Download Hydrogen as a Renewable Energy Source

Unit -V
New Energy Sources
Unit -V
New Energy Sources
Hydrogen as a Renewable Energy Source :







Sources of hydrogen
Fuel for vehicles
Hydrogen Production
Direct Electrolysis of Water
Thermal Decomposition of water
Biological and Biochemical methods of hydrogen Production
Storage of hydrogen gaseous
Cryogenic and metal hydride:
 Fuel cell Principle of working
 Construction and Applications.
Hydrogen as a Renewable Energy Source
 Hydrogen is the most abundant substance within the universe,
making up 3/4 of all matter.
 The sun still being in the early stages of it’s life is made up of 75%
hydrogen.
 Millions of years ago Hydrogen reacted to produce Helium and all
the energy was emitted to space, but a small amount was captured
on Earth by plants that had died and have now become the fossil
fuels that are now the basis of today’s leading world industry.
 Exists in nature, an invisible gas which is extremely flammable, can
produce secondary energy
Hydrogen..
A Plentiful Element
existing freely in nature
an invisible, extremely flammable gas
highly reactive and essential in many chemical and
biological processes
not an energy source, but rather an energy carrier
from which a secondary form of energy must be created
Why Hydrogen? Why Now?
1. Hydrogen production is already large
a) It is used to synthesize ammonia for fertilizer production
b) It is used in high-pressure hydro-treating petroleum in
refineries
2. Transportation and energy-intensive processes depend on oil,
which is a finite, non-renewable energy source
3. Hydrogen promises to lead “better, faster, more efficient,
environmentally clean transportation designs.
4. Clearly, hydrogen has the potential of being a powerful
energy source!!!
5. IN FACT, Hydrogen has the highest heat of combustion of
ANY known SUBSTANCE.
6. Used in rockets, space shuttle, small batteries, etc
7. High energy, low emission = TANTILIZING for fuel in cars
and other
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.
Sources of hydrogen
Where can we get hydrogen?
 Reaction of metal with Acid
• On that Day I demoed Sodium Metal and Water
Na(s) + H2O(l) -> NaOH + H2
• More commonly (a metal w/ Sulfuric acid)
Zn(s) + H2SO4 -> H2(g) + ZnSO4
 Electrolysis
• Demoed the bubbling that occurs at an electrode surface. Remember
the light bulb.
H2O(l) -> H2 + ½ O2
(reverse reaction of combustion)
» Same amount of energy NEEDS TO BE INPUTED
– Discussed feasibility
Sources of hydrogen (Cont’d)
Hot steam over pure carbon (coke)
Input 131 kJ/mol
H2O + C(s) -> H2(g) + CO(g)
CO is carbon MONOXIDE!!
Hot steam over methane (natural gas)
Input 165 kJ/mol
H2O + CH4 -> 4 H2 (g) + CO2(g)
CO2 = Greenhouse gas
Fuel for vehicles
(Hydrogen Vehicles)
 Stores energy more
efficiently than
batteries
 Burns twice as
efficiently in a fuel
cell as gasoline does in
an engine
 Doesn’t rely on any
fossil fuel
 It’s only waste product
is water
Other Modes of Hydrogen Transport
Hydrogen Production
 H is difficult and costly to compress, store, and
transport; it has one of the lowest energy densities of
any fuel, 1/3rd of any natural gas. Hydrogen has major
safety issues; it’s flammable over a wide range of
concentrations and is very easily ignited. Hydrogen is
one of the most leak prone gases, set to a strict set of
regulations and standards.
 Currently in US at 8 billion kg (energy equivalent of
8 bil/gal. of gasoline), Americans consumed 180
bil/gal. gasoline in 2000, hydrogen demand is
growing.
Hydrogen Production
Direct Electrolysis of Water
 Electrolysis is a process that
splits Hydrogen from water,
which results in no emission
but is very expensive at
present, It accounts for only
4-5% of Hydrogen production
in the United States today, due
mostly to the greater cost.
