intercepted? (See

-Under-sea tide turbines are out of sight, there should not be any objections to the visual

tiredness, and nausea. Exposure to low levels can also result in fluid build-up in

lecture notes of L17) (d) For reference, find the radioactivity in Bq/m 3 in a 100 m 2

impact as in the case of wind turbines

the lungs 1 or 2 days after exposure

9. The mass ratio of aqueous PM2.5 to PM10 particles in the atmosphere is

European home due to radon and in a typical human body due to K-40 (potassium 40) and

Disadvantages of Tidal Power

-Triggers asthma in asthmatics

0.25, the particulate concentration is 100 μg/m3 , find the number of PM2.5

other radioactive isotopes using the data given in lecture notes of L17. (e) If the iodine-131

-Limited availability - Few suitable sites.

Sulfur oxides/dioxide(gas) : (1)nasty, sharp smell (2)burning coal (50%)

and PM10 particles per m3 of air, assuming the average diameter of PM10 and

is decay by emitting a beta particle (β - ), what is this new daughter product? Solution: (a)

-Presently costly and expensive to build and maintain.

(3)heating oil (25-30%) (4)roasting metal sulphide ores (5)acid rain, sulfate

PM2.5 particles to be 6 μm and 1 μm respectively. The PM2.5 to PM10

The volume of the region = π×(30×103 ) 2×10×103 m 3=9π×1012 m 3 . The radioactivity =

-Tidal power schemes have a high capital cost

aerosols& smog, irritate eyes, nose, throat, lungs

concentrations are 20 μg/m3 and 80 μg/m3 . Density of water = 1000 kg/m3 .

1.3×1017 Bq /9π× 1012 per m3= 4600 Bq/m3 . Since the half-life of iodine-131 is 8 days,

-Barrage style only produces energy for about 10 hours out of the day.

Carbon monoxide: road traffic emissions. CO survives in the atmosphere for

The mass of a 6μm diameter spherical water drop = 1000 kg/m3×(4π/3)(3×10-

the average amount of iodine-131 staying in air on 5 April 2011is less than 1/8 of the

-Barrage style has environmental effects Such as fish and plant migration & Silt deposits

about one month before it is oxidized to CO2. When it enters the bloodstream,

6 ) 3m 3 =113×10-6 μg The mass of a 1μm diameter spherical water drop =

original amount. (b) The radius is larger than the 30 km radius by 100 times, and the height

-Local tides change - effects still under study

CO can reduce oxygen delivery to the body’s organs and tissues. Typical

(1/6)3×113×10-6 μg The number of PM10 particles = 80/113×106 /m3 ≈ 0.71×

is larger by a factor of 3, the volume is larger by a factor of 3×104 . The average value of

Global wind capacity; Wind Power; windmills; Wind power in UK, China, and HK

symptoms of CO poisoning include shortness of breath, chest pain, headaches,

106 /m3 The number of PM2.5 particles = 20 / (113/216) ×106 /m3 ≈

iodine-131 radioactivity reaching Hong Kong = 4600/30000 Bq/m3= 0.15 Bq/m3 , which is

Chapter19 Wind Power

and loss of co-ordination. The health threat from CO is more severe for those

38×106 /m3 . The PM2.5 particles are more numerous than PM10 particles by

quite insignificant. (c) The radioactivity of 10 kg of coal ash is 20,000 Bq, if 10% of the

Power density of wind KE=1/2mv^2=1/2ρAtv^3, Power=1/2ρAv^3

who suffer from heart diseases

more than 50 times There is a 6% power loss over a distance of 30 km when the

radioactivity decay intercepted, the corresponding radioactivity is 2000 Bq/9π× 1012 per

Power of windmill When air flows past a windmill, it is slowed down and spread out. The

Secondary pollutants: formed in the atmosphere by a series of chemical

electricity is transmitted from a 350 MW unit the Castle Peak Power Station via

m3 = 7×10-11 Bq/m3 , which is more than 13 orders less than the result of (a). (d) The

windmill cannot stop the wind, otherwise flowing of wind cannot continue. The max.

