Green energy Physics

Unit 5

Classification

• Renewable/ non conventional• Non renewable/ conventional

How much solar energy?

The surface receives about 47% of the total solar energy that reaches the Earth. Only this amount is usable.

Direct Conversion into Electricity• Photovoltaic cells are capable of

directly converting sunlight into electricity.

• A simple wafer of silicon with wires attached to the layers. Current is produced based on types of silicon (n- and p-types) used for the layers. Each cell=0.5 volts.

• Battery needed as storage• No moving partsdo no wear out,

but because they are exposed to the weather, their lifespan is about 20 years.

PH 0101 Unit-5 Lecture-2 5

• A proper metal contacts are made on the n-type and p- type side of the semiconductor for electrical connection

Working:

• When a solar panel exposed to sunlight , the light energies are absorbed by a semiconduction materials.

• Due to this absorded enrgy, the electrons are libereted and produce the external DC current.

• The DC current is converted into 240-volt AC current using an inverter for different applications.

PH 0101 Unit-5 Lecture-2 6

Mechanism:

• First, the sunlight is absorbed by a solar cell in a solar panel.

• The absorbed light causes electrons in the material to increase in energy. At the same time making them free to move around in

the material.

• However, the electrons remain at this higher energy for only a short time before returning to their original lower energy position.

• Therefore, to collect the carriers before they lose the energy gained from the light, a PN junction is typically used.

PH 0101 Unit-5 Lecture-2 7

• A PN junction consists of two different regions of a semiconductor material (usually silicon), with one side called the p type region and the other the n-type region.

• During the incident of light energy, in p-type material, electrons can gain energy and move into the n-type region.

• Then they can no longer go back to their original low energy position and remain at a higher energy.

• The process of moving a light- generated carrier from p-type region to n-type region is called collection.

• These collections of carriers (electrons) can be either extracted from the device to give a current, or it can remain in the device and gives rise to a voltage.

PH 0101 Unit-5 Lecture-2 8

• The electrons that leave the solar cell as current give up their energy to whatever is connected to the solar cell, and then re-enter the solar cell. Once back in the solar cell, the process begins again:

PH 0101 Unit-5 Lecture-2 9

The mechanism of electricity production- Different stages

Conduction band High density

Valence band Low density

E

The above diagram shows the formation of p-n junction in a solar cell. The valence band is a low-density band and conduction band is high-density band.

PH 0101 Unit-5 Lecture-2 10

Stage-1

Therefore, the hole (vacancy position left by the electron in the valence band) is generates. Hence, there is a formation of electron-hole pair on the sides of p-n junction.

When light falls on the semiconductor surface, the electron from valence band promoted to conduction band.

Conduction band High density

Valence band Low density

E

PH 0101 Unit-5 Lecture-2 11

Stage-2

In the stage 2, the electron and holes are diffuse across the p-n junction and there is a formation of electron-hole pair.

Conduction band High density

Valence band Low density

Ejunction

PH 0101 Unit-5 Lecture-2 12

Stage-3

In the stage 3, As electron continuous to diffuse, the negative charge build on emitter side and positive charge build on the base side.

Conduction band High density

Valence band Low density

Ejunction

PH 0101 Unit-5 Lecture-2 13

Stage-4When the PN junction is connected with external circuit, the current flows.

Conduction band High density

Valence band Low density

Ejunction

Power

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A solar panel (or) Solar array

Single solar cell

• The single solar cell constitute the n-type layer sandwiched with p-type layer.

• The most commonly known solar cell is configured as a large-area p-n junction made from silicon wafer.

• A single cell can produce only very tiny amounts of electricity

• It can be used only to light up a small light bulb or power a calculator.

• Single photovoltaic cells are used in many small electronic appliances such as watches and calculators

PH 0101 Unit-5 Lecture-2 15

N-type

P-type

Single Solar cell

PH 0101 Unit-5 Lecture-2 16

Solar panel (or) solar array (or) Solar module

The solar panel (or) solar array is the interconnection of number of solar module to get efficient power.

• A solar module consists of number of interconnected solar cells.

• These interconnected cells embedded between two glass plate to protect from the bad whether.

• Since absorption area of module is high, more energy can be produced.

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PH 0101 Unit-5 Lecture-2 18

Based on the types of crystal used, soar cells can be classified as,1. Monocrystalline silicon cells2. Polycrystalline silicon cells3. Amorphous silicon cells

1. The Monocrystalline silicon cell is produced from pure silicon (single crystal). Since the Monocrystalline silicon is pure and defect free, the efficiency of cell will be higher.

2. In polycrystalline solar cell, liquid silicon is used as raw material and polycrystalline silicon was obtained followed by solidification process. The materials contain various crystalline sizes. Hence, the efficiency of this type of cell is less than Monocrystalline cell.

Types of Solar cell

PH 0101 Unit-5 Lecture-2 19

3. Amorphous silicon was obtained by depositing silicon film on the substrate like glass plate.

• The layer thickness amounts to less than 1µm – the thickness of a human hair for comparison is 50-100 µm.

• The efficiency of amorphous cells is much lower than that of the other two cell types.

• As a result, they are used mainly in low power equipment, such as watches and pocket calculators, or as facade elements.