•Electrolysis of water Hydrogen Challenger
•Production of hydrogen from water requires large amounts of energy and is uncompetitive with its production
from coal or natural gas. Potential electrical energy supplies include hydropower, wind turbines, or photovoltaic
cells. Usually, the electricity consumed is more valuable than the hydrogen produced so this method has not
been widely used. Other potential energy supplies include heat from nuclear reactors and light from the sun.
Hydrogen can also be used to store renewable generated electricity when it is not needed (like the wind blowing
at night) and then used to meet power needs during the day or to fuel vehicles. The storable quality of hydrogen
helps make hydrogen an enabler of the wider use of renewables,[3] and internal combustion engines.
•High pressure electrolysis
•When water is pressurized and then electrolysis is conducted at those high pressures, the produced hydrogen
gas is pre-compressed at around 120–200 bar (1740–2900 psi).[4] By pre-pressurising the hydrogen in the
electrolyses energy is saved as the need for an external hydrogen compressor is eliminated, the average energy
consumption for internal compression is around 3%.[5] The energy required to compress water is very much less
than that required to compress hydrogen gas.
•High-temperature electrolysis
•When the energy supplied is in the form of heat (originating from solar thermal, or nuclear), the best path to the
production of hydrogen is through high-temperature electrolysis (HTE). In contrast with low-temperature
electrolysis, HTE of water converts more of the initial heat energy into chemical energy (hydrogen), potentially
doubling efficiency to about 50%. Because some of the energy in HTE is supplied in the form of heat, less of the
energy must be converted twice (from heat to electricity, and then to chemical form), and so the process is more
efficient.
•HTE processes are generally only considered in combination with a nuclear heat source, because the other nonchemical form of high-temperature heat (concentrating solar thermal) is not consistent enough to bring down the
capital costs of the HTE equipment. Research into HTE and high-temperature nuclear reactors may eventually
lead to a hydrogen supply that is cost-competitive with natural gas steam reforming. HTE has been
demonstrated in a laboratory, but not at a commercial scale.
Hydrogen Production
Thermal Decomposition of water
1. Thermal decomposition of water
• Thermal decomposition, also called thermolysis, is defined as a chemical
reaction whereby a chemical substance breaks up into at least two chemical
substances when heated. At elevated temperatures water molecules split
into their atomic components hydrogen andoxygen. For example, at
2200 °C about three percent of all H2O molecules are dissociated into
various combinations of hydrogen and oxygen atoms, mostly H, H2, O, O2,
and OH. Other reaction products like H2O2 or HO2 remain minor. At the
very high temperature of 3000 °C more than half of the water molecules are
decomposed, but at ambient temperatures only one molecule in 100 trillion
dissociates by the effect of heat.
• Thermal water splitting has been investigated for hydrogen production
since the 1960s.[15] The high temperatures needed to obtain substantial
amounts of hydrogen impose severe requirements on the materials used in
any thermal water splitting device. For industrial or commercial
application, the material constraints have limited the success of applications
for hydrogen production from direct thermal water splitting and with few
exceptions most recent developments are in the area of
thecatalysis and thermochemical cycles.
Nuclear-thermal decomposition of water
• Some prototype Generation IV reactors, such as the HTTR, operate at
850 to 1000 degrees Celsius, considerably hotter than existing
commercial nuclear powerplants. General Atomics predicts that
hydrogen produced in a High Temperature Gas Cooled Reactor
(HTGR) would cost $1.53/kg. In 2003, steam reforming of natural gas
yielded hydrogen at $1.40/kg. At 2005 gas prices, hydrogen cost
$2.70/kg. Hence, just within the United States, a savings of tens of
billions of dollars per year is possible with a nuclear-powered supply.
Much of this savings would translate into reduced oil and natural gas
imports.
