NEW ENERGY SYSTEMS

DIRECT ENERGY CONVERSION SYSTEMSDirect energy conversion(DEC) or simplydirect conversionconverts a charged particle'skinetic energyinto avoltage. It is a scheme for power extraction fromnuclear fusion

Types.Thermo electric power generationThermo ionic power generationMagneto hydro dynamic systemsPhotovoltaic power systemsFuel cellsThermo nuclear fusion power generation

Thermo electric power generation

Introduction..The pioneer in thermoelectric was a German scientist Thomas Johann Seebeck (1770-1831) Thermoelectricity refers to a class of phenomena in which a temperature difference creates an electric potential or an electric potential creates a temperature difference. Thermoelectric power generator is a device that converts the heat energy into electrical energy based on the principles of Seebeck effectLater, In 1834, French scientist, Peltier and in 1851, Thomson (later Lord Kelvin) described the thermal effects on conductors

Principle.In the purer metallic conductors outer electrons, less connected to others, can move freely around all the material, as if they do not belong to any atom. These electrons transmit energy one to another through temperature variation, and this energy intensity varies depending on the nature of the material.If two distinct materials are placed in contact, free electrons will be transferred from the more loaded material to the other, so they equate themselves, such transference creates a potential difference, called contact potential, since the result will be a pole negatively charged by the received electrons and another positively charged by the loss of electrons.

Seebeck effectWhen the junctions of two different metals are maintained at different temperature, the emf is produced in the circuit. This is known as Seebeck effect. The material A is maintained at T+T temperatureThe material B is maintained at temperature T. Since the junctions are maintained at different temperature, the emf V flows across the circuit.

The electric potential produced by a temperature difference is known as the Seebeck effect and the proportionality constant is called the Seebeck coefficient.

If the free charges are positive (the material is p-type), positive charge will build up on the cold which will have a positive potential.

Similarly, negative free charges (n-type material) will produce a negative potential at the cold end.

Peltier effect

Whenever current passes through the circuit of two dissimilar conductors, depending on the current direction, either heat is absorbed or released at the junction of the two conductors. This is known as Peltier effect.

Thomson effectHeat is absorbed or produced when current flows in material with a certain temperature gradient. The heat is proportional to both the electric current and the temperature gradient. This is known as Thomson effect.

Joule effect.Irreversible conversion of electrical energy into heat when a current I flows through a ressistance R. Qj=I2R

Thermoelectric Power Gener..

Construction..Thermoelectric power generation (TEG) devices typically use special semiconductor materials, which are optimized for the Seebeck effect.

The simplest thermoelectric power generator consists of a thermocouple, comprising a p-type and n-type material connected electrically in series and thermally in parallel.

Heat is applied into one side of the couple and rejected from the opposite side.

An electrical current is produced, proportional to the temperature gradient between the hot and cold junctions.

Therefore, for any TEPG, there are four basic component required such asHeat source (fuel) P and N type semiconductor stack (TE module) Heat sink (cold side) Electrical load (output voltage)

As the heat moves from hot side to cold side, the charge carrier moves in the semiconductor materials and hence the potential deference is created. The electrons are the charge carriers in the case of N-type semiconductor and Hole are in P-type semiconductors. In a stack, number of P-type and N-type semiconductors is connected. A single PN connection can produce a Seebeck voltage of 40 mV. The heat source such as natural gas or propane are used for remote power generation

Analysis..Power P= I2RL V=IR I= V/R =

P max = (when R=RL) =

Figure of merit Z=

Max. Ideal efficiencywhere: w is the power delivered to the external load and qH is the positive heat flow from source to sink

Energy provided to the loadHeat energy absorbed at the hot junctionEfficiency of the generator =

Figure of merit

Diagram showsThe charge buildup at cold side

Material selection criteria.A high electrical conductivity is necessary to minimize Joule heating and low thermal conductivity helps to retain heat at the junctions and maintain a large temperature gradient. A large Seebeck coefficient is advicable.These three properties were later put together and it is called figure-of-merit (Z).

The good thermoelectric materials should possess

Large Seebeck coefficientsHigh electrical conductivity Low thermal conductivity The example for thermoelectric materials

BismuthTelluride (Bi2Te3),Lead Telluride (PbTe), SiliconGermanium (SiGe),Bismuth-Antimony (Bi-Sb)

ZT is maximized when the product RK is minimized, where R is the total couple resistance and K is the couple thermal conductance. This is accomplishedwhen:

and the gure of merit for the couple is given by

The efciency (n) (power generation mode) of the thermoelectric couple is given by the power input to the load (W) over the net heat ow rate (QH), where QH is positive for heat ow from the source to the sink and is given below:

Proportional to (1+ZT)1/2

N-type

V

Cold sideHot sideHeat flowElectron flow

Advantages

Easy maintenance: They works electrically without any moving parts so they are virtually maintenance free.