reactions between NOx, volatile organic compounds (VOCs), CO, etc and oxygen

a high voltage of 400 kV. Find the resistance of the power line per km. Taking

radioactivity due to radon in a 100 m2 European home is 30,000 Bq. The volume of the

fraction of the incoming energy that can be extracted by a disc-like windmill was worked

in the presence of sunlight. Ground-level Ozone. Ozone may remain in the

the simple-minded assumption that the 6% loss per 30 km can be extended to

home= 300 m3 , assuming a height of 3 m. The radioactivity per unit volume = 100 Bq/m3 .

out by a German physicist called Albert Betz in 1919. If the departing wind speed is one

atmosphere for several days before breaking down and can be transported

300 km, what would be the power loss? Solution: Let the resistance per km be r,

The radioactivity due to K-40 and other radioactive isotopes in human body is about 65

third of the arriving wind speed, the power extracted is 16/27 power in the wind.

downwind, thereby causing high concentrations to build up in rural areas. may

the resistance of the 30 km line, R = 30r Ω. For the transmission of a power of

Bq/kg, for a 70 kg person, the radioactivity is 4,550 Bq. Next we need to find the volume of

Power=Efficiency*Power per unit area*area=50%*1/2ρv^3*pi*(d/2)^2

cause permanent damage to the lungs. Even when ozone is present in low

350 MW via a voltage of 400 kV, the transmission current, I = (350×106

a 70 kg person. We are slightly denser than water, with a typical density of 1010 kg/m3

Global Wind Energy Council (GWEC) -Global wind capacity reached 370 GW in 2014

levels, inhaling it can trigger a variety of health problems including chest pains,

/400×103 ) A The power loss = I2 R = (350 ×106 / 400 ×103 ) 2 30r W This is 6%,

(the density of water is 1000 kg/m). The volume = mass/densi ty = 70/1010 m3≈ 0.07 m3 .

Variation of wind speed with height

coughing, nausea, throat irritation, and congestion

or [(350 ×106 / 400 ×103 ) 2 30r] / 350 ×106 = 6/100 The resistance r = 0.91 Ω

The unit volume radioactivity = 4,550 Bq /0.07 m3 = 65,000 Bq/m3 . (e) Iodine-131 ( 131

-Average of the cube>cube of average, calculation: use mean of cube of wind speed

-urban areas ozone is broken down rapidly by other pollutants to form

/km. 300 km is 10 times 30 km. The power loss = 6% ×10 = 60%. More than half

53I) undergoes beta decay to Xenon-131(131 54Xe). 5. A sample of 14C has half-life of

-Taller windmills see higher wind speeds. The way that wind speed increases with height

secondary pollutants such as secondary sulfate

of the power is lost. Power stations would not be built If there are no phosphor

5730 years and a decay rate of 14 disintegration per minute (dpm) per gram of natural

is complicated and depends on the roughness of the surrounding terrain and on the time

coating on the inside of the fluorescent tube, what would you see when the

carbon. If an artifact is found to have radioactivity of 4dpm per gram of its present carbon

of day

lamp is turned on? Solution: We will see no light. Because when the lamp is

C. What is the approximate age of this artifact? (Assume N(t)=Noe -t/τ where τ is the decay

Standard windmill properties

turned on, only ultraviolet light is emitted if there are no phosphor If you

time constant, and half-life t1/2= τln2). Solution: N(t)=Noe -t/τ, where N/No=4/14=0.2857

-A typical 1 MW windmill has a rotor diameter of around 54 m, centered at a height of 80

increase the current flowing through an incandescent light bulb or an LED, (i)

Now τ= t1/2/(ln2)=5730/(ln2)~8267years Then , the age t=- τln(N/No)=-

m. 1 MW “capacity” or “peak power” is the maximum power the windmill can generate

Will the incandescent bulb get brighter? (ii) Will the color of the incandescent

8267ln(0.2857)~10357 years. 6. (a) The top five countries with the most hydro-electric

light bulb change? (iii) Will the LED get brighter? (iv) Will the color of the LED

installed capacity and their respective 2006 annual energy production are listed below:

-Usually, wind turbines are designed to start running at wind speeds somewhere around

change? Explain why for your answers. Solution: (i) Yes. The temperature

Find the load factor of hydroelectricity of each of the countries. (b) Eighteen of the twenty

3 to 5 m/s and to stop if the wind speed reaches gale speeds of 25 m/s.

increases. So the power of the radiation increases. (ii) Yes. The temperature can

700 MW turbine generators in a hydroelectric dam (the Itaipu in Brazil/Paraguay)

-The actual average power delivered is the “capacity” multiplied by a factor that

influence the wavelength of the radiation. (iii) Yes. When increasing the current,

generated 90,620 GWh of electricity in 2007 while the remaining two turbines stay down

in optimal conditions.