• One side benefit of a nuclear reactor that produces both electricity and
hydrogen is that it can shift production between the two. For instance,
the plant might produce electricity during the day and hydrogen at
night, matching its electrical generation profile to the daily variation in
demand. If the hydrogen can be produced economically, this scheme
would compete favorably with existing grid energy storage schemes.
What is more, there is sufficient hydrogen demand in the United
States that all daily peak generation could be handled by such plants
Nuclear-thermal decomposition of water
contd…
• Recent research on the hybrid thermoelectric Copper-chlorine cycle has
focused on a cogeneration system using the waste heat from nuclear
reactors, specifically the CANDU supercritical water reactor.Electrolysis of
water is the decomposition of water (H2O) into oxygen (O2)
and hydrogen gas (H2) due to an electric currentbeing passed through the
water. In chemistry and manufacturing, electrolysis is a method of
separating chemically bonded elements and compounds by passing an
electric current through them. One use of electrolysis of water or artificial
photosynthesis (photoelectrolysis in a photoelectrochemical cell) is to
produce hydrogen. Recently, researchers have shown that water splitting
can be broken into two discrete steps using polyoxometalate based redox
mediators.[2]
• Power to gas production schemes, the excess power or off peak power
created by wind generators or solar arrays is used for load balancing of the
energy grid by storing and later injecting the hydrogen into the natural gas
grid.
Biological and Biochemical methods of hydrogen
Production
• Biological hydrogen production (algae)
• The biological hydrogen production with algae is a method of
photobiological
water
splitting
which
is
done
in
a closed photobioreactorbased on the production of hydrogen as a solar
fuel by algae. Algae produce hydrogen under certain conditions. In 2000 it
was discovered that if C. reinhardtii algae are deprived of sulfur they will
switch from the production of oxygen, as in normal photosynthesis, to the
production of hydrogen.
Photosynthesis
• Photosynthesis in cyanobacteria and green algae splits water into hydrogen
ions and electrons. The electrons are transported over ferredoxins. Fe-Fehydrogenases (enzymes) combine them into hydrogen gas.
In Chlamydomonas reinhardtii Photosystem II produces in direct
conversion of sunlight 80% of the electrons that end up in the hydrogen
gas. Light-harvesting complex photosystem II light-harvesting
protein LHCBM9 promotes efficient light energy dissipation. The Fe-Fehydrogenases need an anaerobic environment as they are inactivated by
oxygen. Fourier transform infrared spectroscopy is used to examine
metabolic pathways
Biological and Biochemical methods of hydrogen
Production Contd…
•
•
•
•
•
•
•
•
•
•
Truncated antenna
The chlorophyll (Chl) antenna size in green algae is minimized, or truncated, to
maximize photo biological solar conversion efficiency and H2 production. The
truncated Chl antenna size minimizes absorption and wasteful dissipation of
sunlight by individual cells, resulting in better light utilization efficiency and
greater photosynthetic productivity by the green alga mass culture.
Bioreactor design issues
Restriction of photosynthetic hydrogen production by accumulation of a proton
gradient.
Competitive inhibition of photosynthetic hydrogen production by carbon dioxide.
Requirement for bicarbonate binding at photosystem II (PSII) for efficient
photosynthetic activity.
Competitive drainage of electrons by oxygen in algal hydrogen production.
Economics must reach competitive price to other sources of energy and the
economics are dependent on several parameters.
A major technical obstacle is the efficiency in converting solar energy into chemical
energy stored in molecular hydrogen.
Attempts are in progress to solve these problems via bioengineering
Challenges of using hydrogen
• Even though, hydrogen is an
attractive alternative to hydrocarbon
fuels such as gasoline in mobile
applications. However, the storage
of hydrogen in these applications
still remains a problem and and
scientists have to come up with
applicable, light, affordable, and
safe method for storing hydrogen in
such applications.