PH 0101 Unit-5 Lecture-2 20

Comparison of Types of solar cell

Material Efficiency (%)

Monocrystalline silicon 14-17

Polycrystalline silicon 13-15

Amorphous silicon 5-7

PH 0101 Unit-5 Lecture-2 21

Advantage, disadvantage and application of Solar cellAdvantage

1. It is clean and non-polluting2. It is a renewable energy3. Solar cells do not produce noise and they are totally silent.4. They require very little maintenance5. They are long lasting sources of energy which can be used

almost anywhere6. They have long life time7. There are no fuel costs or fuel supply problems

PH 0101 Unit-5 Lecture-2 22

Disadvantage

1. Solar power can’t be obtained in night time

2. Solar cells (or) solar panels are very expensive

3. Energy has not be stored in batteries

4. Air pollution and whether can affect the production of electricity

5. They need large are of land to produce more efficient power supply

WIND POWER

• What is it?• How does it work?• Efficiency

WIND POWER - What is it?• All renewable energy (except tidal and geothermal power), ultimately

comes from the sun

• The earth receives 2 x 1017 watts of power (per hour) from the sun

• About 2 percent of this energy is converted to wind energy

• Differential heating of the earth’s surface and atmosphere induces vertical and horizontal air currents that are affected by the earth’s rotation and contours of the land WIND. ~ e.g.: Land Sea Breeze Cycle

•Wind is slowed by the surface roughness and obstacles.

• A wind turbine obtains its power input by converting the force of the wind into a torque (turning force) acting on the rotor blades.

• The amount of energy which the wind transfers to the rotor depends on the density of the air, the rotor area, and the wind speed.

• The kinetic energy of a moving body is proportional to its weight. In other words, the "heavier" the air, the more energy is received by the turbine.

KidWind Project | www.kidwind.org

LARGE TURBINES:

• Able to deliver electricity at lower cost than smaller turbines, because foundation costs, planning costs, etc. are independent of size.

• Well-suited for offshore wind plants.

• In areas where it is difficult to find sites, one large turbine on a tall tower uses the wind extremely efficiently.

SMALL TURBINES:

Local electrical grids may not be able to handle the large electrical output from a large turbine, so smaller turbines may be more suitable.

High costs for foundations for large turbines may not be economical in some areas.

Landscape considerations

Wind Turbines: Number of Blades

Most common design is the three-bladed turbine. The most important reason is the stability of the turbine. A rotor with an odd number of rotor blades (and at least three blades) can be considered to be similar to a disc when calculating the dynamic properties of the machine.

A rotor with an even number of blades will give stability problems for a machine with a stiff structure.

• Wind power generators convert wind energy (mechanical energy) to electrical energy.

• The generator is attached at one end to the wind turbine, which provides the mechanical energy.

• At the other end, the generator is connected to the electrical grid.

• The generator needs to have a cooling system to make sure there is no overheating.

*No other factor is more important to the amount of power available in the wind than the speed of the wind

The power in wind is proportional to the cubic wind speed ( v^3 ).

20% increase in wind speed means 73% more power

Doubling wind speed means 8 times more power

WHY?

~ Kinetic energy of an air mass is proportional to v^2

~ Amount of air mass moving past a given point is proportional to wind velocity (v)

Calculation of Wind Power

•Power in the wind Effect of air density,

– Effect of swept area, A– Effect of wind speed, V

R

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

Power in the Wind = ½ρAV3

• Environmental benefits

• No emissions

• No fuel needed

• Distributed power

• Remote locations

Limitations of Wind Power

Power density is very low. Needs a very large number of wind mills to produce

modest amounts of power. Cost. Environmental costs.

material and maintenance costs. Noise, birds and appearance.

Cannot meet large scale and transportation energy needs.

The Future of Wind Energy

Future of wind energy can be bright if government policies subsidize and encourage its use.

Technology improvements unlikely to have a major impact.

Can become cost competitive for electricity generation if fossil energy costs skyrocket.

Ocean Energy

• Thermal energy-OTEC(Ocean Thermal Electric Conversion)

• Mechanical energy

From tides From waves

Wave Facts:

• Waves are caused by a number of forces, i.e. wind, gravitational pull from the sun and moon, changes in atmospheric pressure, earthquakes etc. Waves created by wind are the most common waves. Unequal heating of the Earth’s surface generates wind, and wind blowing over water generates waves.

• Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 50-Hertz frequency before it can be added to the electric utility grid.

Mechanical energy-From waves

Three Basic Kinds of Systems

• Offshore (so your dealing with swell energy not breaking waves)

• Near Shore (maximum wave amplitude)• Embedded devices (built into shoreline to

receive breaking wave – but energy loss is occurring while the wave is breaking)

3 basic systems for ocean wave energy devices

• 1. Channel systems that funnel waves into reservoirs• 2. Float systems that drive hydraulic pumps• 3. Oscillating water column systems that use waves to

compress air within a container

® mechanical power either directly activates a generator, or transfers to a working fluid, water or air, which then drives a turbine/generator

Wave Power Designs• Wave Surge or Focusing

Devices-Channel SystemThese shoreline devices, also called "tapered channel" systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. These focusing surge devices are sizable barriers that channel large waves to increase wave height for redirection into elevated reservoirs.