Environmental Effect of Ozone

describes the fraction of the time that wind conditions are near optimal.

Ground-level ozone damages plant. interferes with the ability of plants to

more electrons can recombine with holes. So more photons are generated. (i v)

for maintenance. Find the load factor. (c) The flow through each of the 700 MW turbine

-This factor, sometimes called the “load factor” or “capacity factor,” depends on the site;

produce and store food, making them more susceptible to disease, insects,

No. The color of LED is determined by the materials of the semiconductor. What

generators is 700 m3 /s, find the head, the height the water drops to reach the turbine (of

a typical load factor for a good site in the UK is 30%. In the Netherlands, the typical load

other pollutants, and harsh weather

is the temperature difference across a window if the conductive heat flow rate

the Itaipu dam); assuming the efficiency of the generation unit is 90%.

factor is 22%; in Germany, it is 19%, in China it is around 23%

-Particulate matter is also formed as secondary pollutant from precursors such

across it is 20 W? The window is 4.5 m2 in an area that has a U-value of 0.4

Country

Chapter20 Solar Power

as SO2, NOx and VOC in the atmosphere

W/m2 K. Solution: The temperature difference 𝛥𝑇 = heat flow rate / (area×U-

The Solar Spectrum

Particulate Matter: a mixture of solid particles and liquid droplets found in the

value) = 20/(4.5×0.4) K = 11.1 K Suppose an iPhone weighs 137 grams and 65

air. The smaller the particle, the stronger its potential impact (deeper it can

grams of its weight is semiconductor microchips. The embodied energy of 1 kg

China

128,570 MW

416,700 GWh

1,126,273 GWh

0.37

get into respiratory sys) on human health because it can be more easily inhaled.

of microchips has been estimated to be 800 kg of fossil fuel. The iPhone is used

Canada

68,974 MW

356,930 GWh

604,212 GWh

0.59

Brazil

69,080 MW

336,800 GWh

605,141 GWh

0.56

USA

79,511 MW

289,980 GWh

696,516 GWh

0.42

Russia

45,000 MW

167,000 GWh

394,200 GWh

0.42

A tube of sunlight with area πR^2 shining on half of the Earth’s surface, area 2πR^2

-The average intensity (power per area) of sunlight incident on the Earth (from satellite

Installed

Annual Energy

Maximum

Capacity

Production

Energy

Load Factor

Production

8. (a) Calculate the volume of water that has to be stored in an upper reservoir

measurement) is 1361 W/m^2

Chemical and Physical Properties of Particulate Matter

-power incident on the Earth = 174 x10^15W

-(PM) has a variety of chemical composition, a large range of size and very

-This energy is distributed on an area 2πR^2, the half surface of the Earth facing the sun.

different shapes

The average intensity is about 681 W/m^2 On ground=~50%=341 W/m^2

-PM covers sulfate (SO4), nitrate (NO3), ammonium (NH4), elemental carbon

-30% of the incident energy is reflected by clouds, atmosphere and the ground, the

(EC), organic carbon (OC) or organic matter (OM), toxic As, and metals including

remaining 70% absorbed by the land and sea (51%), the atmosphere and clouds (19%)

Pb, Cd, K, Ni, V, Al, Fe and Ca. Also should be noted that fossil fuels may have

-Averaging on day and night, the intensity absorbed ≈ 171 W/m^2

trace amounts of mercury (Hg) that could condense on small particulate matter

-When the Earth is at thermal equilibrium, the same 70% that is absorbed is re-radiated