Hydrogen storage options
• Storage as gas under pressure (250-350 bar)
• Cryogenic storage as liquid hydrogen (temp –253 0C )
• Storage as metallic hydrides
• Carbon adsorption and glass microsphere
storage techniques (under development)
1 methods -Storage of hydrogen
gaseous
• If we succeed in producing H2 cheaply, we are still
faced with the questions:
– How do we store it?
– How do we transport it
• 1 gram occupies about 12 liters
– If stored as gaseous state, large heavy walled containers
will be necessary! This eliminates the benefits of H2 as a
fuel (high energy/low mass ratio)
• Liquefied at -250oC
– A lot of energy would be required!!
2 methods -Storage of hydrogen
gaseous
• Adsorption of H2 onto activated carbon
• Use of Li metal.
– Li is highly reactive metal
– Reaction of H2 gas can reduce the volume of 12 liter to
about 4-5 ml.
Here is the chemistry:
Li(s) + ½ H2(g) -> LiH(s)
Q: Ok … how do we get it back when we need it
A: Drop Lithium hydride (LiH) into water
LiH + H2O -> H2 + LiOH
Produces Hydrogen gas
Compressed hydrogen
• the most straightforward option
at this time
• offers the simplest and least
expensive method for onboard
storage of hydrogen
• The refilling time of compressed
hydrogen tanks is also similar to
that of gasoline tanks.
Problems
• Low energy density (One way to
increase the fuel stored in the container
is to increase pressure, but this requires
more expensive storage containers,
increasing compression costs )
• hydrogen has a tendency to leak
because of its small size. Seals and
valves on the containers need to be
designed to prevent leaks. If a fuel cell
vehicle is stored in a closed garage,
hydrogen that has leaked out could
accumulate and increase the risk of
fire or explosion.in addition to the
explosion could happen from cars
accidents on the road
Problems
• Does not liquefy until (~-253 0C)
Which cost energy
• 40% of energy can be lost(25
percent of LH2 boiled off during
refueling and 1 percent lost per day
for onboard storage.)
• requires excellent insulation of
storage containers; otherwise, left
for a period of time, the storage
tanks could become depleted
Bonded hydrogen (Metal hydride)
• Since heat is required to release the
hydrogen, this method avoids safety
concerns surrounding leakage that
can be a problem with compressed
hydrogen and LH2. In fact, metal
hydrides are one of the safest
methods for storing hydrogen.
Problems
• Heavy weight. (One major obstacle to this method is that the metal
compounds used to attract the hydrogen tend to be very heavy
resulting in only 1.0 to 1.5 percent hydrogen by weight)
• Some of the metals used for hydrides are very expensive. There are
less expensive options but they are impractical for use in fuel cell
vehicles as these cheaper metals require extremely high temperatures
to release the hydrogen
Vehicles requirements of H2
• A modern, commercially available car optimized for
mobility and not prestige with a range of 400km burns
about 24 kg of petrol in a combustion engine; to cover the
same rage by electric car with a fuel cell 4kg hydrogen is
needed (Louis Schlapbach & Andreas Zuttel)
Volume of 4kg hydrogen compacted in different ways,
with size relative to the size of a car
• Cryogenic and metal hydride:
Background of metal hydride
•
the last century, scientists discover
that Pd metal occluded large
amount of H2 at ambient pressure
and temperature. However, it was
not very useful because of issues
associated with the cost and low
capacity of hydrogen storage. The
recent discovery of hydrogen sorption
by intermetallic compounds created
great hopes and stimulated research
and development worldwide of using
the metal hydrides as a new
alternative for storing and delivering
pure hydrogen that can be very useful
for fuel cell technology
Metal hydrides material
•
Hydrogen is a highly
reactive element and has
been shown to form
hydrides and solid
solutions with thousands
of metals and alloys.