Floats or Pitching Devices

These devices generate electricity from the bobbing or pitching action of a floating object. The object can be mounted to a floating raft or to a device fixed on the ocean floor.

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Oscillating Water Columns (OWC)

These devices generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine.

-Advantages and Disadvantages-

• Advantages– The energy is free – no fuel needed, no waste produced– Not expensive to operate and maintain– Can produce a great deal of energy

• Disadvantages– Depends on the waves – sometimes you’ll get loads of

energy, sometimes almost nothing– Needs a suitable site, where waves are consistently

strong– Some designs are noisy. But then again, so are waves,

so any noise is unlikely to be a problem– Must be able to withstand

Tidal Power

• Tidal power generators derive their energy from movement of the tides.

• Has potential for generation of very large amounts of electricity, or can be used in smaller scale.

Tides• The interaction of the Moon and the

Earth results in the oceans bulging out towards the Moon (Lunar Tide). The sun’s gravitational field pulls as well (Solar Tide)

• As the Sun and Moon are not in fixed positions in the celestial sphere, but change position with respect to each other, their influence on the tidal range (difference between low and high tide) is also effected.

• If the Moon and the Sun are in the same plane as the Earth, the tidal range is the superposition of the range due to the lunar and solar tides. This results in the maximum tidal range (spring tides). If they are at right angles to each other, lower tidal differences are experienced resulting in neap tides.

How do tides changing = Electricity?

As usual, the electricity is provided by spinning turbines.

Two types of tidal energy can be extracted: kinetic energy of currents between ebbing (tide going out) and surging tides(tide coming in)

and potential energy from the difference in height (or head) between high and low tides.

The potential energy contained in a volume of water isE = xMg

where x is the height of the tide, M is the mass of water and g is the acceleration due to gravity.

1.) Tidal Barrage

• Two types:

• Single basin system

• Double-basin system

• Utilize potential energy• Tidal barrages are typically dams built across an

estuary or bay. • consist of turbines, sluice gates, embankments,

and ship locks.

Basin

Single basin system-Ebb generation: During flood tide basin is filled and sluice gates are closed

, trapping water. Gates are kept closed until the tide has ebbed sufficiently and thus turbines start spinning and generating electricity.

Flood generation: The basin is filled through the turbine which generate at flood tide.

Two way generation: Sluice gates and turbines are closed until near the end of the flood tide when water is allowed to flow through the turbines into the basin creating electricity. At the point where the hydrostatic head is insufficient for power generation the sluice gates are opened and kept open until high tide when they are closed. When the tide outside the barrage has dropped sufficiently water is allowed to flow out of the basin through the turbines again creating electricity.

Double-basin system

• There are two basins, but it operates similar to en ebb generation, single-basin system. The only difference is a proportion of the electricity is used to pump water into the second basin allowing storage.

Ocean Thermal Energy Conversion

• Ocean thermal energy conversion (OTEC) is a method for generating electricity which uses the temperature difference that exists between deep and shallow waters

The ocean stores thermal energy• Each day, the tropical oceans absorb an amount of solar radiation equal to the heat

content of 250 billion barrels of oil

• The ocean’s surface is warmer than deep water

- Ocean thermal energy conversion (OTEC) is based on this gradient in temperature

- Closed cycle approach = warm surface water evaporates chemicals, which spin turbines

- Open cycle approach = warm surface water is evaporated in a vacuum and its steam turns turbines

- Costs remain high and no facility is commercially operational

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OTEC: What is it?• Thermal energy- form of energy that manifests itself

as an increase of temp.• Method for generating electricity.• Runs a heat engine- a physical device that converts

thermal energy to mechanical output • Uses temp. difference that exists b/w deep & shallow

waters. • Temperature difference between warm surface

water and cold deep water must be >20°C (36°F) for OTEC system to produce significant power.

Ocean Thermal Energy Conversion (OTEC)

• Ocean Thermal Energy Conversion produces electricity from the natural thermal gradient of the ocean, using the heat stored in warm surface water to create steam to drive a turbine, while pumping cold, deep water to the surface to re-condense the steam.

Closed Cycle OTEC

In closed-cycle OTEC, warm seawater heats a working fluid, such as ammonia, with a low boiling point, such as ammonia, which flows through a heat exchanger (evaporator).

The ammonia vapor expands at moderate pressures turning a turbine, which drives a generator which produces energy.

OTEC: Closed Cycle

The vapor is then condensed in another heat exchanger (condenser) by the cold, deep-ocean water running through a cold water pipe.

The working fluid (ammonia) is then cycled back through the system, being continuously recycled.

Ocean Thermal Energy Conversion(OTEC)

Open Cycle OTEC In an open-cycle OTEC plant, warm seawater from

the surface is the working fluid that is pumped into a vacuum chamber where it is flash- evaporated to produce steam at an absolute pressure of about 2.4 kilopascals (kPa).

The resulting steam expands through a low-pressure turbine that is hooked up to a generator to produce electricity.

The steam that exits the turbine is condensed by cold, deep-ocean water, which is returned to the environment.