Smog: specific type of air pollution which may obscure vision. extremely

by the clouds, atmosphere and ground

harmful, with it being responsible each year for elevated rates of death and

respiratory illnesses. caused by reactions between sunlight and atmospheric

pollutants such as hydrocarbons and nitrogen dioxide Smog itself is simply

in a pumped storage arrangement in order to generate 100 GWh of hydroelectricity for a

drop head of (i) 500 m, (ii) 200 m, assuming a turbine efficiency of 90%. Envisage the

volume as a rectangular block with a height of 20 m. (b) Water released back into the

lower reservoir through a turbine generates electricity immediately. Estimate the time it

takes to generate electricity in(a). (c) Assuming a flow rate of 400 m3 /s, how long can the

volume of water in (a) generate electric power and hence find the average power

obtained. Solution: (a) The potential energy of the water stored a height of h = mgh =

ρVgh. The electrical energy E obtained from the conversion of this potential energy with an

efficiency e is given by E = ρVghe. (i) h = 500 m, V =E/ρghe=100×109 ×3600/(1000 ×10 ×

500 ×0.9) = 80 ×106 m 3 . The height is 20 m, the cross-section = 4×106 m 2 , a square with

side of 2km. (ii) h = 200 m, V = 200 ×106 m 3 . The cross-section = 10×106 m 2 , say a 2 km

airborne pollution which may obscure vision. It is caused by small particles of

by 5 km rectangle. Note: when the height of the upper reservoir is reduced, its volume has

material which become concentrated in the air.

to be enlarged. (b) Electricity is generated as soon as the water turbine turns the rotor of

Three ways of understanding emissions

the generator. The turbine is spun by the falling water. Thus the time t it takes to generate

1. Emission inventory; 2. Source apportionment at AQMS; 3. Number of Days

electricity is determined by the time it takes for the water to reach the turbine, given by h

when HK is most affected

= ½ gt2 , and the time it takes for the turbine to reach full speed rotation which is about a

Air pollution in HK

few seconds. (i) h = 500 m, t = 10 s (ii) h= 200 m, t = 6.3 s However, the time it takes for the

Average Insolation

-Local roadside pollutions caused by vehicles

water turbine to reach full speed of revolution is faster for the higher upper reservoir than

-a measure of solar radiation energy received on a given surface area in a given time

-Regional smog caused by a combination of pollutants from vehicles, shipping,

the lower upper reservoir, 2 or 3 sec and 5 or 6 sec respectively. (c) The time it takes to

-Estimate based on the facts that on average: half the incident light reaches the ground;

industry, and power plants both in HK and in Pearl River Delta region

discharge 80 ×106 m 3 of water in the upper reservoir at a flow rate of 400 m3 /s is given

half the time is day time; and the sun isn’t always overhead.

(1) by emission inventory (by tonnage)- 20% local, 80% regional (2) by source

by T =80 ×10 6 m 3 /400 m3 / s =2 ×105 s =55.6 hours Average power = 100 GWh/55.6 h =

-so only about 1/8 of the incident sunlight is typically available at the ground, 170

apportionment at AQMs (by mass concentration)- 30-40% local, 60-

1.8 GW The time it takes to discharge 200 ×106 m 3 of water at the same rate is given by T

W/m^2 on average or 170 W/m^2× 24 h/day = 4.1 kWh/m^2-day.

70%regional (3) by no of days when HK is most affected (by time)- 53% local,

= 20×106 /400 s = 5 ×105 s = 139 hours. Average power = 100GWh / 139 h = 0.72 GW Note

- Land is needed to harvest the sunlight.