Environment friendly: Thermoelectric generators produce no pollution. Therefore they are eco friendly generators.

Compact and less weight: The overall thermoelectric cooling system is much smaller and lighter than a comparable mechanical system.

High Reliability: Thermoelectric modules exhibit very high reliability due to their solid-state construction No noise: They can be used in any orientation and in zero gravity environments. Thus they are popular in many aerospace applications.

Convenient Power Supply: They operate directly from a DC power source.

Scope..

Applications

31Water/Beer Cooler

Cooled Car Seat Electronic CoolingCryogenic IR Night Vision

Laser/OE CoolingTESi bench

Miscellaneous.The standard material we work with is BiTe. The best efficiency that can be achieved with this material is approximately 6%.

But once the material is constructed into a module, efficiency drops to 3 to 4% because of thermal and electrical impedance. No other semiconductor material can perform as well as BiTe as far as efficiency is concerned. Other material such as PbTe are used but are far less efficient, and must be used at significantly higher temperatures (450C- 600C) hot side and arenot commercially available!

Thermoelectric Seebeck effect modules are designed for very high power densities, on the order of 50 times greater than Solar PV!

32

Miscellaneous.Bismuth telluride is the best bulk TE material with ZT=1Trends in TE devices:Superlattices and nanowires: Increase in S, reduction in kNonequilibrium effects: decoupling of electron and phonon transportBulk nanomaterial synthesis Trends in TE systemsMicrorefrigeration based on thin film technologiesAutomobile refrigerationTE combined with fluidics for better heat exchangersTo match a refrigerator, an effective ZT= 4 is neededTo efficiently recover waste heat from car, ZT = 2 is needed

Miscellaneous.

Thermo-ionic generator

Introduction.Thermionic emission is the basis for the working of this system. In 1873, the Britain professor Frederic Guthrie invented the Thermionic phenomenon. In 1883, Thomas A. Edison observed that the electrons are emitted from a metal surface when it was heated. This effect is called Edison effect. Later in 1904, a British physicist John Ambrose Fleming developed two-element vacuum tube known as diode.

Principle.Thermionic power generator (TPG) is a static device that converts heat energy into electrical energy by boiling electrons from a hot emitter surface (= 1800K) across a small inter electrode gap (< 0.5 mm) to a cooler collector surface (= 1000K)

Principle.

The idea of electrons leaving the surface

Principle.

Principle.A thermionic energy converter (or) thermionic power generator is a device consisting of two electrodes placed near one another in a vacuum. One electrode is normally called the cathode, or emitter, and the other is called the anode, or plate. Ordinarily, electrons in the cathode are prevented from escaping from the surface by a potential-energy barrier. When an electron starts to move away from the surface, it induces a corresponding positive charge in the material, which tends to pull it back into the surface. To escape, the electron must somehow acquire enough energy to overcome this energy barrier.At ordinary temperatures, almost none of the electrons can acquire enough energy to escape.

Principle. However, when the cathode is very hot, the electron energies are greatly increased by thermal motion. At sufficiently high temperatures, a considerable number of electrons are able to escape. The liberation of electrons from a hot surface is calledthermionic emission

Potential diagram

Materials..For the electrons to travel, the unit is at vacuum. This limit the size of the generator.

Electron emission is inhibited by space charge, small quantity of Cesium metal is introduced into the evacuated vessel

Molybdenum, tantalum, tungsten impregnated barium oxide.Uranium carbide, zirconium carbide.

Prototype combustion-heated thermionic systems for domestic heat and electric powercogeneration

Co-generation

Advantages

Higher efficiency and high power density Compact to use

Disadvantages

There is a possibility of vaporization of emitter surface Thermal breaking is possible during operation The sealing is often gets failure

Magneto-hydro dynamic generator..

An MHD generator is a device for converting heat energy of a fuel directly into electrical energy without conventional electric generator.

In advanced countries MHD generators are widely used but in developing countries like INDIA, it is still under construction, this construction work in in progress at TRICHI in TAMIL NADU, under the joint efforts of BARC (Bhabha atomic research center), Associated cement corporation (ACC) and Russian technologists.

Introduction.