Figure beside shows the
family tree of hydriding
alloys and complexes
Family tree hydriding alloys and complexes
Metal hydride elements
•
For PEM fuel cell vehicular applications
the range is 0-100 0C and 1-10 atm. This is
based on the possibility of using the waste
heat from the fuel cell to release the
hydrogen from the metal hydride. In the
last century Pd was used to store H2.
However, it is no longer used because it is
very expensive, doesn’t hold much
hydrogen, and requires heating above 100
0C to release that hydrogen. Today
Vanadium (V) and Niobium (Nb)
are well known elements for storing
hydrogen in the range of practical
applications
Van’t Hoff lines (desorption) for elemental hydrides. Box
indicates 1–10 atm, 0–100°C ranges
Metal Hydride Alloys
• Scientists have been required to combine strong hydride forming elements
(A) with weak hydride elements (B) to form alloys (especially intermetallic
compounds) that have the desired intermediate thermodynamic affinities for
hydrogen
• there are some conditions should be considered of choosing these alloys as
metal hydrides:
1-Temperature and pressure of hydride and dehydride
2-Hydrogen storage capacity of the alloys
3-Rate of absorption and desorption
4-Ease of activation
5-Poisoning by impurities
6-Cost and availability
• Typically there are three type of bonding between metals and hydrogen:
Ionic, Covalent, and Metallic
Metallic hydride
• Ionic, Covalent types of bonding are not very practical in mobile
applications because they require extremely high temperature in order to
liberate H2 . Where as the metallic type bond offers the necessary
behavior for hydrogen storage systems (In the metallic hydrides, the
hydrogen acts an electron accepter, the hydrogen atom accept the
electron from the conduction band of the metal and fill its first orbital )
• The conventional metal hydride alloy families to be described here are
the AB5, AB2, and AB intermetallic compounds
Problems of metal hydrides
• Low mass density is the
general weakness of all
known metal hydrides
working near room
temperature. There are
intermetallic compounds and
alloys can form hydrides up
to 9 mass% hydrogen but
they are not reversible within
the required range of
temperature and pressure.
Table beside shows the mass
density of the well-known
compounds and alloys
Intermetallic compounds and their hydrogen-storage properties
•
The other common problem of
storing hydrogen is the impurity
and the most problematic
impurities are: CO, CO2, NH3,
H2S, CH4 and O2. These
impurities reduce the storage
capacity and also could cause
poisoning, retardation, or
reaction. Table beside shows the
effect of impurities on metal
hydride



Poisoning = Rapid loss of H-capacity with cycling
Retardation = Reduction in absorption/desorption kinetics without significant
loss in the ultimate capacity
Reaction = Bulk corrosion was leading to irreversible capacity loss
Liquefied Hydrogen
• Could perform better in an
accident
• high energy density of liquid
hydrogen
• Increase available space
• Reduce environments effect
Fuel cell
(Principle of working, Construction and Applications)
What is fuel cell?
A Fuel cell is a electrochemical device that converts chemical energy
into electrical energy
•
Every fuel cell has two electrodes, one positive and one
negative, called, respectively, the cathode and anode. The
reactions that produce electricity take place at the
electrodes
•
In all types of fuel cell, hydrogen is used as fuel and can be
obtained from any source of hydrocarbon.
•
The fuel cell transform hydrogen and oxygen into
power, emitting water as their only waste product.
electric
39
• Every fuel cell also has an electrolyte, which carries
electrically charged particles from one electrode to the other,
and a catalyst, which speeds the reactions at the electrodes.
• A single fuel cell generates a tiny amount of direct
(DC) electricity.
current
• A converter is used to produce AC current
• In practice, many fuel cells are usually assembled into a stack.
Cell or stack, the principles are the same.
• In 1932, Francis Bacon developed the first successful
used hydrogen, oxygen, an alkaline electrolyte,
and
electrodes.
FC.
He
nickel
40
1. Anode
Parts of a Fuel Cell
• 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.
2. 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.