36% regional, SO2 conc below 20μg/m^3 is referred as low pollution days

that more power is obtained from an upper reservoir at a greater height. But the power

- Energy demand is high in cities where the population density is high and land is scarce

from an upper reservoir at a lower height can provide power for a longer time at a lower

Ways of Using Solar Energy

power level. 9. The Guangzhou Pumped Storage Power Station consists of two reservoirs

Solar heating: Light → Heat, Solar water heating, Solar air heating

which are separated by a height of 535 m and connected by tunnels. At the end of the

Solar thermal power: light → Heat → Electricity

tunnels leading to the lower reservoir, there are 8 reversible turbine generators, each

Solar photovoltaic power: Light → Electricity

operating at a rate capacity of about 300MW. These generators pump water from the

Solar biomass: Using trees, bacteria, algae, corn, soy beans, or oilseed to make energy

lower reservoir to the higher reservoir, storing energy in the form of gravitational

fuels, chemicals, or building materials

potential energy of water and also reverse their operation to generate electricity by a flow

Food: The same as solar biomass, except we shovel the plants into humans or other

of water from the higher reservoir to the lower reservoir. (a) Suppose all the 8 turbine

animals.

generators, each operating at the rate capacity (input power) of 310 MW, are pumping

Solar Heating: harness the heat in solar radiation to produce hot water

water from the lower to the higher reservoirs. Assume that the overall efficiency of this

Parabolic Trough Trough collector focuses the sun’s rays→Concentration ratio 30x to

energy storage process is 87 %.(i) How much water is pumped to the higher reservoir per

100x its normal intensity→Tilt with the sun as the sun moves→Achieving temp higher

second? (ii) If the generators operate in this mode for 8 hours (offpeak hours) per day, how

than 400°C for heat transfer fluid→Gen. electricity in a conventional steam generator

much energy is stored up in a day? How many units (kWh) of electricity does this energy

Solar Power Tower: Hundreds to thousands of flat, sun-tracking mirrors called

correspond to? (b) Suppose this stored energy is retrieved to produce electricity for 7

heliostats→Reflect and concentrate the sun's energy→ Concentration ~1,500 times→ A

hours (peak hours) every day. Assume that the overall efficiency of this retrieving process is

central receiver tower heated up to 1000°C or more→ Minimize energy losses from

87 %. (i) How much energy is converted back into electricity per day? How many units

thermal-energy transport→ Generate electricity in a conventional steam generator.

(kWh) of electricity does this energy correspond to? (ii) Estimate the output power of each

Solar Dish: parabolic-shaped dish composed of many smaller flat mirrors→ Reflects solar

of the 8 generators during the peak hours. (c) What is the overall efficiency of the pump

radiation to the focal point→ Tilt with the sun as the sun moves→ Concentration ratio

storage process (storing and retrieving the energy)? (d) The charge of peakhour electricity

~1000x→ A receiver mounted at the focal point with a working fluid temperature higher

is HK$0.90 per kWh, the pumping cost of off-peak electricity is HK$0.70 per kWh. How

than 750°C→ Stirling cycle engines are used for power conversion.

much money is made by operating the station for one day? Solution: (a) Electrical energy is

used in one second for 8 generators = 8×310 MJ = 2,480 MJ.0.87 of the energy used per

sec is converted in gravitational potential energy of water which is 0.87× 8×310 MJ =

2,157.6 MJ.The gravitational energy of water increases at the rate of 2,158 MJ per sec. (i)

Let m’ be the mass of water pumped to the upper reservoir (535 m above the lower

reservoir) per sec. The increase of potential energy of water pumped to the upper

reservoir per sec is given by m’gh = m’ ×10× 535 = 2,158×106 ; m’ = 4.03×105 kg = 400 tons

(ii) The energy stored in a 8-hour day =8×60×60×2,158 MJ = 62.15×1012 J =

62.15×1012/3.6×106 = 17.26×106 kWh (b) Retrieving the energy (i) 0.87 of the potential

energy of the water in the high reservoir is converted back to electricity. This is

0.87×62.15×1012J = 54.07×1012 J or 15.02×106kWh (ii) The above energy is delivered by 8

generators in 7 hours, thus the output of each generator is 54.07×1012/8 =6.76×1012J.

The power output of each generator is 6.76×1012 J /7×60× 60 s = 268.2 MJ/s or 268.2 MW

(c) The overall efficiency of the pump storage process = 87% ×87%=75.69% (d) The

pumping cost during the 8 off-peak hours = HK$0.70 per kWh ×

17.26×106 kWh = HK$12.082×106 . The amount obtained from 7 peak hours of electricity =

HK$0.90 per kWh ×15.02×106 kWh

= HK$13.518×106 . The money made per day = HK$1,436,000