Magneto hydrodynamics(MHD) (magneto fluid dynamicsorhydro magnetics) is theacademic disciplinewhich studies thedynamicsof electrically conductingfluids. Examples of such fluids includeplasmas, liquid metals, andsalt water. The wordmagneto hydro dynamics (MHD) is derived frommagneto-meaningmagnetic field, andhydro-meaningliquid, and -dynamics meaning movement. The field of MHD was initiated byHannes Alfvn , for which he received theNobel Prizein Physics in 1970

Hannes Alfvn

Principle

PrincipleThis effect is a result of FARADAYS LAWS OF ELECTRO MAGNETIC INDUCTION. (i.e. when the conductor moves through a magnetic field, it generates an electric field perpendicular to the magnetic field & direction of conductor).

The induced EMF is given by Eind = u x B where u = velocity of the conductor. B = magnetic field intensity.

The induced current is given by, Iind = C x Eind where C = electric conductivity

The retarding force on the conductor is the Lorentz force given by Find = Iind X B

PrincipleThe conducting fluid flow is forced between the plates with a kinetic energy and pressure differential sufficient to over come the magnetic induction force Find.

An ionized gas is employed as the conducting fluid.

Ionization is produced either by thermal means I.e. by an elevated temperature or by seeding with substance like cesium or potassium vapors which ionizes at relatively low temperatures.

The atoms of seed element split off electrons. The presence of the negatively charged electrons makes the gas an electrical conductor.

Principle

Principle

Principle

90% conductivity can be achieved with a fairly low degree of ionization of only about 1%.

Comparison..

MHD generator.

MHD generator.

Types.Open cycle MHD

Closed cycle MHDSeeded Inert gas system.Liquid metal system

Temperature of CC MHD plants is very less compared to OC MHD plants. Its about 1400oC.

Open cycle

Open cycleThe fuel used maybe oil through an oil tank or gasified coal through a coal gasification plant

The fuel (coal, oil or natural gas) is burnt in the combustor or combustion chamber.

The hot gases from combustor is then seeded with a small amount of ionized alkali metal (cesium or potassium) to increase the electrical conductivity of the gas.

The seed material, generally potassium carbonate is injected into the combustion chamber, the potassium is then ionized by the hot combustion gases at temperature of roughly 2300 c to 2700c.

Open cycleTo attain such high temperatures, the compressed air is used to burn the coal in the combustion chamber, must be adequate to at least 11000c.

A lower preheat temperature would be adequate if the air is enriched in oxygen. An alternative is used to compress oxygen alone for combustion of fuel, little or no preheating is then required. The additional cost of oxygen might be balanced by saving on the preheater.

The hot pressurized working fluid leaving the combustor flows through a convergent divergent nozzle. In passing through the nozzle, the random motion energy of the molecules in the hot gas is largely converted into directed, mass of energy. Thus , the gas emerges from the nozzle and enters the MHD generator unit at a high velocity.

Closed cycleSeeded Inert gas system

Closed cycleSeeded Inert gas systemIn a closed cycle system the carrier gas operates in the form of Brayton cycle. In a closed cycle system the gas is compressed and heat is supplied by the source, at essentially constant pressure, the compressed gas then expands in the MHD generator, and its pressure and temperature fall. After leaving this generator heat is removed from the gas by a cooler, this is the heat rejection stage of the cycle. Finally the gas is recompressed and returned for reheating.

The complete system has three distinct but interlocking loops. On the left is the external heating loop. Coal is gasified and the gas is burnt in the combustor to provide heat. In the primary heat exchanger, this heat is transferred to a carrier gas argon or helium of the MHD cycle. The combustion products after passing through the air preheater and purifier are discharged to atmosphere.

Closed cycleSeeded Inert gas systemBecause the combustion system is separate from the working fluid, so also are the ash and flue gases. Hence the problem of extracting the seed material from fly ash does not arise. The flue gases are used to preheat the incoming combustion air and then treated for fly ash and sulfur dioxide removal, if necessary prior to discharge through a stack to the atmosphere.

The loop in the center is the MHD loop. The hot argon gas is seeded with cesium and resulting working fluid is passed through the MHD generator at high speed. The dc power out of MHD generator is converted in ac by the inverter and is then fed to the grid.

Closed cycle.liquid metal system

Closed cycle.liquid metal systemWhen a liquid metal provides the electrical conductivity, it is called a liquid metal MHD system.