3. Electrolyte
• Proton exchange membrane.
• Specially treated material, only conducts positively charged ions.
• Membrane blocks electrons.
4. 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.
2.A fuel cell configuration
1. A fuel cell consists of
two
electrodes
namely an anode
and a cathode and
sandwiched around
an electrolyte.
2. An electrolyte is a
substance, solid or
liquid, capable of
conducting
oving
ions
from
one
electrode to other.
(+)
(-)
Anode
Cathode
Electrolyte
42
3. Types of fuel cells
There are different types of fuel cells, differentiated by the
type of electrolyte separating the hydrogen from the oxygen .
The types of fuel cells are:
•
•
•
•
•
•
Alkaline fuel cells (AFC)
Direct methanol fuel cells (DMFC)
Molten carbonate fuel cell (MFFC)
Phosphoric acid fuel cells (PAFC)
Polymer electrolyte membrane fuel cells (PEMFC)
Solid oxide fuel cells (SOFC)
43
44
4. Principle, construction and working of H2-O2 fuel cell
Principle:
The fuel is oxidized on
the anode and oxidant reduced
on the cathode. One species of
ions are transported from one
electrode to the other through
the electrolyte to combine
there with their counterparts,
while electrons travel through Fuel
the external circuit producing
the electrical current.
Fuel
Electrons
(e-)
Cations
(+ve)
Anions (-ve)
Oxidant
Electrolyte
Permeable
Anode
Oxidant
Permeable
Cathode
45
Working
The Fuel gas (hydrogen rich) is passed towards the anode where the
following oxidation reaction occurs:
H2 (g) = 2H+ + 2eThe liberated electrons from hydrogen in anode side do not migrate
through electrolyte.
Therefore, they passes through the external circuit where work is
performed, then finally goes into the cathode.
On the other hand, the positive hydrogen ions (H+) migrate across
the electrolyte towards the cathode.
46
At the cathode side the hydrogen atom reacts with oxygen gas
(from air) and electrons to form water as byproduct according to:
The overall cell reaction is
fuel + oxidant
product + Heat
H2 + 1/2 O2 +2e -
H2O + Heat
47
Fuel Cell Stack
48
Operation of Fuel Cell
49
Fuel Cell Energy Exchange
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/electrol.html
The liberated electrons from the hydrogen are responsible for the
production of electricity.
The water is produced by the combination of hydrogen, oxygen and
liberated electrons and is sent out from the cell.
The DC current produced by fuel cell is later converted into AC current
using an inverter for practical application.
The voltage developed in a single fuel cell various from 0.7 to 1.4 volt.
More power can be obtained by arranging the individual fuel cell as a
stack. In this case, each single cell is sandwiched with one another by
a interconnect.
Therefore, electricity power ranging from 1 kW to 200 kW can be
obtained for domestic as well as industrial application.
51
Electrical power production by fuel cell
Hydrogen
Oxygen
Rotating shaft connected to generator for electricity production
52
Polymères Electrolyte Membrane (PEM) Fuel Celles
H2-O2 Fuel Cell or Polymer electrolyte membrane (PEM) fuel cells—also called
proton exchange membrane fuel cells—deliver high power density and offer the
advantages of low weight and volume, compared to other fuel cells. PEM fuel
cells use a solid polymer as an electrolyte and porous carbon electrodes
containing a platinum catalyst. They need only hydrogen, oxygen from
the air, and water to operate and do not require corrosive fluids like some fuel
cells. They are typically fueled with pure hydrogen supplied from storage tanks or
onboard reformers.
Alkaline Fuel Cells
Alkaline fuel cells (AFCs) were one of the first fuel cell technologies developed,
and they were the first type widely used in the U.S. space program to produce
electrical energy and water onboard spacecraft. These fuel cells use a solution of
potassium hydroxide in water as the electrolyte and can use a variety of nonprecious metals as a catalyst at the anode and cathode. High-temperature AFCs
operate at temperatures between 100°C and 250°C (212°F and 482°F). However,
newer AFC designs operate at lower temperatures of roughly 23°C to 70°C (74°F to
158°F). AFCs high performance is due to the rate at which chemical reactions take
place in the cell. They have also demonstrated efficiencies near 60 percent in space
applications.