If a surface condenser is used, the condensed steam remains separated from the cold ocean water and can be collected as a ready source of desalinated water for commercial, domestic or agricultural use.

OTEC Open Cycle System

• In an open-cycle plant, the warm water, after being vaporized, can be re-condensed and separated from the cold seawater, leaving behind the salt and providing a source of desalinated water fresh enough for municipal or agricultural use.

OTEC Hybrid Cycle System

Hybrid plants, combining benefits of the two systems, would use closed-cycle generation combined with a second-stage flash evaporator to desalinate water.

OTEC limited applicationsVery costlyLimited suitable sitescan’t justify for electricity – must also desalinize, sustain aquaculture, etc…

Geothermal Energy

Sources of Earth’s Internal Energy•70% comes from the decay of radioactive nuclei with long half lives that are embedded within the Earth

•Some energy is from residual heat left over from Earths formation.

•The rest of the energy comes from meteorite impacts.

Geothermal energy• Renewable energy is generated from deep within the

Earth

• Radioactive decay of elements under extremely high pressures deep inside the planet generates heat

- This heat rises through magma, fissures, and cracks

• Geothermal power plants use heated water and steam for direct heating and generating electricity

Different Geothermal Energy Sources1.Hydrothermal resources:

a)Hot Water Reservoirs: As the name implies these are reservoirs of hot underground water. There is a large amount of them in the US, but they are more suited for space heating than for electricity production.

b)Natural Stem Reservoirs: In this case a hole dug into the ground can cause steam to come to the surface. This type of resource is rare in the US.

2.Geopressured Reservoirs: In this type of reserve, brine completely saturated with natural gas in stored under pressure from the weight of overlying rock. This type of resource can be used for both heat and for natural gas.

Normal Geothermal Gradient: At any place on the planet, there is a normal temperature gradient of +300C per km dug into the earth. Therefore, if one digs 20,000 feet the temperature will be about 1900C above the surface temperature. This difference will be enough to produce electricity. However, no useful and economical technology has been developed to extracted this large source of energy.

3.Molten Magma: No technology exists to tap into the heat reserves stored in magma. The best sources for this in the US are in Alaska and Hawaii.

4.Hot Dry Rock: This type of condition exists in 5% of the US. It is similar to Normal Geothermal Gradient, but the gradient is 400C/km dug underground. The simplest models have one injection well and two production wells. Pressurized cold water is sent down the injection well where the hot rocks heat the water up. Then pressurized water of temperatures greater than 2000F is brought to the surface and passed near a liquid with a lower boiling temperature, such as an organic liquid like butane. The ensuing steam turns the turbines. Then, the cool water is again injected to be heated. This system does not produce any emissions. US geothermal industries are making plans to commercialize this new technology.

Geothermal energy is renewable in principle

• But if a geothermal plant uses heated water faster than groundwater is recharged, the plant will run out of water

- Operators have begun injecting municipal wastewater into the ground to replenish the supply

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We can harness geothermal energy for heating and electricity

• Geothermal ground source heat pumps (GSHPs) use thermal energy from near-surface sources of earth and water

- The pumps heat buildings in the winter by transferring heat from the ground into buildings

- In the summer, heat is transferred through underground pipes from the building into the ground

- Highly efficient, because heat is simply moved

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Use of geothermal power is growing

• Currently, geothermal energy provides less than 0.5% of the total energy used worldwide

- It provides more power than solar and wind combined

- But much less than hydropower and biomass

• Commercially viable only in British Columbia

• In the right setting, geothermal power can be among the cheapest electricity to generate

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Geothermal power has benefits and limitations

• Benefits:

- Reduces emissions

- It does emit very small amounts of gases

• Limitations:

- May not be sustainable, as CO2 can be released

- Water is laced with salts and minerals that corrode equipment and pollute the air

- Limited to areas where the energy can be trapped

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Biomass•Biomass is a renewable energy source that is derived from living or recently living organisms. •Biomass includes biological material, not organic material like coal. •Energy derived from biomass is mostly used to generate electricity or to produce heat. •Thermal energy is extracted by means of combustion, torrefaction, pyrolysis, and gasification.•Biomass can be chemically and biochemically treated to convert it to a energy-rich fuel.

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Biomass Resources• Energy Crops

– Woody crops– Agricultural crops

• Waste Products– Wood residues– Temperate crop wastes– Tropical crop wastes– Animal wastes– Municipal Solid Waste (MSW)– Commercial and industrial wastes

http://www.eere.energy.gov/RE/bio_resources.html

Conversion TechnologiesA wide variety of technologies is deployed for

energy production from biomass

→Production of heat , electricity and transport fuels is possible through a portfolio of technologies

Conversion technologies: power and heat

• Digestion : Biogas is released with the digestion of organic material

• Combustion: Because heat releases with the combustion of biomass, electricity can be aroused using a steam turbine

• Gasification: high heating of organic material, releases biogas

• Production of bio-oils

Conversion technologies: biofuels for the transport Sector

• Extraction and production of esters from oilseeds

• Fermentation: production of ethanol

• Methanol, hydrogen and hydrocarbons via Gasification

ENVIRONMENTAL ADVANTAGES

• Renewable resource• Reduces landfills• Protects clean water supplies• Reduces acid rain and smog• Reduces greenhouse gases

– Carbon dioxide– Methane

BIOMASS AND CARBON EMMISIONS

• Biomass emits carbon dioxide when it naturally decays and when it is used as an energy source

• Living biomass in plants and trees absorbs carbon dioxide from the atmosphere through photosynthesis

• Biomass causes a closed cycle with no net emissions of greenhouse gases

GEOGRAPHIC AREAS

• Comes from the forest

• Can also come from plant and animal waste

• Wood and waste can be found virtually anywhere

• Transportation costs

Introduction: What is Biodiesel?