An inert gas is a convenient carrier

The carrier gas is pressurized and heated by passage through a heat exchanger within combustion chamber. The hot gas is then incorporated into the liquid metal usually hot sodium to form the working fluid. The latter then consists of gas bubbles uniformly dispersed in an approximately equal volume of liquid sodium.

The working fluid is introduced into the MHD generator through a nozzle in the usual ways. The carrier gas then provides the required high direct velocity of the electrical conductor.

Closed cycle.liquid metal systemAfter passage through the generator, the liquid metal is separated from the carrier gas. Part of the heat exchanger to produce steam for operating a turbine generator. Finally the carrier gas is cooled, compressed and returned to the combustion chamber for reheating and mixing with the recovered liquid metal. The working fluid temperature is usually around 800c as the boiling point of sodium even under moderate pressure is below 900c.

At lower operating temp, the other MHD conversion systems may be advantageous from the material standpoint, but the maximum thermal efficiency is lower. A possible compromise might be to use liquid lithium, with a boiling point near 1300c as the electrical conductor lithium is much more expensive than sodium, but losses in a closed system are less.

Efficiency..

Material selection.It has no moving parts & the actual conductors are replaced by ionized gas (plasma). The magnets used can be electromagnets or superconducting magnets.The plasma temperature is typically over 2000 C, the duct containing the plasma must be constructed from non-conducting materials capable of withstanding this high temperature. The electrodes must of course be conducting as well as heat resistant. Superconducting magnets of 4~6Tesla are used. Here exhaust gases are again recycled & the capacities of these plants are more than 200MW.Non-conducting walls of the channel must be constructed from an exceedingly heat-resistant substance such as yttrium oxide or zirconium dioxide to retard oxidation

Material selection.Ionization of GAS: Various methods for ionizing the gas are available, all of which depend on imparting sufficient energy to the gas. The ionization can be produced by thermal or nuclear means. Materials such as Potassium carbonate or Cesium are often added in small amounts, typically about 1% of the total mass flow to increase the ionization and improve the conductivity, particularly combustion of gas plasma

AdvantagesIn MHD the thermal pollution of water is eliminated. (Clean Energy System)

Use of MHD plant operating in conjunction with a gas turbine power plant might not require to reject any heat to cooling water.

These are less complicated than the conventional generators, having simple technology.

There are no moving parts in generator which reduces the energy loss.

These plants have the potential to raise the conversion efficiency up to 55-60%. Since conductivity of plasma is very high (can be treated as infinity).

It is applicable with all kind of heat source like nuclear, thermal, thermonuclear plants etc. Extensive use of MHD can help in better fuel utilization.

Dis-advantagesThe construction of superconducting magnets for small MHD plants of more than 1kW electrical capacity is only on the drawing board.

Difficulties may arise from the exposure of metal surface to the intense heat of the generator and form the corrosion of metals and electrodes.

Construction of generator is uneconomical due to its high cost.

Construction of Heat resistant and non conducting ducts of generator & large superconducting magnets is difficult.

MHD without superconducting magnets is less efficient when compared with combined gas cycle turbine.

Photovoltaic Theory

p-Silicon

n-Silicon+ + + + + + + + + + + + + + + + + +

- - - - - - - - - -

The photovoltaic phenomenon is the process by which light is converted into electricity.A solar cell is made by placing a thin layer of phosphorus-doped silicon called n-Silicon (means negative) in a close contact with a layer of boron-doped silicon called p-Silicon (means positive). When light falls on the cell, photons are absorbed and electrons are set free. The excess electrons accumulate in the n-silicon. If one end of a wire is attached to this top layer and the other end is connected to the p-Silicon layer, electrons will flow through the wire, and thus DC electric current will be generated.

PV Systems Components Solar ArrayStorage BatteriesCharge Controller (Regulator)Inverter (For AC Systems Only)

The basic components of a PV system are:Solar array or a photovoltaic arrayStorage batteriesA charge controller or alternatively called charge regulator.If the load operates on AC power a DC/AC inverter will also be required.

Photovoltaic System

BatteryPV ArrayCharge Controller

This picture demonstrates the various components of a PV systemA photovoltaic arrayA battery bank and enclosureAnd a charge controller

PV Systems Components

Load

PhotovoltaicArrayBattery BankInverter(AC loads)

Charge Controller

This is a layout that shows how each component is connected to each other.

Design Strategy PV Array:Type SelectionSizingClimate & Geographical Location Considerations

Lets shed some light on how a PV array is designed.

I will address the following aspects:The array type selection, The array sizing, The climate and geographical location considerations in the following slides.

Design Strategy PV Array Types:

There are many types of PV modules from a manufacturing materials point of view.

