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Comparative understanding of the

energy production and related

issues

Dr. Manish Kumar Energy & Environment

A Focus on Principle of Production

And related issues

Energy Use Through the Ages.

• Prehistory to Industrial Revolution: Heat: Direct Sun, Indirect (burnt biomass) Mechanical/Transport Systems: Biological (water, wind, animals) Units used: 1 horsepower (746 Watts = 746 Joules/sec).

• Early Industrial Revolution (1800s): Fossil Fuels (coal) Steam Engine. Units used: 1 BTU (1055 Joules). • Late Industrial Revolution (1880s): Fossil Fuels (gasoline) Turbines Electricity. Internal Combution cars. Units used: MegaJoules, MegaWatts.

Energy Use Effects Population.

each dot represents

1 million people

John H. Tanton, "End of the Migration Epoch,"

reprinted by The Social Contract , Vol IV, No 3 and Vol. V, No. 1, 1995.

Settlements in Fertile Crescent, Asia, shore regions.

Population Increases Gradually.

More settlement in temperate shore regions. Organized Agriculture reduction of forests.

Pre-Industrial Age Population

Forests depleted in Europe, Asia. Wind power also in use for transport.

Dawn of Industrial Age.

Fossil Fuels coal.

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Industrial Age

Fossil FuelsElectricity in use for Industry, Transport, Food, Medicine. Allows previously non-habitable areas to be settled.

Post WWII

Gasoline/Diesel in use for transport. Nuclear power introduced. Population spreads through commercial air transport.

The Recent Past

Improvements in efficiency (agriculture, medicine,transport). Air conditioning allows arid climates to be settled.

The Near Future

Energy effectively decoupled from geography.

Why Fossil Fuels?

• What’s so special about fossil fuels? Energy content. Gasoline: 115,000 BTU/gal = 120 MJoules/gal Coal: 15,000 BTU/lb = 15 MJoules/lb Compare to:

Wood: 7,500 BTU/lb = 7.5 MJoules/lb A “horse” (working 1 hour) = 2.5 MJoules. A human … = 0.2 MJoules

Fossil Fuels deliver lots of energy in a small volume. Fossil Fuels are transportable.

How Do Fossil Fuels Work?

CH4 Methane, the simplest Hydrocarbon,

burns (well, all hydrocarbons burn):

Burning is a process of combining with oxygen.

1 Methane + 2 O2 2 H20 + CO2 + Energy

Hydrocarbons burn fast.

Hydrocarbon burning releases water and CO2

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More Hydrocarbons

2 Carbon Atoms ETHANE

3 Carbon Atoms PROPANE

4 Carbon Atoms BUTANE

And so on. Five Carbon Atoms give you PENTANE. Six Carbon Atoms give you HEXANE. Seven give you HEPTANE.

Bigger is Better The bigger the hydrocarbons get: - The more energy per molecule you get from burning. - The easier it is to Liquefy them.

Methane is very difficult to liquefy. Propane will liquefy at 40 below zero. Butane will liquefy on a cold winter day.

The World’s Favorite Hydrocarbon

Octane: Eight Carbons. The main ingredient in gasoline.

The Trouble with Hydrocarbons

It’s all those Carbon atoms. CO2 is a greenhouse gas. They trap infrared radiation in the troposphere, heating lower atmosphere.

Earth’s Surface absorbs visible light. emits thermal radiation in infrared.

CO2 CO2

CO2

CO2

CO2

CO2

CO2 CO2

CO2

CO2

Is Greenhouse Effect Bad? Let’s compare Mars, Earth, Venus.

Alt

itud

e (k

m)

50

100

Temperature (Kelvin) 100 400 800

A little greenhouse effect is good. ’s show surface

temperature without the greenhouse effect.

A lot of greenhouse effect is very bad. Example: Venus.

Can We See the Increase in CO2?

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CO2 Levels Historically

• 1800: 280 ppm

• 1850s: 290 ppm

• 1850 – 1960 310 ppm

• 1960 – 2000 365 ppm

10 ppm in 50 yrs (pioneer effect)

20 ppm in 100 yrs (industrial rev.)

55 ppm in 40 yrs.

Does it Affect Temperature?

Problem: We’ve only been looking for a few decades. Answer: Paleoclimatology: ice cores, tree rings, etc.

Crowley et al July 14, 2000 Science, 289: 270-277

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Non-renewable

Fossil Fuels

Nuclear Energy

Renewable Energy

Hydroelectric Power

Tidal Power

Wind Power

Wave Power

Biomass

Solar Power 22

Thermal power stations (be they fossil or nuclear) have a heating

element, a boiler and a turbine. We know that the Carnot

efficiency, η, of a heat engine is given by:

where Th is the temperature of the hot reservoir and Tc is the temperature of

the cold reservoir. In case the cold reservoir is the environment

(usually a river): Tc = 150C (288 K) and Th =

600-7000C (900 K or thereabouts). This gives Carnot efficiencies of the order of 70 %.