• A diesel fuel replacement produced from vegetable oils or animal fats through the chemical process of transesterification– Mono-alkyl esters

• Biodiesel can be used in any diesel motor in any percent from 0-100% with little or no modifications to the engine

Why make biodiesel?

Diesel fuel injectors are not designed for viscous fuels like vegetable oil

Glycerin (thick)

Biodiesel

The Chemistry of Biodiesel

• All fats and oils consist of triglycerides– Glycerol/glycerine = alcohol– 3 fatty acid chains (FA)

• Transesterification describes the reaction where glycerol is replaced with a lighter and less viscous alcohol– e.g. Methanol or ethanol

• A catalyst (KOH or NaOH) is needed to break the glycerol-FA bonds

Transesterification (the biodiesel reaction)

Fatty Acid Chain

Glycerol

Methanol (or Ethanol)

One triglyceride molecule is converted into three mono alkyl ester (biodiesel) molecules

Biodiesel

Triglyceride

Vegetable Oil as Feedstocks

• Oil-seed crops are the focus for biodiesel production expansion

• Currently higher market values for competing uses constrain utilization of crops for biodiesel production

• Most oil-seed crops produce both a marketable oil and meal– Seeds must be crushed to extract

oil– The meal often has higher market

value than the oil

Soybeans• Primary source for biodiesel production in U.S.• Approximately 2 billion gallons of oil produced annually

Canola/Rapeseed

• Rapeseed is a member of the mustard family

• Canola is a variety of rapeseed bred to have low levels of erucic acid and glucosinolates (both of which are undesireable for human consumption)

• Good oil yield

Sunflowers• Wide geographical range for

production• Market value is high for

edible oil and seeds, birdseeds

• Second largest biodiesel feedstock in the EU

CamelinaCamelina sativa is a member of mustard familySummer annual crop suited to grow in semi-arid climates and northern U.S.

Advantages of Biodiesel• Biodegradable• Non-toxic• Favorable Emissions Profile• Renewable• Carbon Neutrality• Requires no engine modifications (except

replacing some fuel lines on older engines).• Can be blended in any proportion with

petroleum diesel fuel.• Can be made from waste restaurant oils and

animal fats

Disadvantages of biodiesel

• Lower Energy Content– 8% fewer BTU’s per gallon, but also higher cetane #, lubricity, etc.

• Poor cold weather performance– This can be mitigated by blending with diesel fuel or with

additives, or using low gel point feedstocks such as rapeseed/canola.

• Stability Concerns– Biodiesel is less oxidatively stable than petroleum diesel fuel. Old

fuel can become acidic and form sediments and varnish. Additives can prevent this.

• Scalability– Current feedstock technology limits large scalability

Fuel Cells

PEM Fuel Cell

Parts of a Fuel Cell• Anode

– Negative post of the fuel cell. – Conducts the electrons that are freed from the hydrogen molecules so that they

can be used in an external circuit. – Etched channels disperse hydrogen gas over the surface of catalyst.

• Cathode– Positive post of the fuel cell– Etched channels distribute oxygen to the surface of the catalyst.– Conducts electrons back from the external circuit to the catalyst– Recombine with the hydrogen ions and oxygen to form water.

• Electrolyte– Proton exchange membrane.– Specially treated material, only conducts positively charged ions.– Membrane blocks electrons.

• Catalyst – Special material that facilitates reaction of oxygen and hydrogen– Usually platinum powder very thinly coated onto carbon paper or cloth.– Rough & porous maximizes surface area exposed to hydrogen or oxygen– The platinum-coated side of the catalyst faces the PEM.

Fuel Cell Operation• Pressurized hydrogen gas (H2) enters cell on anode side. • Gas is forced through catalyst by pressure.

– When H2 molecule comes contacts platinum catalyst, it splits into two H+ ions and two electrons (e-).

• Electrons are conducted through the anode– Make their way through the external circuit (doing useful work such as

turning a motor) and return to the cathode side of the fuel cell. • On the cathode side, oxygen gas (O2) is forced through the

catalyst– Forms two oxygen atoms, each with a strong negative charge. – Negative charge attracts the two H+ ions through the membrane, – Combine with an oxygen atom and two electrons from the external

circuit to form a water molecule (H2O).