I will, however, concentrate on the two most commercially-available technologies:The crystalline silicon PV modulesThe amorphous silicon modules (thin film) which are primarily manufactured in two types:Single junction modules(single p-n junction)Multi-junction PV modules(multiple p-n junctions) (6 or more stacked a-Si films)

The basic criteria for selection are The module efficiency that compares how much of the sun energy is converted into electricity.The cost of each solar module.

As we can see the multi-junction amorphous silicon is the most economically-feasible type.

Design Strategy PV Array Sizing:De-rating FactorsAging 20%Dirt Accumulation 20%Future Growth 10%Recharging Period4 daysSystem VoltageLoad Profile

Because of the time limitation, I am not going through details calculation in this presentation on how to size a PV array. However the following factors have to be taken into consideration:First it is a recommended practice to de-rate the PV array by 20% for aging, Another 20% for dirt accumulation, And another 10% or so for future expansion.The period needed for the solar array to recharge the battery is a major contributing factor in PV array sizing. This is totally application-dependant. Four days of battery recharge time has been traditionally acceptable figure for many applications.The system voltage will determine the number of solar modules connected in series.And the load current will determine the number of solar modules connected in parallel.

(JPL 5101-161) [Jet Propulsion Laboratories SOLAR CELL MODULE DESIGN AND TEST SPECIFICATION FOR INTERMEDIATE LOAD CENTERS APPLICATIONS]

Design StrategyPV Array Climate & Geographical Location:

Solar Insolation (Radiation)Effective Sun HoursArray OrientationDirection (Toward South)Tilt AngleFixed Angle (Latitude + 10 Degrees)Adjustable (Sun Tracking)

The climate and geographical location play a major role in the design of the PV system. The following are crucial factors to be considered when designing a PV system:

Solar insolation which is the amount of light radiation in kWh falling on each m2 every day.Effective sun hours in which the the PV array can produce useful solar power.The orientation of the PV array is also very essential. It should be directed toward the South in the Northern Hemisphere, toward the North in the Southern Hemisphere and should be set flat at the equator.The tilt angle can either be fixed or adjustableIf it is fixed then as a rule of thumb the latitude of the location plus 10-20 degrees is the optimum tilt angle.More advanced designs use sun tracking system which involves motors and a complicated control. This consumes additional power and increases maintenance of the system. More practically, manual seasonal adjustments every three month are recommended.

500W/m2, for 10 hours (?) or1000W/m2, for 5 hours

Sun Insolation

5.0 kW/m2/day5.0

This is an example of the sun insolation contour map based on sun intensity measurements over the years.

Notice that most of Saudi regions receive a solar radiation of around 5.0 kWh/m2/day

Photovoltaic Arrays Field

This is another view of a huge PV installation. Notice the water sprinklers to flush out the arrays from accumulated dirt.

Design Strategy Storage Battery:Type SelectionSizingEnvironment Considerations

Similarly, the storage batteries have to be especially designed for photovoltaic applications.

I will briefly address:The selection of battery type, Sizing And the impact of environment conditions on the design of batteries for PV systems.

Detail design of battery is out of the scope of this presentation.

Design Strategy Storage Battery:

Type Selection (cyclic application)

Tubular Plate Lead-AcidPocket Plate Nickel-Cadmium

PV array produces electric power only during the sunny hours of the day. It produces no electricity at night and produces very little electricity during hazy days. Because of the cyclic nature of the PV, most importantly, the battery has to be suitable for cyclic and deep discharge applications such as:

Tubular plate lead acid.Pocket plate nickel cadmium.

System VoltageLoad ProfileBackup Time (Autonomy) 7 daysDe-rating Factors Lead-Acid Ni-CadAging 25% 10% Temp. Compensation19%14%Design10%10%

Design Strategy Storage Battery:

Sizing

Battery sizing:Usually, the system voltage determines the number of cells needed.The load profile will determine the Ah capacity of the batteryThe backup time is the required time for the battery to supply the load independent of the PV array. This is experienced during the overcast/cloudy days and usually called autonomy. Seven days is reasonable figure to design to depending on the criticality of the application and location metrological data.Some design de-rating factors have also to be taken into account when designing both lead acid and nickel cadmium batteries:AgingTemperature compensationDesign factor.

AH = IL x BT x TC x AF x DFBattery end of discharge voltage 1.85V (LA), 1.15V (NiCad)SAES-P-103, 4.3.14

No Temperature Control Temp. CompensationOutdoor Battery EnclosureShade Requirement

Design Strategy Storage Battery:

Environment Considerations

Most PV applications are installed in deserted areas where the environment is usually not controlled (no air conditioning).