Phosphoric Acid Fuel Cells
Phosphoric acid fuel cells (PAFCs) use liquid phosphoricacid as an
electrolyte—the acid is contained in a Teflon-bonded silicon carbide
matrix—and porous carbon electrodes containing a platinum catalyst.
The chemical reactions that take place in the cell are shown in the
diagram to the right. The phosphoric acid fuel cell is considered the "first
generation" of modern fuel cells. It is one of the most mature cell types
and the first to be used commercially, with over 200 units currently in
use. This type of fuel cell is typically used for stationary power
generation, but some PAFCs have been used to power large vehicles such
as city buses.
Solid Oxide Fuel Cells
Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte.
Since the electrolyte is a solid, the cells do not have to be constructed in the plate-like
configuration typical of other fuel cell types. SOFCs are expected to be around 50-60
percent efficient at converting fuel to electricity. In applications designed to capture and
utilize the system's waste heat (co-generation), overall fuel use efficiencies is 80-85 percent.
Solid oxide fuel cells operate at very high temperatures—around 1,000°C (1,830°F). High
temperature operation removes the need for precious-metal catalyst, thereby reducing cost. It
also allows SOFCs to reform fuels internally, which enables the use of a variety of fuels and
reduces the cost associated with adding a reformer to the system. SOFCs are also the most
sulfur-resistant fuel cell type; they can tolerate several orders of magnitude more sulfur than
other cell types. In addition, they are not poisoned by carbon monoxide (CO), which can
even be used as fuel. This allows SOFCs to use gases made from coal.
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%
5. Advantage, disadvantage and applications
Advantages
• Zero Emissions: a fuel cell vehicle only emits water
Therefore, no air pollution occurs.
vapour.
• High efficiency: Fuel cells convert chemical energy
directly
into electricity without the combustion process.
As a result, Fuel
cells can achieve high efficiencies in energy conversion.
• High power density: A high power density allows fuel cells
be relatively compact source of electric power,
beneficial
application with space constraints.
to
in
58
• Quiet operation: Fuel cells can be used in residential or built-up
areas where the noise pollution can be avoided.
• No recharge: Fuel cell systems do not require recharging.
Disadvantages
• It is difficult to manufacture and stores a high pure hydrogen
• It is very expense as compared to battery
59
Applications
1. Portable applications
•
They used in portable appliances and power tools
•
They can be used in small personal vehicles
•
They are used Consumer electronics like laptops, cell phones can
be operated
•
They can be used in Backup power
60
Applications
1. Portable applications
•
They used in portable appliances and power tools
•
They can be used in small personal vehicles
•
They are used Consumer electronics like laptops, cell phones can
be operated
•
They can be used in Backup power
61
2. Transportation applications
•
They can be used for transport application in the
following
areas,
•
Industrial transportation
•
Public transportation
•
Commercial transportation (truck, tractors)
•
Marine and Military transportation
62
3. Power distribution application
• Fuel cells can be used for the distribution of
various fields such as,
power
in
• Homes and small businesses
• Commercial and industrial sites
• Remote, off-grid locations (telecom towers, weather
stations)
63
Problems regarding hydrogen fuel cells
•Lack of hydrogen infrastructure
•Need for refueling stations
•Lack of consumer distribution system
•Cost of hydrogen fuel cells
•2009 Department of Energy estimated $61/kw
•Honda FCX Clarity costs about half a million dollars to make
•Carbon cost of producing hydrogen
•Problems with HFC cars
•Short range (~260 miles)
•Warm up time (~5 minutes)
Thanks ………..