Proton-Exchange Membrane Cell

http://www.news.cornell.edu/releases/Nov03/Fuelcell.institute.deb.html

Fuel Cell Energy Exchange

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html

PEM Fuel Cell Schematic

Hydrogen Fuel Cell Efficiency• 40% efficiency converting methanol to

hydrogen in reformer • 80% of hydrogen energy content converted to

electrical energy • 80% efficiency for inverter/motor

– Converts electrical to mechanical energy• Overall efficiency of 24-32%

Auto Power Efficiency Comparison

TechnologySystem

EfficiencyFuel Cell 24-32%

Electric Battery 26%Gasoline Engine 20%

http://www.howstuffworks.com/fuel-cell.htm/printable

Other Types of Fuel Cells• Alkaline fuel cell (AFC)

– This is one of the oldest designs. It has been used in the U.S. space program since the 1960s. The AFC is very susceptible to contamination, so it requires pure hydrogen and oxygen. It is also very expensive, so this type of fuel cell is unlikely to be commercialized.

• Phosphoric-acid fuel cell (PAFC)– The phosphoric-acid fuel cell has potential for use in small stationary power-

generation systems. It operates at a higher temperature than PEM fuel cells, so it has a longer warm-up time. This makes it unsuitable for use in cars.

• Solid oxide fuel cell (SOFC)– These fuel cells are best suited for large-scale stationary power generators that could

provide electricity for factories or towns. This type of fuel cell operates at very high temperatures (around 1,832 F, 1,000 C). This high temperature makes reliability a problem, but it also has an advantage: The steam produced by the fuel cell can be channeled into turbines to generate more electricity. This improves the overall efficiency of the system.

• Molten carbonate fuel cell (MCFC)– These fuel cells are also best suited for large stationary power generators. They

operate at 1,112 F (600 C), so they also generate steam that can be used to generate more power. They have a lower operating temperature than the SOFC, which means they don't need such exotic materials. This makes the design a little less expensive.

http://www.howstuffworks.com/fuel-cell.htm/printable

Advantages/Disadvantages of Fuel Cells

• Advantages– Water is the only discharge (pure H2)

• Disadvantages– CO2 discharged with methanol reform– Little more efficient than alternatives– Technology currently expensive

• Many design issues still in progress

– Hydrogen often created using “dirty” energy (e.g., coal)– Pure hydrogen is difficult to handle

• Refilling stations, storage tanks, …

What is a Gas Hydrate?

A gas hydrate is a crystalline solid; its building blocks consist of a gas molecule surrounded by a cage of water molecules.

It is similar to ice, except that the crystalline structure is stabilized by the guest gas molecule within the cage of water molecules.

Suitable gases are: carbon dioxide, hydrogen sulfide, and several low-carbon-number hydrocarbons. Most gas hydrates , however are Methane Hydrates.

What are Methane Hydrates?

• Methane Hydrates are one example of ‘clathrates’

• Clathrates are compounds which consist of a ‘cage structure’, in which a gas molecule is trapped inside a cage of water molecules

• Methane (CH4) is trapped in Water (H2O) forming an “ICE”

1 m3 of hydrate -> ~170 m3 methane gas (STP)

Grey=carbon

Green=hydrogen in CH4

Red = oxygen

White= hydrogen in H2O

Hydrate Samples

Gas hydrates in sea-floor mounds Here methane gas is actively dissociating from a hydrate mound.

Gas hydrate can occur as nodules, laminae, or veins within sediment.

QuickTime™ and aTIFF (LZW) decompressorare needed to see this picture.

Gas Hydrate on the Sea floor

Beasties!

Origin of natural methane

• Bacterial degradation of organic matter in low-oxygen environments within sediments

• Thermal degradation of organic matter, dominantly in petroleum (e.g., Gulf of Mexico)

Where do clathrates occur?How much clathrate is there?

• Methane and water must be available (organic matter: produced by biota; in oceans: close to continents)

• Clathrate must be stable (ice): cold and/or high pressure

High latitudes (permafrost)

In medium deep sea sediments (300-2000 m)

How much hydrate is there?• Estimates vary widely: globally 600,000

to 2,000,000 Tcf (trillion cubic feet)• 1 Tcf ~ 1 quadrillion Btu (quad)• World energy use (2000): about 375-400

Quad = 500 Tcf hydrate gas per year• US gas hydrates: estimated at about

100,000 to 600,000 Tcf• Gas hydrates abundant in oil-poor

countries (Japan, India)

Why are CH4 Hydrates a good energy resource

• The gas is held in a crystal structure, therefore gas molecules are more densely packed than in conventional or other unconventional gas traps.

Hydrate forms as cement in the pore spaces of sediment and has the capacity to fill sediment pore space and reduce permeability. CH4 - hydrate-cemented strata thereby act as seals for trapped free gas

• Production of gas from hydrate-sealed traps may be an easy way to extract hydrate gas because the reduction of pressure caused by production can initiate a breakdown of hydrates and a recharging of the trap with gas

A Proposed Method• For the gas production from

hydrates and the seabed stability after the production, we proposed a new concept. The figure illustrates the molecular mining method by means of CO2 injection in order to extract CH4 from gas hydrate reservoirs. The concept is composed of three steps as follows; 1) injection of hot sea water into the hydrate layer to dissociate the hydrates, 2) produce gas from the hydrate, 3) inject CO2 to form carbon dioxide hydrate with residual water to hold the sea bed stable

CH4 Hydrates and Climate Change

• Methane is a very effective greenhouse gas. It is ten times more potent than carbon dioxide.