If temperatue is not controlled, then temperatue compensation feature is required as we will see later when we talk about the charge controller. This feature eliminates the effect of the charging current variations with temperature.Battery enclosure suitable for outdoor application is required to reduce the effect of environment on the performance and life of the battery.Also, battery shall be located in a shaded location to reduce the effect of direct sun light on the life of the battery.

Design Strategy Charge Regulator:Type SelectionSingle Stage MultistageSizing(Array Rated Currents)Temperature CompensationLead-Acid-5mV/oC/cellNi-Cad-3mV/oC/cellLow Voltage Disconnect Lead-Acid1.85V/cellNi-Cad1.15V/cell

The Charge controller or regulator is a device that regulates the charges from the PV array to the battery.Charge controllers are made in several types. Single stage and multistage are common types of charge regulators:Single stage and Multistage which splits the PV array into multiple stages - Multistage does a better charge regulation while being easy on the battery.The size of the charge regulator should be based on the maximum amount of current that the PV array can deliver.It should be equipped with a temperature compensation probe that allows the regulator to raise the charging voltage at lower temperatures and reduce the charging voltage at higher temperatures while maintaining a constant charging current. This probe compensates in a rate of around-5mV/oC/Cell for lead acid and-3mV/oC/Cell for nickel cadmiumIt should also be equipped with a Low Voltage Disconnect switch to disconnect the load at a battery end of discharge voltage of:1.85 V/Cell for lead acid and1.15 V/Cell for nickel cadmiumThe low voltage disconnect feature protects the battery from severe damage caused by very deep discharge.

ApplicationsCathodic Protection SystemsTelecommunications SystemsSCADA SystemsOffshore PlatformsHighway Lighting Remote HomesIrrigation Water Pumping

PV systems are not cost-effective for all applications. If connected to a utility grid or within a reasonable distance from it, PV is not the right choice.Feasibility can only be determined by economical study.

I will list some of the applications that PV might be the right choice because of its remoteness or inaccessibilityCathodic protectionTelecommunicationsSCADA systemsNon-electrified Offshore PlatformsHighway Lighting and SignsRemote homesWater pumping

AdvantagesReliableNo FuelsLow MaintenanceLong-term SavingsNo PollutionNo Noise

$ $ $

PV has some advantages and disadvantagesIf designed correctly, the PV systems are very reliable.PV systems consumes no fuel.Due to the fact that PV system contains no moving parts, minimum maintenance is required compared to the conventional diesel generatorsBecause of the long expected life of a PV system with minimal maintenance, long-term savings are anticipated.It is very friendly to the environment since it produces no pollutionAnd Solar has an advantage that nothing else can match. It is QUIET. This is especially important for people who like to stay away from the noise of the city.

DisadvantagesHigh Initial Cost (3-10 times)Specialized MaintenanceBatteriesPower Conditioning EquipmentLarge Space

$

$

$$

$

$

However, the drawbacks of the the PV system are:Although the suns energy is free, the PV equipment is not free. High initial investment is usually anticipated.It requires specialized technicians to maintain both:BatteriesAnd power conditioning equipment such as charge controllers and inverters.And also PV array occupies a lot of space.

Fuel Cells

The Promise of Fuel Cells

A score of nonutility companies are well advanced toward developing a powerful chemical fuel cell, which could sit in some hidden closet of every home silently ticking off electric power.

Theodore Levitt, Marketing Myopia, Harvard Business Review, 1960Theodore Levitt, Marketing Myopia, Harvard Business Review, 1960

Parts of a Fuel CellAnodeNegative 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.CathodePositive post of the fuel cellEtched channels distribute oxygen to the surface of the catalyst.Conducts electrons back from the external circuit to the catalystRecombine with the hydrogen ions and oxygen to form water. ElectrolyteProton exchange membrane.Specially treated material, only conducts positively charged ions.Membrane blocks electrons. Catalyst Special material that facilitates reaction of oxygen and hydrogenUsually platinum powder very thinly coated onto carbon paper or cloth.Rough & porous maximizes surface area exposed to hydrogen or oxygenThe platinum-coated side of the catalyst faces the PEM.

Fuel Cell OperationPressurized 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 anodeMake 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 catalystForms 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).