Issues

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Real power stations are not reversible Carnot engines and cannot

reach efficiencies of 70%.

42 % would be reckoned to be good for a normal coal-fired power-station as:

• Boilers can reach efficiencies of 90%, • a typical power station will have three steam turbines with

the total efficiency of about 48 %.

• There are some mechanical and miscellaneous hot losses

Comparing renewable vs. non-renewable energy, we'd suggest creating a

Pro and Con list for each energy source. That will give you a way to

compare the various energy resources. One device to improve the utilization of the system is to construct a combined heat and power generator (CHP). The

overall efficiency of this, ηCHP is defined as:

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There may be three ways of obtaining power from nuclear energy: (i) thermal reactors (from the fission of uranium or thorium),

(ii) breeder reactors (which in addition convert U238 to Pu239), and

(iii) fusion reactors

The important points are:

(i) the large amount of energy released, (ii) more neutrons back than are consumed and

(iii)the unavoidable production of radio-active

isotopes.

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Control k needs to be close to 1. Thus

we require something to absorb

enough of the neutrons to ensure that

this is the case.

The moderator like graphite and

heavy water. Neutrons are slowed

down by allowing them to hit the atoms of a moderator (light nuclei

that take away the initial KE of the

neutrons).

Issues

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• There are two basic problems with this method of energy generation:

(i) the possibility of a major release of radioactivity; the Chernobyl explosion is the clearest example,

(ii) the problem of disposal of the radioactive waste.

Radioactive waste is conventionally divided into three types:

• Low level, which includes the waste produced by therapy in hospitals,

• Medium level. An example would be the fabric, particularly the metals of a reactor. • High level. Medium and long-lived decay products of the

nuclear reaction, including actinides produced by neutron capture rather

than nuclear fission.

Nuclear Power • Excellent energy output:

= 1014 J/kg, = 10,000 gallons of gasoline.

• Problem: Radioactivity

•Answer: Containment, disposal.

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These amount, in the end, to harnessing solar energy directly or

indirectly (with the exception of tidal power and geothermal).

In principle there is a lot of solar energy: about 18000 TW falls on the Earth.

The basic problem is collecting it as the energy density is very low. The current uses are as follows:

Hydroelectric, 6 % of global energy requirements,

Biomass burning, 1.5 % of global requirements, Tidal, solar, geothermal and wind, together, provide about

0.5 % of global requirements.

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Water passes from a dam down a tube and through a turbine. The idea is to convert the

potential energy of the water first into kinetic and then into electrical energy.

Where, ρ = the density of water,

Q is the flow-rate and

P0= the maximum power available to

be generated

The main advantage of hydroelectric power is

that the energy density is high. The drawbacks are serious: hydroelectric

schemes require large dams that cause large

social and ecological changes.

Of all renewables, wind is the closest to being competitive with conventional fossil fuels.

Most commercial projects are based on wind farms. The individual

generators must be separated by about ten times the blade length and a further buffer zone round the farm is required. 30

The basic idea is to trap the kinetic energy

of the wind.

The generation of energy is about 95 % efficient

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About 11 percent of the entire world's wind-

generated electricity is found in California,

followed by Denmark and Germany

Issues: The main problem is that the peak wind and the peak demand

are unlikely to coincide.

Further, large wind farms are unpopular. They are very visible and often on sites of considerable natural beauty.

Since wind energy is variable they need a backup, i.e. a battery or the grid itself.

Wind Power • Turbines can provide ~ ½ MWatt when running. • Wind farms can have up to 200 turbines. over 500 gallons of gas/day.

BBC NEWS: The Irish Government has approved

plans for the world's largest offshore electricity- generating wind farm, to be built on a sandbank in the Irish Sea south of Dublin.

When completed, the 200 turbines will produce 10% of the country's electricity needs.

• Problem: calm. • Answer: storage.

fan gearbox dynamo

Wave and Geothermal Power

• Wave farms: Convert wave motion to circular drive turbines: ~50 kWatts/m Salter ducks

• At tectonic plate boundaries, geothermal plants can tap the heat of the earth’s interior

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3ways: Use the ocean's waves, use the ocean's

high and low tides, or we can use temperature

differences in the water.

Issues: A number of prototypes have been

tried but the economics of the

power generation is not yet good enough for a full commercial trial.

OCEAN ENERGY

Wave Energy

Tidal Energy

Ocean Thermal Energy Conversion (OTEC)

Issues: i) Tidal barrages are expensive, (ii) drastically change the environment of the estuary. iii) too crude. iv) It is necessary to

further average the tides over a month. And v) Not possible to get

significant power out close to low tide. 35

The basic idea is to trap the tide behind a

barrier and let the water out through a

turbine at low tide.