• There is increasing evidence that points to the periodic massive

release of methane into the atmosphere over geological timescales. Are these enormous releases of methane a cause or an effect of global climate change?

• Global warming may cause hydrate destabilization through a rise in ocean bottom water temperatures. The increased methane content in the atmosphere in turn would be expected to accelerate warming, causing further dissociation, potentially resulting in run away global warming.

• Sea level rise, however, during warm periods may act to stabilize hydrates by increasing hydrostatic pressure, thereby acting as a check on warming.

• Hydrate dissociation may act as a check on glaciations, whereby reduced sea levels may cause seafloor hydrate dissociation, releasing methane and warming the climate.

CH4 Hydrates and the Atmosphere

• An important aspect of methane hydrates and their affect on climate change is their potential to enter the atmosphere

• Methane concentration in seawater is observed to decrease by 98% between a depth of 300m and the sea surface as a result of microbial oxidation.

• The flux of methane into the atmosphere is thus lowered 50-fold (Mienert et al., 1998)

• However during catastrophic events such as large–scale sediment slumping much higher proportions of methane would be released.

The Future of Methane Hydrates

• Worldwide gas production in the next 30-50 years• Areas with unique economic and/or political motivations could see

substantial production within 5-10 years• We need to better understand the mechanisms of hydrate

disassociation and its role in global warming, either as an accelerator or and inhibitor

CARBON CAPTURE AND SEQUESTRATION

Carbon Dioxide Emission: 24 billion tons per year

CARBON CAPTURE AND STORAGE

Carbon capture and storage is mostly used to describe methods for removing CO2 emissions from large stationary sources, such as electricity generation and some industrial processes, and storing it away from the atmosphere.

Carbon Capture Technology•Post- combustion capture

•React the flue gas with chemicals that absorb CO2 and then heat the chemicals to release CO2.

•NOTE:Flue gas : Mixture of nitrogen , water vapor and 15 % of Carbon dioxide

.

Carbon Capture Technology

Pre- combustion captureRemove carbon before combustion. By gasifying the coal through the reaction with more oxygen, it is possible to a mix of mostly CO2 and hydrogen.

Carbon Capture Technology

• Oxy-fuel combustion– Use pure oxygen to support the fossil fuel

combustion. The flue gas is then mostly CO2 and water making it to separate easily.

Transportation

• Many point sources of captured CO2 would not be close to geological or oceanic storage facilities. In these cases, transportation would be required.

• The main form of transportation – pipeline. – Shipping

CO2 storage

• Various forms have been conceived for permanent storage of CO2. These forms include gaseous storage in various deep geological formations (including saline formations and exhausted gas fields), liquid storage in the ocean, and solid storage by reaction of CO2 with metal oxides to produce stable carbonates

Carbon Storage technology

•Geological storage•Oceanic storage

Geological storage

Oceanic Storage

Two storage mechanism has been proposed

– Dissolving CO2 at mid-depth.

– Injecting the CO2 at depths in excess of 3 km , where it would form lakes of liquid CO2 . Bellow 3 km liquid CO2 would be denser than sea water and would sink to the ocean floor.

Carbon Storage Concerns• CCS technologies actually require a lot of energy to

implement and run• transporting captured CO2 by truck or ship, require fuel. • Creating a CCS-enabled power plant also requires a lot of

money. • What happens if the carbon dioxide leaks out

underground? We can't really answer this question. Because the process is so new, we don't know its long-term effects. Slow leakage would lead to climate changing. Sudden catastrophic leakage is dangerous, and causes asphyxiation.

• The more CO2 an ocean surface absorbs, the more acidic it becomes, higher water acidity adversely affects marine life.

What might Carbon Capture and Storage look like?

The diagram is from a BP news release from the abandoned Miller project, UK North Sea, which is no longer available online.

FutureGenFutureGen is a public-private partnership to build a first-of-its-kind coal-fueled, near-zero emissions power plant. It will use cutting-edge technologies to generate electricity while capturing and permanently storing carbon dioxide deep beneath the earth. The plant will also produce hydrogen and byproducts for possible use by other

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the "forever fuel" that we can never run out of

HYDROGEN

Water + energy hydrogen + oxygen

Hydrogen + oxygen water + energy

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Hydrogen is ~75% of the known universe

On earth, it’s not an energy source like oil or coal Only an energy carrier like electricity or gasoline — a form of energy, derived from a source, that can be moved around

The most versatile energy carrier - Can be made from any source and used for any service - Readily stored in large amounts

Why is hydrogen so important?

Sources of Hydrogen

Sources that Hydrogen can be extracted from:• Natural Gas, Water, Coal, Gasoline, Methanol,

Biomass• Other sources being researched include the uses

of solar energy, photosynthesis, decomposition, and fuel cells themselves can tri-generate electricity, heat, and hydrogen.

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Is it safe?: A primer on Hydrogen safety

All fuels are hazardous, but…

Hydrogen is comparably or less so, but different:

Clear flame can’t sear you at a distance; no smoke

Hard to make explode; can’t explode in free air; burns first

22× less explosive power

Rises, doesn’t puddle

Hindenburg myth (1937) – nobody was killed by hydrogen fire

Completely unrelated to hydrogen bombs

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Where Does Hydrogen Come From?