PEM Fuel Cell Schematic

96Figure 5. In a protonexchangemembrane fuel cell, hydrogen and oxygen react electrochemically. At the anode, hydrogen molecules dissociate, the atoms are ionized, and electrons are directed to an external circuit; protons are handed off to the ionexchange membrane and pass through to the cathode. There, oxygen combines with protons from the ionexchange membrane and electrons from the external circuit to form water or steam. The energy conversion efficiency of the process can be 60% or higher.

Proton-Exchange Membrane Cell

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

97How a fuel cell works: In the polymer electrolyte membrane (PEM) fuel cell, also known as a proton-exchange membrane cell, a catalyst in the anode separates hydrogen atoms into protons and electrons. The membrane in the center transports the protons to the cathode, leaving the electrons behind. The electrons flow through a circuit to the cathode, forming an electric current to do useful work. In the cathode, another catalyst helps the electrons, hydrogen nuclei and oxygen from the air recombine. When the input is pure hydrogen, the exhaust consists of water vapor. In fuel cells using hydrocarbon fuels the exhaust is water and carbon dioxide. Cornell's new research is aimed at finding lighter, cheaper and more efficient materials for the catalysts and membranes.

Fuel Cell Stack

http://www.nrel.gov/hydrogen/photos.html

98Tomorrow, hydrogen's use as a fuel for fuel cells will grow dramatically-for transportation, stationary and portable applications. (PlugPower 5-kW fuel cell (large cell), H2ECOnomy 25-W fuel cell (small silver cell), and Avista Labs 30-W fuel cell).

Hydrogen Fuel Cell Efficiency40% efficiency converting methanol to hydrogen in reformer 80% of hydrogen energy content converted to electrical energy 80% efficiency for inverter/motorConverts electrical to mechanical energyOverall efficiency of 24-32%

Auto Power Efficiency ComparisonTechnologySystemEfficiencyFuel Cell24-32%Electric Battery26%Gasoline Engine20%

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

100Maybe you are surprised by how close these three technologies are. This exercise points out the importance of considering the whole system, not just the car. We could even go a step further and ask what the efficiency of producing gasoline, methanol or coal is. Efficiency is not the only consideration, however. People will not drive a car just because it is the most efficient if it makes them change their behavior. They are concerned about many other issues as well. They want to know: Is the car quick and easy to refuel? Can it travel a good distance before refueling? Is it as fast as the other cars on the road? How much pollution does it produce? This list, of course, goes on and on. In the end, the technology that dominates will be a compromise between efficiency and practicality.

Fuel Cell Energy Exchange

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

101Hydrogen and oxygen can be combined in a fuel cell to produce electrical energy. A fuel cell uses a chemical reaction to provide an external voltage, as does a battery, but differs from a battery in that the fuel is continually supplied in the form of hydrogen and oxygen gas. It can produce electrical energy at a higher efficiency than just burning the hydrogen to produce heat to drive a generator because it is not subject to the thermal bottleneck from the second law of thermodynamics. It's only product is water, so it is pollution-free. All these features have led to periodic great excitement about its potential, but we are still in the process of developing that potential as a pollution-free, efficient energy source (see Kartha and Grimes).

Other Types of Fuel CellsAlkaline 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 CellsAdvantagesWater is the only discharge (pure H2)DisadvantagesCO2 discharged with methanol reformLittle more efficient than alternativesTechnology currently expensiveMany design issues still in progressHydrogen often created using dirty energy (e.g., coal)Pure hydrogen is difficult to handleRefilling stations, storage tanks,

Thermo nuclear fusion energy

Nuclear Fission.

Nuclear Fusion.

Nuclear Fusion.There are great challenges that are associated with fusion, but there are also very large possible benefits

A coal power plant uses 9000 tons of coal a day to produce 1000 MW and emits many pollutants including 30,000 tons of carbon dioxide

A fusion power plant would use 5.35Kg of deuterium and tritium for the same amount of power and would emit only 4.28Kg of helium

The amount of lithium contained in a single computer battery along with about half of a bathtub full of water can produce as much energy as 40 tons of coal

Principle..

Possible reactions.

Deuterium ------------ In ocean water---- 1 D atom for every 6500 ordinary H atom in sea water.

Tritium is produced innuclear reactorsbyneutron activationoflithium-6.Tritium is also produced inheavy water-moderated reactorswhenever adeuteriumnucleus captures a neutron.Tritium is an uncommon product of thenuclear fissionofuranium-235,plutonium-239, anduranium-233, with a production of about one per each 10,000 fissions

Theelectrostatic forcebetween the positively charged nuclei is repulsive, but when the separation is small enough, the attractive nuclear forceis stronger.