Where, R = tidal range,

A=the estuary area is A,

The mass of water trapped behind

the barrier is ρAR, and the centre

of gravity is R/2 above the low tide

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The essential difference between this and fossil fuels is that the biomass cycle is a true cycle provided that for each plant used as fuel

a replacement is Planted.

BIOMASS ENERGY

Biomass is dumped into huge hoppers and then fed into a furnace where it is burned. The heat is used to boil water in the boiler, and

the energy in the steam is used to turn turbines and generators

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Covers domestic, industrial and

agricultural dry waste material, wet waste

material and crops.

Issues: Environmental Friendly

A major user of biomass is Brazil: the source being waste from the

sugar-cane industry. Bagasse (residue after crushing the cane), and barbojo (leaves of the cane). Perhaps 67 % of the 80 sugar-cane

producing countries can use this as fuel.

BIOMASS ENERGY

Types of Biofuel:

Gaseous bio-fuels eg. biogas (CH4 and CO2) from anaerobic

digestion of plant and animal wastes, and producer gas(CO & N2) from gasification of plants, wood and wastes.

Liquid bio-fuels eg. oils from crop seeds (e.g. rape, sunflower), esters produced from such oil, ethanol from fermentation

and methanol from acidification and distillation of woody crops.

Solid bio-fuels eg: charcoal from pyrolysis, and refuse derived fuels, e.g. compressed pellets.

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The simplest way of making use of energy

from the Sun is to turn it into heat. A black

surface directly facing full sunlight can absorb 1 kW/m2.

Issues: Only direct radiation can be concentrated. Depends on the latitude, time of day and season.

To maximise the solar energy absorbtion orientation should change

during the day, from day to day and with season

SOLAR ENERGY

Solar hot water

Solar thermal electricity

Solar Cells

Solar Power

•Sun’s main process: Turning H to He (fusion). •Sun’s output 4 x 1026 Watts (or Joules/sec).

•So at 15% efficiency, 1 m2, 10 hrs of sunlight 1 MJoule/day. so 100 m2, will give equivalent of 1 gallon of gas per sunny day.

• Problem: Night, clouds. • Answer: Storage. (batteries, fuel cells).

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DRAWBACKS OF RENEWABLE ENERGY

The fluid most often used with solar thermal electric generation is

very toxic and spills can happen.

Need large tracts of land as a collection site Manufacturing this equipment has environmental impacts.

All the solar production facilities in the entire world only make enough solar cells to produce about 350 megawatts, about enough

for a city of 300,000 people. that's a drop in the bucket compared to

our needs. Wind farms could cause erosion in desert areas. Most often, winds

farms affect the natural view because they tend to be located on or just below ridgelines. Bird deaths also occur due to collisions with

wind turbines and associated wires. This issue is the subject of on-

going research.

Problem with Alternatives to Hydrocarbons

• Hydrocarbons: 1) store a lot of energy compactly.

2)are cheap.

• Alternatives: 1) have large footprint.

2) enough total energy,

but at low power rates. 3) low duty cycle.

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FUTURE STEPS

Reduce, Recycle & Reuse (More R’s)

Thermal insulation

Future energy source (Hydrogen cells, Fuel Cell)

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Answer: Fuel Cells • A simple but effective chemical reaction: 2 H2 + O2 2 H2O + Energy

• Can be run in reverse! 2 H2O + Energy 2 H2 + O2

Anode: Strips the e- from the hydrogen sends it through a wire, provides power. Membrane: Separates Anode and Cathode. Takes the proton (hydrogen stripped of e-) and pushes it through to the Cathode. Cathode: Strips O2 into two O (platinum catalyst). Grabs two protons through the membrane combine with one O to make one water molecule

Fuel Cell Points • Each individual cell provides ~0.7 V. Use many in a stack.

• Where do you get Hydrogen? can use hydrocarbons,

wastewater digesters, landfills, biomass.

can also run the fuel cell backward (use solar, wind, etc. power to convert

water to H and O).

Possibilities with Fuel Cells • Clean power (solar, wind, etc.) have - large footprint. - small duty cycle.

• Can use this power to run a fuel cell backwards!

- Disassociate water into H2 and O2 gas.

- Store the gases until needed (safely).

- Pump gases into fuel cell and make electricity.

Hindenburg burns over Lakehurst NJ May 6 1937

Examples

1. Solar Cell Direct:

2. Solar Cell output makes H2, O2, at Fuel Cell A, and the H2, O2, gases make electricity at Fuel Cell B.

Solar cell

Solar cell

Fuel Cell A

H2

O2

Fuel Cell B

Conclusion • Fossil fuels have been great. Have enabled mass of humanity to move beyond subsistence living. But we really need to figure out how to live without them. • Carbon loading of the atmosphere is reaching terrifying levels. Scientific consensus on global warming. • Clean alternatives like solar, wind, etc. have problems of rate, efficiency, size. Hydrogen is abundant. Problems of storage, distribution, etc. can be solved.