95% of hydrogen is currently produced by steam reforming

Partial Oxidation

Steam Reforming

Electrolysis

Thermochemical

Fossil Fuels

Water

Biomass

currently most energy efficient

requires improvements

not cost effective

requires high temperatures

Gasification

Microbial

requiresimprovements

slow kinetics

Hydrogen carries energy

Most of the energy we use today—94% comes from fossil fuels…

Fossil fuels are oil, coal, and natural gas and have developed over thousands of years from decomposing prehistoric plants and animals…since these plants and

animals no longer exist, making new fossil fuels cannot happen. Only 6% of the energy we use comes from renewable energy sources…

But people want to use more renewable energy. It is usually cleaner and can be replenished in a short period of time compared to fossil fuels.

The problem is that renewable energy sources—like solar and wind—can’t produce energy all the time…

The sun doesn’t always shine. The wind doesn’t always blow. Sometimes the sun and wind provide more energy than we need at that moment.

Hydrogen can store and carry the energy until it’s needed and can be moved to where it’s needed.

Why are Energy Carriers good?

Every day, we use more energy, mostly coal, to make electricity. Electricity is an energy carrier.

Energy carriers can store, move, and deliver energy to consumers.

We convert energy source like coal and natural gas to electricity because it is easier for us to move and use.

Electricity gives us light, heat, hot water, cold food, TVs, and computers.

Life would be really hard if we had to burn the coal, split the atoms, or build our own dams.

Energy carriers make life easier.

Hydrogen is an energy carrier like electricity. It can be used in places where it’s hard to use electricity.

Electricity requires wires and poles, like you see along the highway and in your neighborhood, to be delivered to a home.

Hydrogen can be shipped by a pipeline or produced at the home directly.

How does Hydrogen turn into useable Electricity?

Hydrogen cannot directly make the lights turn on, the water run, or the heat work.

It must be converted into electricity. This happens in a fuel cell.

This is a

real live

fuel cell

The only waste

product is water

Uses for Hydrogen Energy

NASA uses hydrogen as an energy carrier; it has used hydrogen for years in the space program. Hydrogen fuel lifts the space shuttle into orbit.

Hydrogen fuel cells power the shuttle’s electrical systems. The only by-product is pure water,

which the crew uses as drinking water.

Hydrogen fuel cells are very efficient, but expensive to build.

Small fuel cells can power electric cars. An engine that burns pure hydrogen produces almost no

pollution. It will probably be many years, though, before you can walk into a car dealer and drive away in

a hydrogen-powered car.

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HYDROGEN IN TRANSPORTATION

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Options for Storing Hydrogen Today

HYDROGEN STORAGE OPTIONS

HYBRIDTANKS

LIQUID HYDROGEN

COMPRESSEDGAS

PHYSICAL STORAGE Molecular

H2

REVERSIBLE

Compressed Storage

• Prototype vehicle tanks developed• Efficient high-volume

manufacturing processes needed• Less expensive materials desired

– carbon fiber– binder

• Evaluation of engineering factors related to safety required– understanding of failure

processes

Liquid Storage• Prototype vehicle tanks developed• Reduced mass and especially volume needed• Reduced cost and development of high-volume production processes

needed

• Extend dormancy (time to start of “boil off” loss) without increasing cost, mass, volume

• Improve energy efficiency of liquefaction

Hybrid Physical Storage

• Compressed H2 @ cryogenic temperatures

– H2 density increases at lower temperatures

– further density increase possible through use of adsorbents – opportunity for new materials

• The best of both worlds, or the worst ??• Concepts under development

HYDROGEN STORAGE OPTIONS

REVERSIBLE

HYBRIDTANKS

LIQUID HYDROGEN

COMPRESSEDGAS

PHYSICAL STORAGE Molecular

H2

REVERSIBLE

CHEMICAL STORAGE Dissociative

H2 2 H

COMPLEX METAL HYDRIDES

CONVENTIONALMETAL HYDRIDES

LIGHT ELEMENT SYSTEMS

NON-REVERSIBLE

REFORMED FUEL

DECOMPOSED FUEL

HYDROLYZED FUEL

Non-reversible On-board Storage

• On-board reforming of fuels has been rejected as a source of hydrogen because of packaging and cost– energy station reforming to provide compressed hydrogen is

still a viable option• Hydrolysis hydrides suffer from high heat rejection on-

board and large energy requirements for recycle• On-board decomposition of specialty fuels is a real option

– need desirable recycle process– engineering for minimum cost and ease of use

Reversible On-board Storage

• Reversible, solid state, on-board storage is the ultimate goal for automotive applications

• Accurate, fast computational techniques needed to scan new formulations and new classes of hydrides

• Thermodynamics of hydride systems can be “tuned” to improve system performance– storage capacity– temperature of hydrogen release– kinetics/speed of hydrogen refueling

• Catalysts and additives may also improve storage characteristics

The Future of Hydrogen

Before hydrogen becomes a significant fuel energy picture, many new systems must be built.

We will need systems to make hydrogen, store it, and move it. We will need pipelines and economical fuel cells.

And consumers will need the technology and the education to use it.