Therefore the prerequisite for fusion is that the nuclei have enough kinetic energy that they can approach each other despite the electrostatic repulsion.

Condition for a fusion reactionLawson criterion, first derived on fusion reactors (initially classified) byJohn D. Lawsonin 1955 and published in 1957.

Is an important general measure of a system that defines the conditions needed for a fusion reactor to reachignition, that is, the heating of the plasma by the products of the fusion reactions is sufficient to maintain the temperature of the plasma against all losses without external power input.

Breakeven is the point in which the energy supplied equals or exceeds the energy output

Ignition is the point in which the energy from fusion supplies the heat necessary to sustain the reaction without external sources

Condition for a fusion reactionAs originally formulated the Lawson criterion gives a minimum required value for the product of the plasma (electron) densityneand the "energy confinement time".

Later analysis suggested that a more usefulfigure of meritis the "triple product" of density, confinement time, and plasma temperatureT. The triple product also has a minimum required value, and the name "Lawson criterion" often refers to this inequality

Condition for a fusion reaction

Minimum value of (electron density * energy confinement time) required for self-heating, for three fusion reactions. For DT, neEminimizes near the temperature 25keV(300 million kelvins).

The fusion triple product condition for three fusion reactions.

Condition for a fusion reactionIn terms of reaction rate. (m3/s), break even condition.

For a D-T plasma at 100million oC the break even condition is around 6 X1013 sec/cm3

ConfinementWhy?Even if you manage to generate extremelyhigh temperaturesneeded to initiate nuclearfusion reactions, there is no material container which can withstand such temperatures.

One solution to this dilemma is to keep the hot plasma out of contact with the walls of its container by keeping it moving in circular or helical paths by means of themagnetic force on charged particles.

Magnetic confinement.(1015 particle density, time 0.1sec)Inertial confinement.(1026 nuclei/cm3, 10-12 sec)

ConfinementThe motion of electrically charged particles is constrained by amagnetic field.In the absence of the magnetic field heated particles will move in straight lines in random directions, quickly striking the walls of the container. When a uniform magnetic field is applied the charged particles will follow spiral paths encircling the magnetic lines of force. The motion of the particles across the magnetic field lines is restricted and so is the access to the walls of the container.

Magnetic confinementMagnetic fields

Toroidal field

Poloidal field

Inertial confinement 1. Laser beams or laser-produced X-rays rapidly heat the surface of the fusion target, forming a surrounding plasma envelope.(ablation)2. Fuel is compressed by the rocket-like blowoff of the hot surface material.(implosion)3. During the final part of the capsule implosion, the fuel core reaches 20 times the density of lead and ignites at 100,000,000 C.4. Thermonuclear burn spreads rapidly through the compressed fuel, yielding many times the input energy.

Confinement comparison

Confinements...In the inertial confinement fusion method a very large plasma density (more than twenty times the density of lead) is attained at the expense of the energy confinement time.

In the magnetic confinement method an energy confinement time longer than one second is attained in very low density plasmas.

A density of solid D-T (0.2 g/cm) would require an implausibly large laser pulse energy. Assuming the energy required scales with the mass of the fusion plasma (Elaser~R3~2), compressing the fuel to 103or 104times solid density would reduce the energy required by a factor of 106or 108, bringing it into a realistic range.

Confinements...With a compression by 103, the compressed density will be 200 g/cm, and the compressed radius can be as small as 0.05mm. The radius of the fuel before compression would be 0.5mm. The initial pellet will be perhaps twice as large since most of the mass will beablatedduring the compression.

The optimum temperature for inertial confinement fusion is that which maximizes /T 3/2, which is slightly higher than the optimum temperature for magnetic confinement.

Reactor..

Thermo nuclear reactor

Types of Reactors..Magnetic confinement fusion.. Tokamak reactor.

Inertial confinement fusion

Magnetic confinement fusion

Magnetic confinement fusionTokamak reactor

Thermo nuclear reactor

Thank you..Presented ByAnil Kumar(1244408)Rahul Kumar(1244430)Chandan Kumar Chanchal(1244415)Rajkumar Prasad Yadav(1244435)Arjun Kumar(1244409) Anil Kumar(1244407)Ashraful Alom(1244410)

TypeEfficiencyCostEconomical

Feasibility

Crystalline

Silicon (c-Si)High

15-24%HighLow

Amorphous Silicon (a-Si)Single JunctionLow

5-10%LowMedium

Multi-JunctionMedium

7.5-13%LowHigh